[Previous] | [Session 109] | [Next]
D. Koch (NASA Ames Research Center), F. Witteborn (Orbital Science Corp), E. Dunham (Lowell Observatory), J. Jenkins (SETI Institute), W. Borucki, L. Webster (NASA Ames Research Center)
Transit signals produced by Earth-size planets in orbit around solar-like stars are of the order of 8e-5 and have durations from 4 to 16 hours for planets in or near the habitable zone. A mission to search for habitable planets has been proposed (Koch, et al., 1998). At the heart of the mission is an array of CCDs used to continuously measure the relative brightness variations of 100,000 dwarf stars for transits. A testbed facility has been constructed to determine the effects of various induced noise sources on the capability of a CCD photometer to maintain an instrument relative precision of better than 1e-5.
The photometry facility includes: a simulated star field with an approximate solar spectrum, fast optics to simulate the space borne telescope, a thinned back-illuminated CCD similar to those to be used on the spacecraft operating at 1 Mpix/sec read rate, and shutterless operation. The test facility is thermally and mechanically isolated. Each source of noise is introduced in a controlled fashion and evaluated. Pointing noise or changing thermal conditions in the spacecraft can cause star-image motion at the milli-pixel level. These motions are imposed by piezo-electric devices that move the photometer relative to the star field.
Transit signals as small as Earth-size transits of solar-like stars are generated and measured. This is accomplished by electrical self-heating and expansion of fine wires placed across many of the star apertures. The small decrease in stellar brightness is used to demonstrate that Earth-size planets can be detected under realistic noise conditions and at the shot-noise-limited level. The effects of imposing several noise sources are shown and the resulting detectability of planets is presented.
This work is supported in part by the NASA Discovery program and NASA Ames.
Koch, D., Borucki, W., Webster, L., Dunham, E., Jenkins, J., Marriott, J. and Reitsema, H. SPIE Conf. on Space Telescopes and Instruments V, 3356, 599-607 (1998)
The author(s) of this abstract have provided an email address for comments about the abstract: DKoch@mail.arc.nasa.gov