Since 51 Pegasi b in 1995, more than 4,000 exoplanets have been discovered and many of them by the Kepler Space Telescope. Among the latest is GJ 357 d, located only 31 light-years away from us and which, according to astronomers, could shelter life.
Since July 2018, Tess (Transiting Exoplanet Survey Satellite) has been hunting exoplanets within a radius of 300 light-years away from us. And so in early 2019, the satellite was brought to point to a dwarf star of type M, located at about 31 light-years from our Earth and whose mass is about a third that of the Sun for a temperature of 40% lower.
The measurements then showed that the star in question, GJ 357, darkened slightly every 3.9 days. Named GJ 357b, it turned out to be a hot Earth-like planet about 22% larger than our planet. It could interest researchers because it orbits around a relatively bright star and is close to the Sun and is, therefore, an ideal target to study its atmosphere.
But it is by supplementing this information with observations on the ground – thanks to the spectrograph Carmenes installed on the telescope of 3.5 meters of the observatory of Calar Alto (Spain) – that two other exoplanets were discovered around the star by a team of astronomers led by researchers from Cornell University (USA): GJ 357c and GJ 357d. The latter has particularly attracted the attention of astronomers. Because this super-Earth could, according to them, shelter life.
A super-Earth is a planet whose mass is between that of Earth and that of a giant planet. According to the astronomers of the team, with a mass of about six times that of our planet, it would measure about twice its size. It would go around in 55.7 days at about one-fifth of the Earth-Sun distance. It would thus be located in the famous habitable zone of GJ 357.
On the basis of the data available to them, the researchers were able to establish a first model of GJ 357 d. “With a thick atmosphere, this planet could keep liquid water on its surface, like the Earth,” says Lisa Kaltenegger, an astronomer at Cornell University.
“Just knowing that liquid water is likely to flow to the surface of GJ 357 d will motivate scientists to find ways to detect signs of life around this planet,” says PhD student Jack Madden. And maybe finally find the answer to the question: are we really alone in the universe?