Report - School of Physics

Without any further mission dedicated to terrestrial planet searches, there will be no
real understanding of the distribution of such planets in general (e.g., in other parts
of the Galaxy or in clusters), and the number of targets discovered by Kepler may in
any case be very small. Eddington would observe stars in a variety of environments,
i.e., field stars and stars in open clusters, and will thus consolidate the search for
planets across different stellar parameters (including metallicity, age, mass, binary
status, density of surrounding stellar population, etc.).
More generally, experiments need repeatability: single experiment results always
provoke more questions, and if the results are controversial it is only reasonable that
they are checked independently. Having just one mission aimed at the detection of
terrestrial planets appears risky and inadequate, in particular considering the effort
being made for future missions that aim at studying these planets (Darwin/TPF).
The present working group emphasises the value of aiming to launch such a mission
at the earliest opportunity, preferably before 2010. Should it turn out that it is only
possible to launch Eddington significantly later, ESA should consider a larger-scale
post-Kepler mission on a longer time schedule.
OWL and Kepler/Eddington
The OWL science case is currently not so much based on finding Earth-like planets,
but rather on imaging or spectroscopy of nearby candidates detected by other means.
To this extent OWL’s primary science case is as a follow-up instrument. On the
other hand there are no prospects other than Darwin/TPF for finding all nearby
Earth-mass planets (transits can only discover a small fraction), so its use for Earthmass
planet searches in a survey-type mode would be valuable, and should add to
its contribution to the field. Such a survey might be undertaken during the mirrorfilling
phase, although detailed feasibility studies of this approach have not yet been
made.
OWL/Dome C versus Darwin/TPF
As summarised in Section 3.1.2 and Table 8, appropriate Antarctic observations
could at least partially compete with some aspects of the Darwin/TPF missions.
However, some key spectral regions are accessible only from space, e.g. O 3 at 9.6 µm
and CO 2 at 15 µm. Trade-offs would depend on the number of objects visible,
the S/N ultimately attainable from Darwin, and the accessible spectral range and
the resulting scientific information that can be inferred for exo-planetology and
exobiology. Further investigations will be needed in order to understand whether
such Antarctic-based observations could be considered as realistic in the medium
term.
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