

A Mote in Hubble's Eye

On April 6, 1994 NASA's Hubble Space Telescope (HST) was performing a detailed study of the Sun's nearest stellar neighbor, Proxima Centauri, using the Fine Guidance Sensors to search for small deviations in the position of Proxima Centauri that could reveal the presence of an unseen planetary companion. Rather than sit idle while this study went on, the Wide Field and Planetary Camera 2 (WFPC2) was activated using the observing strategy set out in a program initiated by Dr. Ed Groth (Princeton) designed to make use of this otherwise wasted time. The image captured by this WFPC2 parallel observation is a typical Milky Way star field in the constellation Centaurus. Such images can be used to study the evolution of stars that make up our galaxy. Most of the stars in this image lie near the center of our galaxy some 25,000 light-years distant. But one object, the blue curved streak, is something much closer. An uncatalogued, mile-wide bit of rocky debris orbiting the Sun only light-minutes away strayed into WFPC2's field while the image was being exposed. This and about a hundred other interlopers have been found by Jet Propulsion Laboratory astronomers Dr. Robin Evans, Dr. Karl Stapelfeldt, and collaborators, who have systematically searched the HST archive for these nearby objects. Their analysis indicates this asteroid's orbit could cross Mars' path. Seen briefly by HST, these asteroids are too small and faint to track from the ground long enough for precise orbits to be determined. They are destined to return to their unseen wanderings for hundreds or thousands of years until once again, by chance, they may flicker across the view of some watchful eye peering off into the depths of space.

Acknowledgment: R. Evans and K. Stapelfeldt (Jet Propulsion Lab)