Evidence for a high mutual inclination between the cold Jupiter and transiting super Earth in \(\pi\) Men

Jerry Xuan (Cambridge, now at Caltech), Mark Wyatt (Cambridge)

Link to \(\pi\) Men paper

2nd paper on planet-disk mutual inclinations


We combine Gaia DR2 and Hipparcos astrometry to constrain the 3-D orbit of \(\pi\) Men b (\(P\approx2100\) d, \(m \sin{I}\approx10.0 M_{\rm{Jup}}\)), and find its orbit is highly misaligned with that of the inner transiting planet, \(\pi\) Men c (\(P\approx6.3\) d, \(m\approx4.8 M_{\oplus}\)), with \(49^\circ < \Delta I < 131^\circ\) at \(1\sigma\).

The \(\pi\) Men system

Parameters from Huang+2018
Planet \(a\) \(m \sin{I} \textrm{(b)}\ / m \textrm{(c)}\) \(e\)
\(\pi\) Men b \(3.31\) au \(10.02\) \(M_{\rm{Jup}}\) \(0.637\)
\(\pi\) Men c \(0.068\) au \(4.8\) \(M_{\oplus}\) \(<0.3\)

Gaia-Hipparcos Astrometry

Fig 1. Illustration of the astrometric method, image from Kervella+2019.

3-D Orbit of \(\pi\) Men b

Fig 2. \(I, \Omega, m\) for \(\pi\) Men b

Mutual inclination \(\Delta I\) between \(\pi\) Men b and c:
  • \(49^\circ < \Delta I < 131^\circ\) at \(1\sigma\),
  • \(28^\circ < \Delta I < 152^\circ\) at \(2\sigma\),
  • \(9^\circ < \Delta I < 171^\circ\) at \(3\sigma\),

Nodal Precession and Consequences

Video 1. Nodal precession of the inner orbit around the outer orbit.

Two major consequences:
  • \(\pi\) Men c only transits 10-20% of the time from our N-body simulations.
  • \(\pi\) Men c is likely misaligned with the stellar spin axis. This was confirmed by Kunovac Hodžic+2020.