Barnard's Star b
Barnard's Star b — the first confirmed planet of Barnard's Star, a sub-Earth world (minimum mass ~0.3 Earth) on a scorching 3.15-day orbit. Never imaged; its true size, surface and atmosphere are unknown.
Key facts
Science
Physical
- Minimum mass (m·sin i)
- 1.79 × 10²⁴ kg · 0.299 M⊕
- Radial-velocity detection measures m·sin i; the true mass depends on the unknown orbital inclination.
- Radius
- Not measured
- No transit has ever been seen, so the radius has never been measured; the value shown is a model estimate for a rocky world of this minimum mass. Its true size and appearance are unknown.
Orbital
- Semi-major axis
- 3,425,791 km
- From the NASA Exoplanet Archive (ESO/ESPRESSO radial-velocity orbit)
- Eccentricity
- 0.03
- From the NASA Exoplanet Archive (ESO/ESPRESSO radial-velocity orbit)
- Inclination
- 0.00 °
- From the NASA Exoplanet Archive (ESO/ESPRESSO radial-velocity orbit)
- Orbital period
- 3.2 days
- From the NASA Exoplanet Archive (ESO/ESPRESSO radial-velocity orbit)
- Perihelion
- 3,323,018 km
- Computed from the orbital elements
- Aphelion
- 3,528,565 km
- Computed from the orbital elements
- Mean orbital velocity
- 79 km/s
- Computed from the orbital elements
Composition
- Bulk composition
- Presumed rocky (minimum mass ~0.3 Earth), but never imaged — surface and composition unknown.
- Surface appearance
- Appearance based on ESO/M. Kornmesser's artist's concept. No spacecraft has imaged this world, so its real appearance is unknown — The surface shown is an artistic representation, shown only in Visual mode; Realism shows a plain spectral colour.
Radiation & temperature
- Insolation
- 6.67 S⊕ · 6.67× the sunlight Earth receives
- Computed from Barnard's Star's luminosity and the orbital distance (inverse-square; Earth's sunlight = 1).
- Equilibrium temperature
- 438 K (165 °C)
- Computed model value (assumes no atmosphere) for the intense flux on its 3.15-day orbit — not a measured temperature.
Discovery & history
- Method
- Radial-velocity detection (stellar wobble)
- Name
- Designated 'b' as the first planet found around Barnard's Star, following the IAU convention of lettering planets in discovery order starting at 'b'.
Announced on 1 October 2024 by ESO's ESPRESSO team (J. I. González Hernández et al.) after years of radial-velocity monitoring at the VLT — the first confirmed planet of Barnard's Star, ending a century of false claims. The star's spectrum shifts by less than a metre per second every 3.15 days, betraying a world of only ~0.3 Earth masses.
Images
Never imaged — this world is known only from the tiny gravitational tug it exerts on its star (radial velocity). An artist's impression of the whole system is on the system view; the planet's own appearance is unknown.