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SUMMARY:What makes a planet “giant”?  - Ravit Helled
DTSTART:20250227T160000Z
DTEND:20250227T170000Z
UID:TALK226222@talks.cam.ac.uk
CONTACT:Matthew Grayling
DESCRIPTION:The formation history of giant planets\, both within and beyon
 d our solar system\, remains an open question. I propose a new pathway for
  giant planet formation\, where runaway gas accretion begins only when a p
 lanet reaches about 100 Earth masses and occurs only after a few million y
 ears (Myrs). This suggests that the transition to a gas giant—defined as
  a planet primarily composed of hydrogen and helium—occurs at around Sat
 urn’s mass. The delay in runaway gas accretion to later stages and highe
 r planetary masses results from an intermediate phase of efficient heavy-e
 lement accretion. This process generates enough energy to hinder rapid gas
  accretion. Consequently\, Saturn may never have undergone runaway gas acc
 retion\, classifying it as a "failed giant planet."\nThis proposed transit
 ion to a gas giant planet above Saturn’s mass naturally explains the dis
 tinct bulk metallicities and internal structures of Jupiter and Saturn\, a
 s well as the unique characteristics of Uranus and Neptune. In the context
  of giant exoplanets\, postponing runaway gas accretion to planets exceedi
 ng Saturn’s mass explains the transitions in the mass-radius (M-R) relat
 ions of observed exoplanets\, the relatively low occurrence of gas giants\
 , and the high metallicity of intermediate-mass exoplanets.\n\n
LOCATION:Hoyle Lecture Theatre\, Institute of Astronomy
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