Dynamical constraints on outer planets in super-Earth systems

Abstract

This paper considers secular interactions within multi-planet systems. In particular we consider dynamical evolution of known planetary systems resulting from an additional hypothetical planet on an eccentric orbit. We start with an analytical study of a general two-planet system, showing that a planet on an elliptical orbit transfers all of its eccentricity to an initially circular planet if the two planets have comparable orbital angular momenta. Application to the single Super-Earth system HD38858 shows that an additional hypothetical planet below current radial velocity (RV) constraints with Msini=3-10M ⊕ , semi-major axis 1-10au and eccentricity 0.2-0.8 is unlikely to be present from the eccentricity that would be excited in the known planet (albeit cyclically). However, additional planets in proximity to the known planet could stabilise the system against secular perturbations from outer planets. Moreover these additional planets can have an Msini below RV sensitivity and still affect their neighbours. For example, application to the two Super-Earth system 61Vir shows that an additional hypothetical planet cannot excite high eccentricities in the known planets, unless its mass and orbit lie in a restricted area of parameter space. Inner planets in HD38858 below RV sensitivity would also modify conclusions above about excluded parameter space. This suggests that it may be possible to infer the presence of additional stabilising planets in systems with an eccentric outer planet and an inner planet on an otherwise suspiciously circular orbit. This reinforces the point that the full complement of planets in a system is needed to assess its dynamical state.

Cometary impactors on the TRAPPIST-1 planets can destroy all planetary atmospheres and rebuild secondary atmospheres on planets f, g, and h

“…Guided by the results of Frewen & Hansen (2014) we consider 1 and 10M⊕ planets with a 0.4 eccentricity orbiting at 1au to be representative of the kind of planets that are able to put comets on orbits that are capable of colliding with the seven known TRAPPIST-1 planets. We note that such planets are not massive enough and not close enough to gravitationally disturb the orbits of the seven currently known planets as can be checked directly from Read & Wyatt (2016), so that the system of the seven inner planets stays stable even in the presence of such an additional planet (see also Quarles et al 2017). We also note that these planet masses agree with current mass upper limits by Boss et al (2017) (i.e < 4.6MJup within a 1 yr period, and < 1.6MJup within a 5 yr period).…”

ALMA observations of the multiplanet system 61 Vir: what lies outside super-Earth systems?

“…Less massive planets and closer in (a plt = 4 − 20 AU) could have stirred the disc, but with e 0.1. For the allowed combinations of M plt and a plt even a highly eccentric planet will not induce an eccentricity higher than the observed on 61 Vir b and c or cause close encounters (see Figure 5 in Read & Wyatt 2016). Moreover, an eccentric planet will impose an eccentricity on the disk which may be detectable by imaging .…”

A review of the discovery reach of directional Dark Matter detection

“…Late merging halos are dragged into the disk by dynamical friction, where they are destroyed, leading to the formation of a co-rotating dark disk (DD) [132,133]. While the contribution of the DD to the local DM density is uncertain, it is currently expected to be small, owing to the relatively quiescent merger history of the MW [134].…”