Thirteen years of Doppler velocity measurements have revealed the presence of two planets orbiting the star 47 Ursa Majoris on low eccentricity orbits .
A 2-Keplerian fit to the radial velocity data suggests that the inner planet has a period P _ { b } = 1089.0 \pm 2.9 d , and a nominal ( \sin ( i ) = 1 ) mass M \sin i~ { } = 2.54 M _ { JUP } , while the outer planet has a period P _ { c } = 2594 \pm 90 d , and a mass M \sin i~ { } = 0.76 M _ { JUP } .
These mass and period ratios suggest a possible kinship to the Jupiter-Saturn pair in our own solar system .
We explore the current dynamical state of this system with numerical integrations , and compare the results with analytic secular theory .
We find that the planets in the system are likely participating in a secular resonance in which the difference in the longitudes of pericenter librates around zero .
Alternately , it is possible that the system is participating in the 7:3 mean motion resonance ( in which case apsidal alignment does not occur ) .
Using a self-consistent fitting procedure in conjunction with numerical integrations , we show that stability considerations restrict the mutual inclination between the two planets to \sim 40 degrees or less , and that this result is relatively insensitive to the total mass of the two planets .
We present hydrodynamical simulations which measure the torques exerted on the planets by a hypothesized external protoplanetary disk .
We show that planetary migration in response to torques from the disk may have led to capture of the system into a 7:3 mean-motion resonance , although it is unclear how the eccentricities of the planets would have been damped after capture occured .
We show that Earth-mass planets can survive for long periods in some regions of the habitable zone of the nominal co-planar system .
A set of planetary accretion calculations , however , shows that it is unlikely that large terrestrial planets can form in the 47 UMa habitable zone .