Extreme planet discovered challenging theories on the formation of planets

 Astronomers have discovered a massive planet, TOI-4603b, which challenges our understanding of planetary formation and evolution. With nearly 13 times the mass of Jupiter, this unique exoplanet orbits remarkably close to its star, completing its orbit in just 7.25 days. Identified by a team of astronomers led by Akanksha Khandelwal from the Physical Research Laboratory in India, TOI-4603b is considered one of the densest known transiting giant planets.

Planetary mass has its limits, as nuclear fusion – the merging of atoms to create heavier elements – is triggered once a critical threshold is reached. For a star, hydrogen fusion starts at around 85 times the mass of Jupiter, while the upper mass limit for a planet lies between 10 and 13 Jupiters. This includes brown dwarfs, which lack sufficient mass for hydrogen fusion but can fuse deuterium, a heavy isotope of hydrogen.

Stars form as dense clusters within molecular clouds collapse under gravity, creating a protostar that grows by absorbing material from the surrounding cloud. Planets, on the other hand, develop from the remnants of dust and gas, forming as debris pieces attach and eventually grow into planets. Brown dwarfs are believed to form similarly to stars, resulting from molecular cloud clusters collapsing under gravity. They are often found orbiting stars at a considerable distance, at least five times the distance between Earth and the Sun.

TOI-4603b was initially detected using data from NASA's TESS space telescope, which searches for exoplanets by observing faint, regular dips in stellar light. By knowing the star's mass, researchers can calculate the exoplanet's mass based on the star's movement. This method led to an estimated mass of 12.89 times that of Jupiter for TOI-4603b. Its average density is calculated at 14.1 grams per cubic centimeter, significantly denser than Earth, Jupiter, and even lead.

Although TOI-4603b meets most criteria for classification as an exoplanet, it sits on the edge of the brown dwarf mass limit, making it a vital world for understanding both brown dwarf and giant planet formation and their relationship with their stars. The exoplanet's notably eccentric orbit and a brown dwarf companion orbiting at about 1.8 astronomical units suggest that TOI-4603b is migrating closer to the star. This intriguing research has been accepted for publication in Astronomy & Astrophysics Letters and is available on arXiv.