Exoplanets · Space Codex
TOI-700 d
An Earth-sized planet around a quiet red dwarf, found by TESS in 2020.
TESS's first Earth-size habitable-zone world
Artist's concept. No telescope has seen TOI-700 d as more than a point of light, and most exoplanets not even that. What we know comes from how a planet dims or tugs its star. Any picture of its surface, colour or sky, anywhere, is an illustration, not an observation.
At a glance
Key points
A slightly smaller sibling, TOI-700 e, followed in 2023.
- First Earth-size habitable-zone planet from TESS
- Its star rarely flares
- Has an Earth-size sibling, TOI-700 e
How it was found
TOI-700 lies near the south ecliptic pole, inside the zone TESS watched almost continuously in its first year: 11 of 13 sectors of roughly 27 days each. The star was first catalogued as Sun-like, which made its planets look larger and hotter. Once the team, helped by a high-school student working with them, corrected it to a small M dwarf, the outer planet shrank to Earth size inside the habitable zone. Spitzer then confirmed the transit.
A family of four
Planet b is almost exactly Earth-sized on a 10-day orbit; c is a sub-Neptune about 2.5 times Earth's width; d takes 37 days. When TESS returned in its third year, the extra data revealed e, slightly smaller than Earth, on a 28-day orbit in the optimistic habitable zone, between c and d.
A quieter star
Unlike many red dwarfs, TOI-700 flares rarely, which improves the odds that its planets kept their atmospheres. Climate models allow both a temperate ocean world and a dry, Mars-like one.
Habitable on paper
A 2020 study ran 20 three-dimensional climate simulations, varying air, pressure, spin and water. Many kept the surface temperate, but every version produced spectral features under 10 parts per million, too small for JWST. Whether TOI-700 d is habitable remains a modelling question, not an observation.
What we still don't know
Its mass and whether it has air. Its transits are too shallow for current atmosphere studies.
Missions
- 2018–
TESS
NASAActiveAll-sky transit survey; over 1,000 confirmed planets.
Related entries
- LHS 1140 bA temperate super-Earth, possibly icy
- Exoplanets: the censusPlanets around other stars
Sources
- Gilbert et al. 2020, AJ 160:116 (arXiv) (opens in a new tab)
- Suissa et al. 2020, AJ (arXiv) (opens in a new tab)
- Gilbert et al. 2023, ApJL 944:L35 (arXiv) (opens in a new tab)
- NASA JPL: NASA planet hunter finds Earth-size habitable-zone world (opens in a new tab)
- NASA Exoplanet Archive: TOI-700 overview (opens in a new tab)
- Rodriguez et al. 2020, AJ (arXiv) (opens in a new tab)
Last reviewed against these sources. Built from public NASA, ESA and JPL data; not affiliated with or endorsed by any agency.