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yesterday

Webb Data Point to Thick Atmosphere on Ultra‑Hot Super‑Earth TOI‑561 b

A cooler‑than‑expected dayside measured by Webb’s NIRSpec points to heat redistribution by a volatile envelope over a global magma ocean.

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Exoplanet TOI-561 b is the closest of four worlds orbiting a 10-billion-year-old G-type star roughly 280 light-years from Earth.
Exoplanet TOI-561 b is the closest of four worlds orbiting a 10-billion-year-old G-type star roughly 280 light-years from Earth.
Exoplanet TOI-561 b is the closest of four worlds orbiting a 10-billion-year-old G-type star roughly 280 light-years from Earth.

Overview

  • Secondary‑eclipse observations show a dayside temperature near 3,200°F (≈1,800°C), far below the ≈4,900°F (≈2,700°C) expected for bare molten rock.
  • The results come from JWST General Observers Program 3860, which continuously monitored the TOI‑561 system for more than 37 hours across nearly four orbits.
  • The evidence supports a substantial, volatile‑rich atmosphere that best explains the thermal signature and helps account for the planet’s unusually low bulk density.
  • Researchers propose a magma–atmosphere equilibrium in which outgassing and reabsorption by the molten interior help the small, highly irradiated planet retain its gases.
  • TOI‑561 b is a roughly 1.4‑Earth‑radius, ~2‑Earth‑mass ultra‑short‑period world orbiting an ancient, iron‑poor thick‑disk star, and the team is now analyzing the full dataset to map temperatures and constrain atmospheric composition.