New planets and signs of life in space
|"When you discover a new planetary system, you are overwhelmed and sit and think, here is an entire new world, and I’m the only one who knows about it at this moment." Dr. Bill Cochran|
Credit: Marsha Miller
Blame it on the TV show "The Jetsons" or maybe it was the movie "Bladerunner," but somehow a few of us got the notion, way back in the ’70s and ’80s, that the future would end up being more "futuristic." Well into the 21st century we’re asking, "Where are the flying cars and the hourly shuttles from Earth to the moon, the Burger Kings, penthouses and strip malls on Mars?"
It’s like we were let down by the sexy side of science. Or maybe it just seems that way.
If you corner an astronomer like Dr. Bill Cochran and talk to him for an hour or two, suddenly life in outer space, for example, doesn’t seem nearly so improbable. Cochran, who is a senior research scientist in the College of Natural Sciences’ Department of Astronomy at The University of Texas at Austin, believes it’s an exciting time to be studying the sky and stars and that the future is much, much closer than most of us think.
"Earth is a planet around what is a very common, boring star the Sun," says Cochran. "And there are literally millions of other stars like our Sun nearby, as well as out in the galaxy. There’s really no reason to believe that there is not an Earth-like planet with life on it around at least one of those millions of other stars. Discovering new planets is the first step in finding life in outer space I don’t know that the average person realizes just how likely it is that life did or does exist on other planets out there."
Granted, the phrase "cosmic cowboy" has a corny ring, but there definitely is a rogue aura of romance and a renegade quality to someone like Cochran, who is a modern-day explorer of infinitude.
In the 15 years since Cochran has been a planet hunter, he has discovered six planets outside our solar system. In the year 2000 alone, nine planet discoveries were announced at the International Astronomical Union meeting, and Cochran’s research team was able to boast one of those planet findings.
For physicists and others who are following the lightning-speed advances in space exploration and marveling over the Cassini orbiter’s breathtaking photos of Saturn or NASA’s renewed interest in exploration of Mercury, these are days of miracle and wonder, a renaissance that recalls the Apollo 11 mission and a walk on the moon.
According to Cochran, recent discoveries of giant Jupiter- and Saturn-like planets around faraway stars like our Sun are a first, and very important, step in answering the big question, "Is there life out there?"
"The next step is to find smaller, Earth-like planets around these stars," says Cochran, "but that’s not as simple as swinging a telescope in the right direction and snapping a photo. You go about it in a rather indirect way, and the process takes quite a lot of patience."
|Looking back, no signs of civilization on the blue planet appear except water and clouds.|
To accomplish this second stage of planet discovery, Cochran is working with NASA on the Kepler Mission, which is scheduled to launch in 2007 and search for Earth-like planets around stars beyond our solar system.
Kepler will be roaming the heavens as a sky spy, taking images in the constellation of Cygnus, an enormous area in the Milky Way that many nighttime stargazers know as the Northern Cross.
The spacecraft will make measurements of the brightness of 170,000 stars every three seconds, and these measurements will reveal to Cochran and the rest of the Kepler research team if there is a drop in brightness. If this drop in brightness lasts for a few hours and recurs at regular intervals, Cochran can deduce that the star has a planet orbiting around it. As the planet passes between its parent star and the telescope, it will block out a little bit of the star’s light for a short amount of time. Because of the regularity of periodic dimming, Cochran will be able to predict when he will see the planet again and can determine its size and orbit.
This technique and the concept around which the Kepler imaging is built may sound familiar to anyone who donned dark glasses and watched the rare transit of Venus across the Sun on June 8 of this year. For the brief time that Venus was moving across the line-of-sight between the observer and the Sun, you could look at the Sun and see a little black dot orbiting slowly and blocking out a small bit of the bright disc’s light.
|In a universe brimming with stars, it is difficult to imagine that life exists nowhere else.|
Credit: NASA/ STScI/ ESA
Kepler also is being designed to detect planets in an orbit like the Earth at the same distance from their star as the Earth is from our Sun. With a measure of the orbit of the planet and with information about the planet’s star, scientists can determine if the planet might have liquid water on its surface and, perhaps, sustain life.
"With Kepler, we’ll be looking at 170,000 stars," says Cochran, "and if every star like our Sun has a planet like the Earth orbiting around it, then statistically we should find about 30 to 50 Earth-like planets at Earth-like distances from these stars. If we don’t see any when we expect to see 30 to 50, then that’s a terribly significant result, very important and really surprising."
If Cochran seems unduly obsessed with Earth-like distances and orbits, it’s because most scientists agree that "life," by definition, is carbon-based and requires water and that life forms will be found in a planet environment approximating the delicate balance found on Earth. If a planet is too far away from its star and is frozen or if it’s too close to its star, like fiery Mercury, and is too hot to have water, then scientists say the planet is not in a habitable zone.
"Why does ‘life’ on other planets have to mean the same thing as life on Earth?" asks Cochran. "Well, although we don’t know all there is to know about outer space, we do know chemistry. We know all of the elements that exist naturally and what combinations you can put those elements in, and knowing all of that, we have reason to believe that life elsewhere would resemble life here. Some people have tried to make an argument for silicon-based life on another planet, but you can’t build the nice long strings of molecules out of silicon that you can with carbon. People just haven’t been able to come up with a very good argument for the other side."
|An illustration of the Kepler spacecraft.|
Image Credit: NASA/Ames
In determining if carbon-based life forms could exist on one of the smaller planets, images from Kepler are only one part of the equation. Once Kepler has identified the promising Earth-like planets, the next step is to take starlight that has passed through the atmosphere of the planets and analyze it for any evidence of life
When Cochran describes the tool he uses to detect the presence of planets and stars, he is as animated as a boy with the best toy on the block. Which is not surprising since the best is exactly what he’s got.
"About a decade ago people started building extremely large telescopes that were running in the $100 to $200 million range," says Cochran. "Here at The University of Texas at Austin we quickly realized that to be competitive with the rest of the world we needed to have a large telescope of our own. We couldn’t exactly afford the $200 million price tag, which is what we were looking at if we went with the common design that others were using. So we decided to break the mold, do something ‘uncommon’ and not construct a general-purpose telescope. We intentionally ‘crippled’ the telescope, drastically cut costs and built one that does one thing and does it really, really well."
Built by a consortium of five universities, with The University of Texas at Austin being the lead partner, the Hobby-Eberly Telescope (HET) sits at the McDonald Observatory in the Davis Mountains of West Texas and is able to collect about 10 times as much light as the other telescopes at the observatory.
The result of a creative idea from two astronomers at Pennsylvania State University, the HET boasts a completely revolutionary design that reduced the cost to around 15 to 20 percent of other telescopes in its class without reducing functionality. Unlike larger all-purpose telescopes such as the four built in Chile by a consortium of European nations, the HET cannot point at every spot in the sky, but instead is always pointing, as it rotates, 35 degrees from the zenith.
This "limitation" of covering around 70 percent of the sky dropped the cost far below $100 million and still allows scientists to gather the data they need. Stars rise in the east and move across the sky, setting in the west. At some point during the night, most of the stars pass through the HET’s viewable zone and can be seen for around 45 minutes during each transit.
|The gravitational pull of an unseen planet causes a star to wobble. As the star moves toward an observer, the wavelength of the star’s light is squeezed and becomes more blue. As the star moves away from the observer, the wavelength is stretched and the light becomes more red.|
"That’s the big innovation that made this telescope affordable," says Cochran. "Another novel feature of the HET that also made it less expensive is that rather than having an enormous mirror or a small number of fairly big mirrors, we built a huge number of small mirrors. They’re all around one yard in size, so they’re very easy to build and maintain and are completely interchangeable. The penalty we paid is that we’re unable to take sharp pictures with the telescope. We were fine with throwing that task overboard and letting telescopes in much better sites, and that already do it better, deliver that product. The HET is built to excel in another area, and we are a world leader in this area."
The area to which Cochran refers is the very precise measurement of the velocity of a star as both the star and planet orbit around an imaginary point between them called the center of gravity. Planet hunters are a bit handicapped in not being able to simply aim a telescope and view the planets that may orbit stars outside our solar system. Once again, an indirect method of detection and powers of deduction based on scientific evidence must be used.
If a planet is orbiting the star, there will be telltale signs of that in the orbit of the star itself viewed from Earth, the star will seem to be pulled and be wobbling slightly from the influence of the unseen planet. A series of measurements by the HET of the star slightly coming toward us, then slightly moving away from us as it makes its tight orbit, cues astronomers that a planet or perhaps more than one planet is present.
Although the technologically advanced, cathedral-like HET provides the means to locate new planets, a final quirk of the telescope that has nothing to do with the actual machinery is proving to be its best trait. Unlike other large telescopes, the HET is accessed by astronomers through something called "queue scheduling" 100 percent of the time.
This simply means that, rather than reserving viewing time at the observatory and physically traveling to West Texas to operate the telescope, astronomers can give a list of projects to a resident astronomer at the HET. The projects are flagged high or low priority, and the resident astronomer and telescope operator select the project best suited to a given night’s weather conditions and Moon phase.
"This makes the HET truly superior," says Cochran. "It works very well for planet detection because I’m not limited to gathering data on one night that was assigned to me six months ago, when the weather may turn out to be rotten or something, and then again on some random night next month when, again, conditions may not be what I need them to be. I can, if I need it, have 15 or 20 minutes every night, for example, taking advantage of optimal viewing times. The astronomers control the schedule rather than the schedule dictating what they can accomplish."
Cochran attributes some of the efficiency and speed with which he now is locating new planets to the queue scheduling. Earlier in July, Cochran made newspaper headlines with the discovery of the first planet outside our solar system found using the HET.
"If the HET had employed a ‘normal’ scheduling system," says Cochran, "it would have taken us a year or two to confirm the existence of this planet."
The recent discovery with HET of the lyrically named planet HD 37605b in the constellation Orion brought a special thrill of excitement to Cochran. It was hard proof that a telescope that is still the new kid on the block had hit its stride and was performing as it should.
"Building the HET cheaply was very difficult, and the HET staff has worked quite hard over the past two years to get it working to specs," says Cochran. "This latest planet find is a true victory and exhibits to everyone the power of queue scheduling. When I told our resident astronomer that I needed new data every three days for two weeks, for example, he could react. Right now, we’re the best in the world at doing this."
|Earth as seen by the departing Voyager spacecraft: a tiny, pale blue dot. Credit: NASA|
For Cochran, the promise of the future is irresistible and past victories make him bold in his predictions for what lies just over the horizon. Cochran says there is every reason to believe that in his lifetime Earth-like planets around Sun-like stars will be found. These Earth-like planets will be in a habitable zone, where water could exist in liquid form on the surface and photosynthesis could occur. He believes that astronomers will image these planets and determine the nature of their atmospheres. And will there be life on any of those planets? There is every suggestion of a "yes" on his lips, but he hesitates and goes with, "I sure hope so."
To scientists like Cochran, proof that all of those Earth-like planets are not habitable would be equally startling and thought-provoking.
"Just the mere existence of life out there whether it’s advanced, ‘intelligent’ life or otherwise is of tremendous importance," says Cochran. "Also, if there isn’t life out there, it’s almost frightening. If we here represent the only life that exists in our galaxy, you have to ask why. Why is this place special? What’s so special about it? Either way, you’ve opened up issues well beyond science and ventured into philosophy, religion and so on."
For right now, Cochran is content to leave the existential ponderings to theologians and enjoy a career that’s rocketing skyward and taking him thousands of light years out into our galaxy. He is blessed with topnotch equipment, gifted colleagues and a surge of public interest in astronomy and space exploration that lends an extra dash of spice and excitement to his incredible discoveries.
"It’s a wonderful time to be doing this," he says. "You stand under a night sky, look up and you see a star. That star’s got some planets around it and you say to yourself, we found them here at The University of Texas. Now that’s huge."
Related Web Pages
The Great Debate: Is Complex Life Common in the Universe?
Cause for Optimism: Part III : The Drake Equation Revisited
Extrasolar Planets Encyclopedia
Planet Quest (JPL)
Habitability: Betting on 37 Gem
Infrared Telescope Powers Up
Alpha and Omega: Part II
The Mystery of Standard Candles
Inevitability Beyond Billions