For the vast
majority of extrasolar planets -- those for whom
the only information we have is radial velocity
measurements --
we know nothing directly about the planet itself.
We can infer the planet's minimum mass
and orbital distance, and that's it. We know
nothing about the composition or physical
conditions on those planets.
(An exception is
this
planet.)
Bad news for
astrobiology.
The chief practioners of extrasolar planet detection
are a group of researchers led by
Prof. Geoff Marcy; their website is
at
exoplanets.org.
The primary European group is headed by
Michel Mayor (Switzerland); their web page
is
here.