Scientists at Massachusetts Institute of Technology (MIT), the University of Birmingham, and elsewhere say that astronomers’ best chance of finding liquid water, and even life on other planets, is to look for the absence, rather than the presence, of a chemical feature in their atmospheres.
The researchers’ hypothesis proposes that if a terrestrial planet has substantially less carbon dioxide in its atmosphere compared to other planets in the same system, it could be a sign of liquid water — and possibly life — on that planet’s surface. What’s more, this new signature is within the sights of the National Aeronautics and Space Administration's (NASA) James Webb Space Telescope (JWST).
While scientists have proposed other signs of habitability, those features are challenging, if not impossible, to measure with current technologies.
The team says this new signature, of relatively depleted carbon dioxide, is the only sign of habitability that is detectable now.
Beyond a glimmer, astronomers have so far detected more than 5,200 worlds beyond our solar system. With current telescopes, astronomers can directly measure a planet’s distance to its star and the time it takes it to complete an orbit.
Those measurements can help scientists infer whether a planet is within a habitable zone. But there’s been no way to directly confirm whether a planet is indeed habitable, meaning that liquid water exists on its surface.
Across our own solar system, scientists can detect the presence of liquid oceans by observing “glints” — flashes of sunlight that reflect off liquid surfaces. These glints, or specular reflections, have been observed, for instance, on Saturn’s largest moon, Titan, which helped to confirm the moon’s large lakes.
Detecting a similar glimmer in far-off planets, however, is out of reach with current technologies.
But Venus, Earth, and Mars share similarities in that all three are rocky and inhabit a relatively temperate region with respect to the Sun. Earth is the only planet among the trio that currently hosts liquid water. And the team noted another obvious distinction: Earth has significantly less carbon dioxide in its atmosphere.
The researchers surmised that these planets were created in a similar fashion, and if we see one planet with much less carbon now, it must have gone somewhere, adding, that the only process that could remove that much carbon from an atmosphere is a strong water cycle involving oceans of liquid water.
Indeed, the Earth’s oceans have played a major and sustained role in absorbing carbon dioxide.
