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SUMMARY:Formation of compact systems of super-Earths via dynamical instabi
 lities and giant impacts - Sanson Poon (QMUL)
DTSTART:20200310T160000Z
DTEND:20200310T170000Z
UID:TALK137716@talks.cam.ac.uk
CONTACT:Richard Booth
DESCRIPTION:The origins of compact exoplanet systems consisting of super-E
 arths and mini-Neptune are not yet well understood. Using N-body simulatio
 ns\, we examine the in situ final stage assembly of multiplanet systems vi
 a the collisional accretion of protoplanets. Two different prescriptions f
 or treating planetary collisions are adopted. In this talk\, I will discus
 s a number of important issues: how do the results depend on the accretion
  prescription?\; do the resulting systems resemble the Kepler systems\, an
 d do they reproduce the observed distribution of planetary multiplicities 
 when synthetically observed?\; do collisions lead to significant modificat
 ion of protoplanet compositions\, or to stripping of gaseous envelopes?\; 
 do the eccentricity distributions agree with those inferred for the Kepler
  planets? We find that the accretion prescription is unimportant in determ
 ining the outcomes. The final planetary systems look broadly similar to th
 e Kepler templates adopted\, but the observed distributions of planetary m
 ultiplicities or eccentricities are not reproduced\, because scattering do
 es not excite the systems sufficiently. Post-processing the collision outc
 omes suggests that they would not significantly change the ice fractions o
 f initially ice-rich protoplanets\, but significant stripping of gaseous e
 nvelopes appears likely. Hence\, it may be difficult to reconcile the obse
 rvation that many low-mass Kepler planets have H/He envelopes with an in s
 itu formation scenario that involves giant impacts after dispersal of the 
 gas disc. Finally\, I will also talk about how the eccentricity dichotomy 
 inferred from Kepler data for single and multiple planets may arise throug
 h perturbations provided by outer systems of ice/gas giants.
LOCATION:Martin Ryle Seminar Room\, Kavli Institute
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