At a conference in Hawaii, a unique group of researchers announced the discovery of a new exoplanet in a “habitable zone”. An opportunity to take stock of a confusing term.
Credits: NASA’s Goddard Space Flight Center.
Even a measurement error could not prevent the discovery of this exoplanet. A group of Californian researchers, assisted by a student and a high school student, were supposed to verify measurements taken by the Transiting Exoplanet Survey Satellite (TESS), a space telescope dedicated exclusively to the search for planets outside our Solar System As its name suggests, the TESS observes part of the galaxy and quantifies the radiation of distant stars. When a planet orbiting a star passes between the telescope and the star, or “transits”, the radiation emitted by the star and received by the telescope decreases. Depending on the magnitude of the recorded radiation differences, the TESS measuring instruments can deduce the size and orbital position of the planet in question.
Astronomers and their young acolytes at the Jet Propulsion Laboratory of the U.S. Space Agency (NASA) have discovered the existence of three exoplanets orbiting in space around a star named TOI 700. This one, initially identified as similar to the Sun, is in fact a red dwarf, much less hot and massive than our star. During their checks, they also found that the third planet, the one furthest from the star, was in an area considered “habitable. “This means that YOU 700’s rays give it enough temperature to shelter water and not just ice or gas.
The group of exoplanet hunters validated their hypothesis with another space telescope called Spitzer. Thanks to him, they were able to confirm its density. YOU 700-d is 20% smaller than the Earth and circles its star in only 37 days. In addition, the solar energy it benefits from is equivalent to 86% of the energy received by the Earth from the Sun. Finally, the rotation of this planet around YOU 700 would be synchronous: like the Moon around the Earth, the same face of the planet is always oriented towards the star around which it orbits. Apart from this little information, scientists are not yet able to determine what its surface or atmosphere looks like – let alone whether it may be composed of oxygen. According to them, YOU 700-d would be either a “young Mars” covered with oceans or, conversely, an Earth without water.
The paradox of the “habitable zone”…
While the search for exoplanets similar to the Earth continues to make us dream in the midst of the climate crisis it is necessary to remember that the term used to qualify them can be confusing. An exoplanet located in a “habitable zone” in no way means that it could be inhabited by human beings. As mentioned above, this qualification corresponds only to the proven possibility – according to certain astrophysical criteria – of containing water, one of the elements necessary for life as we know it on Earth. It does not concern the composition of its atmosphere: if water is necessary for us, so is the oxygen in the air.
As an example, Mars and the Moon, our satellite, are also located in the “habitable zone”. However, they do not include the necessary conditions of habitability. The discoverer of the first exoplanet and recent winner of the Nobel Prize in Physics, Michel Mayor, himself advised against having too many illusions. Even if some of these exoplanets were truly habitable, “we will never be able to get there,” said the Swiss astrophysicist. And to conclude: above all, “we must take care of our planet. »