A Jupiter-size exoplanet formed around a tiny star. Astronomers aren't sure how

Around a small star, an exoplanet the size of Jupiter developed. A giant planet the size of Jupiter has been discovered circling a tiny, low-mass star, startling scientists and casting doubt on beliefs about how planets develop.

The red dwarf TOI-4860 circles the extrasolar planet, also known as an exoplanet. TOI-4860, which is in the constellation Corvus, has a mass that is just around one-third that of the sun. The exoplanet in question, TOI-4860 b, is suitably named since it orbits its star roughly once every 1.5 Earth days, making it a "warm Jupiter."

For two reasons, this is rare.

First, planets like this one aren't intended to develop around low-mass stars; their widths are about similar to that of Jupiter. Second, a significant percentage of metals, which astronomers use to refer to elements heavier than hydrogen and helium, appear to be concentrated in TOI-4860 b.

"Under the canonical planet formation model, the less mass a star has, the less massive is the disk of material around that star," team member and Ph.D. candidate at the University of Birmingham, George Dransfield, said in a release. "High-mass planets like Jupiter were generally believed not to exist since planets are formed from that disk. However, we were interested in this and sought to investigate planetary prospects to determine whether it was feasible. Our first confirmation comes from TOI-4860, which is also the lowest mass star to support a planet with such a high mass.

NASA's Transiting Exoplanet Survey Satellite (TESS), which seeks planets outside the solar system by looking for minute variations in the brightness of light produced by stars, was the first to discover TOI-4860 b. These dips occur when a planet in orbit crosses or transits its parent star.

Following this encounter, Dransfield and colleagues continued to monitor the system using the SPECULOOS South Observatory to search for habitable planets eclipsing ultra-cool stars. Speculos utilizes the same methodology as TESS to look for exoplanets, but it concentrates on dim, cold stars. As a result, instead of much bigger gas giants like TOI-4860 b, the facility located at the Paranal Observatory in Chile's Atacama Desert typically searches for Earth-size planets.

The scientists saw the planet using SPECULOOS as it emerged from and vanished behind its star. This observation was then followed up on by teammates using the Subaru Telescope in Hawaii.

It is unclear how such a massive exoplanet got to circle a low-mass star, but information on TOI-4860 b's makeup may provide some insight.

Amaury Triaud, a professor at the University of Birmingham and the team's head, claimed that the planetary features, which seem unusually richer in heavy metals, may contain a clue as to what may have happened. "We have found a similar phenomenon in the host star as well."

Triaud continued by saying that it's probable that the planet's development was accelerated by the presence of heavy elements.

Given TOI-4860 b's short orbital period and the high metallicity of its parent star, this system may be especially helpful for researching the warm Jupiters' atmospheres and better understanding how these gas giants form.

The team that discovered this exoplanet now plans to use the Very Large Telescope (VLT), situated in the Atacama Desert of northern Chile, to look for similar planets orbiting tiny parent stars.

I will always be grateful to our team's talented Ph.D. students for suggesting that we examine systems like TOI-4860, Triaud said in his conclusion. Since planets like TOI-4860 b are essential to improving our understanding of planet formation, their labors have really paid off.

The discovery of the new exoplanet was documented in a paper published Aug. 4 in the journal Monthly Notices of the Royal Astronomical Society: Letters.