Artist’s impression of NASA’s New Horizons spacecraft encountering a Kuiper Belt object, as part of an extended mission after the spacecraft’s July 2015 Pluto flyby. New Horizons is set to fly past 2014 MU69 – a KBO currently about a billion miles (1.6 billion kilometers) beyond Pluto – on Jan. 1, 2019. Recent data from the Hubble Space Telescope suggests 2014 MU69 has a reddish hue, even redder than Pluto. The object is the smallest KBO to have its surface properties measured. Credits: NASA/JHUAPL/SwRI
The next target for NASA’s New Horizons mission – which made a historic flight past Pluto in July 2015 –– apparently bears a colorful resemblance to its famous, main destination.
Hubble Space Telescope data suggests that 2014 MU69, a small Kuiper Belt object (KBO) about a billion miles (1.6 billion kilometers) beyond Pluto, is as red, if not redder, than Pluto. This is the first hint at the surface properties of the far flung object that New Horizons will survey on Jan. 1, 2019.
Mission scientists are discussing this and other Pluto and Kuiper Belt findings this week at the American Astronomical Society Division for Planetary Sciences (DPS) and European Planetary Science Congress (EPSC) in Pasadena, California.
“We’re excited about the exploration ahead for New Horizons, and also about what we are still discovering from Pluto flyby data,” said Alan Stern, principal investigator from Southwest Research Institute in Boulder, Colorado. “Now, with our spacecraft transmitting the last of its data from last summer’s flight through the Pluto system, we know that the next great exploration of Pluto will require another mission to be sent there.”
Partly Cloudy on Pluto? Pluto’s present, hazy atmosphere is almost entirely free of clouds, though scientists from NASA’s New Horizons mission have identified some cloud candidates after examining images taken by the New Horizons Long Range Reconnaissance Imager and Multispectral Visible Imaging Camera, during the spacecraft’s July 2015 flight through the Pluto system. All are low-lying, isolated small features—no broad cloud decks or fields – and while none of the features can be confirmed with stereo imaging, scientists say they are suggestive of possible, rare condensation clouds. Credits: NASA/JHUAPL/SwRI
Stern said that Pluto’s complex, layered atmosphere is hazy and appears to be mostly free of clouds, but the team has spied a handful of potential clouds in images taken with New Horizons’ cameras. “If there are clouds, it would mean the weather on Pluto is even more complex than we imagined,” Stern said.
Scientists already knew from telescope observations that Pluto’s icy surface below that atmosphere varied widely in brightness. Data from the flyby not only confirms that, it also shows the brightest areas (such as sections of Pluto’s large heart-shaped region) are among the most reflective in the solar system. “That brightness indicates surface activity,” said Bonnie Buratti, a science team co-investigator from NASA’s Jet Propulsion Laboratory in Pasadena. “Because we see a pattern of high surface reflectivity equating to activity, we can infer that the dwarf planet Eris, which is known to be highly reflective, is also likely to be active.”
While Pluto shows many kinds of activity, one surface process apparently missing is landslides. Surprisingly, though, they have been spotted on Pluto’s largest moon, Charon, itself some 750 miles (1,200 kilometers) across. “We’ve seen similar landslides on other rocky and icy planets, such as Mars and Saturn’s moon Iapetus, but these are the first landslides we’ve seen this far from the sun, in the Kuiper Belt,” said Ross Beyer, a science team researcher from Sagan Center at the SETI Institute and NASA Ames Research Center, California. “The big question is will they be detected elsewhere in the Kuiper Belt?”
Both Hubble and cameras on the New Horizons spacecraft have been aimed at KBOs over the past two years, with New Horizons taking advantage of its unique vantage point in the Kuiper Belt to observe nearly a dozen small worlds in this barely explored region. MU69 is actually the smallest KBO to have its color measured – and scientists have used that data to confirm the object is part of the so-called cold classical region of the Kuiper Belt, which is believed to contain some of the oldest, most prehistoric material in the solar system.
Scientists from NASA’s New Horizons mission have spotted signs of long run-out landslides on Pluto’s largest moon, Charon. This image of Charon’s informally named Serenity Chasma was taken by New Horizons’ Long Range Reconnaissance Imager (LORRI) on July 14, 2015, from a distance of 48,912 miles (78,717 kilometers). Arrows mark indications of landslide activity. Credits: NASA/JHUAPL/SwRI
“The reddish color tells us the type of Kuiper Belt object 2014 MU69 is,” said Amanda Zangari, a New Horizons post-doctoral researcher from Southwest Research Institute. “The data confirms that on New Year’s Day 2019, New Horizons will be looking at one of the ancient building blocks of the planets.”
The New Horizons spacecraft is currently 3.4 billion miles (5.5 billion kilometers) from Earth and about 340 million miles (540 million kilometers) beyond Pluto, speeding away from the sun at about nine miles (14 kilometers) every second. About 99 percent of the data New Horizons gathered and stored on its digital recorders during the Pluto encounter has now been transmitted back to Earth, with that transmission set to be completed Oct. 23. New Horizons has covered about one-third of the distance from Pluto to its next flyby target, which is now about 600 million miles (nearly 1 billion kilometers) ahead.
As we described in our article last year, most of the methane on Earth comes from active life (usually microbes). The rest is formed when hot water interacts with rock. Either way, we are very interested in homing in on where the methane on Mars is coming from and when. Is it seasonal? Does it happen only in certain locations? Is the methane production stable year after year or does it alter with time? With its four instruments capable of sniffing out hydrocarbons like methane in less than 1% of the atmosphere, the Trace Gas Orbiter will start to answer those questions once ExoMars has maneuvered into position to peer through the Martian atmosphere for signs of breathing microbes, active geology, or, possibly, both.
Artist’s impression of the ExoMars 2016 Trace Gas Orbiter (TGO) and Schiaparelli – the entry, descent and landing demonstrator module. Copyright: ESA/ATG medialab
Mystery Methane on Mars: The Saga Continues(Originally published on May 14, 2015)
A scientist has raised questions about the latest detection of methane on Mars, suggesting that NASA’s rover could be responsible for the mysterious burp. Highly unlikely, but not impossible, says the Curiosity team.
By Johnny Bontemps
NASA’s Curiosity rover has detected methane on Mars. Could the gas be coming from the rover itself? Credit: NASA/JPL
Is the Red Planet giving off methane?
The question has taunted scientists for nearly 50 years, ever since the Mariner 7 spacecraft detected a whiff of the gas near Mars’ south pole. Researchers retracted the finding a month later after realizing that the signal was in fact coming from carbon dioxide ice.
Then in 2003 and 2004, earthbound telescopes and orbiting spacecraft rekindled the mystery with reports of large methane clouds in Mars’ atmosphere. Most of Earth’s methane comes from living organisms, though a small fraction can form when rocks and hot water interact. A burp of methane on Mars would indicate that the planet might be more alive than previously thought—whether biologically or geologically. But the “plumes” mysteriously vanished a few years later, sparking intense debate over whether they might have been seasonal, or the results of flawed measurements.
NASA’s Curiosity rover would resolve the matter, everyone hoped. The rover sampled Mars’ atmosphere six times for methane between October 2012 and June 2013—and detected none. But the case for Martian methane remained far from settled. A few months later, Curiosity detected a sudden burst of the gas in four measurements over a period of two months.
Working hard to rule out potential anomalies and monitor the evolution of the burst over time, the Curiosity team waited an entire year before announcing the new results at a meeting of the American Geophysical Union in December 2014. A paper was published in the journal Science in January 2015. Whether microbes hid below the Martian surface or geology was at play, the Red Planet could well be alive in some way after all.
“I am convinced that they really are seeing methane,” he said. “But I’m thinking that it has to be coming from the rover.”
Methane From Earth
Zahnle, who was also critical of the 2003 and 2004 methane reports, said that it wouldn’t take much from the rover to lead scientists astray. After all, the rover contains within a chamber some methane at a concentration 1,000 times higher than the puff supposedly found in Mars’ atmosphere. That methane had come from Earth.
Upon landing in Gale Crater, the rover’s tunable laser spectrometer gave off an unusually high reading for methane. The scientists on the team quickly realized that some terrestrial air had leaked into the instrument while the rover was sitting on the launch pad at Cape Canaveral. They pumped out most of that methane, keeping a small amount in the antechamber to the sample cell for calibration purposes.
The Tunable Laser Spectrometer on NASA’s Curiosity Mars Rover. The foreoptics chamber contains a small amount of methane for calibration purpose. Credit: NASA/JPL
But Curiosity’s team insists that this known source hasn’t interfered with the discovery.
“We are continuously monitoring that methane amount and there hasn’t been evidence of any leakage during the entire mission,” says Chris Webster, a senior research scientist at NASA’s Jet Propulsion Laboratory and lead author of the study. “And while it’s true that the concentration of methane in that chamber is 1,000 times higher than in Mars’s atmosphere, the comparison is actually misleading.”
“You have to look at the amount of methane, not the concentration,” he explains. The concentration of methane on the rover may seem high, but the actual amount is very small because the chamber is very small. To produce the amount we detected in Mars’s atmosphere, you’d need a gas bottle of pure methane leaking from the rover. And we simply don’t have it.”
Zahnle also contends that the terrestrial air could have infiltrated other areas on the rover.
“Ruling out the rover entirely as a cause is a hard thing to do,” he says. “You’d have to know about every place where methane could be stored.”
Chris McKay, a researcher at NASA Ames and co-author on the January paper, thinks that Zanhle’s concerns are valid. “I think the possibility of a methane source aboard should still be considered until completely ruled out,” he says.
But Paul Mahaffy, the principal investigator on the Sample Analysis at Mars (SAM) suite of instruments, doubts that the rover could be a possible source. “It seems unlikely that after more than a year on the surface of Mars a sudden source of methane from the spacecraft would appear, persist for 60 days and then disappear,” he says. “Methane is a very volatile gas and any residual methane brought to Mars should be long gone.”
Webster agrees that an unknown source on the rover seems highly unlikely, but he says it’s not impossible.
“There are a few areas that are sealed,” he says. “They could, in theory, be a source if some methane had made its way into them and was then leaking out, but we’ve looked very hard for other sources and we haven’t identified any.”
Curiosity is gearing up for new measurements later this year around the holiday season, which is when the mysterious burst was detected in 2013, one Mars year ago. “If the methane comes back around that time, that will tell us that something seasonal is going on,” Webster says. “That would be a huge discovery, and would put to rest the questions about the rover being a potential source.”
Daybreak at Gale Crater. Credit: NASA/JPL
Meanwhile, McKay is exploring another possibility—namely, that a meteorite may have recently fallen within the vicinity of the rover. Carbonaceous meteorites contain a small amount of organic materials, which can give off a plume of methane when broken down by ultraviolet radiation.
“It’s probabilistically unlikely, but those events do happen,” McKay says. “If the rover had been in the town of Murchison when the meteorite fell in 1969, it would have detected a pulse of methane.”
The Curiosity team has searched for fresh craters near the rover by looking at images taken from orbit. They haven’t found any. However, McKay noted that, unlike stony-iron meteorites, carbonaceous meteorites don’t leave craters. Instead, they typically break apart in the atmosphere and fall into a rain of small organic fragments. McKay is currently working with a meteorite expert to determine the size of a potential object that could have produce the methane spike detected by Curiosity.
The ExoMars Trace Gas Orbiter, a new mission led by the European Space Agency and planned for 2016, will also scan the Martian atmosphere for trace amounts of methane and other exotic gases. India’s Mars mission currently in orbit may also soon report its methane findings. Both will survey an area much greater than covered by Curiosity, which will spend its lifetime in Gale Crater. Will they finally resolve the mystery behind Mars’s capricious methane plumes? Time will tell.
This artistic rendering shows the distant view from Planet Nine back towards the sun. The planet is thought to be gaseous, similar to Uranus and Neptune. Hypothetical lightning lights up the night side. Credit: Caltech/R. Hurt (IPAC)
The large and distant planet may be adding a wobble to the solar system, giving the appearance that the sun is tilted slightly.
“Because Planet Nine is so massive and has an orbit tilted compared to the other planets, the solar system has no choice but to slowly twist out of alignment,” says Elizabeth Bailey, a graduate student at Caltech and lead author of a study announcing the discovery.
All of the planets orbit in a flat plane with respect to the sun, roughly within a couple degrees of each other. That plane, however, rotates at a six-degree tilt with respect to the sun—giving the appearance that the sun itself is cocked off at an angle. Until now, no one had found a compelling explanation to produce such an effect. “It’s such a deep-rooted mystery and so difficult to explain that people just don’t talk about it,” says Brown, the Richard and Barbara Rosenberg Professor of Planetary Astronomy.
Brown and Batygin’s discovery of evidence that the sun is orbited by an as-yet-unseen planet—that is about 10 times the size of Earth with an orbit that is about 20 times farther from the sun on average than Neptune’s—changes the physics. Planet Nine, based on their calculations, appears to orbit at about 30 degrees off from the other planets’ orbital plane—in the process, influencing the orbit of a large population of objects in the Kuiper Belt, which is how Brown and Batygin came to suspect a planet existed there in the first place.
“It continues to amaze us; every time we look carefully we continue to find that Planet Nine explains something about the solar system that had long been a mystery,” says Batygin, an assistant professor of planetary science.
Their findings have been accepted for publication in an upcoming issue of the Astrophysical Journal, and will be presented on October 18 at the American Astronomical Society’s Division for Planetary Sciences annual meeting, held in Pasadena.
The tilt of the solar system’s orbital plane has long befuddled astronomers because of the way the planets formed: as a spinning cloud slowly collapsing first into a disk and then into objects orbiting a central star.
Planet Nine’s angular momentum is having an outsized impact on the solar system based on its location and size. A planet’s angular momentum equals the mass of an object multiplied by its distance from the sun, and corresponds with the force that the planet exerts on the overall system’s spin. Because the other planets in the solar system all exist along a flat plane, their angular momentum works to keep the whole disk spinning smoothly.
Planet Nine’s unusual orbit, however, adds a multi-billion-year wobble to that system. Mathematically, given the hypothesized size and distance of Planet Nine, a six-degree tilt fits perfectly, Brown says.
The next question, then, is how did Planet Nine achieve its unusual orbit? Though that remains to be determined, Batygin suggests that the planet may have been ejected from the neighborhood of the gas giants by Jupiter, or perhaps may have been influenced by the gravitational pull of other stellar bodies in the solar system’s extreme past.
For now, Brown and Batygin continue to work with colleagues throughout the world to search the night sky for signs of Planet Nine along the path they predicted in January. That search, Brown says, may take three years or more.
MAVEN’s Imaging UltraViolet Spectrograph obtained images of rapid cloud formation on Mars on July 9-10, 2016. The ultraviolet colors of the planet have been rendered in false color, to show what we would see with ultraviolet-sensitive eyes. Mars’ tallest volcano, Olympus Mons, appears as a prominent dark region near the top of the image, with a small white cloud at the summit that grows during the day. Three more volcanoes appear in a diagonal row, with their cloud cover (white areas near center) merging to span up to a thousand miles by the end of the day. Credits: NASA/MAVEN/University of Colorado
New global images of Mars from the MAVEN mission show the ultraviolet glow from the Martian atmosphere in unprecedented detail, revealing dynamic, previously invisible behavior. They include the first images of “nightglow” that can be used to show how winds circulate at high altitudes. Additionally, dayside ultraviolet imagery from the spacecraft shows how ozone amounts change over the seasons and how afternoon clouds form over giant Martian volcanoes. The images were taken by the Imaging UltraViolet Spectrograph (IUVS) on the Mars Atmosphere and Volatile Evolution mission (MAVEN).
“MAVEN obtained hundreds of such images in recent months, giving some of the best high-resolution ultraviolet coverage of Mars ever obtained,” said Nick Schneider of the Laboratory for Atmospheric and Space Physics at the University of Colorado, Boulder. Schneider is presenting these results Oct. 19 at the American Astronomical Society Division for Planetary Sciences meeting in Pasadena, California, which is being held jointly with the European Planetary Science Congress.
Nightside images show ultraviolet (UV) “nightglow” emission from nitric oxide (abbreviated NO). Nightglow is a common planetary phenomenon in which the sky faintly glows even in the complete absence of external light. Mars’ nightside atmosphere emits light in the ultraviolet due to chemical reactions that start on Mars’ dayside. Ultraviolet light from the sun breaks down molecules of carbon dioxide and nitrogen, and the resulting atoms are carried around the planet by high-altitude wind patterns that encircle the planet. On the nightside, these winds bring the atoms down to lower altitudes where nitrogen and oxygen atoms collide to form nitric oxide molecules. The recombination releases extra energy, which comes out as ultraviolet light.
This image of the Mars night side shows ultraviolet emission from nitric oxide (abbreviated NO). The emission is shown in false color with black as low values, green as medium, and white as high. These emissions track the recombination of atomic nitrogen and oxygen produced on the dayside, and reveal the circulation patterns of the atmosphere. The splotches, streaks and other irregularities in the image are indications that atmospheric patterns are extremely variable on Mars’ nightside. The inset shows the viewing geometry on the planet. MAVEN’s Imaging UltraViolet Spectrograph obtained this image of Mars on May 4, 2016 during late winter in Mars Southern Hemisphere. Credits: NASA/MAVEN/University of Colorado
Scientists predicted NO nightglow at Mars, and prior missions detected its presence, but MAVEN has returned the first images of this phenomenon in the Martian atmosphere. Splotches and streaks appearing in these images occur where NO recombination is enhanced by winds. Such concentrations are clear evidence of strong irregularities in Mars’ high altitude winds and circulation patterns. These winds control how Mars’ atmosphere responds to its very strong seasonal cycles. These first images will lead to an improved determination of the circulation patterns that control the behavior of the atmosphere from approximately 37 to 62 miles (about 60 to 100 kilometers) high.
Dayside images show the atmosphere and surface near Mars’ south pole in unprecedented ultraviolet detail. They were obtained as spring comes to the southern hemisphere. Ozone is destroyed when water vapor is present, so ozone accumulates in the winter polar region where the water vapor has frozen out of the atmosphere. The images show ozone lasting into spring, indicating that global winds are inhibiting the spread of water vapor from the rest of the planet into winter polar regions. Wave patterns in the images, revealed by UV absorption from ozone concentrations, are critical to understanding the wind patterns, giving scientists an additional means to study the chemistry and global circulation of the atmosphere.
This ultraviolet image near Mars’ South Pole was taken by MAVEN on July 10 2016 and shows the atmosphere and surface during southern spring. The ultraviolet colors of the planet have been rendered in false color, to show what we would see with ultraviolet-sensitive eyes. Darker regions show the planet’s rocky surface and brighter regions are due to clouds, dust and haze. The white region centered on the pole is frozen carbon dioxide (dry ice) on the surface. Pockets of ice are left inside craters as the polar cap recedes in the spring, giving its edge a rough appearance. High concentrations of atmospheric ozone appear magenta in color, and the wavy edge of the enhanced ozone region highlights wind patterns around the pole. Credits: NASA/MAVEN/University of Colorado
MAVEN observations also show afternoon cloud formation over the four giant volcanoes on Mars, much as clouds form over mountain ranges on Earth. IUVS images of cloud formation are among the best ever taken showing the development of clouds throughout the day. Clouds are a key to understanding a planet’s energy balance and water vapor inventory, so these observations will be valuable in understanding the daily and seasonal behavior of the atmosphere.
“MAVEN’s elliptical orbit is just right,” said Justin Deighan of the University of Colorado, Boulder, who led the observations. “It rises high enough to take a global picture, but still orbits fast enough to get multiple views as Mars rotates over the course of a day.”
Comets are travellers in time as well as space. Coming to us from the very beginning of our Solar System — 4-billion-years ago or so — their dark bodies brighten as they approach the Sun, offering us an unparalleled window into our ancient chemical origins.
Thanks to Rosetta, we know for sure that chemicals living in our own DNA, proteins, and cell membranes can be found in the furthest corners of the Solar System. More such discoveries likely lie in store as researchers troll through two years of streaming data — a stream that finally came to an end on September 30th, 2016, as Rosetta dove into comet C-G, reporting on everything it saw, touched, and smelled with its many sensors, right up to when it finally came to rest on the face of that dark, slightly-less-mysterious-than-before, wandering body.
To Catch a Comet by the Tail: Rosetta’s historic meet and greet with Churyumov-Gerasimenko (Originally posted on June 2, 2014)
ESA’s Rosetta spacecraft carries 11 scientific instruments that it will use to examine two asteroids while en route to its final destination, comet 67P Churyumov-Gerasimenko. Credits: ESA/AOES Medialab
The European Space Agency’s Rosetta spacecraft has been traveling for a decade to meet comet 67P/Churyumov-Gerasimenko (C-G). Rosetta is expected to finally catch up with C-G in August. Then in November, Rosetta will eject a lander called Philae onto the comet’s surface: a one-way trip to a totally unknown landscape.
You might be wondering: How does one build a lander for an unknown land?
To start with: prepare for a hard landing and a soft landing at the same time. To that end, Philae’s 100 kilogram (220 lb.) payload includes a spring-tipped landing tripod and two harpoons.
That’s right, harpoons. If the comet has a hard surface, Philae’s harpoons will hopefully keep it from bouncing off the comet and floating away. In case harpoons alone don’t suffice, Philae also has a jet full of cold gas that can fire to keep it pinned to C-G’s surface.
How much dust lies on the surface of a comet is anyone’s guess. It could be a few inches, a few feet or few meters. In case comet 67P/is covered in a thick coat of soft dust, Philae’s three human-sized tripod legs have drills on their tips to keep the lander from sliding around or sinking too far down.
“We’re landing in complete unknown. That’s where the tricky engineering is. There’s a lot of dust on the surface brought up by the gas,” said U.S. project manager Art Chmielewski during a teleconference in March 2014. “It will be pretty exciting to see how deep these [tripod] legs go into the dust.”
After the lander’s release from the orbiter, the rest is up to automation, chance, good luck and incredible engineering, and example of which is its solar panels. Philae has a solar panel on each of its six sides. If it hits the dust and sinks or rolls into a gully, one of the solar panels will hopefully still be able to take in enough energy to continue making observations. For now, we don’t know how long the landing itself will take or where Philae will land. For many of the questions that you would ask before kicking a satellite the size of a dishwasher onto an active comet, the answer is likely, “We don’t know yet, but we will soon.”
Sometimes the best way, or the only way, to learn about what’s going on the Universe is to reach out and touch it.
Comets are fascinating for many reasons.
Scientifically speaking, comets are complex remnants from the very earliest times in our Solar System. They accreted, or grew, out of the same spinning gas cloud that gave rise to the Sun. Comets are believed to be at least as old as the gas giants Jupiter and Saturn, yet were recently discovered to be rich in organic molecules.
Artist Rendition of Rosetta releasing the Philae lander. Credit: NASA JPL and and Art B. Chmielewski
Credible theories maintain that comets may have introduced the basic components of life to Earth. If that’s true, it’s likely that they have introduced life’s building blocks to other bodies in our solar system, such as Mars and the moons Enceladus and Europa. From an astronomer’s perspective, we have many reasons to be chasing after comets.
In terms of the strictly human experience, comets captivate not just our curiosity, but also our attention, in a very unique way.
“Seeing a comet in the sky is a powerfully visceral experience,” said Claudia Alexander, the Rosetta project scientist at NASA’s Jet Propulsion Laboratory. “It appears as something that shouldn’t be there, and if you didn’t know better it’s easy to see them as scary.”
With comets, part of the fear factor is that they come streaking through the darkness seemingly out of nowhere. Most of the time comets slip along unnoticed. We only see them clearly for what amounts to an astronomical split-second as they come charging towards the Sun or go streaking away from it.
Because of their stealth and seeming unpredictability, comets have traditionally invoked terror, suspicion and awe in human kind. In many ways they resemble tigers, not just in their quiet approach and dramatic charge, but also in appearance. The similarity, of course, is their tails. Tails are the feature most people think about first when they think about comets.
Tails add vastly to comets’ mystique and render them unique as astronomical phenomena. Tails mark the approach to the solar apex of a comet’s long orbit, when surface temperature, dust halo thickness and geologic activity all change. Most of these attributes contribute to the production of the tail, which can be observed from Earth with the naked eye over the course of weeks and, in the case of Halley’s comet, from one generation to the next.
Throughout the ages, whenever these bright-tailed visitors have come by Earth we wished we could keep them longer, look at them closer, and understand them better. After millennia of watching in wonder from the ground-and more than 15 years after the Rosetta mission was approved-we are swiftly approaching our long-awaited rendezvous.
Join Claudia Alexander as she provides an overview of the Rosetta mission and its plans to encounter a comet to learn more about the formation of the solar system. Credit: JPL
Whether or not the lander Philae makes it down in one piece, a year from now we will have a whole new world of knowledge about these tigers of space.
Rosetta: Humanity’s first attempt to land on a comet
The European Space Agency named the mission Rosetta after the Rosetta Stone, a key discovery in human history that allowed us to unlock critical components of our own history.
“They chose that name because they wanted the mission to provide a ‘bridge’ to the past of our solar system, the same way that the original Rosetta Stone provided a bridge to an ancient culture that had previously not been understood,” said Alexander.
Previous comet-centered missions have revealed just enough to allow us to unseat prevailing theories, but not enough to firm up new ones.
In 1986, Images of Halley’s comet nucleus showed us a dark, jelly-bean-shaped object very distinct from the traditional “dirty snowball” postulated by astronomer Fred Whipple in the 1950s. In 2005, NASA threw a coffee-table-sized spacecraft at comet Temple. The resulting Deep Impact explosion was shallower than anticipated, but nonetheless implied that comets may be more porous the previously thought and not armored with an icy exterior or shell.
Artist’s impression of the Philae lander with Rosetta in the distance. The CONCERT instrument will pass signals back and forth between the two to determine. Credit: ESA
Then, there’s the “dirty” part of the “dirty snowball” comet theory. Comet surfaces are covered in some inky-colored material, which may be hydrocarbons (the result of interactions between nitrogen, methane and energetic particles) or may be something else entirely. Whatever the dark material is composed of, after examining the aftermath of Deep Impact we discovered that comets may not only be coated in dark material: they may be entirely composed of it.
The Deep Impact and the EPOXI missions also showed us that comets possess distinct geology — ridges, cracks and even cliffs that sprout jets. NASA’s Stardust spacecraft chased down comet Wild 2 and discovered glycine, one of the basic building blocks of life, streaming out of its nucleus.
The list of comet missions goes on. Each revealed an abundance of surprises. None have been as ambitious as Rosetta.
Rosetta is essentially a flying comet laboratory. It carries 16 experiments on 11 instruments jointly managed by the US and Europe. These will measure the volume and contents of the gas in the comet’s coma, bounce radio signals off the comet’s nucleus, measure thermal and electrical properties of the surface, count water, carbon monoxide, ammonia, and methanol molecules, and take high-resolution infrared images. Experimenters will try to figure out what causes the famous jets on comet surfaces by comparing maps of surface temperature to where the jets appear, in the hope of discovering whether or not hot spots create jets.
One Rosetta instrument called COSIMA (Cometary Secondary Ion Mass Analyser) will literally put comet C-G under the microscope by examining the dust from Philae’s landing. Another instrument called CONSERT (Comet Nucleus Sounding Experiment by Radio wave Transmission) lives partly on the orbiter and partly on the lander. By sending and transmitting radio signals back and forth, CONSERT will effectively ultrasound comet C-G’s nucleus.
Philae’s landing could easily end up less than ideal: with two legs in a rut or with the lander lying on its side. But as long as CONSERT arrives in working order, Rosetta should be able to discover whether comet Churyumov-Gerasimenko is loosely packed, made of discrete layers or dense all the way through. Even if Philae crash-lands, or its sensors become coated in sticky, electrically-charged dust, CONSERT will take initial readings of C-G’s surface layer during the descent to the surface.
If Philae lands upright and all systems are a go, we may get answers to many long-standing mysteries, including, to use Whipple’s analogy, what’s making the snowball dirty. Philae’s SD2 instrument is a drill and sample collector with three instruments all its own. Between two gas analyzers, seven micro-cameras, an infrared spectrometer and a light microscope, we may come to learn far more about cometary “dark stuff.”
Approach to comet Churyumov-Gerasimenko. Credit: ESA
Above all, Rosetta’s cameras will watch the C-G come alive in real time at it approaches the Sun.
“The whole idea of the mission is to be close enough to see its changing activity from very nearby, and also to periodically take in particles that are coming off the surface,” said Alexander. “So ‘escorting’ the comet means that we’ll be that close all the time, as the comet comes to life underneath us.”
This transition is important for many reasons, one of which involves the search for life itself. Several experiments are designed to replace long-held speculation with facts about life’s components on comets and in the Solar System at large. For astrobiologists, this is where things get really interesting.
Life in Deep Space
Many of life’s precursors have been found in space, including, some believe, the base pairs that make up our own DNA.
“That’s part of the purpose of the Rosetta mission — to give us concrete evidence that we can use to replace speculation,” said Alexander. “Some sophisticated molecule fragments found in DNA are seen in asteroid chemistry. We really are at the beginning of understanding how some of this chemistry is related to life’s origins (if at all).”
In a manner reminiscent of a forensics lab, Rosetta will look for the chemicals associated with the comet and with life as we know it. The experimenters are asking basic scientific questions about comets: Do comets, like asteroids, harbor basic amino-acid precursors? Are molecules on comets left or right handed?
All life on Earth uses left-handed amino acids to make proteins. In 2011, left-handed amino acids were discovered on asteroids, but so far not on comets, perhaps because on comets the outer layers are destroyed as they heat up. How a comet’s chemical components change as it becomes active it another major focus of Rosetta research.
Rosetta launched in 2004. Three years ago and 163 million kilometers (101 million miles) from comet C-G, Rosetta was put to sleep to wait out the remaining 31-month journey through deep space. It woke up on Jan 20th, 2014 and is moving 3,000 miles closer to its target every minute.
In the meanwhile, comet C-G has also started to stir, growing a dusty veil that makes it visible against the starfield.
How the environment affects a comet, activating it and creating two tails. Credit: ESA
Rosetta caught first site of C-G on March 20th. Now the navigation camera is actively taking the observations and allowing course corrections that will bring the two objects closer together. A few short months from now, in August 2014, Rosetta will be close enough to the comet to chose a target landing site for Philae. Then in November, Philae is expected to be dropped from 1 kilometer above C-G’s surface, with its drills, solar panels and harpoons at the ready.
The Rosetta orbiter itself bears a striking resemblance to a passenger airplane with the wings cut off. Coincidentally, the plan is to to release the lander onto comet C-G from a cruising altitude similar to an airplane on Earth.
“The lander drops. It just drops, but not like the some landers [Mars Curiosity Rover],” said Chmielewski. “Imagine a sheet of paper. Lift it up over your head and let go of it. That’s a better idea of the kind of speed and connotation of what this landing’s going to look like.”
With Philae perched upon its back waiting to fly, and with all of its experiments, sensors, and other in-case gadgetry, Rosetta is speeding towards a long-awaited date with ancient history. In the coming year, this spacecraft will unveil the shape, structure and contents of a comet. Through its infrared eye we will watch C-G respond to solar radiation as it comes closer and closer to the Sun. In the process, we will discover the many differences between a 4 billion-year-old piece of the Solar System quietly moving through space and a 4 billion-year-old piece of the Solar System evaporating into a visually stunning stream across the sky. Which of life’s chemical constituents comets can carry into the Inner Solar System will be explored, and we may, with a little bit of luck, land upright on the surface, dig in our heels and ride the tiger across the sky.
“Comets… are the travelers,” said Alexander. “They come from a distant place in space, and because of we think they represent pristine, unchanged remnants of the distant past. They come to us as ambassadors, if you like, from a different time. At present, we don’t have the capability to travel to those distant solar system locales or to go backwards in time. So comets present a unique ‘archeological dig’ opportunity, so to speak — and they travel to us.”
Research partially funded by Cardiff Centre for Astrobiology, ESA member states and NASA. Airbus Defense and Space built the Rosetta spacecraft. NASA’s Jet Propulsion Laboratory, Pasadena, California, manages the U.S. contribution of the Rosetta mission for NASA’s Science Mission Directorate in Washington.
This jumble of eroded blocks lies along the distinctive boundary between the Red Planet’s southern highlands and the northern lowlands, with remnants of ancient glaciers flowing around them.
This boundary is one of the oldest and most prominent features on Mars, marking a height difference of several kilometres.
The scene presented here, captured by the high-resolution camera on ESA’s Mars Express on 29 May, is just one example of the terrain found along this ancient boundary, and focuses on part of the Colles Nili region.
‘Colles’ comes from the Latin word for ‘hill’, and indeed this region hosts a swath of such features. They are likely erosional remnants of a former plateau, as suggested with their similarity in height seen in the topography map.
Colles Nili in context. Credit: NASA MGS MOLA Science Team
Zooming in to the main colour image and perspective views shows that some of the mounds are surrounded by smooth, layered deposits gently sloping away from the sides of the hills.
An even closer look reveals other finer features on the channel floors around the mounds and inside some of the impact craters: series of ridges and troughs.
Both the layered deposits and the ridges and troughs are thought to be associated with buried ice that has since been covered over by wind-blown dust and local debris from the eroding plateau, perhaps as an underlying ice sheet retreated.
Similar features are found all along the planet-wide boundary and are thought to represent multiple episodes of glaciation within the past several hundred million years.
Later, volcanic dust has blown in from elsewhere to create the striking streaks of dark material seen in various spots, but particularly dominant in the right-hand side of the main colour image.
Looking inside the large impact crater seen in the top right of the main image, and also in the top left of the perspective view, shows this dark material has been piled up into dunes inside the crater, presumably by prevailing winds.
Mars Express has been orbiting the Red Planet since 2003. Next week it will play an important role in listening for signals from Schiaparelli, the ExoMars entry, descent and landing demonstrator, as the lander makes its six-minute descent through the atmosphere to the surface.
Mars Express, Schiaparelli mothership Trace Gas Orbiter and NASA’s Mars Reconnaissance Orbiter will record signals from Schiaparelli to confirm its safe arrival, and they will subsequently act as data relays from the surface.
A new model of canyon-forming floods from UMass Amherst and CalTech researchers suggests that deep canyons can be formed in bedrock by significantly less water than previously thought. Credit: UMass Amherst/Isaac Larsen
Geomorphologists who study Earth’s surface features and the processes that formed them have long been interested in how floods, in particular catastrophic outbursts that occur when a glacial lake ice dam bursts, for example, can change a planet’s surface, not only on Earth but on Mars.
Now geoscience researchers Isaac Larsen at the University of Massachusetts Amherst and Michael Lamb at the California Institute of Technology have proposed and tested a new model of canyon-forming floods which suggests that deep canyons can be formed in bedrock by significantly less water than previously thought. They point out that “reconstructing the magnitude of the canyon-forming floods is essential for understanding how floods modify planetary surfaces, the hydrology of early Mars, and abrupt climate change.”
Larsen and Lamb apply their new model to the “channeled scablands” in eastern Washington State, an area that, like some on Mars, has very deep canyons cut into fractured basalt bedrock. The researchers say their results suggest “there may be a rich imprint of both the history and discharge of flooding in the morphology of canyons” such as terraces, valley shapes and slope profiles on Earth and on Mars “that warrant further investigation.” Details appear in the current issue of Nature.
The researchers say channels in the scablands today, which are up to 650 feet (200 meters) deep and 3 miles (5 km) wide, were likely formed by flood discharges five- to tenfold smaller than brimful estimates, that is by “significantly lower megaflood discharges than previously thought. The channeled scablands are a classic landscape in the history of geomorphology and we’re bringing new views of how it was formed.”
Until the 1920s, scientists did not understand what could have formed the tortured landscape of eastern Washington studied for decades by J Harlen Bretz, a giant figure in geosciences, Larsen recalls. Bretz was the first to suggest that they were formed by catastrophic flooding of unknown origin. His views were dismissed for years, but Bretz was later vindicated when glacial Lake Missoula was identified as the floodwater source.
As most scientists came to accept the catastrophic flood explanation for the canyons and then tried to estimate floodwater discharges, they assumed that floods filled canyons to the brim, a huge amount of water. But an alternate hypothesis proposed and now tested by Lamb and and Larsen posits that as floodwater cuts into bedrock, the canyon deepens, meaning less water is required to shape it.
In areas underlain by fractured bedrock, Larsen says, “our general concept is that the channel floor was being cut and lowered as the floods were happening, and you need to account for that when reconstructing the scenario of flood magnitude. This applies to the scablands, to Mars and other areas where there have been catastrophic outburst floods.”
He and Lamb combine numerical flood models with estimates of the force required to erode basalt bedrock to show that for Moses Coulee, a canyon carved by catastrophic Lake Missoula floods in eastern Washington when an ice dam repeatedly broke and reformed around 15,000 years ago, their “threshold shear stress model” explains the shape and depth of currently observed channels better than the brimful model.
“We numerically routed floods through the canyon in different states, from current configuration and at four different past scenarios,” Larsen notes. “We predicted the discharge from two models and tested which one is most reasonable, based on the depositional evidence from the current bars seen today in the canyons. The size of floods our model predicts from the basalt erosion better match locations of depositional flood bars in the canyon than the brimful model predicts.”
Larsen and Lamb’s new model also works better to explain observed canyon-cutting mechanics and outflow channels observed on Mars, they point out, “supporting the notion of a multi-flood or low-magnitude flood origin for the Mars outflow channels. ” Larsen adds, “There are very similar but larger canyons on the surface of Mars. These outflow channels are much bigger than the ones on Earth, but they look very similar and the assumption is they formed by similar processes. We know in most cases there were not canyons before these floods happened. They had to be carved, so the bottoms were getting lower and lower with each flood. We believe in the final phases of floods, they were not filled to the brim.”
Artist view of a planet orbiting two aging stars that exchange material and spiral closer together. Image by Jon Lomberg
Planets that revolve around two suns may surprisingly survive the violent late stages of the stars’ lives, according to new research out of the NASA Goddard Space Flight Centre and York University. The finding is surprising because planets orbiting close to a single sun, like Mercury and Venus in our solar system, would be destroyed when the aging star swells into a red giant.
Led by Veselin Kostov at the NASA Goddard Space Flight Centre, in collaboration with York University master’s student Keavin Moore and Professor Ray Jayawardhana, the study found that planets orbiting two (binary) stars – also referred to as circumbinary planets or “Tatooine worlds” after the iconic planetary home of Luke Skywalker in Star Wars – often escape death and destruction by moving out to wider orbits.
The paper, “Tatooine’s Future: The Eccentric Response of Kepler’s Circumbinary Planets to Common-Envelope Evolution of their Host Stars,” has been accepted for publication in The Astrophysical Journal.
“This is very different from what will happen in our own solar system a few billion years from now, when our Sun starts to evolve and expand to such a tremendous size that it will engulf the inner planets, like Mercury and Venus and possibly Earth too, faster than they can migrate out to larger orbits,” says Kostov. “It seems that if we had a second star in the center of our solar system, things might go differently.”
Binary star systems are ubiquitous in the Universe and consist of two stars that orbit around a common center of gravity. If the two stars are close enough to each other, when one starts evolving and expanding into a giant, they exchange material and spiral towards each other resulting in their sharing a common atmosphere (also called a common envelope). The binary star system ends up losing a large amount of mass, or might be destroyed in a supernova explosion.
“Given the exciting recent discoveries of planets circling binary stars, some with orbits similar in size to that of Mercury around the Sun, we were curious to explore the ultimate fate of these Tatooine worlds,” says Jayawardhana. “We found that many such planets are likely to survive the messy and violent late stages of their stars’ lives by moving farther out.”
The team, which also included Daniel Tamayo of the Canadian Institute for Theoretical Astrophysics and Stephen Rinehart of NASA Goddard, simulated the fate of nine circumbinary planets recently discovered by NASA’s Kepler mission. They found that the planets will predominantly survive the common envelope phase – even those orbiting very close to their stars. In addition, the planets can migrate to farther orbits similar to what it would be like if Venus moved out to where Uranus orbits our Sun. In some cases, planets can even reach more than twice the distance to Pluto.
Interestingly, when there are multiple planets orbiting a binary star, some can be ejected from the system, while others can switch places or even collide with their stars.
“The reconfiguration can be quite dramatic when there are several planets,” says Moore. “Although all of the known circumbinary planets are gas giants, it is possible that somewhere out there is a terrestrial circumbinary planet that migrates to an orbit that now makes the planet potentially habitable for a little while.”
Lawrence Livermore National Laboratory researchers have demonstrated for the first time how an asteroid or comet could have caused the mega crater on Phobos without completely destroying the Martian moon.
Mars’ largest moon, Phobos, has captured public imagination and been shrouded in mystery for decades. But numerical simulations recently conducted at Lawrence Livermore National Laboratory (LLNL) have shed some light on the enigmatic satellite.
The dominant feature on the surface of Phobos (22-kilomters across) is Stickney crater (9-km across), a mega crater that spans nearly half the moon. The crater lends Phobos a physical resemblance to the planet-destroying Death Star in the film “Star Wars.” But over the decades, understanding the formation of such a massive crater has proven elusive for researchers.
For the first time, physicists at LLNL have demonstrated how an asteroid or comet impact could have created Stickney crater without destroying Phobos completely. The research, which also debunks a theory regarding the moon’s mysterious grooved terrain, was published in Geophysical Review Letters.
“We’ve demonstrated that you can create this crater without destroying the moon if you use the proper porosity and resolution in a 3D simulation,” said Megan Bruck Syal, an author on the paper and member of the LLNL planetary defense team. “There aren’t many places with the computational resources to accomplish the resolution study we conducted.”
The study showed that there is a range of possible solutions for the size and speed of the impactor, but Syal says one possible scenario is an impact object 250 meters across traveling close to 6 kilometers per second (kps).
Previous studies used 2D simulations at lower resolutions, and they were ultimately unable to replicate Stickney crater successfully. Additionally, prior studies failed to account for the porosity of the Phobos’ crust in their calculations, critical given that Phobos is less dense than the Martian surface.
While the simulations show how a massive impact could have created Stickney crater, they also appear to disprove a related theory. Some have theorized that the hundreds of parallel grooves that appear to radiate from the crater were caused by the impact. However, the simulations in this study show that fracture patterns in the crust of Phobos would be nothing like the straight, long, parallel grooves. On the other hand, the simulations do support the possibility of slow-rolling boulders mobilized by the impact causing the grooves. But more study would be required to fully test that theory.
The research served as a benchmarking exercise for the LLNL planetary defense team in their use of an open source code developed at LLNL called Spheral. The team uses codes like Spheral to simulate various methods of deflecting potentially hazardous Earth-bound asteroids.
“Something as big and fast as what caused the Stickney crater would have a devastating effect on Earth,” Syal said. “If NASA sees a potentially hazardous asteroid coming our way, it will be essential to make sure we’re able to deflect it. We’ll only have one shot at it, and the consequences couldn’t be higher. We do this type of benchmarking research to make sure our codes are right when they will be needed most.”
The dusty side of the Sword of Orion is illuminated in this striking infrared image from ESA’s Hershel Space Observatory. Within the inset image, the emission from ionized carbon atoms (C+) is overlaid in yellow. Credits: ESA/NASA/JPL-Caltech
Life exists in a myriad of wondrous forms, but if you break any organism down to its most basic parts, it’s all the same stuff: carbon atoms connected to hydrogen, oxygen, nitrogen and other elements. But how these fundamental substances are created in space has been a longstanding mystery.
Now, astronomers better understand how molecules form that are necessary for building other chemicals essential for life. Thanks to data from the European Space Agency’s Herschel Space Observatory, scientists have found that ultraviolet light from stars plays a key role in creating these molecules, rather than “shock” events that create turbulence, as was previously thought.
Scientists studied the ingredients of carbon chemistry in the Orion Nebula, the closest star-forming region to Earth that forms massive stars. They mapped the amount, temperature and motions of the carbon-hydrogen molecule (CH, or “methylidyne” to chemists), the carbon-hydrogen positive ion (CH+) and their parent: the carbon ion (C+). An ion is an atom or molecule with an imbalance of protons and electrons, resulting in a net charge.
“On Earth, the sun is the driving source of almost all the life on Earth. Now, we have learned that starlight drives the formation of chemicals that are precursors to chemicals that we need to make life,” said Patrick Morris, first author of the paper and researcher at the Infrared Processing and Analysis Center at Caltech in Pasadena.
In the early 1940s, CH and CH+ were two of the first three molecules ever discovered in interstellar space. In examining molecular clouds — assemblies of gas and dust — in Orion with Herschel, scientists were surprised to find that CH+ is emitting rather than absorbing light, meaning it is warmer than the background gas. The CH+ molecule needs a lot of energy to form and is extremely reactive, so it gets destroyed when it interacts with the background hydrogen in the cloud. Its warm temperature and high abundance are therefore quite mysterious.
Why, then, is there so much CH+ in molecular clouds such as the Orion Nebula? Many studies have tried to answer this question before, but their observations were limited because few background stars were available for studying. Herschel probes an area of the electromagnetic spectrum — the far infrared, associated with cold objects — that no other space telescope has reached before, so it could take into account the entire Orion Nebula instead of individual stars within. The instrument they used to obtain their data, HIFI, is also extremely sensitive to the motion of the gas clouds.
One of the leading theories about the origins of basic hydrocarbons has been that they formed in “shocks,” events that create a lot of turbulence, such as exploding supernovae or young stars spitting out material. Areas of molecular clouds that have a lot of turbulence generally create shocks. Like a large wave hitting a boat, shock waves cause vibrations in material they encounter. Those vibrations can knock electrons off atoms, making them ions, which are more likely to combine. But the new study found no correlation between these shocks and CH+ in the Orion Nebula.
Herschel data show that these CH+ molecules were more likely created by the ultraviolet emission of very young stars in the Orion Nebula, which, compared to the sun, are hotter, far more massive and emit much more ultraviolet light. When a molecule absorbs a photon of light, it becomes “excited” and has more energy to react with other particles. In the case of a hydrogen molecule, the hydrogen molecule vibrates, rotates faster or both when hit by an ultraviolet photon.
It has long been known that the Orion Nebula has a lot of hydrogen gas. When ultraviolet light from large stars heats up the surrounding hydrogen molecules, this creates prime conditions for forming hydrocarbons. As the interstellar hydrogen gets warmer, carbon ions that originally formed in stars begin to react with the molecular hydrogen, creating CH+. Eventually the CH+ captures an electron to form the neutral CH molecule.
“This is the initiation of the whole carbon chemistry,” said John Pearson, researcher at NASA’s Jet Propulsion Laboratory, Pasadena, California, and study co-author. “If you want to form anything more complicated, it goes through that pathway.”
Scientists combined Herschel data with models of molecular formation and found that ultraviolet light is the best explanation for how hydrocarbons form in the Orion Nebula.
The findings have implications for the formation of basic hydrocarbons in other galaxies as well. It is known that other galaxies have shocks, but dense regions in which ultraviolet light dominates heating and chemistry may play the key role in creating fundamental hydrocarbon molecules there, too.
“It’s still a mystery how certain molecules get excited in the cores of galaxies,” Pearson said. “Our study is a clue that ultraviolet light from massive stars could be driving the excitation of molecules there, too.”
Gene puddle primeval, a drawing by first author Christine He illustrates her discovery that viscosity moves spontaneous gene strand copying forward. Credit: Georgia Tech / Christine He
The original recipe for gene soup may have been simple — rain, a jumble of common molecules, warm sunshine, and nighttime cooling. Then add a pinch of thickener.
The last ingredient may have helped gene-like strands to copy themselves in puddles for the first time ever, billions of years ago when Earth was devoid of life, researchers at the Georgia Institute of Technology have found. Their novel discoveries add to a growing body of evidence that suggests first life may have evolved with relative ease, here and possibly elsewhere in the universe.
And they offer a straightforward answer to a gnawing 50-year-old question: How did precursors to the present-day genetic code first duplicate themselves before the existence of enzymes that are indispensable to that process today?
The spice of life?
For generations, scientists pursuing an answer performed experiments in water but hit a wall.
Georgia Tech researchers Christine He and Isaac Gállego overcame it by adding an off-the-shelf viscous solvent (the thickener). In separate experiments with DNA then RNA, the copying process proceeded.
“I think it’s very, very different from anything that’s been done before,” said researcher He. “We can change the physical environment in an easy way, and promote these processes that wouldn’t happen in conditions ordinarily being used.”
Easy is crucial, said Martha Grover, a professor who oversaw the research at Georgia Tech’s School of Chemical and Biomolecular Engineering. Easy reactions are likely to be more productive and more prevalent.
“A simple and robust process like this one could have operated in a variety of environments and concentrations making it more realistic in moving evolution forward,” she said.
Grover’s lab and that of Nick Hud at Georgia Tech’s School of Chemistry and Biochemistry published the results on Monday, October 10, 2016 in the journal Nature Chemistry. Their research has been funded by the National Science Foundation and the NASA Astrobiology Program under the NASA/NSF Center for Chemical Evolution.
Researcher Christine He shows Professor Martha Grover a gel slide that separates out gene strands. Credit: Georgia Tech / Rob Felt
Earliest life was based on RNA, or a similar polymer, according to a hypothesis called the RNA World. In that scenario, on the evolutionary timeline, the self-replication of RNA strands long enough to be potential genes would roughly mark the doorstep to life.
Those long nucleotide chains may have been mixed together in puddles with shorter nucleotide chains. Heat from the sun would have made long strands detach from their helix structures, giving short ones a chance to match up with them, and become their copies.
But there’s a problem.
In water alone, when cooling sets in, the long chains snap back into their helix structure so rapidly that there’s no time for the matching process with the shorter chains. That snapping shut, which happens in both RNA and DNA, is called “strand inhibition,” and in living cells, enzymes solve the problem of keeping the long chains apart while gene strands duplicate.
More like a stew
“The problem is a problem in water, which everybody sort of looks at in prebiotic (pre-life) chemistry,” said graduate research assistant He. She felt it was time to rethink that, and her expertise in chemical engineering helped.
High viscosity has been known to slow down the movement of long strands of DNA, RNA and other polymers.
“It’s a little like making them swim in honey,” Grover said. Applying that to origin-of-life chemistry seemed obvious, because in prebiotic times, there probably were quite a few sticky puddles.
“In that solution, it gives the short nucleotides, which move faster, time to jump onto the long strand and piece together a duplicate of the long strand,” researcher He said. In her experiments, it worked.
Image “a” shows that water alone will not allow copying to go forward. Image “b” shows that viscosity allows gene strands to pair up with components of potential copies. Credit: Georgia Tech / Christine He
Hairpins in the soup
And it produced an encouraging surprise. The DNA and RNA strands folded onto themselves forming shapes called hairpins.
“In the beginning, we didn’t realize the importance of the internal structure,” Christine He said. Then they noticed that the shape was helping keep RNA and DNA available for the pairing process. “Hairpin formation is integral to keeping them open,” Grover said.
But it also could have accelerated chemical evolution in another way. “The solution is selecting here for sequences that fold, and that would have more potential for functional activity – like a ribozyme,” said researcher He.
Ribozymes are enzymes made of RNA, and enzymes catalyze biochemical processes. To have them evolve in the same solution that promotes genetic code replication could have shortened the path to first life.
“You really need to amplify functional sequences for evolution to move forward,” Grover said. The folds were an unexpected side-effect, and finding them paves the way for future research.
The Georgia Tech scientists used real gene strands in their experiments, which may sound mundane, but in the past, some researchers have specially engineered DNA and RNA sequences in attempts to arrive at similar results.
He and Gállego’s use of a naturally occurring gene, rather than a specifically engineered sequence, shows that viscosity could have been a very general solution to promote copying of nucleic acids with mixed length and sequences.
To facilitate quick, clear outcomes, the Georgia Tech researchers used purified short nucleotide chains and applied them in ratios that favored productive reactions. But they had started out with messier, less pure ingredients, and the experience was worthwhile.
“Considering a pre-biotic soup, it’s probably messy; it’s got a lot of impurities,” Christine He said. “When we first started out with more impure nucleotides, it still worked. Maybe the same reaction really could have happened in a messy puddle billions of years ago.”
The viscous solvent was glycholine, a mixture of glycerol and choline chloride. It was not likely present on pre-biotic Earth, but other viscous solvents likely were.
Also, after the short strands matched up to each long one, the researchers did apply an enzyme to join the aligned short pieces into a long chain, in a biochemical process called ligation.
The enzymes would not have been present on a prebiotic Earth, and although there are chemical procedure for ligating RNA, “no one has developed a chemistry so robust yet that it could replace the enzyme,” Grover said.
Finding one that could have worked on a prebiotic Earth would be a worthy aim for further research.
Will astronauts traveling to Mars remember much of it? That’s the question concerning University of California, Irvine scientists probing a phenomenon called “space brain.”
UCI’s Charles Limoli and colleagues found that exposure to highly energetic charged particles – much like those found in the galactic cosmic rays that will bombard astronauts during extended spaceflights – causes significant long-term brain damage in test rodents, resulting in cognitive impairments and dementia.
Their study appears today in Nature’s Scientific Reports. It follows one last year showing somewhat shorter-term brain effects of galactic cosmic rays. The current findings, Limoli said, raise much greater alarm. (Link to study: www.nature.com/articles/srep34774)
“This is not positive news for astronauts deployed on a two-to-three-year round trip to Mars,” said the professor of radiation oncology in UCI’s School of Medicine. “The space environment poses unique hazards to astronauts. Exposure to these particles can lead to a range of potential central nervous system complications that can occur during and persist long after actual space travel – such as various performance decrements, memory deficits, anxiety, depression and impaired decision-making. Many of these adverse consequences to cognition may continue and progress throughout life.”
For the study, rodents were subjected to charged particle irradiation (fully ionized oxygen and titanium) at the NASA Space Radiation Laboratory at New York’s Brookhaven National Laboratory and then sent to Limoli’s UCI lab.
Six months after exposure, the researchers still found significant levels of brain inflammation and damage to neurons. Imaging revealed that the brain’s neural network was impaired through the reduction of dendrites and spines on these neurons, which disrupts the transmission of signals among brain cells. These deficiencies were parallel to poor performance on behavioral tasks designed to test learning and memory.
In addition, the Limoli team discovered that the radiation affected “fear extinction,” an active process in which the brain suppresses prior unpleasant and stressful associations, as when someone who nearly drowned learns to enjoy water again.
“Deficits in fear extinction could make you prone to anxiety,” Limoli said, “which could become problematic over the course of a three-year trip to and from Mars.”
Most notably, he said, these six-month results mirror the six-week post-irradiation findings of a 2015 study he conducted that appeared in the May issue of Science Advances.
Similar types of more severe cognitive dysfunction are common in brain cancer patients who have received high-dose, photon-based radiation treatments. In other research, Limoli examines the impact of chemotherapy and cranial irradiation on cognition.
While dementia-like deficits in astronauts would take months to manifest, he said, the time required for a mission to Mars is sufficient for such impairments to develop. People working for extended periods on the International Space Station, however, do not face the same level of bombardment with galactic cosmic rays because they are still within the Earth’s protective magnetosphere.
Limoli’s work is part of NASA’s Human Research Program. Investigating how space radiation affects astronauts and learning ways to mitigate those effects are critical to further human exploration of space, and NASA needs to consider these risks as it plans for missions to Mars and beyond.
Partial solutions are being explored, Limoli noted. Spacecraft could be designed to include areas of increased shielding, such as those used for rest and sleep. However, these highly energetic charged particles will traverse the ship nonetheless, he added, “and there is really no escaping them.”
Preventive treatments offer some hope. Limoli’s group is working on pharmacological strategies involving compounds that scavenge free radicals and protect neurotransmission.
Artist’s impression of a gamma ray burst hitting the Earth. The gamma rays would trigger changes in the Earth’s atmosphere. Credit: NASA
Despite the obvious doom and gloom associated with mass extinctions, they have a tendency to capture our imagination. After all, the sudden demise of the dinosaurs, presumably due to an asteroid strike, is quite an enthralling story.
But not all mass extinctions are quite as dramatic and not all have an easily identified culprit. The Ordovician extinction — one of the “big five” in Earth’s history — occurred around 450 million years ago when the population of marine species plummeted. Evidence suggests that this occurred during an ice age and a gamma ray burst is one of several possible mechanisms that may have triggered this extinction event.
Gamma ray bursts (GRBs) are the brightest electromagnetic blasts known to occur in the Universe, and can originate from the collapse of the most massive types of stars or from the collision of two neutron stars. Supernovae are stellar explosions that also can send harmful radiation hurtling towards Earth. Both GRBs and supernovae are usually observed in distant galaxies, but can pose a threat if they occur closer to home, where they can strip the Earth’s upper atmosphere of its protective ozone layer leaving life exposed to harmful ultraviolet radiation from the Sun.
A new paper, titled “Ground-Level Ozone Following Astrophysical Ionizing Radiation Events – An Additional Biological Hazard?” published in the journal Astrobiology took a look at the ramifications of a nearby GRB or supernova and the effects on life. The research was funded by the Exobiology and Evolutionary Biology element of the NASA Astrobiology Program.
The marine life of the Ordovician fell victim to a mass extinction, the cause of which might have been a gamma ray burst. Credit: William B.S. Berry
Less ozone there, more ozone here
Normally, the ozone layer in the upper atmosphere shields the Earth’s surface from harmful ultraviolet light. But a GRB or supernova would quickly eviscerate that layer. As the UV rays penetrate the planet’s surface they would break apart oxygen molecules and ground-level ozone would form, according to Washburn University astrophysicist Brian Thomas. We see this kind of ozone on hot, polluted days when smog alerts warn us to stay indoors for health reasons. But would the ground-level ozone created after a GRB pose a longterm biological threat? Thomas and his colleague Byron Goracke investigated the severity of this ground-level ozone and its potential effects on life using an atmospheric model to simulate a particular case of a GRB occurring over the South Pole.
“A GRB could happen over any latitude or time but we chose the South Pole mainly to look at a very high depletion case,” explains Thomas. “When the radiation enters the atmosphere over a pole, the depletion is concentrated there instead of spread around the globe.”
This is because the radiation produces chemical changes in the middle atmosphere, and atmospheric transport from this region is mainly towards the pole making the effect of the GRB most extreme in this location. A burst at the South Pole fits in with theories of the Ordovician extinction because the measured extinction rates match the models that predicts latitude-dependent biological damage.
The ozone layer in the stratosphere blocks harmful UV radiation from reaching the surface of the Earth. A gamma ray burst would deplete the ozone layer, allowing UV radiation through. Credit: NASA
Thomas and his team of researchers used computer models to determine that the amount of ozone present in the lower atmosphere following a GRB concentrated on the South Pole is around 10 parts per billion (ppb) and this amount varies with the seasons.
However, it takes at least 30 ppb of ozone to increase the risk of death due to respiratory failure in humans. Ground-level ozone can also damage plants by reducing chlorophyll production or killing the cells outright, but once again there needs to be at least 30 ppb in the atmosphere before ozone becomes a risk to vegetation.
Ozone is also water soluble, which is particularly relevant to the Ordovician mass extinction as most life at the time was marine life. If all of the 10 ppb of ozone generated by a GRB became dissolved in the oceans, it would still only have a very minor impact, if any, on some bacteria and fish larvae, and wouldn’t have played a part in the Ordovician mass extinction. It’s quite clear, therefore, that a GRB event alone does not cause the kind of elevated ground-level ozone that’s deadly to life.
However, this negative result is still vital to understanding what would or wouldn’t happen to the Earth’s atmosphere and its inhabitants following the energy from a GRB or supernova reaching our planet. A GRB would deplete the ozone layer in the upper atmosphere, allowing harmful UV radiation to reach the ground and thus have dire consequences for life. However, the ground-level ozone caused by the GRB would not be an additional hazard for life.
Understanding what causes mass extinctions is also important for the search for life in the Universe. Discovering a planet that ticks all the boxes for habitability may sound promising, but perhaps less so if a GRB or supernova recently occurred nearby. In the hunt for life we also need to consider the possibility that any life that might have existed on a distant planet could already be extinct.
Two 2001 images from the Mars Orbiter Camera on NASA’s Mars Global Surveyor orbiter show a dramatic change in the planet’s appearance when haze raised by dust-storm activity in the south became globally distributed. The images were taken about a month apart. Credits: NASA/JPL-Caltech/MSSS
Global dust storms on Mars could soon become more predictable — which would be a boon for future astronauts there — if the next one follows a pattern suggested by those in the past.
A published prediction, based on this pattern, points to Mars experiencing a global dust storm in the next few months. “Mars will reach the midpoint of its current dust storm season on October 29th of this year. Based on the historical pattern we found, we believe it is very likely that a global dust storm will begin within a few weeks or months of this date,” James Shirley, a planetary scientist at NASA’s Jet Propulsion Laboratory, Pasadena, California.
Local dust storms occur frequently on Mars. These localized storms occasionally grow or coalesce to form regional systems, particularly during the southern spring and summer, when Mars is closest to the sun. On rare occasions, regional storms produce a dust haze that encircles the planet and obscures surface features beneath. A few of these events may become truly global storms, such as one in 1971 that greeted the first spacecraft to orbit Mars, NASA’s Mariner 9. Discerning a predictable pattern for which Martian years will have planet-encircling or global storms has been a challenge.
The most recent Martian global dust storm occurred in 2007, significantly diminishing solar power available to two NASA Mars rovers then active halfway around the planet from each other — Spirit and Opportunity.
“The global dust storm in 2007 was the first major threat to the rovers since landing,” said JPL’s John Callas, project manager for Spirit and Opportunity. “We had to take special measures to enable their survival for several weeks with little sunlight to keep them powered. Each rover powered up only a few minutes each day, enough to warm them up, then shut down to the next day without even communicating with Earth. For many days during the worst of the storm, the rovers were completely on their own.”
This graphic indicates a similarity between 2016 (dark blue line) and five past years in which Mars has experienced global dust storms (orange lines and band), compared to years with no global dust storm (blue-green lines and band). The horizontal scale is time-of-year on Mars. Credits: NASA/JPL-Caltech
Dust storms also will present challenges for astronauts on the Red Planet. Although the force of the wind on Mars is not as strong as portrayed in an early scene in the movie “The Martian,” dust lofted during storms could affect electronics and health, as well as the availability of solar energy.
The Red Planet has been observed shrouded by planet-encircling dust nine times since 1924, with the five most recent planetary storms detected in 1977, 1982, 1994, 2001 and 2007. The actual number of such events is no doubt higher. In some of the years when no orbiter was observing Mars up close, Mars was poorly positioned for Earth-based telescopic detection of dust storms during the Martian season when global storms are most likely.
Shirley’s 2015 paper in the journal Icarus reported finding a pattern in the occurrence of global dust storms when he factored in a variable linked to the orbital motion of Mars. Other planets have an effect on the momentum of Mars as it orbits the solar system’s center of gravity. This effect on momentum varies with a cycle time of about 2.2 years, which is longer than the time it takes Mars to complete each orbit: about 1.9 years. The relationship between these two cycles changes constantly. Shirley found that global dust storms tend to occur when the momentum is increasing during the first part of the dust storm season. None of the global dust storms in the historic record occurred in years when the momentum was decreasing during the first part of the dust storm season.
The paper noted that conditions in the current Mars dust-storm season are very similar to those for a number of years when global storms occurred in the past. Observations of the Martian atmosphere over the next few months will test whether the forecast is correct.
Researchers at Malin Space Science Systems, in San Diego, post Mars weather reports each week based on observations using the Mars Color Imager camera on NASA’s Mars Reconnaissance Orbiter. A series of local southern-hemisphere storms in late August grew into a major regional dust storm in early September, but subsided by mid-month without becoming global. Researchers will be closely watching to see what happens with the next regional storm.
Artist concept of Transiting Exoplanet Survey Satellite. Credits: NASA’s Goddard Space Flight Center/Chris Meaney
NASA’s search for planets outside of our solar system has mostly involved very distant, faint stars. NASA’s upcoming Transiting Exoplanet Survey Satellite (TESS), by contrast, will look at the brightest stars in our solar neighborhood.
After TESS launches, it will quickly start discovering new exoplanets that ground-based observatories, the Hubble Space Telescope and, later, the James Webb Space Telescope, will target for follow-up studies. TESS is scheduled to launch no later than June 2018. Astronomers are eagerly anticipating the possibility that, in the near future, all three space missions could be studying the sky at the same time.
“The problem is that we’ve had very few exoplanet targets that are good for follow-up,” said TESS Project Scientist Stephen Rinehart at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “TESS will change that.”
Planets around closer, brighter stars are ideal for follow-up study because they’ll produce stronger signals than planets around more distant stars. These planets have a higher signal-to-noise ratio, which measures the ratio of useful information — the signal — to non-useful information — the noise — that a telescope receives. These signals might also include a chemical sampling of an exoplanet’s atmosphere, which is an exciting prospect for scientists hoping to search for signs of life on distant worlds.
TESS will do the initial roundup of exoplanets, with the potential to identify thousands during its projected two-year mission. One of TESS’ main science goals is to identify 50 rocky worlds, like Earth or Venus, whose masses can be measured.
“The search for exoplanets is a bit like a funnel where you pour in lots of stars,” said TESS Deputy Science Director Sara Seager at the Massachusetts Institute of Technology (MIT), Cambridge. “At the end of the day, you have loads of planets, and from there you need to find the rocky ones.”
The TESS Science Center will help identify and prioritize the TESS Objects of Interest (TOI) for follow-up. TOI are objects that scientists believe could be exoplanets based on TESS data. Ground-based telescopes will confirm which TOI are exoplanets, and from there will help determine which are rocky. The center is a partnership between MIT’s Physics Department and Kavli Institute for Astrophysics and Space Research — where TESS Principle Investigator George Ricker resides — the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, and NASA’s Ames Research Center in Moffett Field, California.
The main thing space- and ground-based telescopes hope to find out about the TESS targets with follow-up observations is what these exoplanet atmospheres are like. Exoplanet atmosphere exploration is one of the Webb telescope’s four main science goals.
NASA’s Webb telescope and ground-based telescopes will determine the atmospheres of exoplanets using spectroscopy. In this process, telescopes look at the chemical signatures of the light passing through exoplanet atmospheres. This signature can tells scientists what chemicals are in the planetary atmosphere, and how much of each there are. It can also help scientists determine whether a planet could be habitable.
“There are a couple of things we like to see as a potential for habitability – one of them is water, which is probably the single most important, because as far as we know, all life that we’re familiar with depends on water in some way,” Rinehart said. “The other is methane, which on our Earth is produced almost entirely biologically. When you start seeing certain combinations of all of these things appearing together – water, methane, ozone, oxygen – it gives you a hint that the chemistry is out of equilibrium. Naturally, planets tend to be chemically stable. The presence of life throws off this balance.”
Exoplanets aren’t the only science that will come out of the TESS all-sky survey, however. While scientists expect to spot a transit signal that could reveal exoplanets around only about one out of 100 stars, virtually every star in the sky will be monitored carefully and continuously for at least 27 days, resulting in a wide variety of variability to be explored.
The TESS Guest Investigator (GI) Program will allow for deeper investigations of astronomically interesting objects, either through TESS data alone, or by identifying interesting variables for further study with the Webb telescope, Hubble and other ground- and space-based telescopes. The GI Program will look at variable objects, such as flare stars, active galaxies and supernovae, and may even discover optical counterparts to distant transient events, such as gamma-ray bursts. Only the number and type of exciting proposed ideas the program receives limit what TESS will find through the GI Program.
Between the mission’s exoplanet survey and the GI Program, TESS will provide the best follow-up targets for many missions to come.
“TESS not only will provide targets for the Webb telescope, but for every telescope we plan to build on the ground and in space over the next two decades,” said Mark Clampin, director of the Astrophysics Science Division at Goddard. With such an exciting future, scientists from around the world are watching the progress of the TESS mission, and anxiously awaiting its launch.