TOI-791 c: Less Dense Than Cork
Ice giant around TOI-791
It is 1.15 times Jupiter's radius, closest in size to Jupiter, and 18.6 times Earth's mass, at 0.05 g/cm3, less dense than Earth. A year there lasts 232.02 days, on an orbit 2.2 times Mercury's distance from the Sun. Its equilibrium temperature is 363 K, hotter than any desert. The host star TOI-791 runs at 6294 K with 1.28 times the Sun's mass.
Radius
12.95 Earth radii
Mass
18.6 Earth masses
Equilibrium temperature
363 K (measured)
One year
232.02 days
Orbit radius
0.8630 AU
Host star
TOI-791 at 6294 K
Distance
1113 light-years
Starlight blocked
0.647% at each transit
0.05g/cm3: less dense than cork
The habitability checklist, honestly scored
Orbits inside the computed habitable zone. No.
Dense enough to be rock rather than gas, at 0.05 g/cm3. No.
A measured mass, not just a radius. Yes.
A measured temperature rather than one derived from the star. Yes.
Any detection of an atmosphere. Not recorded in the archive.
What you get from the shadow
The depth of the dip is the ratio of the two discs, so the radius follows.
Found by Transiting Exoplanet Survey Satellite (TESS) in 2026. TESS scans most of the sky in 27-day stretches, so it favours bright nearby stars and short orbits over the faint distant ones Kepler specialised in.
A transit gives the radius and a separate measurement gives the mass. Having both is what makes a density, and a density is the only clue to composition at this range.
TOI-791 has 2 known planets. Planets in company tug on each other, and those tugs are measurable, which is how masses get pinned down without a wobble.
