Top Ten 2005 Astrobiology Stories

Bulls-eye. Smashing success with impact. Deep Impact ejecta from interceptor which probed the interior of comet Tempel 1.
Credit: NASA/JPL

The year in space exploration has offered a range of topics for astronomy and astrobiology. Astrobiology Magazine compiled its list of top ten stories for 2005. Exploration of Mars and Saturn was among the highlights in a review of astrobiology advances over the last twelve months in our own solar system and beyond.

10) New planet in our solar system

A planet larger than Pluto has been discovered in the outlying regions of the solar system. Currently about 97 astronomical units from the sun (an astronomical unit is the distance between the sun and Earth), the planet becomes the farthest-known object in the solar system, and the third brightest of the Kuiper belt objects.

9) Possible martian frozen sea

Scientists announced they had found a frozen sea on the martian equator. Mars was warm and wet during its first billion years, and has probably had vast underground water reserves ever since, from 3 or 4 billion years ago to at least 5 million years ago. But water ice is not stable under Mars atmospheric pressure. The obvious candidate for the covering is volcanic ash and dust. When this volcanic eruption happened, there’s evidence that the Cerberus Fossae spewed both volcanic ash and dust. The water filled a vast area the size of Lake Michigan, and the surface then froze.

8) "SuperEarth" extrasolar planet

In the land rush known as extrasolar planet hunting, the most prized real estate is advertised as "Earth-like." On June 13, scientists raced to plant their flag on a burning hunk of rock orbiting a red star. This newly discovered planet is about seven times the mass of Earth, and therefore the smallest extrasolar planet found to orbit a main sequence, or "dwarf" star (stars, like our sun, that burn hydrogen). Planets that are ten Earth masses or less are thought to be rocky, while more massive planets are probably gaseous, since their stronger gravity means they collect and retain more gas during planetary formation. 155 extrasolar planets have been found so far, but most of them have masses that are more comparable to gaseous Jupiter than rocky Earth (Jupiter is 318 times the mass of Earth). The Kepler mission, due to launch in June 2008, will search for terrestrial planets orbiting distant stars. The mission defines an Earth-size planet as being between 0.5 and 2.0 Earth masses, or between 0.8 and 1.3 Earth’s diameter. Planets between 2 and 10 Earth masses, such as the planet announced in June, are defined as Large Terrestrial planets.

7) Extrasolar planets around "M" red dwarf stars

Empty nest view back to landing petal from the mobile Opportunity rover, which has ventured across the surface for two years. Credit: NASA/JPL

When you look up at the night sky, none of the stars you see are M dwarfs. These diminutive stars, much smaller and dimmer than our own sun aren’t bright enough to see with the naked eye. Yet M dwarfs (also known as red dwarfs) are by far the most common stars around, comprising some 70 percent of all the stars in our galaxy. Historically, scientists interested in the search for extrasolar life have shied away from studying M dwarfs. Because they put out much relatively paltry amounts of light and heat, compared to the sun, the general feeling among scientists was that they were unlikely to host habitable planets. That view is changing. The big argument has always been that to put a planet in the so-called habitable zone [of an M dwarf], you have to move it in so close to the star – because the star is so much cooler and has less radiation – that it locks, just like the moon tidally locks to the Earth. And so you have the same face of the planet facing the star all the time. And if you do that, it has been said, that you’d be boiling away any atmosphere or ocean on the side facing the star and it would be trapped on the dark side and would freeze out. It turns out that’s probably not right. The locking would occur. But it doesn’t take that much atmosphere to redistribute the heat.

6) Mars Rovers, still exploring

Life may have had a tough time getting started in the ancient environment that left its mark in the Martian rock layers examined by NASA’s Opportunity rover. Two years following the rover’s successful landing, the most thorough analysis yet of the Opportunity’s discoveries reveals the challenges life may have faced in the harsh Martian environment. Scientists have been able to deduce conditions in the Meridiani Planum region of Mars were sometimes wet, strongly acidic and oxidizing. Those conditions probably posed stiff challenges to the origin of Martian life. The stack of layers in Endurance Crater resulted from a changeable environment perhaps 3.5 to 4 billion years ago. The area may have looked like salt flats occasionally holding water, surrounded by dunes. The White Sands region in New Mexico bears a similar physical resemblance.

5) First image of extrasolar planet

Composite image of the brown dwarf object 2M1207 (center) and the fainter object seen near it that may be an extrasolar planet candidate. The photo is based on three near-infrared exposures (in the H, K and L’ wavebands) with the NACO adaptive-optics facility at the 8.2-m VLT Yepun telescope at the ESO Paranal Observatory. The discovery designated 2MASSWJ1207334-393254, 2M1207, was made with the adaptive-optics supported NACO facility at the 8.2-meter VLT Yepun telescope at the ESO Paranal Observatory (Chile).
Credit: ESO

An international team of astronomers reported confirmation of the discovery of a giant planet, approximately five times the mass of Jupiter, that is gravitationally bound to a young brown dwarf. This puts an end to a year long discussion on the nature of this object, which started with the detection of a red object close to the brown dwarf. The planet is near the southern constellation of Hydra, approximately 200 light years from the Earth. The planet is located at a distance of 55 AU from it host brown dwarf. The spectrum of the giant planet presents a strong signature of water molecules, thereby confirming that it must be cold.

4) Deep Impact: Collision with a Comet

The comet Tempel 1 has a new crater, the result of a fatal encounter with a NASA spacecraft. This is the first time a man-made spacecraft has touched the surface of a comet. The first medium resolution images of the impact show a starburst on the bottom half of a lumpy, potato-looking nucleus. Both the crater and the impact ejecta will indicate what lies under the comet’s icy surface, helping scientists better understand how comets are constructed. This, in turn, could lead to a better understanding of the origin of the solar system. Comets formed in the outer solar system 4.5 billion years ago, at the same time that the planets were forming.

3) Cassini images and data of Saturn system

On June 30, 2004 Cassini became the first spacecraft to orbit Saturn and began a four-year study of the planet, its rings and its 31 known moons. Launched in 1997, Cassini carries 12 scientific instruments imaging the saturnian system with radar and at various wavelengths. Since the two Voyager spacecraft sped past Saturn nearly 25 years ago, scientists have marveled at its giant magnetosphere and the plasma — a complex magnetized fluid of hot charged particles — confined within it. Plasma trapped around Earth is a comparatively simple mix of ingredients drawn exclusively from the solar wind and the Earth’s atmosphere — our Moon contributes virtually nothing. In contrast, icy moons, rings, and the atmosphere of the giant moon Titan all contribute to Saturn’s swirling plasma. Using new data from the Cassini mission, scientists began in 2005 to tease out the mélange of ingredients and processes that contribute to the ringed planet’s surprisingly complicated magnetosphere.

2) Huygens landing

The Huygens probe parachuted down to Titan’s icy surface on January 14, 2005. Although the Saturn’s giant moon is shrouded by a thick atmospheric haze which continues all the way down to the surface, the probe still was able to capture images of mountains and dark river channels as it descended. These now-dry channels led scientists to believe that liquid methane must flow on Titan’s surface periodically. Several hundred images were captured by the Huygens probe during its descent through the atmosphere of Titan. They revealed a world of diverse landforms, shaped at least in part by fluid erosion. Two of the images are reminiscent of early photographs of Mars. Titan’s surface, shows a pattern of branching channels that look like canyons on Earth cut by water. It’s unlikely that water was responsible in Titan’s case, though; Titan is far too cold for liquid water to flow on its surface. Surface imagery, however, was perhaps the most stunning of all. Taken from the surface of Titan, the lander’s view shows a plain of what appear to be boulders stretching to the horizon. At first glance, it resembles a martian landscape. The Huygens landing site is probably an icy mixture of granular materials and methane.

Shorelines may be dry but intermittently defined by drainage channels of methane rain. Click image for larger view. Credit: ESA

1) Titan, revealed

Titan is often described as a passport to the early Earth, showing us what our own planet may have been like before life developed. Titan is the only moon in the solar system with a substantial atmosphere. On Earth, methane (CH4) is produced by life, the degradation of organic material, or geologic processes. On freezing cold Titan, where methane is the second-most abundant gas next to nitrogen, it’s long been a mystery how the methane is produced. If there is life on Saturn’s moon Titan, it’s not producing all that methane in the atmosphere. That is one conclusion in a series of Cassini/Huygens mission reports published in December by the journal Nature. Methane is constantly being broken apart by sunlight and cosmic radiation in Titan’s upper atmosphere, so something must be replenishing it. Measurements of the moon’s atmospheric argon and carbon isotopes have led the Huygens scientists to conclude that the methane most likely comes from geologic activity in the moon’s interior rather than from biological processes. The harsh chemistry and frigid temperatures of the moon make many scientists skeptical about the current potential for life on Titan. But precursor organic materials continually rain out of the atmosphere and blanket the surface with a layer of organics that is somewhere between 500 meters and a kilometer thick (1,640 to 3,280 feet).

Related Web Pages

The Search for More Earths
Speeding Up in the Zone
Super-Earth Sought and Found
Rendezvous with Titan
Huygens, Phone Home
Saturn– JPL Cassini Main Page
Saturn Edition, Astrobiology Magaz.
Saturn’s Rings in UV
Cassini Closes In on Saturn

2003: Year in Review
Solar System Exploration Survey
2004: Year in Review