Scientists from Liège discover a potentially habitable super-Earth

Scientists from Liège discover a potentially habitable super-Earth

An international team of scientists, led by an astrophysicist from ULiège, has just announced the discovery of two “super-Earth” planets. A super-Earth is a planet located outside our solar system, more massive and larger than Earth and a priori rocky like it. These two super-Earths revolve around Speculoos 2, a small, cool star located about 100 light-years from our Earth and the second-coolest star around which planets have been detected. This important discovery is the subject of a publication in the journal astronomy and astrophysics.

A first planet, the innermost of the system, was initially identified by NASA’s Tess space mission, dedicated to the search for exoplanets in orbit around nearby stars. This planet, which is about 30% larger than Earth, completes one orbit around the star in just 2.7 days. ULiège researchers used their Speculoos ground-based telescopes to confirm and characterize this planet, and also to probe the system in depth for other planets that Tess might have “missed”. The observations proved fruitful, as they not only helped confirm the first planet, but also led to the detection of a second, previously unknown planet.

maybe liquid water

This second planet, named Speculoos-2c by the ULiège researchers, is similar in size to the first (about 40% larger than Earth) but has a longer orbital period of about 8.5 days. This orbital period places the planet in the so-called “habitable” zone around its star, that is, the region of space where conditions are favorable for the appearance of life as we know it on Earth: not too far from its ” sun” so that the water does not freeze or get too close so that it does not evaporate. “Although this planet is very close to its star, at a distance about ten times less than that of Mercury around our Sun, the amount of stellar radiation it receives is still small, and could allow the presence of liquid water on the surface of the planet. planet. , as long as it has a sufficient atmosphere”, explains Francisco J. Pozuelos, a researcher at the Institute of Astrophysics of Andalusia, a former postdoctoral researcher at the ULiège and one of the main co-authors of the article. The presence of liquid water is considered a necessary condition for the appearance of life.

©Adeline Deward (RISE-Illustration) Comparison between the Speculoos 2 system and the inner solar system. The Speculoos 2 system is much more compact: its two planets could easily fit within the orbit of Mercury, the innermost planet in our solar system.

Then the team of researchers will study the atmosphere of this planet, in particular with the James Webb Telescope. In this environment, the idea is to look for chemical abnormalities or imbalances that can be explained by life. For James Webb, Speculoos 2c would be the second most favorable target among the currently known potentially habitable terrestrial planets. It is only surpassed by the Trappist-1 planets, also discovered by astrophysicists from Liège, in 2016. “However, this comparison does not take into account the fact that Speculoos 2c lies near the inner edge of the habitable zone and therefore could have an atmosphere that is particularly rich in water vapour, which would increase its atmospheric signatures.“, explains Laetitia Delrez, the astrophysicist at ULiège, lead author of the study. “Furthermore, models often differ as to the exact position of this inner limit of the habitable zone depending on the characteristics of the star. Therefore, the discovery of Speculoos 2c offers a unique opportunity to better understand and constrain the habitability conditions around the smaller, cooler stars in our solar neighborhood.”.

Like Earth, Speculoos 2c is probably made of rocks, given its size. “We’re not 100% sure the planet is rocky because we don’t know its mass, but its size is smaller than all known ‘mini-Neptunes’ and so its rocky nature is very likely.astronomer Michaël Gillon (ULiège) tells us. In fact, when we look at all exoplanets between 1 and 1.6 Earth radii in size and of known mass, almost all of them are rocky. So statistically, Speculoos-2c (1.4 Earth radius) probably is too.”

Beyond 1.6 Earth radii, most exoplanets have an extended gaseous envelope and we speak more of “mini-Neptunes”. When we get to sizes similar to Uranus and Neptune, then we talk about exo-Neptunes, or just giant planets.

Scientists from Liège discover a potentially habitable super-Earth
©University of Birmingham/AJSmith

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