nai

Project Progress

Brownlee and Matrajt have continued their investigation of the organic materials delivered to Earth by the 40,000 tons of asteroid and comet dust that is annually accreted from space. This laboratory study on extraterrestrial samples includes both work on nanogram particles collected from the both the stratosphere and microgram particles collected from Antarctic ice. These samples will soon be suplimented by comet samples to be returned by the Stardust mission. All of these materials are believed to be identical to the partilces that carried extraterrestrial organic materials to Earth during Earth’s prebiotic history.

In collaboration with S. Taylor and S. Pizzarello, they discovered the first amino acids in extraterrestrial dust. The concenration of AIB in these 100µm samples is being used as a basis for estimating the total delivery rate of amino acids to the early Earth over the time period when dust accretion by Earth was greatly enhanced by the early evolution of the asteroid belt and the comet belts.

A major issue of organics delivery by small extraterrestrial partices is modification by high speed entry into the atmosphere. Matrajt and Brownlee have expored the survival of a variety of organics that are carried in small extraterrestrial particles. They built a special furnace that duplicates the ~5 second heat pulse and atmosperic environment that entering particles are exposed to. They have made10µm thin films of nano-porous alumina particles impregnated, in different runs, with lysine, coronene, and 2 pentadecanone (a ketone) and exposed them to the simulated atmospheric entry heating environment. By measuring pre and post-heating concentrations with GC/MS and electrospray/MS, they have been able to determine survival curves with temperature. Remarkably, all three of these relatively volatile compounds survive at the several percent level for the dynamic pulse heating to 600 C, a common maximum temperature during atmospheric entry. Lesser amounts survive even a >800C! The survival of these compounds in pulse-heated is enhanced by the poor thermal conductivity of their porous inorganic host and the effects of ablative cooling. This work will be used to estimate the fraction of volatile organics that that survive atmospheric entry and arrive at the Earth’s surface.

In complimentary work, Brownlee and Kress are working with G. Cody in experiments to determine the nature of compounds that escape from pulse heated partilces, the ones that directly enter the atmosphere.

Related work in the 2004-2005 time period has invovled electron energy loss spectroscopy in a field emission transmission electron microscope to determine the nature of carbon in small extraterrestrial partilces. This work has invovled developing special techniques for mictotoming et particles in a way that leaves no residual carbon from mounting media. This has worked quite with a special acrylic media that can be removed after mircotomy.