Where are the massive close-in extrasolar planets?

Abstract

About 68 extrasolar planets around main-sequence stars of spectral types F, G and K have been discovered up to now. The minimum masses (Mp sin i) of these planets are ranging from fractions of a Jupiter mass (MJ) to 15 MJ. The semimajor axes of the planetary orbits range from 0,04 out to 4 AU. At large semimajor axes, only massive planets have been discovered because of the observational selection effects. For semimajor axes less the 0.1 AU, however, there seems to be an observational lack of very massive planets (>1 MJ). Here we explain the absence of massive planets ath these distances by tidal interactions between planets and their central star that lead to a rapid decay of a planetary orbit toward the Roche zone of the star within a short timescale. A higher metallicity of planet-bearing stars and the recent discovery of a 6Li excess of a G0 star might further indicate that planets can indeed get lost in their host stars.