The James Webb telescope finally ready to explore other “lands”

Is another planet Earth possible? The James Webb Space Telescope is set to open a new chapter on December 22 in the search for conditions conducive to life beyond our solar system, sparking immense hope among astrophysicists.

This part of history is recent, the discovery of the first exoplanet dating back to 1995. It was called “51 Pegasi b” and since then, nearly 5,000 planets orbiting around stars other than the Sun have been listed.

Among these planets are gas giants, similar to Jupiter or Neptune, and rocky ones, like Earth. Some are located in the so-called habitable zone, neither too close nor too far from their star – principle giving it the name of Goldilocks.

But what are these planets made of? It is extremely difficult to know it so far these planetary systems, of which only the star can be seen directly. A fortiori for the rocky planets, smaller and yet the only ones capable of sheltering life as we know it.

To detect them, astronomers use in particular an indirect technique called the transit method: it makes it possible to capture the minute variations in luminosity caused by the passage of a planet in front of its host star, such as a micro-eclipse.

This makes it possible to detect new ones, to characterize their size, their density … But there is almost virgin land: the composition of their atmosphere, a reflection of what is happening on the surface.

“See their guts”

This is where NASA’s James Webb Space Telescope (JWST), the most powerful and largest ever to go into space, heralds a turning point.

“To say that twenty years ago we hardly knew any exoplanets and that we will soon know what their atmospheres are made up of is enormous”, is moved by AFP Pierre Ferruit, astrophysicist and JWST scientific co-leader for the European Space Agency (ESA).

“This will revolutionize our way of seeing the atmospheres of these planets. We will see their guts a little!”, Enthuses Pierre-Olivier Lagage, co-head of the MIRI instrument, resulting from European cooperation. and American.

Involved in the mission since 1998, this CEA astrophysicist has developed an innovative technique that will operate in the medium infrared, a wavelength hitherto unexploited.

The scenario should unfold as follows: during transit, the star’s light will be filtered by molecules contained in the planet’s atmosphere. However, it turns out that molecules have a specific signature in this infrared, in particular water vapor, carbon monoxide and methane, explains Pierre Ferruit.

Three molecules present in the Earth’s atmosphere, and which can therefore potentially come from a biological activity on the surface.

Trappist-1, the favorite

“My dream would be to detect an atmosphere around a rocky planet, in a habitable zone, with water molecules”, that is to say three conditions united for life, confides René Doyon, director of the Institute for research on exoplanets of Montreal, and principal investigator of the Canadian instrument NIRISS.

But be careful, because there are pitfalls. As with Venus, where researchers believed they detected phosphine: a gas associated with life on Earth, but which elsewhere may only come from geochemical processes.

Finding a biological origin for atmospheric molecules will therefore be “probably out of reach” for James Webb, underlines the Quebec astrophysicist.

“Biosignatures will be for later. We are already looking for conditions favorable to life, such as the presence of water in a liquid state”, explains Pierre Ferruit. Major clues to put future missions on the right track, and to understand if “the Earth is unique, or not”.

The projectors of the JWST will be focused mainly on the Trappist-1 system, located 40 light years from Earth, and discovered with a Belgian telescope. This earned him this reference to a type of beer brewed by Belgian monks.

It is the ideal candidate: seven planets, including three in the habitable zone, pass a dwarf star – not too bright, which makes it easier to detect the signal from the atmosphere.

Other instruments, direct imaging this time, will examine the atmosphere enveloping “hot Jupiters” and other “mini-Neptunes” … A new class of exoplanets could even be found, anticipates Professor Doyon.

With his colleagues, he also expects surprises because “the history of the discovery of exoplanets was only made of that”.

With AFP