Don Brownlee, University of Washington
Stardust, the first sample return mission to a primitive body, collected thousands of well-preserved 1-60 µm solid particles from an active 4 km comet. Nearly all the comet silicate materials >2µm formed at high temperature and most are chondrule fragments that could not have formed in the same environment where the cometary volatiles condensed. A fundamental and distinctive property of the comet dust is that it is an unequilibrated weak carbon-rich aggregate of anhydrous rocky nebular materials that were previously packed in ice but do not contain significant amounts of secondary minerals such as phyllosilicates, carbonates and phosphates that are abundant in carbon rich meteorites and samples returned from primitive asteroids. The sampled comet, as well as porous interplanetary dust particles of probable cometary origin, preserve primary nebular solids such as chondrule and CAI fragments as well as presolar grains probably because most comets formed small, far from the Sun, and their interiors never had the internal pressure and temperature needed to melt ice and produce extensive aqueous alteration.
About the presenter
Don Brownlee is a professor of astronomy at the University of Washington. He has spent his entire career collecting and analyzing "meteoritic materials” from space, the stratosphere, polar regions and the abyssal sediments. He was the Principle Investigator of the NASA Stardust mission that returned the only laboratory samples that are known to be from a comet that formed at the edge of the solar system. He received the Meteoritical Society Leonard Medal in 1996.