The world of exoplanets which opened up to the noosphere in 1995 is increasingly fascinating and we expect many future discoveries about it with instruments like the James-Webb or Plato (Planetary transits and oscillations of stars). We see a new example with an article published in the famous newspaper Nature and showcasing the work of an international team of astronomers led by members of the Trottier Institute for Research on Exoplanets (iREx) at the University of Montreal. A press release accompanies this publication, rich in information that we include.
We thus learn that it is by using archived data from the defunct Spitzer telescope and the living good Transiting Exoplanet Survey Satellite (Tess) that the team of Professor Björn Benneke, from the Department of Physics at UdeM, led by Merrin Peterson – a student of Professor Benneke’s team at iREx – has come to the conclusion that the exoplanet LP 791-18 d orbiting a red dwarf about 86 light-years from the Sun in the southern constellation of the Cup could very well be a super Io.
Io is the closest of Jupiter’s largest moons and the most volcanic world in our Solar System, with over 300 active volcanoes, thanks to its proximity to Jupiter’s enormous gravitational pull. Explanations by Brian Cox. To obtain a fairly accurate French translation, click on the white rectangle at the bottom right. The English subtitles should then appear. Then click on the nut to the right of the rectangle, then on “Subtitles” and finally on “Translate automatically”. Choose “French”. © BBC Earth
LP 791-18 d, a volcanic exo-earth?
“LP 791-18 d” has a radius and a mass comparable to those of the Earth, but it is in synchronous rotation around the M-type dwarf LP 791-18 which was already known to have a planetary cortege, LP 791-18 b and LP 791-18 c. The exoplanet is located just at the edge of the habitability zone, a concept that must be handled with care as explained to readers of Futura on several occasions by astrophysicist Franck Selsis, member of the CNRS and the Laboratory of astrophysics of Bordeaux (LAB).
LP 791-18 d had been detected by Spitzer using the transit method in October 2019, which made it possible to estimate its size and orbital period, in this case 2.8 days around its host star. But as it is much smaller and less bright than the Sun, the temperature on LP 791-18 d is therefore only slightly higher than that of the Earth. It might have an atmosphere and since it is close to the Solar System, the James-Webb might be talkative about it in the near future.
The other two exoplanets discovered, with Tess – but still by the planetary transit method – are such that LP 791-18 b is about 20% larger than Earth and completes its orbit in just under an Earth day. , while LP 791-18 c is about 2.5 times larger than Earth and has an orbital period of about five days.
As a result, the last discovered exoplanet, LP 791-18 d, moves between the orbits of the two previous ones. His study shows that subject to the gravitational disturbances of the other planets, it is caused to adopt an elliptical orbit which leads it to periodically approach the red dwarf, undergoing significant tidal forces as a consequence not only of the star, but also from the other two planets which, at their closest, are only separated by 1.5 million kilometers – a distance 33 times smaller than that between Mars and the Earth when they are at their closest, as the press release explains. the iREx.
If we trust the calculations whose validity has already been tested in the case of the Solar System with the moon Io around Jupiter, we are led to think that LP 791-18 d must be a covered super Io like the Jupiter’s volcanic moon of many volcanoes (the comparison is all the more justified since the red dwarf LP 791-18 is barely larger than Jupiter). By somehow kneading the elastic bodies that are Io and LP 791-18 d, the tidal forces must indeed produce a dissipation of gravitational energy in the form of heat to the point of strongly heating the two celestial bodies.
LP 791-18 d, a laboratory for comparative geology?
LP 791-18 d being the size of the Earth, we can expect a significant volcanic outgassing at some point in its history and it may have an atmosphere as a result, which means that the exoplanet could also be an analogue of Venus. All these possibilities make Björn Benneke say that ” the discovery of this exoplanet is extraordinary. The similarity of the properties of LP 791-18 d and the Earth as well as the prospect of detectable geological activity and volcanism make it a key object for better understanding the formation and evolution of the terrestrial worlds. This system provides astronomers with a valuable laboratory to test various hypotheses relating to the formation and evolution of terrestrial planets. The study of the planet LP 791-18 d, an Earth-sized world probably covered in volcanoes, will undoubtedly advance not only astronomy, but also many other scientific fields, including geology, earth sciences, atmospheric sciences and possibly exobiology ».
Caroline Piaulet, doctoral student at UdeM, who participated in the discovery, explains for her part – and still in the same press release from iREx – that “ the significant friction caused by the presence of a planet which passes very close to LP 791-18 d considerably increases the temperature of the interior of this planet and undoubtedly allows the existence of an ocean of magma under the surface. In our Solar System, we know that Io, a moon of Jupiter, is affected in the same way by Jupiter and its other moons, and this world is the most volcanic that we know ».
We can therefore clearly do comparative planetology, especially since the observations of variations in the transit times of planets c and d with terrestrial telescopes, by delivering the effects of gravitational attractions between exoplanets, also make it possible to estimate their masses and therefore their densities, knowing their radii. LP 791-18 thus has a mass comparable to that of the Earth and in fact a density compatible with a rocky composition like that of the Earth. LP 791-18 c is about seven times more massive than Earth, so researchers believe it likely retained a significant amount of gas or lighter material, making it even a mini-Neptune.
In 1995, the detection of an exoplanet, a planet in orbit around another Sun, opened up the dream of other worlds to the entire Universe. How many habitable or even inhabited planets are there in our Galaxy: billions or just one? New observation techniques from space improve sensitivity. With the Kepler space telescope, the number of exoplanets explodes. In 2018, there were nearly 4,000. Discover exoplanets through our web series in nine episodes. A video to be found every week on our Youtube channel. A playlist proposed by the CEA and the University of Paris-Saclay as part of the European research project H2020 Exoplanets-A. © CEA Research
