Exoplanets like Earth? 3 pitfalls to avoid

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The one in the “habitable zone”, called TOI-700e, was detected by the TESS satellite (Transiting Exoplanet Research Satellite ). Another, LHS-475 b, is the first rocky exoplanet confirmed by the James-Webb telescope (we suspected its existence thanks to data from TESS). This suggests that there will be other discoveries of this type.

However, as he explains Rumor Detector There are three pitfalls to beware of those who immediately envision extraterrestrial life whenever these types of announcements occur during pre-2017 discovery.

Pitfall #1: “habitable zone” does not mean habitable

In 2017, NASA’s press conference announced with great fanfare the discovery of seven planets around the same star (TRAPPIST-1), three of which are in the “habitable zone”, which dominated the “life forms” exchanges. But the problem with the term “habitable zone” is that Venus and Mars are also in the “habitable zone” around our Sun. So there are other criteria to consider:

• Is there an atmosphere? Although the discovery of the first exoplanet—or planet orbiting a star other than our Sun—dates back to the 1990s, it wasn’t until 2016 that astronomers identified an atmosphere around it for the first time. These types of detection instruments are beginning to arrive, and of the telescopes launched in this hunt, only the James-Webb (JW) will theoretically be able to identify some components of these atmospheres.
• What does it contain? But the presence of atmosphere does not mean the presence of life. For example, one of Saturn’s moons, Titan, is surrounded by a thick atmosphere of nitrogen and methane, an inhospitable mixture.
• is there water Water is the ideal ingredient for holding together the molecules that make up the “bricks” of life, and it must still be in a liquid state, ie between 0 and 100 degrees Celsius. In theory, analyzing the atmospheres of these planets – if they exist – would allow us to detect water vapor there, which would be a great point for astronomy. We still don’t know what happened to the two new exoplanets, LHS-475 b and TOI-700e. They are part of a short list of candidates who will be JW’s special focus in the coming months and years.

Pitfall #2: Detection does not mean photography

Since the first exoplanet announcement, more than 5,200 have been confirmed, and 9,000 “candidates” are awaiting confirmation. But for the most part, it’s an indirect detection: only about thirty planets have been photographed—and even then, the photos show a spot a few pixels wide, at best. The depictions of these planets are systematically artists’ depictions. Everything we know about them – mass, size, temperature, etc. — comes from indirect measurements or deductions.

Indirect detection can be done in two ways. From one side, natural oscillations A star can betray that a more or less massive “object” is rotating around it, sometimes “pulling” it to one side, and sometimes to the other. On the other hand, a decrease in brightness A star can betray that something has passed between it and us – this is the so-called “transit” method. These are small changes that are difficult to detect when the planet is as small as Earth.

Pitfall #3: “Earth-like planet” doesn’t mean… Earth-like planet!

When the hunt for exoplanets, or extrasolar planets, found its first prey about 30 years ago, they were giant planets, and even very giant planets: a few were more than 10 times larger than Jupiter—only they could contain more. thousand Earth. The term “Earth-like planet” (Earth-like planet) was therefore more of an ambition than a realistic definition: the hope that one day the technology would enable the detection of “rocky” planets (such as Venus, Earth, and Mars). Now that astronomers are well and truly there, the focus turns to the clues that distinguish Earth from its rocky counterparts: atmosphere, but especially water.

Image: Artist’s rendering of LHS-475 b and its star / ESA / NASA