Observations show that TOI-1685 b is a hot, rocky super-Earth exoplanet

An international team of astronomers has carried out follow-up observations of a nearby alien body called TOI-1685 b. The observations, published on May 21 on the preprint server arXiv, suggest that TOI-1685 b is a hot, rocky alien world with a density similar to Earth. So-called “super-Earths” are planets that are more massive than Earth but less than the mass of Neptune. Although the term “super-Earth” refers only to the mass of the planet, astronomers also use it to describe planets that are larger than Earth and smaller than so-called “mini-Neptunes” (with a radius between 2 and 4 Earth radii). Discovered in 2021, TOI-1685 b is an ultra-short-period super-Earth (USP) orbiting an M dwarf star about half the size and mass of the Sun. The star system is located about 122.5 light-years away. Observations so far have shown that TOI-1685 b orbits its host every 16.5 hours. However, the physical properties of the planet remain uncertain. Some studies report that TOI-1685 b is a watery world (about 50% water) about 70% larger than Earth, while others suggest that TOI-1685 b is a rocky planet about 1,46 times the radius of Earth, without any significant water. To resolve these data discrepancies, a group of astronomers led by Jennifer A. Burt of the California Institute of Technology (Caltech) used NASA’s Transiting Exoplanet Survey Satellite (TESS) and various ground-based observation facilities visited to determine TOI-1685 b.

“Here we find a refined stellar classification focusing on the metallicity of the parent star, updated planetary radius measurements including two sectors of TESS data and multicolor photometry from various ground facilities, and more precise dynamical mass measurements from the combined CARMENES, IRD and MAROON-X radial velocity datasets,” the researchers explained. The new observations reveal that TOI-1685 b has a radius of about 1.47 times that of the Earth, a mass about three times that of the Earth, and a density of 5.3 g/cm3. This means that the density of TOI-1685 b is only 4% lower than the bulk density of the Earth. The astronomers emphasize that the similarity with the density of the Earth suggests that TOI-1685 b is also a rocky planet with minimal volumetric contributions from hydrogen and helium atmospheric components. In addition, TOI-1685 b was found to have a high equilibrium temperature of about 1,062 K. In summary, the study authors note that while they rule out TOI-1685 b as being a water world, it could still have an atmosphere with a high average molecular weight.

source: https://dx.doi.org/10.48550/arxiv.2405.14895