If E.T. is phoning home, how do we phone E.T.? Researchers at Caltech’s or ET Lab—Exoplanet Technology Laboratory—may have the answer.
In the wake of the Trappist-1 discovery, it seems everyone is scrambling to find signs of extraterrestrial life in space. Biosignatures such as oxygen and methane could be potential indicators of life (at least as we know it on Earth). These chemicals are everywhere on Earth because they are expelled by living organisms, and while they vanish quickly because of their tendency to bind with other chemicals, oxygen or methane molecules on another planet could be a sign that something is crawling out there. Now Caltech Associate Professor of Astronomy Dimitri Mawet and his team have figured out a sci-fi-sounding strategy to detect biosignatures in alien worlds.
The strategy is high-dispersion coronagraphy (HDC), which involves a coronagraph, optical fibers, and a high-res spectrometer that will join forces to dissect exoplanet atmospheres on a molecular level and measure how fast these planets rotate, and make Doppler mapping of atmospheric aberrations possible.
"This new innovation of combining the coronagraph with a high-res spectrometer gives us a clear pathway to ultimately search for life beyond Earth," says Mawet. "It's a long shot, but we might even have the ability to look for continents on candidate Earth-like planets."
Mawet’s team have already published two papers demonstrating the technique in the Astrophysical Journal and Astronomical Journal. They plan to do a test run at the W.M. Keck Observatory in Hawaii within the next year. While scientists will need the power of the Thirty Meter Telescope (which will be the largest optical telescope ever once completed) and other upcoming telescopes such as NASA's proposed Habitable Exoplanet Imaging Mission (HabEx) and Large UV/Optical/IR Surveyor (LUVOIR) to explore Earth-like planets in the future and identify potential biosignatures, HDC will still provide invaluable information about the atmospheres of cool M-dwarf stars and exotic exoplanets, especially gas monsters that lurk far beyond our solar system.
HDC is designed to image far-off planets and then use a spectrometer to search for possible biosignatures. Planets are often difficult to make out because the stars they orbit outshine them by a few thousand to a blinding few billion times, but spectrometers disperse a planet’s reflected light while coronagraphs make seeing them even easier by blocking or removing excess starlight. While most spectrometers used alongside coronagraphs are low-res, Mawet’s use of a hi-res spectrometer is even more of an asset in improving planetary visibility because it breaks down more starlight, making it able observe things in more detail on a molecular level—and putting less pressure on the coronagraph to see everything. Even the optical fibers accidentally ended up helping the process when the researchers realized they were getting rid of even more light.
So will HDC enable Earthlings to find some previously unknown life form? Everything is theoretical right now, but the lab results look promising. Postdoctoral scholar Ji Wang, who leads research in the ET Lab and is one of the main authors on the two new papers next to Mawet, is optimistic. "We've shown this technique works in theory and in the lab,” he said. “so our next step is to show it works on the sky."