Long wavelength observations of Epsilon Indi A b suggest a metal rich atmosphere and the presence of clouds

Star system: Epsilon Indi A | Distance from the Sun: 11.9 light years

The nearby star Epsilon Indi hosts a cold gas giant planet, Epsilon Indi A b, located just under 12 light years from Earth. Using the James Webb Space Telescope (JWST), astronomers captured the longest-wavelength image ever taken of an exoplanet, extending up to 25 micrometers. By combining these new images with decades of radial velocity and astrometric data, the team precisely determined the planet’s orbit and mass.

The planet’s light was measured across a wide range of wavelengths, creating the first complete spectral energy distribution for a cold gas giant outside our Solar System. The data suggest that Epsilon Indi A b has a metal-rich atmosphere, in line with trends seen in other giant planets. While the presence of water ice clouds is not confirmed, the planet’s brightness at the longest wavelengths fits better with models that include clouds. The team also calculated the planet’s total energy output and found it matches predictions for old, low-mass, and faint gas giants. These results make Epsilon Indi A b a key reference for understanding how giant planets evolve over time.

Key findings
- JWST imaged Epsilon Indi A b at wavelengths up to 25 micrometers, the longest for any exoplanet
- The planet’s orbit and mass were precisely determined using multiple techniques
- Epsilon Indi A b’s atmosphere appears metal-rich, consistent with other giant planets
- The planet’s brightness at long wavelengths suggests the possible presence of clouds
- The planet’s total energy output matches evolutionary models for old, cold gas giants

Scientific study

Worlds Next Door. IV. Mapping the Late Stages of Giant Planet Evolution with a Precise Dynamical Mass and Luminosity for Ind Ab (external link)