Planets Close-in and Far-out
The data-rich Kepler mission provided an unprecedented view of the demographics of planetary systems. Close to the star (at orbital periods shorter than ~100 days), super-Earths (~1-4 R_earth) and Earth-sized planets dominate. These small planets are evenly distributed in log orbital period down to ~10 days, but dwindle in number at shorter periods. I will demonstrate that both the break at ~10 days and the slope of the occurrence rate down to ~1 day can be reproduced if planets form in situ in disks that are truncated by their host star magnetospheres at co-rotation. Planets can be brought from disk edges to ultra-short (<1 day) periods by tides raised on their stars. The bulk compositions of planets inform us the time and the location of their birth. Close-in super-Earths are massive enough to trigger runaway gas accretion, yet they accreted atmospheres that weigh only a few percent of the total mass, keeping their sizes below that of the Neptune. This puzzle is solved if super-Earths formed late, in the inner cavities of transitional disks. Over a wide range of nebular depletion histories, super-Earths can robustly build their ~1% by mass envelopes. Super-puffs present the inverse problem of being too voluminous for their small masses. I will show that super-puffs most easily acquire their thick atmospheres as dust-free, rapidly cooling worlds outside 1 AU, and then migrate in just after super-Earths appear. I will conclude by discussing pathways toward understanding the diversity of exoplanets in preparation for the upcoming and planned space missions and ground-based instruments.
Date: Thursday, 25 January 2018 Time: 11:00 Where: McGill University Ernest Rutherford Physics Building, R.E. Bell Conference Room (room 103)