Mission from Mars: ET in a Minienvironment
By Susan English
Houston, TX–Contamination control is the first crucial step in studying meteorites. U.S. scientists pay strict attention to keeping contamination out of the meteorite`s environment and to keep anything harmful out of scientists` environment.
The U.S. Antarctic Meteorite Program, a joint project of the National Science Foundation, NASA and the Smithsonian Institution, has collected meteorites from the frozen Antarctic tundra. The rocks are shipped frozen in Teflon bags to minimize hydrocarbon contamination to be curated at the Antarctic Meteorite Processing Laboratory at NASA`s Johnson Space Center–a special Class 10,000 “clean lab” similar to that which houses the Apollo Moon rocks.
Curation of meteorites involves storing, describing, classifying and announcing new meteorites for study and later splitting them for distribution to investigators around the world. Judith Allton, a Principal Scientist with Lockheed Martin in Houston supporting the Solar System Exploration Division at Johnson Space Center, has been involved in hands-on curation of lunar rocks since 1974. Currently, she`s working with contamination control for meteorite curation. Antarctic meteorites are generally handled like lunar rocks, stored in dry, nitrogen-purged cabinets to slow oxidation from atmospheric oxygen and moisture and to protect them from many types of contaminants.
Originally, says Allton, the purpose was to “quarantine” the Moon rocks for possible harmful contaminants. They were handled under vacuum, which is technically challenging. As scientists gained experience in handling the rocks, they saw that nitrogen had no adverse reaction, so a switch was made to gloved cabinets flowing with dry, clean nitrogen.
Usually, meteorites are split into smaller chips. These delicate chipping or extraction operations are carried out on laminar flow benches to keep the samples clean. All tools used in sawing, chipping, packaging and storing the meteorites are pre-cleaned in a Class 1,000 soft-wall, vertical flow module and final cleaned in a Class 100 soft-wall, vertical-flow module housed in the clean lab running at Class 1,000. Composition of tool materials is restricted to certain alloys of stainless steel, aluminum and Teflon, although some nylon bagging is also used. According to Allton: “Our contamination concern is to ban any elements that would interfere with scientific measurements, such as age-dating isotopes. The rationale is to use materials of a restricted and known composition so that any contaminants can be easily recognized.”
About the recent Mars rocks notoriety, Allton says, “we are reevaluating what we do with them.” Recent reports suggest the presence of Martian organic material in one, or even two other meteorites in the group. While particle counts are not taken inside the nitrogen cabinets, there is an air shower in the meteorite lab.
Employees access a security-controlled entry room, put on paper shoe covers, walk into a change room, where they don outer shoe covers and a smock and a cap, then proceed through an air shower, out into the lab. The rocks are moved to cabinets and worked on under nitrogen by a mechanism of double-bagging and heat-sealing of Teflon or nylon bags.
An advance over the process for handling lunar rocks is the use of 18.24 ultrapure water to clean the tools instead of freon, which had been used for years, says Allton. “We had used fluid freon initially because we didn`t want to add any organics.
Then it became an environmental problem, so last year we switched over to ultrapure water. All our tools are clean and particle counts are done on the effluent. Cabinets are also flushed with the ultra pure water.” n