Report - School of Physics

1 Survey of the Field
1.1 Introduction
The field of exo-planet research has exploded dramatically since the discovery of
the first such systems in 1995. Underlying this huge interest three main themes
of exo-planet research can be identified: (a) characterising and understanding the
planetary populations in our Galaxy; (b) understanding the formation and evolution
of planetary systems (e.g., accretion, migration, interaction, mass-radius relation,
albedo, distribution, host star properties, etc.); (c) the search for and study of
biological markers in exo-planets, with resolved imaging and the search for intelligent
life as ‘ultimate’ and much more distant goals.
Detection methods for extra-solar planets can be broadly classified into those based
on: (i) dynamical effects (radial velocity, astrometry, or timing in the case of the pulsar
planets); (ii) microlensing (astrometric or photometric); (iii) photometric signals
(transits and reflected light); (iv) direct imaging from ground or space in the optical
or infrared; and (v) miscellaneous effects (such as magnetic superflares, or radio
emission). Each have their strengths, and advances in each field will bring specific
and often complementary discovery and diagnostic capabilities. Detections are a
pre-requisite for the subsequent steps of detailed physical-chemical characterisation
demanded by the emerging discipline of exo-planetology.
As of December 2004, 135 extra-solar planets have been discovered from their radial
velocity signature, comprising 119 systems of which 12 are double and 2 are
triple. One of these planets has also been observed to transit the parent star. Four
additional confirmed planets have been discovered through transit detections using
data from OGLE (and confirmed through radial velocity measurements), and one,
TrES-1, using a small 10-cm ground-based telescope. One further, seemingly reliable,
planet candidate has been detected through its microlensing signature. The
planets detected to date (apart from those surrounding radio pulsars, which are not
considered further in this report) are primarily ‘massive’ planets, of order 1 M J , but
extending down to perhaps 0.05 M J (around 15 M ⊕ ) for three short-period systems,
although the inclination (and hence true mass) of two of these is unknown 1 .
Detection methods considered to date are summarised in Figure 1, which also gives
an indication of the lower mass limits which are likely to be reached in the foreseeable
future for each method. More information and ongoing projects are given in Jean
Schneider’s www page: http://www.obspm.fr/encycl/searches.html.
An earlier ESO Working Group on the ‘Detection of Extra-Solar Planets’ submitted
a report with detailed recommendations in 1997 (Paresce et al., 1997). A summary
and status of these recommendations is attached as Appendix C.
1 the following notation is used: M J = Jupiter mass; M ⊕ = Earth mass ∼ 0.003 M J .
1