Hot and massive planet discovered orbiting a young dwarf star

Astronomers have discovered a young exoplanet orbiting the star TOI-5734, located about 106 light-years away. Smaller than Neptune but larger than Earth, this planet has a radius of 2.1 Earth radii and a mass of 9.1 Earth masses with a density slightly lower than Earth’s. It is classified as a hot sub-Neptune exoplanet due to its size and how close it orbits its host (6.18-day orbit at 0.06 AU proximity). Due to this proximity, it is very hot with an estimated temperature of about 688 K.

The TOI-5734 star is a relatively young K-type dwarf star 0.72 times the Sun’s mass and 0.64 times the Sun’s radius. TOI-5734 b sits near the upper edge of the radius valley, a gap in planet size between 1.5 and 2.0 Earth radii. Very few planets are found in this transition region, showing that TOI-5734 b may be mid-transformation. Studies suggest that the planet may be losing its atmosphere due to photoevaporation and astronomers estimate that it may lose its primordial envelope in about 300 million years, potentially forming a rocky super-Earth.

The first major instrument used in uncovering this event was the Transiting Exoplanet Survey Satellite (TESS). This was used to estimate the size of the planet by watching the star for tiny dips in brightness which occur when a planet passes in front of its star. This was first observed in 2022, and another instrument, HARPS-N, was used for confirmation. Together, they measure the planet’s mass, radius, and overall density, providing valuable insights into how planetary systems mature.