Report - School of Physics

2.2 Space Observations: 2005–2015
In the near-term future of space missions, there are two principal detection approaches:
transits (exemplified by the COROT, Kepler and Eddington missions),
and astrometry (exemplified by Gaia and SIM). A non-approved concept, MPF
(originally GEST), uses microlensing to expand on the parameter space for which
statistical information on planet frequency would be provided.
2.2.1 Space Transit Measurements: COROT, Kepler and Eddington
COROT: COROT is a French-European-ESA collaboration, led by CNES, comprising
a 27 cm telescope with a CCD camera, with a launch planned for June 2006.
After MOST, it will be the second satellite dedicated to long-term high-accuracy
photometric monitoring from space. COROT will combine the study of asteroseismology
with the search for exo-planetary transits. The observation of 60 000 stars
(12 000 stars simultaneously for 150 days each) is expected to result in the detection
of a few hot telluric planets.
As a general remark, which applies to the other predictions in this section, as well
as to the radial velocity and ground-based transit searches discussed previously, it
should be noted that the expected rate of exo-planet detection is difficult to quantify,
given both their unknown frequency of occurrence, and detection uncertainties due
to stellar activity.
The numbers in Table 5 are based on the number of dwarf stars in the COROT
fields, the mass and period distribution of known exo-planets, the probability of
transits, the fact that no more than 1 short-period exo-planet per star is expected,
and the expected accuracy of COROT as a function of magnitude. Table 3 in Bordé
et al. (2003) assumes one planet per dwarf star, and a uniform orbital distribution
law. This leads to a significantly larger number of predicted detections, and is
presumably an overestimate of the actual number of planets expected (as they also
note). In practice, the critical factor in all these predictions is the unknown number
of low-mass planets per star.
Kepler: improved prospects for photometric transit detections will come with
NASA’s Kepler mission, due for launch around 2007. Kepler is a 0.95 m aperture,
differential photometer with a 105 square degree field of view. It focuses on
the detection of Earth-size planets or larger in or near the habitable zone of a wide
variety of stellar spectral types, monitoring some 10 5 main-sequence stars brighter
than 14 mag. Detection of some 50–640 terrestrial inner-orbit planet transits are
predicted, depending on whether their typical radii lie in the range R ∼ 1.0−2.2R E ,
determining the distribution of sizes and orbital characteristics. Kepler will assist
the preparation of future programmes like SIM and Darwin/TPF by identifying the
common stellar characteristics of host stars, and defining the volume of space needed
to search.
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