Tess has discovered hot Jupiters around dying solar-like stars with some of the shortest known orbital periods. These exoplanets are in fact migrating towards their suns and should soon be swallowed up there on the scale of a few million years or so. Their study could give valuable information on the evolution of planetary systems and of course the end of the Solar System.
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[EN VIDÉO] Exoplanets What are exoplanets, where are they found and why are they so interesting? Video answer!
On January 15, 2022, the famous site of The Encyclopedia of Extrasolar Planets mentioned that 4.921 exoplanets were known to mankind. This is only the beginning even if we can think that we have already made extraordinary progress since the discovery of the first exoplanets in orbit around’stars on the famous main sequence, in 1995 (we already knew the case of two exoplanets around a pulsar, PSR B1257+12, since 1992).
We know that the Swiss Michel Mayor and Didier Queloz first revealed the existence of hot Jupiters, from gas giants closer to their host stars in proportion than Mercury of the Sun. This was a surprise, although some theoreticians of planetary cosmogony had already considered migration processes early in the history of exoplanet formation. We will see why, a little later, it was necessary to postulate these processes.
The discovery of these stars was initially made with the radial velocity method (see on this subject one of the videos of the CEA series below) on the ground but the great harvests were essentially made by instruments in orbit using the method of transits planets with the Kepler satellite and today with its successor Tess (Transiting Exoplanet Survey Satellite). We are of course mainly interested in the discovery ofexoterres, from rocky planets of size and mass very close to those of the Earth which would be in orbit in the habitable zone of a sun-like star or a red dwarf. Remember that the question of the definition of the habitability zone is not simple, any more than it is relevant to hunt exoterres around red dwarfs for questions of exobiology.
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 playlist proposed by the CEA and the University of Paris-Saclay as part of the European research project H2020 Exoplanets-A. © CEA Research
Hot Jupiters to understand the dynamics of planetary systems
However, the discovery of other exoplanets than exoterres also brings its share of important information for theastrophysics and theexobiology and we are also preparing to try to do as well, thanks to the instruments of the telescope James Webb, analyzes of the chemical composition ofatmosphere of hot Jupiters, like WASP-62b, than of those perhaps existing around telluric exoplanets like those around Trappist 1.
The theory tells us, beyond a shadow of a doubt, that gas or ice giants form at great distances from young stars in the protoplanetary disc that surrounds them at birth. The hot Jupiters therefore migrated and in doing so, their field of gravitation impacted the rest of the planetary formation.
Making statistics on the chemical composition of these celestial bodies and their occurrence in planetary systems therefore informs us about the general process of the cosmogony of exoplanets in the Milky Way and so, ultimately, on the chances of having habitable exoplanets in our Galaxy. Here is what to specify the parameters of the famous drake equation for the Seti program in particular.
Today, a team of researchers published in Astronomical Journal an open-access article on arXiv which announces the discovery by Tess of three hot Jupiters around subgiant or giant stars which are distinguished by their short orbital periods and the fate that celestial mechanics imposes on such stars. Samuel Grunblatt, postdoctoral researcher at theAmerican Museum of Natural History and at Flatiron Institute of New York, explains about them that ” these findings are crucial to understanding a new frontier in exoplanet studies: how planetary systems evolve over time. These observations offer new Windows on end-of-life planets, before their host stars engulf them “.
Indeed, initially flushed out as candidates for the title of exoplanet in the Tess data, the existence of TOI-2337b, TOI-4329b and TOI-2669b was confirmed by instruments at the WM Keck Observatory atop Maunakea in Hawaii. However, it appears that they are doomed in the short term on the scale of cosmic time. In the case of YOU -2337b, it will continue its migration to the point of being swallowed up in only about a million years.
The end of life of the solar system?
We are therefore in front of laboratories which could give us new ideas on how our Sun will engulf planets in several billion years in phase red giant. Some astrophysicists have even hypothesized that at thedawn of the formation of Solar system he might have swallowed at least one superearth.
What we already know is that these three exoplanets have masses between 0.5 and 1.7 times the mass of Jupiter and sizes ranging from a little smaller to more than 1.6 times the size of Jupiter. Jupiter. They also cover a wide range of densities, from that of mousse of polystyrene to that three times higher than water, which implies a wide variety of origins and therefore, as we have said, valuable clues for the planetary cosmogony in the Milky Way.
What we also know is that, as in the case of the Hot Jupiter discovered in 1995, 51 Pegasi b, they revolve around solar-type stars that are already several billion years old and that according to another of the authors of the discovery, Nick Saunders, it is to be expected ” find dozens to hundreds of these evolved transiting planetary systems with Tess, providing new details about how planets interact with each other, swell and migrate around stars, including those like our Sun “. His colleague and co-author Daniel Huber points out that “ Keck’s observations of these planetary systems are key to understanding their origins, helping to reveal the fate of solar systems like ours “.
Methods for detecting exoplanets have greatly diversified since the 1990s. They can be classified into two main categories, direct methods and indirect methods. The three main methods are the direct imaging method, the indirect transit method and the indirect radial velocity method. © CEA Research
If indeed, as we said, Tess first flushed out these planets by a photometric method giving the radius and the orbital period of these planets, it required a confirmation of their existence by spectroscopy, via the spectrometer at high resolution Hires which made it possible to use the method of radial velocities and to fix the mass, and therefore the density of these stars.
Planetary scientists have reason to believe that the wide variety of densities found suggests that these planetary systems were shaped by chaotic interactions between exoplanets. Indeed, models developed with celestial mechanics to account for such systems not only imply that giant planets should move towards their host stars as stars evolve over time, especially in the last 10 percent of the duration life of the star, but also that this stellar evolution, by loss of mass or swelling, can lead to a rapprochement of the orbits of the planets around the host star, increasing the probability that some of them enter into collision.
As the Keck Observatory release explains, TOI-4329 – in particular – is interesting. Like all the exoplanets that can fall into the net stretched by Tess, it must be in a sphere of 200 light-years radius at most. This means that its atmosphere can be analysed, at least partially, with the James Webb Space Telescope which could reveal the presence of water or carbon dioxide, and more generally data that would provide constraints on where these planets formed and what interactions must have occurred in the planetary orbits we see today.
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