BY RAY VILLARD, Discovery News
NASA is preparing the TESS observatory (Transiting Exoplanet Survey Satellite) to follow-up on the successes of the planet-hunting Kepler observatory by identifying nearby exoplanets that pass in front of, or “transit,” their stars. A small sample of these worlds will be singled out for further scrutiny if they lie within the habitable zone of the parent star. The habitable zone is the distance from a star where temperatures on a world may allow liquid water to exist on the planetary surface.
Kepler showed us an incredible diversity among planetary systems, and that small planets like Earth greatly outnumber bloated Jupiter-class worlds. But the Kepler planets are typically over 1,000 light-years away, so understanding the environments of these worlds is technologically out of the question — at least for the foreseeable future.
It is a reasonable prediction that the first transiting candidate planet to look for the chemical signature of life will be a world orbiting a nearby red dwarf star. There are about 90 red dwarfs within just 20 light-years of Earth, but only seven sun-like stars.
A transiting planet will allow for measuring the fraction of starlight passing through its atmosphere as well as recording the difference in light from the system when the planet passes behind its star.
TESS’ survey should at least find a few nearby transiting worlds within reach of doing a chemical inventory with NASA’s planned James Webb Space Telescope. At the very least, Webb would have a shot at providing evidence for an ocean on a planet. This would further narrow down the candidates for more detailed studies.
Kepler’s survey found a number of super-Earths, planets several times Earth’s mass, and therefore too small to be gassy so-called ice giants like Uranus and Neptune. But what might the spectral fingerprint of a nearby super-Earth look like? And could we unequivocally deduce the planet is inhabited to everyone’s satisfaction?
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