Precise mass and radius measurements reveal diverse compositions for small exoplanets

Star system: TOI-1634 | Distance from the Sun: 115 light years

A new study has analysed six planetary systems, each with at least one small planet passing in front of its star. By combining new and existing observations from space and ground-based telescopes, researchers have measured the mass and size of these planets with high precision. This allows for a better understanding of what these distant worlds are made of and how they might have formed.

The team used data from CHEOPS, K2, TESS, and several ground-based observatories, along with radial velocity measurements from instruments like HARPS-N and ESPRESSO. By modelling both the light dips as planets transit their stars and the subtle movements of the stars themselves, they achieved typical uncertainties of less than 15% for mass and 5% for radius. This level of accuracy enables reliable calculations of the planets' densities.

The results show a wide variety of planet types. Some, like K2-106 b and TOI-1634 b, are rocky and lie near the so-called radius valley, a range where few planets are found. Others, such as K2-111 b and K2-263 b, have intermediate densities, suggesting they contain large amounts of steam or other volatiles. Planets like K2-79 b and K2-222 b are less dense, consistent with being gas dwarfs or water-rich worlds. Some systems also show signs of additional planets detected through radial velocity but not seen in transit.

Key findings
- Mass and radius of small exoplanets measured with high precision
- Planets show a range of compositions from rocky to gas-rich
- Some systems have hidden companions detected by star movements
- CHEOPS and HARPS-N data provide some of the best density measurements yet
- Results help prepare for future studies of exoplanet atmospheres

Scientific study

Constraining Small Planet Compositions for Future Missions (external link)