A serious search for extraterrestrial life

May 26, 2009 By Faye Flam

Things have changed since the original Captain Kirk and Mr. Spock set off to seek out new life and new civilizations. Back in the 1960s, while the Enterprise crew was exploring a galaxy full of exotic life-forms, real astronomers were stuck in a solar system with eight desolate-looking neighbors and no signs of any planets beyond.

Now, finally, astronomers are starting to zero in on Earth-like worlds orbiting other stars. Some of the more recent finds even look potentially habitable.

While technology still hasn't provided anything like warp drive to take us to the stars, it has endowed today's earthlings with tools that were unimaginable in the 1960s -- techniques for doing detective work on objects from quadrillions of miles away.

In the last 13 years, astronomers have used such remote-sending tools to catalog more than 300 outside the solar system.

The first such planets were many times bigger than our own, but progressively smaller ones have been turning up. In March, NASA launched a satellite called Kepler, which is seeking subtle changes in starlight that indicate the presence of little specks the size of Earth.

In the future, astronomers envision observing even more subtle changes in starlight to analyze the atmospheres of such planets.

The lineup of ambitious projects was causing plenty of excited chatter among scientists this month when they met at Baltimore's Space Telescope Sciences Institute for a symposium titled, "The Search for Life in the Universe."

Not only was NASA spending hundreds of millions to comb the galaxy for other worlds and to analyze them, but respectable astronomers, biologists and geologists could now talk seriously about alien life.

Life-detection ideas were thrown around that were, while not easy, at least technologically feasible.

"Why is this interesting?" asked biologist Chris McKay of California's NASA-Ames Research Center. "We have the possibility of a second Genesis. We can have comparative biochemistry," he said, meaning that nature might use alternative ways to construct living things.

Even alien pond scum would change everything about our understanding of life and our place in the universe. We could take it apart and see how it replicated, what it ate, how it evolved.

Scientists have trouble defining life because all living things on Earth use the same building blocks. Is it life if it doesn't involve carbon? What if it doesn't have some equivalent of DNA?

"We use the Justice Potter Stewart definition," said McKay, recalling the famous definition of pornography: We'll know it when we see it.

So many stars ...

In 1966, the year the Star Trek TV series was launched, astronomer Carl Sagan wrote that there were at least 100,000,000,000,000,000,000 stars in the universe -- so that surely some must have solar systems like ours.

But good planets have been hard to find.

Astronomers call those around other stars extrasolar planets, or just exoplanets. Only two such planets have ever appeared in a Hubble picture.

The rest show themselves only indirectly, through tiny wobbles or other subtle changes detected in their stars.

The wobble idea works on the principle that planets don't actually orbit their suns, as kids learned in school. Instead, a planet and star both orbit a center of gravity. Though the center of gravity is much closer to the star, the mutual forces still make the star circle around a tiny path that could appear as a wobble from Earth.

But the effect is subtle, and several astronomers were burned by false alarms. Finally, in 1995, the first exoplanet was solidly confirmed. From the wobbles, the astronomers could tell the planet was the size of Jupiter and orbited its star closer than Mercury is to the sun. Each "year" on this planet lasts just four days.

More planets soon were found, but all of them were huge, about the size of Jupiter. The problem with Jupiter and planets of comparable size is they are all atmosphere with no solid surface.

But in the 21st century, more refined techniques have picked up a few planets small enough to have rocky or icy surfaces. Called super earths, they range from two to 10 times the size of our planet.

Some were found through the wobble method while others showed up when they passed in front of their stars. Such "transits" create a tiny eclipse that dims the starlight by a fraction of a percent.

This is how the satellite Kepler is supposed to find planets similar to Earth in the next several years, even though an earth would dim the star by less than a hundredth of a percent. The idea was rejected by NASA year after year until agency scientists finally demonstrated in lab tests that, in principle, it could work.

Kepler will stare constantly at just one spot in the sky, near the constellation Cygnus, where it can continue to monitor a group of about 100,000 stars.

Even if everything works, the satellite will detect only 1 in 100 of the Earth-size planets up there, since these tiny eclipses will be visible only if the orbit of a planet is in a plane angled toward us.

A planet like Earth would transit once a year, and astronomers would wait for several such transits before they could tell if it's really there.

After 3 { years, astronomers hope to get a cosmic census -- a representative sample of Earth-size planets in our galaxy.

OPTIMISM ABOUNDS

But is there anything alive up there?

The biologists at the Baltimore meeting were optimistic. Life is tougher than anyone thought. Chemical traces of past life show it goes back at least 3.5 billion years into Earth's 4.6 billion-year existence.

Life may go back further. "This is a key fact," said NASA's McKay. As soon as the planet became remotely habitable, it was taken over by microbes.

The one necessary feature that everyone agreed on was liquid water. There's plenty of water out there, but for any of it to condense or melt into a liquid, a planet would have to orbit at just the right distance from its star.

A few years ago, James Kasting of Pennsylvania State University helped calculate what astronomers have come to know as the "habitable zone" around other stars. That's a distance that would make conditions somewhat cooler than Venus, and at least as warm as Mars.

A few of the known exoplanets fall in the habitable zone, including one recently announced super earth 12 light-years away. Kepler could find more. But ultimately the scientists are after something bigger: actual alien life.

At the meeting, Harvard-Smithsonian astronomer Lisa Kaltenegger asked the scientists to imagine how we would detect life on Earth if our planet's exact twin were orbiting a star light-years away. "We would see this tiny point of light -- this speckle of light -- but there's a lot of information we can actually get from that," she said.

The key is in the atmospheres, said Penn State's Kasting. Our planet's atmosphere is full of oxygen and methane that can't easily be explained by any nonliving chemical process, he said. If we could detect that, we'd have a good case.

The Hubble's instruments have analyzed the atmospheres around several giant planets as they pass in front of their stars. With its repair, which astronauts completed this month, scientists plan to use it to study more.

It will take more elaborate space telescopes -- or perhaps whole fleets of them -- to analyze atmospheres with planets the size of Earth. All this is on the drawing board.

The gases wouldn't tell us what type of life was out there _ whether it could take the form of intelligent beings, for example. It could be mostly weeds, or pond scum, or slime molds, or something we can't even imagine because we've never seen it.

But even that would go a long way toward explaining what life on this planet is all about, what it's doing here, and how it fits into this vast universe of 100,000,000,000,000,000,000 stars.

___

(c) 2009, The Philadelphia Inquirer.
Visit Philadelphia Online, the Inquirer's World Wide Web site, at www.philly.com/
Distributed by McClatchy-Tribune Information Services.

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User comments : 13

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deatopmg
2 / 5 (2) May 26, 2009
We need go no further than Mars to get the first examples of extraterrestrial life.
Archivis
5 / 5 (1) May 26, 2009
Over all a great article. However I take issue with the statement:

"The one necessary feature that everyone agreed on was liquid water. There's plenty of water out there, but for any of it to condense or melt into a liquid, a planet would have to orbit at just the right distance from its star."

I've long had a problem with the idea of the habital zone. First of all, different types of stars have different "heat" output. This would alter the habitable zone based on type of star. Secondly, even if you assume a yellow star such as our sun, there is still other problems. Even in our own solar system we are looking beyond the so called habitable zone when looking at the moons around Saturn or Jupiter. While yes these moons dont recieve enough of the sun's light to be warmed, gravitational pull from the large planitary bodies they orbit can generate heat through the friction pressure exerted on the crust.

Granted I doubt we would find "little green men" there, but who knows, pond scum may be there :)

I understand that we are limited to what we can "see" but perhaps we should put more effort into getting out there and seeing first hand instead of constantly roadblocking ourselves.



MorganW
4.5 / 5 (2) May 26, 2009
We are constantly being surprised at where we find life here on Earth. I agree that water and oxygen along with proximity to the host star are necessary for life "as we know it", and therefore the most logical forms to look for, but we should also bear in mind that life might come in forms as we don't know it; in fact, we are probably more likely to overlook it when/if we do see it than to recognize it for what it is.
It is also possible that sentience may exist in the absence of life if intelligent machines have evolved elsewhere in the universe. Are we looking for evidence of life or sentience (or both)?
nkalanaga
3.7 / 5 (3) May 26, 2009
Archivis, all of your points are valid, but the first has been taken into consideration. A given star's habitable zone is considered to be centered where an Earth-like planet would receive the same total energy from its star as Earth receives from the Sun. So, HZs come in all sizes, from narrow, close zones around red dwarfs, to wide, distant zones around stars brighter than the Sun. Of course, a planet would receive different proportions of infrared, visible, and ultraviolet light depending on the temperature of the star, close orbits are prone to tidal locking, and hot, massive stars are probably too short-lived for advanced life to evolve, but the standard HZ itself does vary with the star.
brant
5 / 5 (1) May 26, 2009
Suppose life doesnt need a planet, or for that matter a flesh(matter) body.

Then what are we looking for??
nkalanaga
1 / 5 (1) May 26, 2009
God.
brianweymes
1 / 5 (2) May 27, 2009
the habitable zone can probably be extended farther than previously believed because of subsurface liquid oceans under ice which can remain liquid farther from the normal habitable zone. I doubt youd find anything 'intelligent' in them, but microscopic life is a possibility.
finitesolutions
not rated yet May 27, 2009
I live at the edge of the Universe.
nkalanaga
2.5 / 5 (2) May 27, 2009
BrianWeymes: You're right, and that may actually be the most likely place to find life in many systems. But it would be very hard to detect remotely, so the traditional HZ represents the worst-case scenario. If we can figure out how to find life as , and where, we know it, any other would be a bonus.
Teonanacatl
not rated yet May 31, 2009
Some UFO's are extra terrestrial spacecraft. This is well documented.
HPesonen
not rated yet Jun 01, 2009
It is also possible that sentience may exist in the absence of life if intelligent machines have evolved elsewhere in the universe. Are we looking for evidence of life or sentience (or both)?


Aren't we intelligent machines? If not, what is the definition of a machine? Anyhow, I wouldn't put my money on finding Transformer-robots anytime soon...

It would be nice to know what theoretical limits exist in visibility of distant objects. Would it be possible to even see continents etc. in the future?

Archivis
not rated yet Jun 01, 2009
Thanks nkalanaga, I honestly didn't know that, so again, thank you :)
yyz
not rated yet Jun 03, 2009
On a closely related note, 2 Penn State researchers have just released a paper entitled 'The Sustainability Solution to the Fermi Paradox' (The Fermi Paradox is basically saying that if intelligent extraterrestial life exists, where is it? We should have detected it or have been visited by now. See Wiki for an excellent overview). Anyway, the authors conclude that "The Fermi Paradox cannot logically conclude that humans are the only intelligent civilization in the galaxy." This short, nontechnical paper can be found here: http://arxiv.org/...0568.pdf . The authors explain their 'Sustainability Solution' and bring up good points for future SETI searches.

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