The Occurrence and Mass Distribution of Close-in Super-Earths, Neptunes, and Jupiters

Abstract

The questions of how planets form and how common Earth-like planets are can be addressed by measuring the distribution of exoplanet masses and orbital periods. We report the occurrence rate of close-in planets (with orbital periods less than 50 days), based on precise Doppler measurements of 166 Sun-like stars. We measured increasing planet occurrence with decreasing planet mass (M). Extrapolation of a power-law mass distribution fitted to our measurements, df/dlogM = 0.39 M(-0.48), predicts that 23% of stars harbor a close-in Earth-mass planet (ranging from 0.5 to 2.0 Earth masses). Theoretical models of planet formation predict a deficit of planets in the domain from 5 to 30 Earth masses and with orbital periods less than 50 days. This region of parameter space is in fact well populated, implying that such models need substantial revision.

Evidence for a spectroscopic direct detection of reflected light from 51 Pegasi b

“…On the detection side, the radial velocity (e.g., Lovis & Fischer 2010;Bonfils et al 2013) and transit methods (e.g., Borucki et al 2010;Winn 2010) have been the most prolific. One of the most important results of planet detection surveys is the ubiquity of planets around solar-type stars (e.g., Howard et al 2010). …”

The debris disk – terrestrial planet connection

“…Given the existence of false positives and negatives, the significant uncertainties in our initial conditions, and the existence of other potentially important processes, a detailed statistical analysis is needed to use our simulations to estimate the frequency of debris disks into a robust estimate of the fraction of stars that will be found to harbor terrestrial planets (η E arth from the famous 88 S. Raymond et al Drake equation;see Raymond et al 2011). Nonetheless, we note that the frequency of 70 µm debris disks (15-20%) is very close to estimates of the frequency of close-in, few Earth-mass planets (10-30% - Howard et al 2010;Mayor et al 2009) and our simulations suggest that this is not a coincidence but a natural outcome of planet formation.…”

“…First, current migration theories fail to reproduce most characteristics of the known exoplanets (Howard et al 2010). Second, the effects of giant planet migration on terrestrial planet formation are thought to be weak (Raymond et al 2006;Mandell et al 2007;Fogg & Nelson 2007) compared with the effect of instabilities (Veras & Armitage 2006).…”

Astronomy: Beyond the stars

“…But that hasn't prevented other scientists from making preliminary estimates. In 2010, for example, a group led by Andrew Howard, an astronomer at the University of California, Berkeley, took the size distribution of planets found by the radial-velocity method and, by extrapolating to lower masses, predicted that Kepler will find that roughly 22% of stars are orbited by Earth-size planets 8 . Borucki is sceptical.…”