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As astronomical instrumentation becomes more sophisticated, we are rapidly approaching a crossroads in the search for extraterrestrial life, according to a leading planetary scientist. It’s also “inevitable” that alien life exists in the universe given the preponderance of extrasolar planets that are being discovered — it’s up to us to seek out the extraterrestrial biosignatures.
These conclusions are outlined by Sara Seager, Professor of Planetary Science and Physics at the Massachusetts Institute of Technology (MIT), in a paper published in the journal Proceedings of the National Academy of Sciences on Aug. 4.
“In the coming decade or two, we will have a lucky handful of potentially habitable exoplanets with atmospheres that can be observed in detail with the next generation of sophisticated space telescopes,” writes Seager, pointing out that NASA’s James Webb Space Telescope (JWST) and a planned direct-imaging space telescope will be able to seek out biosignatures (i.e. chemicals created by extraterrestrial biology) in the atmospheres of nearby exoplanets. The JWST is set for launch in 2018.
“Life can be inferred by the presence of atmospheric biosignature gases — gases produced by life that can accumulate to detectable levels in an exoplanet atmosphere,” she writes.
To date, a handful of exoplanetary atmospheres have been studied through the analysis of their host star’s light passing through their atmospheres. As an alien world orbits its star, from our perspective, it may block some of the starlight from view and be registered as a “transit.” The transit method is used by NASA’s Kepler space telescope and has so far confirmed the detection of hundreds of exoplanets. But this method can also help us analyze the chemicals contained in exoplanetary atmospheres.
During a transit, if that exoplanet has an atmosphere, some of the starlight is filtered through its atmosphere. Some wavelengths of that light are absorbed by specific chemicals, leaving a spectroscopic ‘fingerprint’ in the starlight we detect. Although only the largest class of exoplanets have so far had their atmospheres analyzed in this way (gas giants with tight orbits around their stars known as “hot-Jupiters”), Seager argues that with the advent of advanced space telescopes, the composition of smaller worlds’ atmospheres could also studied. Habitable “super-Earths” fall into this category.
Once this happens, we can begin to observe small rocky worlds, potentially detecting spectroscopic signatures of chemicals associated with life.
Looking at a distant planet's atmosphere isn't easy, of course, scientists have two options—both involve studying planets as they pass in front of their star (transits). The first involves using telescopes that use mirrors to blot out the light from the star, leaving just data from the planet. The second approach involves deploying a starshade, a space vehicle positioned between a telescope and the object under study. The starshade blots out the light from the star, allowing for better examination of the planet and its atmosphere.
Fortunately for space science, new technology is on the way, the James Webb Space Telescope is set for launch in 2018—it's expected to offer unprecedented views of so-called super Earth's (those similar to Earth, but somewhat larger) though it will still rely on transits. What's really needed is new technology to allow for studying planets without having to wait for their transit.
The holdup is in figuring out how to capture imagery from such a relatively small object, one that is merely reflecting the light from its own star and is thus much dimmer. Seager suggests the solution is building much bigger telescopes with huge apertures. We'll have to wait as see, as only time will tell if we humans deem it important enough to invest the massive amount of money that would be needed for such a telescope.