Contents

01 February 1991
Vol 251, Issue 4993

About The Cover

A 10 by 10 micrometer ``layer silicate'' interplanetary dust particle collected from the stratosphere by the NASA Johnson Space Center Cosmic Dust Collection Program. Data from analytical electron microscopic studies establish that some (and potentially all) interplanetary dust particles of the "layer silicate" subset are derived from asteroids. See page 549. [Scanning electron micrograph by J. P. Bradley; image processing by J. Barabe and S. Kilbourne]