227.04 - Microlensing Results Challenge the Core Accretion Run-away Growth Scenario for Gas Giants

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Jan 8th at 2:36 PM until 2:48 PM

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Author(s): D. Suzuki, ISAS / JAXA, Sagamihara, Kanagawa, JAPAN|D. Bennett, NASA / GSFC, Greenbelt, Maryland, UNITED STATES|S. Ida, ELSI / Tokyo Tech, Tokyo, Maryland, JAPAN|C. Mordasini, University of Bern, Bern, Maryland, SWITZERLAND|
Institution(s): 1. ISAS / JAXA, Sagamihara, Kanagawa, Japan. 2. NASA / GSFC, Greenbelt, MD, United States. 3. ELSI / Tokyo Tech, Tokyo, Japan. 4. University of Bern, Bern, Switzerland.
Contributing team(s): (none)
The favored core accretion model of planet formation predicts a deficit of planets between the masses of Neptune and Saturn. This planet desert is a consequence of the runaway gas accretion process, which is thought to cause protoplanetary cores of about 10 Earth masses to rapidly grow to ~300 Earth masses rapidly through rapid accretion of Hydrogen and Helium gas. This process is expected to result in Jupiter-like planets and more numerous ~10 Earth mass failed Jupiter cores, in cases when the gas disk dissipated before runaway accretion could begin. This prediction can be tested with a comparison to results from ground-based microlensing surveys, which is sensitive to planets down to an Earth mass orbiting beyond the snow line. In this talk, we compare the microlensing measurement of the planet mass-ratio distribution to population synthesis models based on the core accretion theory. We show that the models predict ~10 times fewer planets at mass-ratios of 10^{-4} < q < 4\times 10^{-4} than found by the microlensing observations. This implies that the formation of gas giants may involve more complicated processes than assumed by the standard core accretion theory. Or, it implies that the planet formation process may vary significantly as a function of host star mass, because the population synthesis models have been calibrated for planets around solar-type stars while microlensing observations are biased toward lower-mass stars. Finally, we briefly discuss the mass measurements of host stars (and planets) that the WFIRST microlensing survey will make for most planetary microlensing events.