September 17, 2007 Melted Crumbs from Asteroid Vesta --- Researchers studying some of the rarest of the smallest meteorites call them melted crumbs from asteroid Vesta. Written by Linda M. V. Martel Hawai'i Institute of Geophysics and Planetology Micrometeorite bombardment accounts for almost 30,000 tons of material entering Earth's atmosphere each year. Though most of the material evaporates during entry or is lost to sea or falls on the land unnoticed, thousands of micrometeorites have been collected successfully from deep-sea sediments and from the snow and ice of the polar caps. Susan Taylor (Cold Regions Research and Engineering Laboratory) and colleagues collected micrometeorites with an ingeniously designed robot from a decidedly out- of-the-way place: Amundsen-Scott South Pole Station water well. She and Greg Herzog and Jeremy Delaney (Rutgers University) selected 10 out of thousands of these extraterrestrial particles, 75 to 700 micrometers in size, because of their unusual shapes and mineralogy, and measured the Fe/Mn and Fe/Mg elemental ratios, which are known to help constrain the type and source of meteorites. The results show that nine of the cosmic spherules are broadly chondritic in composition as expected. However, one, along with six others reexamined from a previous study, are atypical with nonchondritic compositions. Taylor and coauthors propose an origin from an achondrite, Howardite-Eucrite-Diogenite (HED)-like parent body such as asteroid Vesta. HED-like objects account for about 6% of all meteorites, and only about 0.5% of all micrometeorites perhaps because of a natural mechanical toughness that would resist breakup and fragmentation. Reference: z Taylor, S., Herzog, G. F., and Delaney, J. S., 2007, Crumbs from the Crust of Vesta: Achondritic Cosmic Spherules from the South Pole Water Well, Meteoritics and Planetary Science, v. 42, p. 223-233. PSRDpresents: Melted Micrometeorites --Short Slide Summary (with accompanying notes). Concentrations of Cosmic Debris What better way to handle the summer heat than with a cool little story about ice ...Antarctic ice, that is, studded with the most minuscule grains from the cosmos. Researchers are studying extraterrestrial materials that are literally particles and spherules less than a millimeter in size but whose combined mass accounts for about 1,000 tons of new stuff added to Earth yearly. A micrometeorite is generally defined as a tiny meteorite larger than 50 micrometers but smaller than a millimeter. Micrometeorites that have melted, either partially or completely when plunging through Earth's atmosphere, are called cosmic spherules. PSRD: Melted Crumbs from Asteroid Vesta Page 1 of 6 http://www.psrd.hawaii.edu/Sept07/cosmicSpherules.html