Exoplanet water-detection strategy now possible, say researchers
Researchers from MIT and the University of Birmingham (UB) believe that they've cracked the formula for detecting habitable planets using currently available technology. It all has to do with an exoplanet's levels of carbon dioxide and ozone.
There's been a lot of talk about how rising levels of carbon dioxide in the Earth's atmosphere is contributing to global warming, but the fact is that our planet has a remarkably low level of the gas compared to other, less habitable worlds like Venus. A whopping 96.5% of that planet's atmosphere is composed of the gas, while Mars has an atmosphere containing 95% CO2. Earth, on the other hand, has an atmospheric concentration of just .04% carbon dioxide. That's because our oceans absorb about 80% of the planet's carbon dioxide.
This fact has led researchers to develop a new method of identifying exoplanets that might have liquid water, by searching their atmospheres for low levels of carbon dioxide. Specifically, the researchers propose using our solar system as a model, and lay out a plan of looking for a grouping of planets that fall within a distance from their sun where water might exist in liquid form. Then, if an analysis of the atmospheres of those worlds reveals one with lower atmospheric carbon dioxide than the others, the likelihood that the gas is trapped by large bodies of water would be high, they say.
One particularly exciting part of this plan, says the research team, is that the James Webb Space Telescope can currently measure the carbon dioxide on the planets it is able to observe, much like it did with Jupiter's moon, Europa earlier this year.
"The Holy Grail in exoplanet science is to look for habitable worlds, and the presence of life, but all the features that have been talked about so far have been beyond the reach of the newest observatories," says study co-author Julien de Wit, assistant professor of planetary sciences at MIT. "Now we have a way to find out if there’s liquid water on another planet. And it’s something we can get to in the next few years."
Water doesn't equal life
While such a method might help determine if a planet does indeed hold liquid water, the researchers acknowledge that this doesn't necessarily mean it will contain life. But the team has a plan for that as well.
Again, using our own planet as inspiration, the researchers point out that when lifeforms on Earth (including plants and some microbes) take in carbon dioxide, they emit oxygen, which can be converted to ozone by photons from the sun. Like carbon dioxide, ozone has a signature that is detectable by the James Webb telescope. Use that telescope to find a planet in the habitable zone with low CO2 and high ozone, says the researchers, and you will likely have found a planet with life.
"If we see ozone, chances are pretty high that it’s connected to carbon dioxide being consumed by life," said study co-author Amaury Triaud of UB. "And if it’s life, it’s glorious life. It would not be just a few bacteria. It would be a planetary-scale biomass that’s able to process a huge amount of carbon, and interact with it."
The research has been published in the journal, Nature Astronomy.