No universal minimum-mass extrasolar nebula: Evidence against in-situ accretion of systems of hot super-Earths

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摘要：

It has been proposed that the observed systems of hot super-Earths formed insitu from high-mass disks. By fitting a disk profile to the entire populationof Kepler planet candidates, Chiang & Laughlin (2013) constructed a"minimum-mass extrasolar nebula" with surface density profile Sigma r^-1.6.Here we use multiple-planet systems to show that it is inconsistent to assume auniversal disk profile. Systems with 3-6 low-mass planets (or planetcandidates) produce a diversity of minimum-mass disks with surface densityprofiles ranging from Sigma r^-3.2 to Sigma r^0.5 (5th-95th percentile). Bysimulating the transit detection of populations of synthetic planetary systemsdesigned to match the properties of observed super-Earth systems, we show thata universal disk profile is statistically excluded at high confidence. Rather,the underlying distribution of minimum-mass disks is characterized by a broadrange of surface density slopes. Models of gaseous disks can only explain anarrow range of slopes (roughly between r^0 and r^-1.5). Yet accretion ofterrestrial planets in a gas-free environment preserves the initial radialdistribution of building blocks. The known systems of hot super-Earths musttherefore not represent the structure of their parent gas disks and can nothave predominantly formed in situ. We instead interpret the diversity of diskslopes as the imprint of a process that re-arranged the solids relative to thegas in the inner parts of protoplanetary disks. A plausible mechanism is inwardtype 1 migration of Mars- to Earth-mass planetary embryos, perhaps followed bya final assembly phase.

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关键词：

planets and satellites: detection planets and satellites: formation planets and satellites: terrestrial planets protoplanetary discs

DOI：

10.1093/mnrasl/slu011

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年份：

2014