Have we found a habitable exoplanet?

In the search for a habitable planet outside our solar system, the TRAPPIST-1 system is a favorite. A scientific publication has just announced that a planet in TRAPPIST-1 could have an atmosphere suitable for life, in addition to the possibility of harboring water on its surface. PHOTO NASA/JPL-Caltech

Although it may be located 40 light-years from Earth, the Trappist-1 planetary system has continued to fascinate since its discovery was announced in 2017. And for good reason: some of the seven exoplanets that make it up could support life.

One of them, Trappist-1 e, is believed to have not only the capacity to harbor liquid water, but also an atmosphere conducive to life.

An artist's impression of the Trappist-1 planetary system. Located 40 light-years from Earth, it is composed of seven planets orbiting a small star, a "red dwarf." Some of its exoplanets are at a distance compatible with the presence of water on their surfaces. PHOTO NASA/JPL-Caltech

Trappist-1 e and two of its neighbors are located in what is called the star's "habitable zone," meaning they are close enough to their star for liquid water to be present on their surface.

But if water is a condition a priori necessary for life to develop, it is not sufficient...

“Even if you are at the right distance from the Sun, you just need to not have the right atmosphere to be a furnace like Venus, or
an icebox like Mars.”

Matthew Genge, planetary scientist, in New Scientist

Thanks to the James Webb Space Telescope (JWST), which has been exploring the far corners of the universe for more than three years, researchers discovered that Trappist-1 e's atmosphere was likely rich in nitrogen. Like Earth's.

In 2023, JWST pointed its ultra-sophisticated NIRSpec instrument at Trappist-1 e as it transited in front of its star.

“When a planet passes in front of its host star, the starlight is filtered by the planet's atmosphere. Astronomers can determine which molecules are present in its atmosphere by observing the variations in light at different wavelengths.
wave.”

Trappist-1 is a red dwarf star, much cooler than our Sun. In their analysis, scientists struggled to determine whether a molecular signature came from the atmosphere of the planet Trappist-1 e or from the star. — Trappist-1 is a red dwarf star, much cooler than our Sun. In their analysis, scientists struggled to determine whether a molecular signature came from the atmosphere of Trappist-1 e or from the star. PHOTO NASA/JPL-Caltech

The analysis took a long time because the small star, which is a red dwarf, shines much less brightly than our Sun, so the signals can be difficult to interpret.

These initial results will therefore need to be confirmed.

“The next step could be to look for gases like methane or _CO2 and, using climate models, determine the likely temperature of the planet's surface. This could then be used to deduce whether liquid water is present – which would increase the planet's chances of supporting life,” New Scientist lists.

The fact remains that the quest for a habitable planet outside our solar system is well and truly underway.

Courrier International