StarTOI-700 system
TOI-700
A small, unusually quiet red dwarf 100 light-years away, with four transiting planets, including two Earth-sized worlds inside its habitable zone.
- Star type
- M2.5V red dwarf
- Distance
- 101.5 light-years · 31.1 parsecs
- Mass
- 0.416 solar masses
- Mean radius
- 0.420 solar radii
- Luminosity
- About 0.023 solar luminosities
- Surface temperature
- About 3,480 K
- Rotation
- About 54 days
- Age
- Not precisely known; the star is relatively quiet
A quiet M dwarf
TOI-700 lies in the southern constellation Dorado. It is a red dwarf of spectral type M2.5V, cooler and smaller than the Sun but larger than stars such as Proxima Centauri. Its name comes from the TESS mission, which logs stars of interest as "TOI" targets before they are confirmed.
What made TOI-700 stand out is its calm. Many M dwarfs flare frequently, which can complicate the search for small planets and erode atmospheres. TOI-700 rotates slowly and shows comparatively little activity, giving astronomers a cleaner view of the periodic dips its planets produce.
Four planets, two in the temperate zone
TESS watched the star in its first year of operations and found three planets: a hot rocky world, a sub-Neptune, and TOI-700 d, the first Earth-sized planet discovered by TESS inside a habitable zone. In 2023, a closer look at additional TESS data revealed a fourth world, TOI-700 e, an Earth-sized planet that orbits between the sub-Neptune and d.
The system is a useful laboratory because it holds both a small gas planet and two rocky, temperate-zone planets around the same star. Comparing those worlds helps separate the effects of size and distance from the star.
How we study it
The planets were found and validated through transit photometry. TESS provided the repeated dips, and the Spitzer Space Telescope confirmed the signal of TOI-700 d at infrared wavelengths, ruling out many false-positive scenarios. Precise radial velocities have so far not measured the planets' masses, which remain unknown.
Future instruments aim to weigh the rocky planets and, eventually, search their atmospheres. TOI-700 d is small enough and cool enough that it may become a target for atmospheric study with the next generation of space telescopes.
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 hosts the first Earth-sized habitable-zone planet found by TESS.
It is unusually calm for an M dwarf, which helps planet searches.
It has both a sub-Neptune and two rocky planets, a useful comparison.