Saturday, September 6, 2014

The Telescope We Need to Find Earth 2.0

Astronomers have discovered a multitude of new exoplanets, but is it possible to detect whether faraway world have water, oxygen, or other ingredients for life as we know it?

The past two decades of exoplanet hunting have turned up hundreds of new worlds, and in recent years, that tally has grown to include many that appear to be close to the Earth in size. Yet most of these new planets are discovered indirectly, though the wobbling or dimming light of their parent stars. The planets themselves are just too far away to see.

For scientists seeking truly Earth-like worlds out there in the cosmos, that's a problem. Those astronomers want to know not just the size and probable temperature of an exoplanet, but also whether it has the ingredients for life. As NASA plans for a new generation of powerful satellite telescopes designed to seek out habitable worlds—the latest design being the Advanced Technology Large Aperture Space Telescope —scientists are also wondering if our best tech would even be good enough to catch biomarkers such as water, oxygen, or photosynthetic greenery.

"It's certainly a huge challenge," says Timothy Brandt, an astrophysicist at the Institute for Advanced Study at Princeton University, who likens the task to "trying to catch the light coming off the glow-in-the-dark hand of a wristwatch that's right in front of a floodlight… from [6 miles] away."

We Have the Technology

Brandt and fellow astrophysicist Dave Spiegel have just published a new study detailing the specs that an ATLAST-type telescope would need. And the results were relatively hopeful for next decade's planet hunters.

By using a simple model that produced variable exoplanet atmospheres—and allowing for a small but manageable improvement in technology—an ATLAST-type telescope should be able to confirm the presence of water and (with a bit more difficulty than astrophysicists previously estimated) oxygen. But confirming the presence of molecules like chlorophyll would require an extreme amount of luck—on top of the fact that there's absolutely no guarantee that chlorophyll-like molecules aren't unique to life on Earth, Spiegel says.

Spiegel also emphasizes that finding water and oxygen together does not necessarily mean that planet would be suitable for Earth-like life. Conversely, an exoplanet without water, oxygen, or either may not be hopelessly barren.

"If you look at Earth from 3 billion years ago, you would have certainly seen life, but not oxygen," Spiegel says. Wesley Traub, the chief scientist for NASA's Exoplanet Exploration Program, says that even with those caveats, simply confirming how many other watery, oxygenated Earth-like worlds are out there (assuming there are any) would deeply impact our understanding of how profuse life might be.

"And I don't think people today are aware that with the resources we already have. A mission like ATLAST is entirely within our reach—we just need the funds and authority to do it," Traub says. "When this happens is simply a reflection of when our space agencies decide it is a worthwhile pursuit."

Three-Horse Race

Seth Shostak, the senior astronomer at SETI, says that if we could get a mission like ATLAST off the ground, it would align rather nicely with the other life-seeking endeavors coming to a head over the next couple of decades.

"Of the three horses running this race, SETI is one, because it'll likely be 10 to 20 years before we've scanned through a few million star systems" with radio telescopes, Shostak says. (He says that number is a statistical necessity, based on our best estimates for the possible proliferation of intelligent life, such as the Drake equation).

"The second way we might find [extraterrestrial] life is if it's nearby," Shostak says. Here, he's talking about the possibility of discovering microorganisms on Mars or on Jupiter's moon Europa, missions that could achieve that goal are coming in the next 10 to 20 years.

"The third way we're searching is with what we're talking about here—looking for these biomarkers in the atmospheres of exoplanets," he says, nodding to ATLAST's current NASA slot for 2025.

According to Shostak, we could—if we really wanted to—start to answer the question of whether there is life beyond the earth.

"There are times in history where humanity suddenly gained the tools to explore incredibly old questions," Shostak says, "and we'll be there—should we choose to devote the resources and time.