  Extrasolar planet surveys have begun to detect gas giant planets in orbit
around M dwarf stars. While the frequency of gas giant planets around M dwarfs
so far appears to be lower than that around G dwarfs, it is clearly not zero.
Previous work has shown that the core accretion mechanism does not seem to be
able to form gas giant planets around M dwarfs, because the time required for
core formation scales with the orbital period, which lengthens for lower mass
stars, resulting in failed (gas-poor) cores unless the gaseous protoplanetary
disk survives for > 10 Myr. Disk instability, on the other hand, is rapid
enough (~ 1000 yrs) that it should be able to form gas giant protoplanets
around even low mass stars well before the gaseous disk disappears. A new suite
of three dimensional radiative, gravitational hydrodynamical models is
presented that calculates the evolution of initially marginally gravitationally
unstable disks with masses of 0.021 to 0.065 solar masses orbiting around stars
with masses of 0.1 and 0.5 solar masses, respectively. The models show that gas
giant planets are indeed likely to form by the disk instability mechanism in
orbit around M dwarf stars, the opposite of the prediction for formation by the
core accretion mechanism. This difference offers another observational test for
discriminating between these two theoretical end members for giant planet
formation. Ongoing and future extrasolar planet searches around M dwarfs by
spectroscopy, microlensing, photometry, and astrometry offer the opportunity to
help decide between the dominance of the two mechanisms.
