B.A., Physics, UC Berkeley, 1967

Ph.D., Astronomy, Harvard University, 1971

I have worked on the astrophysics of cold, low density environments.

Now my major current interest is extrasolar planetary systems: their comets, asteroids, and planets. My long term goal is to determine if there is life in these environments.

Evidence is now compelling that the atmospheres of some white dwarf stars are contaminated by the accretion of tidally-disrupted minor planets. At least in the tiny sample observed to-date, we have found that extrasolar planetesimsals are at least 85% by mass composed of oxygen, magnesium, silicon and iron; these same four elements dominate the composition of bulk Earth. While carbon is half as abundant as oxygen in the Sun, it is less than 1% of the mass of both bulk Earth and most observed extrasolar asteroids. It is beginning to appear that our inner solar system evolved in a rather common fashion.