Water found around Earth-like planet, ‘an important landmark’

There was a time when planets discovered around other stars were systematically giants. They were often enough to make our Jupiter, Earth’s largest neighbor, feel self-conscious. With progress, we began to discover minor planets, allowing us to see – at least imagine – worlds close to us elsewhere in the Milky Way.

On Thursday, the European and American space agencies, ESA and NASA, announced the discovery of water vapor around GJ 9827d, a planet just twice the diameter of Earth. That makes it, for the moment, the smallest exoplanet where water has been found.

The “old” Hubble still has resources

Pierre-Alexis Roy, a researcher at the University of Montreal (Canada) and lead author of the work, underlines, “This has not clearly detected molecules, whether water or other, on minor planets.” The reason is a major handicap: when the planets are featherweights, it is difficult to know whether the signals we experience come from them or from their stars. “Even with James Webb (the most capable space telescope), it’s not clear. We can’t distinguish. »

The star GJ 9827 was the target of choice, as it belongs to a category, orange dwarfs, sending faint signals. Between 2017 and 2020, the team will therefore observe the planet eleven times at the right time, i.e. when it passes in front of the star (we call this a transit), to be able to distinguish the elements found in it. one and the other. It’s also called the “old” Hubble, a space telescope launched 33 years ago. “When we repeat observations with Hubble, we are able to compete with James Webb,” assures Pierre-Alexis Roy. Its longevity allows us to push its limits. »

Like water, water everywhere!

Another innovation, which has yet to be confirmed, is not only that there is water in this atmosphere, but that it will be the main nuclear component. “Until today, whenever we detected atmospheres on exoplanets, they were dominated by hydrogen or helium,” asserts Pierre-Alexis Roy. Although, among the planets discovered in recent years, it is possible to find an atmosphere dominated by water, methane or ammonia, we have certainly never succeeded in finding an atmosphere dominated by water. »

“This will be the first time that we have directly shown, through atmospheric detection, that these planets with water-rich atmospheres can actually exist around other stars,” confirmed Bethany Downer, director of scientific communications at ESA. In a press release, Bjorn Benecke, an astrophysicist at the University of Montreal and co-author of the article, claims it is “an important step” in determining “atmospheric diversity on rocky planets.”

A sauna for extremophiles?

So, an aquatic world, GJ 9827d, or not? Researchers strongly believe this possibility. Because the system is six billion years old and the planet is probably so young that time around, helium and hydrogen are the lightest elements in the universe. It must have absorbed all the radiation from the star, close to it and revolve around it in just six days. So close that GJ 9827d is very hot, over 400°C.

Located at a reasonable distance of 97 light-years, the planet discovered in 2017 would therefore be the perfect sauna for extremophiles, those creatures that love extreme environments. But, as Pierre-Alexis Roy suggests, it is too early to speculate about the possible existence of living creatures there.