TOI-791 c
TOI-791 c — the outer of the pair, slightly larger than Jupiter and about nineteen Earth masses, and thinner still than its neighbour. Its year is 232 days and its temperature around 363 K. Known super-puffs are usually young worlds crowded close to their stars, where a hot, distended atmosphere is easier to account for; this one is cool and far out, and how it stays so swollen is unresolved.
Key facts
Science
Physical
- Mass
- 1.11 × 10²⁶ kg · 18.6 M⊕
- NASA Exoplanet Archive (Dransfield et al. 2026, MNRAS) — adopted transit + mass solution, read 2026-09-23
- Radius
- 82,481 km · 12.9× wider than Earth
- NASA Exoplanet Archive (Dransfield et al. 2026, MNRAS) — adopted transit + mass solution, read 2026-09-23
- Density
- 47.3 kg/m³ · 0.047× water
- Computed from mass and radius
- Surface gravity
- 1.09 m/s² · 11% of Earth's gravity
- Computed from mass and radius
- Escape velocity
- 13.4 km/s · 1.2× Earth's escape velocity
- Computed from mass and radius
Orbital
- Semi-major axis
- 0.863 AU
- From the NASA Exoplanet Archive (transit + orbit fit)
- Eccentricity
- 0.028
- From the NASA Exoplanet Archive (transit + orbit fit)
- Inclination
- 0.00 °
- From the NASA Exoplanet Archive (transit + orbit fit)
- Orbital period
- 232.0 days
- From the NASA Exoplanet Archive (transit + orbit fit)
- Perihelion
- 0.839 AU
- Computed from the orbital elements
- Aphelion
- 0.887 AU
- Computed from the orbital elements
- Mean orbital velocity
- 40.5 km/s
- Computed from the orbital elements
Composition
- Bulk composition
- A transiting giant of 12.95 ± 0.45 Earth radii and 18.60 (+2.24/−2.09) Earth masses (Dransfield et al. 2026), and a measured density barely above its neighbour's. Its atmosphere has not been observed. At 363 K and 0.86 AU it is cooler and further out than any other planet of comparable density, and the mechanism keeping it inflated is unresolved.
- Cloud appearance
- Appearance based on NASA/JPL-Caltech's artist's concept. No spacecraft has imaged this world, so its real appearance is unknown — The banded clouds shown are a representation of its class, shown only in Visual mode; Realism shows a plain spectral colour.
Radiation & temperature
- Insolation
- 4.12 S⊕ · 4.12× the sunlight Earth receives
- Computed from TOI-791's luminosity and the orbital distance (inverse-square; Earth's sunlight = 1).
- Equilibrium temperature
- 363 K (90 °C)
- The archive's computed equilibrium value — not measured.
Discovery & history
- Method
- Transit detection
- Name
- Designated 'c' under the IAU convention that letters a star's planets 'b', 'c', 'd'… in the order found (the star is the unwritten 'a'); no IAU proper name has been assigned.
TESS caught its transits and listed them in 2024 as candidate 791.02 on a 928-day period. The 2026 confirmation showed that period was an alias — the real one is a quarter of it, 232 days — and measured the planet's mass.
Images
No telescope has imaged this world — it is known only from the tiny dip it makes crossing its star. Only its host system has been pictured (see the system view); its true surface appearance is unknown.