Research Training Program

Megan Brown
Arizona State University
Tempe, Arizona

Tim McCoy, Ph.D.
Supervising Scientist
Department of Mineral Sciences

"Geology is my passion. Conducting
research at the Smithsonian Institution
this summer was an amazing experience
I will not soon forget."

Sulfur depletion on 433 Eros: Analyzing meteoritic analogs to compare possible causes

Eros, or more specifically 433 Eros, is an asteroid. Unlike most asteroids that orbit between Mars and Jupiter in the Asteroid Belt, 433 Eros orbits around the sun and then passes earth, thereby providing plenatary geologists a unique opportunity to study an asteroid up close. In anticipation of this Earth pass by a mission was launched, sending a spacecraft to meet and rendezvous with Eros. On 14 February 2000, the Near Earth Asteroid Rendezvous (NEAR) Spacecraft entered orbit around 433 Eros where it remained for a year before landing on the surface, becoming the first fact-finding scientific instrument to successfully and on a small body, such as an asteroid, and send back information to a team of waiting scientists. Amoung the information sent back was the discovery that Eros has less concentrations of the element sulfer (S) than other asteroid. There are two theories for this sulfer depletion: tiny meteorite impacts caused the sulfer to turn to gas, or, the asteroid being partially melted, caused the sulfer to sink to the center and then lost during eruptions. Meteorites were analyzed to test the two theories. To evaluate the melting model, the effect of melting on the element chromium (Cr) was studied. Three meteorites that experienced differing amounts of partial melting were studied. It was discovered that the more partially melted the meteorite, the less Cr present. Thus, Cr is a sensitive indicator of partial melting and reanalysis of data from Eros to determine Cr abundances can test the partial melting model. To test the impact model, a meteorite similar to the surface of 433 Eros was studied. The meteorite has two parts, a dark area that was exposed at the surface, and a light area that was never exposed at the surface. No difference was found in the amount of sulfer present in the two parts, possibly because the ancient surfaces preserved by the meteorites differ from those visited by the NEAR mission. A single grain of iron sulfide was identified that contains inclusions of different minerals. Such particles, called agglutinates, are common on the Moon, but rare in meteorites. The presence of this particle suggests that micrometeorite impacts did alter sulfides at the surface of asteroids, probably through melting.

This research was supported by a grant from the National Science Foundation Research Experiences for Undergraduates program, Award Number DBI-0243512.

Letter of gratitude