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Scientists have been listening for a message from ET for years, but none have been forthcoming. That may not be the best way to search the stars for alien life, though. The James Webb Space Telescope (JWST) might have what it takes to detect life on faraway worlds, according to a new study.
Webb was not built to be a dedicated planet hunter like the Kepler Space Telescope, but examining exoplanets is part of its mission profile. It has even detected a few new exoplanets itself. Most exoplanet discoveries from Webb and otherwise are made using the transit method, also known as transit photometry. A telescope does not need to directly image an exoplanet to detect it—the small dip in brightness as it transits in front of its star is enough. Kepler used this method to great success, detecting thousands of new worlds.
Any exoplanet that hosts life as we know it would have an atmosphere, and that’s the key to Webb’s potential life-detecting abilities. When an exoplanet transits a star and blocks light, a small sliver of the starlight passes through its atmosphere. The composition of the atmosphere will cause it to absorb some wavelengths of light while allowing others to pass through. This absorption spectrum can therefore tell us what’s in that exoplanet’s atmosphere. Webb has confirmed that this is possible, too. In late 2022, scientists announced Webb successfully gathered atmospheric data from WASP-39b, some 700 light-years away.
Credit: NASA/JPL-Caltech
Since there are no known planets with alien life, the international team had to devise simulated exoplanets to compare to Webb’s capabilities. They came up with five types of exoplanets to test, some habitable and some not. There was an ocean world, one covered in volcanoes, a young world being torn asunder during its high bombardment period, a super-Earth, and a world like Earth. They assumed all would have an atmosphere no more than five times as dense as Earth, allowing light to pass through and produce spectral data.
Using these artificial worlds, the team calculated the absorbance spectra for several organically linked molecules, including methane, ammonia, and carbon monoxide. While there are natural sources for all these molecules, finding them together in high concentrations is a good indicator that something is alive. According to the pre-print study, Webb’s NIRSpec G395M/H instrument is sensitive enough to detect these biomolecules within ten transits of the exoplanet. For a planet like Earth, that could take a long time with one transit per Earth year. Planets orbiting closer to cooler red dwarf stars might transit once every few hours, making them easier targets for analysis. The Trappist-1 system, which has multiple Earth-sized worlds, could be the perfect place to test this hypothesis.
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