Hubble observations reveal extreme thermal properties of rocky exoplanet TOI-2431 b

Star system: TOI 2431 | Distance from the Sun: 117 light years

The rocky exoplanet TOI-2431 b, which orbits its host star in just 5.4 hours, has been studied using the Hubble Space Telescope to analyze its thermal characteristics. This planet is characterized by an extreme surface environment where day-night heat redistribution appears highly inefficient, preventing the transport of heat from the dayside to the nightside. This finding offers new insights into the nature of ultra-short-period planets.

Researchers observed the planet’s secondary eclipse—the event where a planet passes behind its star—using the Hubble Space Telescope’s WFC3 camera. By combining these near-infrared measurements with existing optical data from the TESS satellite, the team calculated the planet's dayside brightness temperature and evaluated how much light is reflected off its surface, known as albedo.

The collected data indicates that the planet lacks significant nightside emission and shows no measurable hotspot offset. Under the assumption that the planet reflects very little light, its brightness temperature is estimated at approximately 2,524 Kelvin. The results suggest the planet operates near the theoretical limit of zero heat redistribution, distinguishing it from other previously studied lava worlds.

Key findings
- Detection of a secondary eclipse for a rocky planet using the Hubble Space Telescope for the first time.
- Dayside brightness temperature estimated at 2,524 Kelvin under zero-albedo assumptions.
- Evidence of inefficient heat redistribution from the day side to the night side.
- Observations confirm the absence of detectable nightside emission or a significant hotspot offset.
- TOI-2431 b serves as a new benchmark for studying the atmospheres and surfaces of lava worlds.

Scientific study

The First Hubble Detection of a Secondary Eclipse from a Rocky Exoplanet: the 5.4-hour planet TOI-2431 b (external link)