Report - School of Physics

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Space Precursors: Interferometers, Coronographs
and Apodizers
The McKee-Taylor Decadal Survey Committee (McKee & Taylor, 2000) qualified its
endorsement of the TPF mission with the condition that the abundance of Earthsize
planets be determined prior to the start of the TPF mission. Many ideas for
scientific and technological precursors for TPF have been examined. The main
contenders are summarised here for completeness, although with the recent (April
2004) NASA announcement on TPF strategy, it seems unlikely that any of these
concepts will be developed further:
Eclipse (coronography) is a proposed NASA Discovery-class mission to perform a
direct imaging survey of nearby planetary systems, including a complete survey for
Jovian-sized planets orbiting 5 AU from all stars of spectral types A–K within 15 pc
of the Sun (Trauger et al., 2003). Its optical design incorporates a telescope with an
unobscured aperture of 1.8 m, a coronographic camera for suppression of diffracted
light, and precision active optical correction for suppression of scattered light, and
imaging/spectroscopy. A three-year science mission would survey the nearby stars
accessible to TPF. Eclipse may be resubmitted for NASA’s Discovery round in 2004.
Jovian Planet Finder (JPF) was a MIDEX proposal to directly image Jupiter-like
planets around some 40 nearby stars using a 1.5-m optical imaging telescope and
coronographic system, originally on the International Space Station (ISS) (Clampin
et al., 2002). Its sensitivity results from super-smooth optical polishing, and should
be sensitive to Jovian planets at typical distances of 2–20 AU from the parent star,
and imaging of their dusty disks – potentially solar system analogues. A 3-yr mission
lifetime was proposed.
Extra-Solar Planet Imager (ESPI) is another proposed precursor to TPF (Lyon
et al., 2003). Originally proposed as a NASA Midex mission as a 1.5 × 1.5 m 2
apodized square aperture telescope, reducing the diffracted light from a bright central
source, and making possible observations down to 0.3 arcsec from the central
star. Jupiter-like planets could be detected around 160–175 stars out to 16 pc, with
S/N > 5 in observations lasting up to 100 hours. Spectroscopic follow-up of the
brightest discoveries would be made. The Extra-Solar Planet Observatory (ExPO)
is a similar concept proposed as a Discovery-class mission (Gezari et al., 2003).
Self-luminous Planet Finder (SPF) is a further TPF precursor under study by
N. Woolf and colleagues, aiming at the search for younger or more massive giant
planets in Jupiter/Saturn like orbits, where they will be highly self-luminous and
bright at wavelengths of 5–10 µm, where neither local nor solar system zodiacal glow
will limit observations. SPF will demonstrate the key technologies of passive cooling
associated with interferometric nulling and truss operation that are required for a
TPF mission. SPF targets young Jupiter-like planets both around nearby stars such
as ɛ Eri, and around A and early F stars.
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