At Lick Observatory, we surveyed 107 G and K stars. Of these, 7 stars have "planetary" companions, with M sini < 10 Mjup. However none of our 107 stars exhibits a companion that has Msini = 10 - 80 Mjup.
Brown dwarfs are rare around Solar-Type stars. At most 1% of Solar-type stars has a brown dwarf within 5 AU. Thus, planets are distinguished from brown dwarfs by virtue of their relative occurrence.
This shows the histogram of mass (Msini) for all known companions to Main Sequence stars (FGKM type), within the mass range 0 - 15 Jupiter masses. The most massive companions are easiest to detect and virtually no companions are missed above 10 Jupiter masses, if they orbit within 3 AU. Approximately 300 stars are represented in this survey, dominated by the surveys of Marcy/Butler et al. and of Mayor/Queloz et al.. Apparently, the number of companions begins to rise at 5 Juptier masses, and continues to rise toward the lowest detectable masses, ~0.5 Jupiters, where detectabiliy becomes poor.
Several (~12) brown dwarf candidates have been found by Michel Mayor,
Stephane Udry, Antoine Duquennoy, and Tsevi Mazeh. Most have been shown
by Hipparcos astrometry to be hydrogen-burning stars rather than brown
dwarfs. Their survey covered 640 stars using a Doppler precision of +-300
m/s.
Astrometry by Hipparcos shows that almost all of these host stars exhibit
a large wobble in the plane of the sky. This large wobble indicates that
the companions have masses above the hydrogen-burning mass limit, 80 jupiters.
Therefore, most of these 12 companions are stars, not brown dwarfs. Left
behind are the 17 companions that have Msini < 15 Mjup. They appear
as a sharp increase in the mass histogram, rising at least a factor of
5 above a brown-dwarf "desert" within which few brown dwarf "cacti" are
found. At masses below ~5 Jupiters, an oasis appears to exist, populated
by numerous companions of Jupiter mass. The overall distribution of Msini
for Solar-Type stars is shown below.
The figures above show the MASS DISTRIBUTION of ALL companions known around Solar-Type Stars (spectral types FGKM), as of 20 Jan 1997. It includes the companions found by Mayor et al., both from his high precision (elodie) survey and from his lower precision (CORAVEL) survey, and it includes companions found by all other groups, including us. In each mass bin of 5 Jupiter masses, the number of companions found was divided by the number of stars in the survey. This gives the frequency of occurrence of companions, having different values of Msini.
Companions having lowest mass (M < 5 Mjup) occur more frequently than any other mass. Two populations are apparent: M < 5 Mjup and M > 10 Mjup . Those having M > 10 Mjup are likely to be the expected ``brown dwarfs'', which are the extension of the stellar mass distribution at low masses. Those having M < 5 Mjup are so numerous as to dwarf the ``brown dwarfs''. They are likely to be ``planets''.
Note that brown dwarfs are far easier to detect than planets due to the large reflex velocity they impart to their stars (hundreds of meters/sec). Copmpanions having masses from 0 to 5 Mjup have largely avoided detection, especially at 2 - 5 AU. The bin from 0 to 5 Jupiter masses will grow in the future.
Bottom line: Approximately 3% of Solar Type stars harbor planetary companions that have masses from 1 - 10 Mjup and orbit within a several Astronomical Units (AU). At most 1% of stars harbor brown-dwarf companions within several AU. Their masses are spread out from 10 - 70 Mjup, as demonstrated beautifully by the data of Michel Mayor, Antoine Duquennoy, and Didier Queloz at Geneva Observatory and Observatoire de Haute Provence.
Eccentric orbits may occur relatively commonly for extrasolar planets. Just one eccentric giant planet orbiting a star can spell dynamical doom for terrestrial planets, and may bode ill for slowly evolving creatures. The claim that all planetary orbits must be like ours may well be a circular argument.