Measuring the geometry of multi-planet extrasolar systems can provide insight
into their dynamical history and the processes of planetary formation. Such
measurements are challenging for systems detected through indirect techniques
such as radial velocity and transit, having only been measured for a handful of
systems to-date. We aimed to place constraints on the orbital geometry of the
outer planet in the Ο Mensae system, a G0V star at 18.3 pc host to a
wide-orbit super-jovian (Msini=10.02Β±0.15MJupβ) with a
5.7-year period and an inner transiting super-earth (M=4.82Β±0.85Mββ) with a 6.3-d period. We combined astrometric measurements from the
Hipparcos and Gaia satellites with a precisely determined spectroscopic orbit
in an attempt to constrain the inclination of the orbital plane of the outer
planet. We measured an inclination of ibβ=49.9β4.5+5.3β deg for the
orbital plane of Ο Mensae b, leading to a direct measurement of its mass of
13.01β0.95+1.03βMJupβ. We found a significant mutual
inclination between the orbital planes of the two planets; a 95% credible
interval for imutβ of between 34.5β and 140.6β after
accounting for the unknown position angle of the orbit of Ο Mensae c,
strongly excluding a co-planar scenario for the two planets within this system.
All orbits are stable in the present-day configuration, and secular
oscillations of planet c's eccentricity are quenched by general relativistic
precession. Planet c may have undergone high eccentricity tidal migration
triggered by Kozai-Lidov cycles, but dynamical histories involving disk
migration or in situ formation are not ruled out. Nonetheless, this system
provides the first direct evidence that giant planets with large mutual
inclinations have a role to play in the origins and evolution of some
super-Earth systems.Comment: 24 pages, 10 figures, 7 tables. Accepted for publication in Astronomy
& Astrophysic