Barnard's Star b, or Barnard b, is a

sub-Earth A sub-Earth is a planet "substantially less massive" than Earth and Venus. In the Solar System, this category includes Mercury (planet), Mercury and Mars. Characteristics Sub-Earth exoplanets are among the most difficult type to detect becau ...

-mass

exoplanet An exoplanet or extrasolar planet is a planet outside the Solar System. The first confirmed detection of an exoplanet was in 1992 around a pulsar, and the first detection around a main-sequence star was in 1995. A different planet, first det ...

closely orbiting

Barnard's Star Barnard's Star is a small red dwarf star in the constellation of Ophiuchus. At a distance of from Earth, it is the fourth-nearest-known individual star to the Sun after the three components of the Alpha Centauri system, and is the c ...

, a nearby

red dwarf A red dwarf is the smallest kind of star on the main sequence. Red dwarfs are by far the most common type of fusing star in the Milky Way, at least in the neighborhood of the Sun. However, due to their low luminosity, individual red dwarfs are ...

star six

light-year A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by the International Astr ...

s from Earth. The planet was discovered using

radial velocity The radial velocity or line-of-sight velocity of a target with respect to an observer is the rate of change of the vector displacement between the two points. It is formulated as the vector projection of the target-observer relative velocity ...

observations from the

ESPRESSO Espresso (, ) is a concentrated form of coffee produced by forcing hot water under high pressure through finely ground coffee beans. Originating in Italy, espresso has become one of the most popular coffee-brewing methods worldwide. It is cha ...

spectrograph on the

Very Large Telescope The Very Large Telescope (VLT) is an astronomical facility operated since 1998 by the European Southern Observatory, located on Cerro Paranal in the Atacama Desert of northern Chile. It consists of four individual telescopes, each equipped with ...

, and was announced on 1 October 2024. It is the second from its star of four known planets in its system. The designation "Barnard's Star b" was first used for a different planetary candidate announced in 2018, the existence of which was later refuted.

Characteristics

Barnard b orbits close to its star, completing an orbit every 3.15 days at a distance of . It orbits closer to the star than the

habitable zone In astronomy and astrobiology, the habitable zone (HZ), or more precisely the circumstellar habitable zone (CHZ), is the range of orbits around a star within which a planetary surface can support liquid water given sufficient atmospheric pressu ...

and so is too hot to be potentially habitable, with an estimated

equilibrium temperature The planetary equilibrium temperature is a theoretical temperature that a planet would be if it were in radiative equilibrium, typically under the assumption that it radiates as a black body being heated only by its parent star. In this model, th ...

of . Its

orbital eccentricity In astrodynamics, the orbital eccentricity of an astronomical object is a dimensionless parameter that determines the amount by which its orbit around another body deviates from a perfect circle. A value of 0 is a circular orbit, values be ...

is near zero, meaning its orbit is nearly circular. Barnard b is a

, with a

minimum mass In astronomy, minimum mass is the lower-bound calculated mass of observed objects such as planets, stars, binary systems, nebulae, and black holes. Minimum mass is a widely cited statistic for extrasolar planets detected by the radial velocit ...

of 0.3 times the

mass of Earth An Earth mass (denoted as ''M''🜨, ''M''♁ or ''M''E, where 🜨 and ♁ are the astronomical symbols for Earth), is a unit of mass equal to the mass of the planet Earth. The current best estimate for the mass of Earth is , with a relative ...

, and is thus likely a

rocky planet A terrestrial planet, tellurian planet, telluric planet, or rocky planet, is a planet that is composed primarily of silicate, rocks or metals. Within the Solar System, the terrestrial planets accepted by the IAU are the inner planets closest to ...

. Its true mass is uncertain since its

orbital inclination Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a reference plane and the orbital plane or axis of direction of the orbiting object. For a satellite orbiting the Earth ...

is unknown. The radius of Barnard b is also unknown, and TESS observations show no evidence that it transits 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-quarters that of Earth. The lack of a transit sets an upper limit of on the orbital inclination. The discovery paper of Barnard b also found evidence for three additional planetary candidates, which were confirmed in 2025. These are all low-mass planets in close orbits, similar to Barnard b.

History of observations

Refuted 2018 candidate

In November 2018, an international team of astronomers led by Ignasi Ribas announced the detection by

of a candidate

super-Earth A super-Earth is a type of exoplanet with a mass higher than Earth, but substantially below those of the Solar System's ice giants, Uranus and Neptune, which are 14.5 and 17.1 times Earth's, respectively. The term "super-Earth" refers only to t ...

orbiting Barnard's Star, which was referred to as Barnard's Star b. 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. Further studies in the following years confirmed this result. This planet was thought to orbit every 233 days at 0.4 AU, near the stellar system's

snow line The climatic snow line is the boundary between a snow-covered and snow-free surface. The actual snow line may adjust seasonally, and be either significantly higher in elevation, or lower. The permanent snow line is the level above which snow wil ...

, and to have a

of . The planet would have most likely been frigid, with an estimated

of about , placing it outside its host star's presumed

2024 confirmation

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 the

spectrograph An optical spectrometer (spectrophotometer, spectrograph or spectroscope) is an instrument used to measure properties of light over a specific portion of the electromagnetic spectrum, typically used in spectroscopic analysis to identify mate ...

on the

. 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 the

. Barnard's Star b (or Barnard b) is a re-use of the designation originally used for the refuted super-Earth candidate.

References

{{2024 in space Barnard's Star Exoplanets detected by radial velocity Exoplanets discovered in 2024 Sub-Earth exoplanets

Characteristics

History of observations

Refuted 2018 candidate

2024 confirmation

See also

References