.jpg) Artist's impression of Barnard b | |
| Discovery[1] | |
|---|---|
| Discovered by | González Hernándezet al. |
| Discovery site | ESPRESSO (VLT) |
| Discovery date | October 2024 |
| Radial velocity | |
| Designations | |
| Barnard b, GJ 699 b | |
| Orbital characteristics[2] | |
| 0.0229±0.0003 AU | |
| Eccentricity | 0.03+0.03 −0.02 |
| 3.1542±0.0004 d | |
| Semi-amplitude | 0.440±0.036 m/s |
| Star | Barnard's Star |
| Physical characteristics[2] | |
| Mass | ≥0.299±0.026 M🜨 |
| Temperature | 438 K (165 °C; 329 °F,equilibrium) |
Barnard's Star b, orBarnard b, is asub-Earth-massexoplanet closely orbitingBarnard's Star, a nearbyred dwarf star sixlight-years from Earth. The planet was discovered usingradial velocity observations from theESPRESSO spectrograph on theVery Large Telescope, and was announced on 1 October 2024.[3] It is the second from its star of four known planets in its system.[2]
The designation "Barnard's Star b" was first used for a different planetary candidate announced in 2018,[4] the existence of which was later refuted.[5]
Barnard b orbits close to its star, completing an orbit every 3.15 days at a distance of 0.023 AU (3.4 million km; 2.1 million mi).[1] It orbits closer to the star than thehabitable zone and so is too hot to be potentially habitable, with an estimatedequilibrium temperature of 438 K (165 °C; 329 °F). Itsorbital eccentricity is near zero, meaning its orbit is nearly circular.[2]
Barnard b is asub-Earth, with aminimum mass of 0.3 times themass of Earth,[2] and is thus likely arocky planet. Its true mass is uncertain since itsorbital inclination is unknown.[1] The radius of Barnard b is also unknown, andTESS observations show no evidence that ittransits its host star, which would otherwise allow its radius to be measured. Based on mass-radius relationships, its radius is predicted to be about three-quartersthat of Earth. The lack of a transit sets an upper limit of87.9° on the orbital inclination.[6]
The discovery paper of Barnard b also found evidence for three additional planetary candidates,[1] which were confirmed in 2025. These are all low-mass planets in close orbits, similar to Barnard b.[2]
In November 2018, an international team of astronomers led by Ignasi Ribas announced the detection byradial velocity of a candidatesuper-Earth orbiting Barnard's Star, which was referred to as Barnard's Star b.[4][7] However, the existence of this planet was refuted in 2021, when the radial velocity signal was found to originate from long-term activity on the star itself, related to its rotation.[5] Further studies in the following years confirmed this result.[8][1]
This planet was thought to orbit every 233 days at 0.4 AU, near the stellar system'ssnow line, and to have aminimum mass of 3.2 ME. The planet would have most likely been frigid, with an estimatedequilibrium temperature of about 105 K (−168 °C; −271 °F), placing it outside its host star's presumedhabitable zone.[4]
On 1 October 2024, the discovery of the planet now known as Barnard b was announced by a team of astronomers led by Jonay González Hernández, using radial velocity data from theESPRESSOspectrograph on theVery Large Telescope. This constituted the first convincing evidence for a planet orbiting Barnard's Star. Additionally, three other candidate low-mass planets were proposed in this study, all orbiting closer to the star than thehabitable zone.[1][3] Barnard's Star b (or Barnard b) is a re-use of the designation originally used for the refuted super-Earth candidate.
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