GJ 3929 b (Gliese 3929 b, TOI-2013 b) is a confirmed exoplanet located 52 light-years away orbiting the red dwarf star GJ 3929.^[3] It is an Earth-sized planet, having a radius only 9% larger than that of Earth.^[4] It orbits its star at a distance of 0.0252 astronomical units (3,770,000 km), being located in the "Venus zone" of its star, and completes one orbit around it every 2 days and 15 hours.^[4] Because of the proximity of its star, GJ 3929 b has an equilibrium temperature of around 300 °C and receiving planetary insolation 17 times more intense than Earth receives from the Sun.^[4]

Characteristics

Atmosphere

The high density of GJ 3929 b does not suggest a dense atmosphere.^[4] Atmospheric scenarios such as a thin atmosphere of volatiles, a thin atmosphere of silicate enriched in refractory elements, or even no atmosphere at all are plausible.^[4] Due to its proximity to its star, GJ 3929 b has probably already lost much of its atmosphere since its formation.^[4]

GJ 3929 b has been studied with the James Webb Space Telescope in the search for an atmosphere. The search yield no detected molecular features, which rule out certain compositions such as a thick atmosphere rich in carbon dioxide. The observations also measured the dayside temperature, which is consistent with that of a zero-albedo planet with no heat distribution, and indicate that GJ 3929 b is likely a bare rock.^[7]

Discovery

GJ 3929 b was discovered by a team of astronomers led by Jonas Kermer, from the Heidelberg University in Germany.^[2] They reported a transit signal identified in the host star (GJ 3929)'s light curve detected by NASA's Transiting Exoplanet Survey Satellite (TESS).^[2] Afterwards, the planetary nature of this transit signal was confirmed using radial velocity observations with the CARMENES spectrograph, in addition to transit observations made with SAINT-EX and LCOGT.^[5][2] The discovery was announced in 2022.^[1]

The radial velocity observation with CARMENES also helped discover another planet in the planetary system, GJ 3929 c, a sub-Neptune detected by radial velocity.^[5]

Host star

GJ 3929 is a red dwarf of spectral type M3.5V^[8] that is located 51.6 light years from Earth, in the constellation Corona Borealis.^{[3][note 1]} This star is smaller, cooler and less luminous than the Sun, having a radius of 0.32 R_☉, an effective temperature of 3,384 K (3,111 °C) and a luminosity equivalent to 1% of solar luminosity.^[4] Its age is estimated between 2.2 and 11 billion years.^[4]

The star also hosts another planet, called GJ 3929 c, a sub-Neptune orbits 3 times further than the innermost planet, at a distance of 0.081 astronomical units (12,100,000 km),^[5] but still below the habitable zone.^[9]

Notes and references