GJ 849 is an M dwarf star located at a distance of 8.77 parsecs (29 light years) in the constellation Aquarius. Its planetary system diverges widely from theoretical expectations regarding M dwarfs. Instead of a close-in Neptune-mass planet like the companions of GJ 674 and GJ 436, GJ 849 harbors a single gas giant reminiscent of Jupiter, orbiting beyond 2 AU.

With a spectral type of M3.5 and a mass of 0.49 MSOL, GJ 849 is relatively heavy for a red dwarf in the Solar neighborhood. By comparison, it has 50% more mass than GJ 876, an M dwarf with two gas giants and two lower-mass planets, and 41% less mass than HD 37124, a G-type star with three gas giants. Moreover, GJ 849 has the highest metallicity of any known M dwarf planet host. Its estimated value of +0.41 is even higher than that of our Sun (Schlaufman & Laughlin 2010).

The ice line of the GJ 849 system is located around 0.4 AU (Ida & Lin 2005). The star’s single known planet orbits well beyond this distance, at a semimajor axis of 2.35 AU (Butler et al. 2006b). This architecture makes GJ 849 one of the closest analogs to our Solar System yet discovered.

With a minimum mass estimated at 0.83 MJUP, GJ 849 b may have formed more or less in situ, as Jupiter did in the Solar System. Although the planet’s separation from the host star is equal to that of our own system’s Asteroid Belt, the star’s low luminosity implies a temperature range more typical of Jupiter or Saturn than of a main-belt asteroid. Given the planet's mass and semimajor axis, we can expect a family of satellites, perhaps icy bodies resembling the moons of Jupiter and Saturn.

The discovery team found no indications of any additional planets in the residuals of the radial velocity data (Butler et al. 2006b). Therefore it seems unlikely that any other giant planets exist closer than 2 AU. This absence is fortuitous, since terrestrial-mass planets remain possible, especially in the system’s habitable zone. This region has approximate boundaries of 0.1 and 0.2 AU (Mandell et al. 2007).

Last update July 2010