An international team of scientists - including researchers from the University of Liège - has just discovered an unusual Jupiter-sized planet orbiting a low-mass star called TOI-4860, located in the Corvus constellation. This discovery - made using the telescopes of the SPECULOOS consortium led by Michaël Gillon, an astrophysicist at ULiège - has been published in the journal Monthly Notices of the Royal Astronomical Society.
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he study, led by astronomers from the University of Birmingham and involving researchers from the University of Liège, led to the discovery of the gas giant. Named TOI-4860 b, this Jupiter-sized exoplanet is unusual for two reasons: stars of such low mass are not expected to host planets like Jupiter, and the planet appears to be particularly enriched in heavy elements.
The planet was first identified by NASA's Transiting Exoplanet Survey Satellite (TESS) as a drop of brightness while transiting in front of its host star. Still, that data alone was insufficiant to confirm that it was indeed a planet. The team then used the SPECULOOS South observatory - directed by Michaël Gillon, FNRS research director at ULiège - located in the Atacama desert in Chile to measure the planetary signal in several wavelengths and was able to validate the planetary nature of the object. The astronomers also observed the planet just before and after it disappeared behind its host star and noticed no change in light, meaning that the planet was not emitting any. Finally, the team collaborated with a Japanese group using the Subaru telescope in Hawaii. Together, they measured the mass of the planet to confirm it.
Following this star and confirming its planet is the initiative of a group of doctoral students as part of the SPECULOOS project. George Dransfield, who recently defended his thesis at the University of Birmingham, explains: "According to the canonical model of planet formation, the less mass a star has, the less massive the disc of matter that surrounds it. As planets are created from this disc, it was generally expected that high-mass planets, such as Jupiter, would not form. However, we were curious about this and wanted to check the planetary candidates to see if it was possible. TOI-4860 is our first confirmation and also the lowest mass star hosting such a high mass planet".
Amaury Triaud, Professor of Exoplanetology at the University of Birmingham, who led the study, said: "This discovery is the result of a proposal from our PhD students to observe systems like TOI-4860. Their work has paid off, as planets like TOI-4860 are essential for furthering our understanding of planet formation. A hint of what may have happened is hidden in the planet's properties, which appear to be particularly enriched in heavy elements. We have also detected something similar in the host star, so an abundance of heavy elements likely catalysed the planet formation process".
The new gas giant takes around 1.52 days to complete a full orbit around its host star, but because the host star is a cold, low-mass star, the planet itself can be described as a "warm Jupiter". This is a sub-class of planet that holds particular interest to astronomers wishing to deepen their initial observations and learn more about the formation of this type of planet.
Mathilde Timmermans, a doctoral student in ULiège's ExoTIC Lab (Astrobiology/Faculty of Science) and a collaborator in the SPECULOOS project, concludes: "Thanks to its very short orbital period and the properties of its host star, the discovery of TOI-4860 b offers a brilliant opportunity to study the atmospheric properties of a warmJupiter and to learn more about the formation of gas giants."
The team recently obtained observing time at the Very Large Telescope in Chile, which they intend to use to confirm several other planets with similar properties.
SPECULOOS is a project led by the University of Liège (project leader: Michaël Gillon) and carried out in partnership with the University of Cambridge, the University of Birmingham, the Massachusetts Institute of Technology, the University of Bern, the Canary Islands Institute of Astrophysics, and the European Southern Observatory (ESO). It is based on a network of robotic telescopes whose main cores are the observatories SPECULOOS-South at ESO’s Paranal Observatory in Chile (4 telescopes) and SPECULOOS-North in Tenerife (currently 1 telescope), complemented by the SAINT-EX (1 telescope in Mexico) and TRAPPIST (2 telescopes, 1 in Chile and 1 in Morocco) telescopes.
Triaud A. & al., An M dwarf accompanied by a close-in giant orbiter with SPECULOOS, MNRAS 00, L1 (2023) https://doi.org/10.1093/mnrasl/slad097
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