GJ 876 was the first red dwarf found to host a giant planet, and it turned out to host two. Three of its four planets - c, b and e - are locked in a 1:2:4 Laplace resonance, the same kind of gravitational lockstep that binds Io, Europa and Ganymede at Jupiter.
Fly there in 3DThe resonance here is not a static coincidence: the three planets actively exchange angular momentum, and the pattern librates on a decade timescale. It is the only extrasolar Laplace resonance close enough that we have watched it evolve over a full cycle.
The two giants both orbit within the star’s habitable zone. Neither has a surface; whether either has a large moon is entirely unknown.
| Spectral type | M3.5 V |
| Surface temperature | 3,294 K |
| Mass | 0.32 solar masses |
| Radius | 0.3 solar radii |
| Luminosity | 0.0124 times the Sun |
| Apparent magnitude | 10.19 |
| Distance from the Sun | 15.2 light-years (4.7 parsecs) |
| Position (J2000) | RA 343.3197°, Dec -14.2637° |
| Constellation | Aquarius |
| Planet | Year | Orbit | Radius | Mass | Found |
|---|---|---|---|---|---|
| GJ 876 d | 46.5 hours | 0.0208 AU | 2.51 R⊕ estimated | 6.83 M⊕ | Radial Velocity, 2005 |
| GJ 876 c | 30.1 days | 0.130 AU | 14 R⊕ estimated | 226.98 M⊕ | Radial Velocity, 2000 |
| GJ 876 b | 61.1 days | 0.208 AU | 13.3 R⊕ estimated | 723.22 M⊕ | Radial Velocity, 1998 |
| GJ 876 e | 124.3 days | 0.334 AU | 3.92 R⊕ estimated | 14.6 M⊕ | Radial Velocity, 2010 |
Values are the NASA Exoplanet Archive’s composite parameters. A radius marked estimated comes from a mass–radius relation; a mass marked minimum is M sin i. Planet sizes and colours in the 3D view are renderings: none of these worlds has been photographed as more than a point of light.