Report - School of Physics

2 The Period 2005–2015
2.1 Ground Observations: 2005–2015
There are many ongoing ground-based surveys. At the time of writing, the Planets
Encyclopaedia www page (http://www.obspm.fr/encycl/searches.html) lists as
either ongoing or planned: 18 radial velocity searches, 15 transit searches, 5 microlensing
programmes, 10 imaging/direct detection programmes, 2 radio surveys,
and 3 astrometric efforts. An overview of efforts and expected results is given in
this section, with a particular focus on the ESA and ESO contributions.
2.1.1 Radial Velocity Searches
A summary of ongoing or planned radial velocity experiments is given in Table 1.
It is certainly incomplete, and is intended only to give a flavour for the activity
in the field. The vast majority of extra-solar planets discovered so far have been
found by radial velocity searches, which have a natural bias for the discovery of
massive planets orbiting close to their central star (hot Jupiters). As the surveys
continue for longer periods of time they become more and more sensitive to planets
having longer periods, and to additional planets in systems in which one hot Jupiter
is already known. Dedicated designs have brought spectrographs very close to the
practical accuracy limit for ground-based radial velocity searches of ∼ 1 m s −1 ,
allowing detection of lower mass planets. HARPS has recently detected a second
planet around µ Arae, with a period of 9.5 days, a velocity semi-amplitude of less
than 5 m s −1 (Santos et al., 2004), and a derived M sin i of only 14 M ⊕ (about one
Uranus mass), making it the lowest mass planet found so far (as of December 2004).
A planet of ∼ 17 M ⊕ has been discovered orbiting the M dwarf GJ 436 based on
Keck data (Butler et al., 2004), and of ∼ 18 M ⊕ reported for 55 Cnc using HET
observations (McArthur et al., 2004).
Another trend is that larger telescopes are being used for the radial velocity searches.
As a result the limiting magnitude of such searches has increased from typically
V = 7.5 a few years ago to V ∼ 12, with the number of stars thus available for
radial velocity study increasing by almost two orders of magnitude. For example,
the N2K Consortium is using the Keck, Magellan and Subaru telescopes to track the
next 2000 (N2K) closest (