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SUMMARY:Inside-Out Planet Formation - Jonathan Tan (University of Florida)
DTSTART:20151209T164500Z
DTEND:20151209T173000Z
UID:TALK62346@talks.cam.ac.uk
CONTACT:Dr B.-O. Demory
DESCRIPTION:The Kepler-discovered systems with tightly-packed inner planet
 s (STIPs)\, typically with several planets of Earth to super-Earth masses 
 on well-aligned\, sub-AU orbits may host the most common type of planets i
 n the Galaxy. They pose a great challenge for planet formation theories\, 
 which fall into two broad classes: (1) formation further out followed by m
 igration\; (2) formation in situ from a disk of gas and planetesimals. I r
 eview the pros and cons of these classes\, before focusing on a new theory
  of sequential in situ formation from the inside-out via creation of succe
 ssive gravitationally unstable rings fed from a continuous stream of small
  (~cm-m size) "pebbles\," drifting inward via gas drag. Pebbles first coll
 ect at the pressure trap associated with the transition from a magnetorota
 tional instability (MRI)-inactive ("dead zone") region to an inner MRI-act
 ive zone. A pebble ring builds up until it either becomes gravitationally 
 unstable to form an Earth to super-Earth-mass planet directly or induces g
 radual planet formation via core accretion. The planet continues to accret
 e until it becomes massive enough to isolate itself from the accretion flo
 w via gap opening. The process repeats with a new pebble ring gathering at
  the new pressure maximum associated with the retreating dead-zone boundar
 y. I discuss the theory’s predictions for planetary masses\, relative ma
 ss scalings with orbital radius\, and minimum orbital separations\, and th
 eir comparison with observed systems. Finally I speculate about potential 
 causes of diversity of planetary system architectures\, i.e. STIPs versus 
 Solar System analogs.\n
LOCATION:Martin Ryle Seminar Room\, Kavli Institute
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