Report - School of Physics

Figure 5: Example of multiple-planet microlensing light curves from the simulation of planetary
systems with the same planetary mass ratios and separations as in our solar system, from the
MPF/GEST studies of Bennett & Rhie (2002). Left: an example of a Jupiter/Saturn detection.
Right: an example of the detection of an Earth and a Jupiter.
The Design Reference Mission (http://www.jwst.nasa.gov/ScienceGoals.htm) describes
the exo-planet programmes currently foreseen for JWST. The survey programmes
are aimed at finding giant planets and isolated objects using direct imaging,
and bound planets using coronography. Follow-up studies are planned using tunable
filter imaging (R ∼ 100) and slit spectroscopy. For isolated sources, objects
at AB = 30 mag can be reached using the near-infrared camera (NIRCam). The
tunable filter can reach AB = 27 mag, while mid-infrared spectroscopy (with MIRI)
can reach AB = 23 mag at R ∼ 3000. For widely-separated giant planets, R ∼ 100
coronography will provide preliminary temperature estimates and for these and for
isolated systems, R ∼ 1000 near-IR spectroscopy will access metallicity indicators.
Synoptic observations of bodies in our own Solar System, such as Titan, over the
10-year lifetime of JWST will begin the study of secular surface and atmospheric
changes.
A report on ‘Astrobiology and JWST’ (Seager & Lunine, 2004) listed three areas
where the technical capabilities of JWST should be optimised for the follow-up of
transit events: (1) in principle, JWST can measure the transmission spectra of giant
planet atmospheres during planet transits of bright stars (7–14 mag) but this requires
capabilities of rapid detector readout and high instrument duty-cycle in order
to achieve very high S/N over a typical transit time (12 hr). If Earth-sized planets
are common and detected in transit around stars brighter than 6 mag, the JWST
near-IR spectrograph (NIRSpec) could detect atmospheric biomarker signatures; (2)
the collection of ∼ 10 8 photons per image for NIRSpec, by spreading photons over
10 5 spatial+spectral pixels, would enable JWST to characterise atmospheres during
the transit of a terrestrial planet in the habitable-zone of a solar-type star; (3)
NIRSpec is important for characterising transiting extra-solar planets. Many tran-
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