Report - School of Physics

3.2 Space Observations: 2015–2025
The literature makes no reference to transit missions beyond Kepler and Eddington,
nor astrometric missions beyond SIM and Gaia, all due for completion around 2015.
Rather, space missions projected for 2015–20 and beyond fall into the category of
‘imaging’ or ‘direct detection’ concepts, notably Darwin and/or TPF. ‘Imaging’ here
generally refers to imaging of the exo-planetary system, i.e. direct detection of the
exo-planet as a point source of light distinct from that of the parent star, and not
to resolved imaging of the exo-planet surface.
The next major break-through in exo-planetary science will be the detection and
detailed characterisation of Earth-like planets in habitable zones. The prime goals
would be to detect light from Earth-like planets and to perform low-resolution spectroscopy
of their atmospheres in order to characterise their physical and chemical
properties. The target samples would include about 200 stars in the Solar neighbourhood.
Follow-up spectroscopy covering the molecular bands of CO 2 , H 2 O, O 3 ,
and CH 4 will deepen understanding of Earth-like planets in general, and may lead
to the identification of unique biomarkers. The search for life on other planets will
enable us to place life as it exists today on Earth in the context of planetary and
biological evolution and survival.
In the more distant future, perhaps well beyond 2025, a successful Darwin/TPF
would logically be followed by ‘life finders’ and true ‘planet imagers’. At present
they appear only as more distant goals, and a brief discussion of them is given in
Appendix B. They are unlikely to affect ESA/NASA policy over the next decade
or more, at least until the prospects for the success of Darwin/TPF can be quantified,
except in the areas of advanced technology studies. Similarly, ideas beyond
Darwin/TPF are unlikely to influence the choices or prospects for the very large
(50–100 m) telescopes on ground.
3.2.1 Darwin
Darwin is the ESA mission concept aiming at the direct detection of exo-planets,
and is focused on an interferometer configuration. It was originally conceived as
a set of eight spacecraft at L2 (6 telescopes, one beam combination unit, and one
communication unit) that would survey 100 of the closest stars in the infrared,
searching for Earth-like planets and analysing their atmospheres for the chemical
signature of life (Fridlund, 2000), scientific objectives in common with those of TPF.
More recent studies have identified a simplified option, employing 4 telescopes separated
by up to 50–100 m operated in a ‘dual-Bracewell’ configuration (or possibly
3×3.5 m telescopes), requiring a dual Soyuz-Fregat launch, and a target launch date
of 2015. The mission foresees a detection phase of 2 years (allowing the follow-up
of 150–200 stars), and a spectroscopy phase of 3 years. Specific precursor efforts
include a possible space mission (Smart-3) to demonstrate the concept of forma-
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