Report - School of Physics

Figure 6: A 2 × 2 arcsec 2 simulated image of our Solar System viewed from 10 pc using the
(former) 6-telescope Darwin configuration. Observations are over 6–18 µm in a 10-hour exposure,
with the system viewed at 30 ◦ inclination, and assuming zodiacal emission as for our Solar System.
The Sun is located at the centre. Venus, Earth and Mars are visible.
tion flying. The emphasis on the infrared rather than the optical is guided by: (i)
the less-stringent requirements on technology (contrast and resolution); (ii) infrared
spectroscopy allows characterisation in a direct and unambiguous manner; (iii) infrared
interferometry allows a larger sample of objects to be surveyed for Earth-like
planets (150–200 versus 32 for visual coronography); (iv) it provides the heritage for
the next generation of missions which will demand higher resolution spatial imaging.
Figure 6 is a simulated image of our Solar System viewed from 10 pc.
Table 8, from Angel (2003), is a summary of detection capabilities for an Earth-Sun
system at 10 pc for various experiments being studied, including TPF and Darwin.
It shows that even for the most ambitious projects being planned at present, direct
detection of even a nearby Earth represents a huge challenge.
Table 9 summarises the estimated integration times for a variety of stellar types
(target stellar types are F–G with some K–M), and a range of distances. Broadly,
these are consistent with the simplified summary given in Table 8. Typical distance
limits are out to 25 pc. A terrestrial planet is considered as R max ∼ 2R ⊕ . The
spectral range is 6–18 µm, covering the key absorption lines, with a spectral resolution
of 20 (50 is required for CH 4 in low abundance). Integration time estimates
are given for a S/N = 5 in imaging (i.e. detected planetary signal/total noise) and
S/N = 7 in the faintest part of spectrum for spectroscopy, for the following assumptions:
total collecting area for all telescopes of 40 m 2 ; telescopes at 40 K; effective
planetary temperature 265 K (signal scales as T 4 eff); R = R ⊕ ; integrated over 8–16
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