A. Cassan, D. Kubas, J. -P. Beaulieu, M. Dominik, K. Horne, J. Greenhill, J. Wambsganss, J. Menzies, A. Williams, U. G. Jorgensen, A. Udalski, D. P. Bennett, M. D. Albrow, V. Batista, S. Brillant, J. A. R. Caldwell, A. Cole, Ch. Coutures, K. H. Cook, S. Dieters, D. Dominis Prester, J. Donatowicz, P. Fouque, K. Hill, N. Kains, S. Kane, J. -B. Marquette, R. Martin, K. R. Pollard, K. C. Sahu, C. Vinter, D. Warren, B. Watson, M. Zub, T. Sumi, M. K. Szymanski, M. Kubiak, R. Poleski, I. Soszynski, K. Ulaczyk, G. Pietrzynski, L. Wyrzykowski
Most known extrasolar planets (exoplanets) have been discovered using the
radial velocity$^{\bf 1,2}$ or transit$^{\bf 3}$ methods. Both are biased
towards planets that are relatively close to their parent stars, and studies
find that around 17--30% (refs 4, 5) of solar-like stars host a planet.
Gravitational microlensing$^{\bf 6\rm{\bf -}\bf 9}$, on the other hand, probes
planets that are further away from their stars. Recently, a population of
planets that are unbound or very far from their stars was discovered by
microlensing$^{\bf 10}$. These planets are at least as numerous as the stars in
the Milky Way$^{\bf 10}$. Here we report a statistical analysis of microlensing
data (gathered in 2002--07) that reveals the fraction of bound planets 0.5--10
AU (Sun--Earth distance) from their stars. We find that 17$_{\bf -9}^{\bf +6}$%
of stars host Jupiter-mass planets (0.3--10 $\MJ$, where $\MJ {\bf = 318}$
$\Mearth$ and $\Mearth$ is Earth's mass). Cool Neptunes (10--30 $\Mearth$) and
super-Earths (5--10 $\Mearth$) are even more common: their respective
abundances per star are 52$_{\bf -29}^{\bf +22}$% and 62$_{\bf -37}^{\bf
+35}$%. We conclude that stars are orbited by planets as a rule, rather than
the exception.
View original:
http://arxiv.org/abs/1202.0903
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