GJ 849 is an M dwarf star located at a distance of 8.77 parsecs (29 light years) in the constellation Aquarius. Its recently detected planetary system diverges widely from theoretical expectations regarding red 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 three 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 0.16 is even higher than Sol’s.

The ice line of the GJ 849 system may be 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). With a minimum mass estimated at 0.83 MJUP, this gas giant 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 smaller moons of 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. Nevertheless, terrestrial-mass planets remain possible, especially in the system’s habitable zone, which has an approximate range of 0.1 to 0.2 AU (Mandell et al. 2007).

Last update April 2007