In 1993, ALH84001 was examined by researcher David Mittlefehldt of Lockheed-Martin. Mittlefehldt, an expert on meteorites, noticed that it appeared unusual and that it had features in common with other known martian meteorites. Further analysis by Bob Clayton of the University of Chicago secured the rock’s martian pedigree. Thus, ALH84001 became the twelfth known martian meteorite on Earth.
After it was reclassified as a rock from Mars, Mittlefehldt began a more in-depth study of the meteorite using an electron microscope. He saw some very unusual features, including some roundish “globs” of carbonate salt. By chance, Mittlefehldt’s lab was across the hall from geochemist Christopher Romanek, another expert on meteorites. Mittlefehldt asked Romanek to check out what he was seeing, and the other scientist became immediately fascinated by what he saw in the slices of ALH84001. Romanek then embarked on his own research, focusing on the carbonate salt globules seen by Mittlefehldt.
Romanek discovered that the globules were composed of magnesium, iron, and calcium, and that they also contained carbon and oxygen. When he compared the composition of the globules to the surrounding material, he concluded that the globules formed at a low temperature, and that they probably formed on Mars.
Romanek recalls having a “eureka moment” every time the team had a scanning session with the electron microscope. “We were looking at this material at a resolution that not a lot of people have used before in this way,” he said. “And we had to be so careful about what we were seeing. Were [the globules] artifacts that didn’t originate on the rock? Were they dust grains? All of this had to be addressed in highly constrained experiments.”
Romanek’s work dramatically shifted the thrust of the research into this martian meteorite. The focus was no longer geochemical processes. It became instead a search for evidence of possible relic forms of prebiotic life.
A team of scientists led by NASA’s David S. McKay and Everett K. Gibson, Jr. began scrutinizing glass-thin sections sliced from the meteorite. They were stunned when they discovered a distribution of organic molecules within this martian meteorite. Organic molecules, or molecules containing carbon, are the sorts of molecules found on Earth in all living things. These particular molecules are called “polycyclic aromatic hydrocarbons,” or PAHs. They are the first organic molecules ever seen in a rock from Mars.
Closer observations made with an electron microscope also revealed intriguingly shaped ovoids and elongated features that resemble fossilized “nanobacteria” on Earth.
The NASA team of scientists had to keep reminding themselves that this rock did not originate on Earth, but on the planet Mars! Since Mars was first observed telescopically by Galileo in the 17th century, it has been associated with the possibility of extraterrestrial life, both intelligent and otherwise. With ALH84001, it appears to some scientists that what once seemed fantastical literally has come down to Earth. They believe that Martians, or perhaps all that the Martians ever became, have arrived at last.