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