A close-in world around a tiny, ancient red dwarf
Teegarden's Star b
Orbits Teegarden's Star · 12.5 light-years · discovered 2019 (radial velocity)
Teegarden's Star b orbits one of the smallest and faintest stars near the Sun, a red dwarf about 12.5 light-years away in the constellation Aries. The planet completes an orbit in under five days, but its star is so dim that the planet receives roughly the same amount of energy as Earth gets from the Sun.
Its minimum mass is only slightly above Earth's, which for a time gave it the highest score on the popular Earth Similarity Index of any known exoplanet. That index is a rough comparison of a few numbers, though, not a measure of habitability. Nothing is known about the planet's size, atmosphere or surface.
Key facts
- Star
- Teegarden's StarM7V red dwarf
- Distance
- 12.5 light-years
- Radius
- Not measuredIt has not been seen to transit its star
- Mass
- ≥ 1.16 × EarthMinimum mass (radial velocity)
- Orbital period
- 4.91 days
- Equilibrium temperature
- 277 K (4 °C)Before any greenhouse warming
- Starlight received
- 1.08× Earth's
- Surface gravity
- ≈ 1.07 gRough estimate (rocky composition assumed)
- Discovered
- 2019Radial velocity
- Star
- Teegarden's Star (M7V red dwarf)
- Distance
- About 12.5 light-years
- Discovered
- 2019, radial velocity
- Mass
- At least about 1.16 Earth masses (minimum mass)
- Radius
- Unknown — estimated at roughly 1 Earth radius if rocky
- Orbital period
- About 4.9 days
- Starlight received
- About 1.08 times what Earth gets from the Sun
- Equilibrium temperature
- About 277 K (4 °C) in published estimates, which ignore any atmosphere
- Constellation
- Aries
Measured values follow the NASA Exoplanet Archive and discovery papers; many carry large uncertainties. The 3D globe and walkable surface on this page are an artist's impression generated from these numbers.
What we know
Teegarden's Star b was detected through the slight wobble it causes in its star. A 2024 reanalysis of the data put its minimum mass at about 1.16 Earth masses and its orbital period at just under 4.91 days. Its true mass depends on the orbit's unknown tilt.
The planet has not been observed transiting its star, so its radius — and therefore its density and composition — has not been measured. It may well be rocky, but that is an assumption.
Its star
Teegarden's Star has less than a tenth of the Sun's mass and is so faint that it was only identified in 2003, when astronomers searching old asteroid survey images noticed its unusually fast motion across the sky. It is thought to be very old — probably around eight billion years or more — and appears relatively quiet, with modest flare activity for a star of its type.
Could it be habitable?
With Earth-like levels of incoming energy, Teegarden's Star b sits within its star's habitable zone. Whether that means liquid water depends on an atmosphere that has never been detected.
Red dwarfs like this one shine fiercely in ultraviolet and X-rays during their youth, and they stay bright for a long time before settling down. Any planet this close may have lost much of its original water and air early on. The star's apparent calm today is encouraging, but it says little about the planet's past.
Orbit and climate
The planet orbits roughly 0.026 astronomical units from its star — under 4 million kilometres, less than a tenth of Mercury's distance from the Sun. It is almost certainly tidally locked, with permanent day on one side and permanent night on the other. Its starlight would be dominated by deep red and infrared wavelengths.
Discovery
The CARMENES survey, run from the Calar Alto Observatory in Spain, announced planets b and c in 2019 in a study led by Mathias Zechmeister. Follow-up work published in 2024 refined their properties and reported a third planet, Teegarden's Star d, on a 26-day orbit.
Teegarden's Star c
The second planet, with a minimum mass of roughly one Earth mass and an orbit of about 11 days, lies near the cooler outer part of the habitable zone.
Future observations
Because the planet does not appear to transit, its atmosphere cannot be studied with the transit technique. Detecting it directly is extremely hard, as it sits very close to its star on the sky. Characterising it will likely require future giant telescopes and instruments designed to pick out faint planets beside bright stars.
About the 3D impression
Artist's impression — the real surface has never been seen. The globe and the surface you can walk on are generated from what is measured — size, the starlight it receives and the kind of star it orbits — using the same procedural engine as our imaginary worlds. Seas, ice, clouds and any plant-like colours are possibilities, not observations: around a red dwarf the daylight is redder, so the scene uses warmer skies and darker vegetation.
Earth-like exoplanets compared
| Planet | Distance | Radius | Year | Sunlight |
|---|---|---|---|---|
| Proxima Centauri b | 4.2 ly | — | 11.2 days | 0.65× Earth |
| Ross 128 b | 11.0 ly | — | 9.87 days | 1.38× Earth |
| Teegarden's Star b | 12.5 ly | — | 4.91 days | 1.08× Earth |
| Gliese 667 Cc | 23.6 ly | — | 28.1 days | 0.88× Earth |
| TRAPPIST-1d | 40.5 ly | 0.79 R⊕ | 4.05 days | 1.11× Earth |
| TRAPPIST-1e | 40.5 ly | 0.92 R⊕ | 6.10 days | 0.65× Earth |
| TRAPPIST-1f | 40.5 ly | 1.04 R⊕ | 9.21 days | 0.37× Earth |
| TRAPPIST-1g | 40.5 ly | 1.13 R⊕ | 12.4 days | 0.25× Earth |
| LHS 1140 b | 48.9 ly | 1.73 R⊕ | 24.7 days | 0.43× Earth |
| TOI-700 d | 101 ly | 1.07 R⊕ | 37.4 days | 0.87× Earth |
| Kepler-186f | 580 ly | 1.17 R⊕ | 129.9 days | 0.30× Earth |
| Kepler-22b | 635 ly | 2.10 R⊕ | 289.9 days | 1.01× Earth |
| Kepler-62f | 980 ly | 1.41 R⊕ | 267.3 days | 0.41× Earth |
| Kepler-442b | 1,194 ly | 1.34 R⊕ | 112.3 days | 0.70× Earth |
| Kepler-452b | 1,800 ly | 1.63 R⊕ | 384.8 days | 1.10× Earth |
Surprising facts about Teegarden's Star b
- Teegarden's Star went unnoticed until 2003 despite being one of the nearest stars to the Sun — it is too faint to see without a sizeable telescope.
- A full year on Teegarden's Star b lasts less than five Earth days.
- Its host star is thought to be considerably older than the Solar System, perhaps around eight billion years old.
- At least three planets have been found around the star, all with minimum masses close to Earth's.