Confirmed planetTOI-700 system
TOI-700 d
The first Earth-sized planet discovered by TESS inside a habitable zone, orbiting a calm red dwarf 100 light-years away.
- Orbital period
- 37.42 days
- Distance from the star
- 0.163 AU · 24.4 million km
- Radius
- 1.073 Earth radii
- Mass
- Not yet measured
- Equilibrium temperature
- About 268 K without an atmosphere
- Discovery
- 2020 · transit
- Host star
- M2.5V red dwarf · about 0.42 solar masses
- Distance from the Sun
- 101.5 light-years
A milestone for TESS
TOI-700 d was the first Earth-sized planet that NASA's TESS mission found inside a star's habitable zone. Announced in 2020, it orbits a small, unusually quiet M dwarf once every 37.4 days and is about 7% larger than Earth.
Confirming the planet took careful follow-up. TESS's large pixels made the signal easy to confuse with background stars, so the Spitzer Space Telescope and ground-based observations were used to pin down the transit and rule out false positives.
A temperate-zone Earth-sized world
TOI-700 d receives about 86% of the energy Earth receives from the Sun, giving it an equilibrium temperature near 268 K. If it has an atmosphere with a suitable greenhouse effect, its surface could hold liquid water; without one, it would be a frozen or airless rock.
The host star's low activity improves the odds that an atmosphere, if one exists, could have survived. That combination of an Earth-sized world, a habitable-zone orbit, and a calm star makes TOI-700 d a priority target for future study.
What we don't know
The planet's mass is still unknown, so its density and composition are uncertain, and no atmosphere has been detected. Future radial-velocity and spectroscopy campaigns will try to weigh it and look for signs of an atmosphere.
- What is its mass and bulk composition?
- Does it have an atmosphere capable of sustaining liquid water?
- How did two habitable-zone Earths end up in the same system?
Key publications
| Year | Paper | Venue | Link |
|---|---|---|---|
| 2020 | Gilbert et al., The First Habitable-zone Earth-sized Planet from TESS. I. Validation of the TOI-700 System | The Astronomical Journal 160, 116 | DOI |
| 2020 | Rodriguez et al., The First Habitable-zone Earth-sized Planet from TESS. II. Spitzer Confirms TOI-700 d | The Astronomical Journal 160, 117 | DOI |
| 2023 | Gilbert et al., A Second Earth-sized Planet in the Habitable Zone of the M Dwarf, TOI-700 | The Astrophysical Journal Letters 944, L35 | DOI |
Values compiled from the NASA Exoplanet Archive and the papers listed above.
Worth knowing
It was the first Earth-sized habitable-zone planet found by TESS.
It receives about 86% of Earth's solar energy.
Its year lasts about 37.4 Earth days.