TOI-700 d: Habitable Zone, 37-Day Year
Terrestrial around TOI-700
It is 1.07 times Earth's radius, closest in size to Earth. A year there lasts 37.42 days, on an orbit 2 times closer to its star than Mercury is to the Sun. Its equilibrium temperature is 245 K (derived from the star rather than measured), in the range where liquid water is possible. The host star TOI-700 runs at 3459 K with 0.41 times the Sun's mass.
What this planet has and has not got
Inside the habitable zone, computed from the star's luminosity. Yes.
A measured mass, not just a radius. No.
A measured temperature rather than one derived from the star. No.
Any detection of an atmosphere. Not recorded in the archive.
TOI-700 from the inside out
Orbit
/
Planet
Radius
1.07 Earth radii
Equilibrium temperature
245 K (derived)
One year
37.42 days
Orbit radius
0.1633 AU
Host star
TOI-700 at 3459 K
Distance
102 light-years
Starlight blocked
0.054% at each transit
What you get from the shadow
The fraction of starlight blocked sets the radius against the star's.
The archive lists no measured equilibrium temperature for this planet. The 245 K quoted here is derived from the star's output and the orbital distance, assuming a third of the light is reflected. It is an estimate from two numbers, not an observation.
A transit is a silhouette. It gives a width and says nothing about how heavy the thing casting it is, so this planet has no mass on record.
TOI-700 has 4 known planets. Systems like this are the ones where architecture can be studied instead of guessed at.
Found by Transiting Exoplanet Survey Satellite (TESS) in 2020. 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.
TOI-700 d sits in the habitable zone on the arithmetic alone. That says where \
it orbits, not what it is like. What would you want measured next before calling it promising?
