Ancient meteorite hints at origins of our water
BOSTON — When Michael Zolensky first saw the meteorite that had recently punched a crater in a west Texas road, it looked like a fairly common piece of space rock.
"We didn't know it was unusual until we brought it into the lab, broke it open, and saw purple deposits," says Dr. Zolensky, curator of NASA's collection of cosmic dust and moon-rock samples.
A close look at those deposits has revealed crystalline time capsules whose surprising contents - tiny amounts of liquid water 4.5 billion years old - could provide the first direct test of theories to explain the sources of the solar system's water. They also could help fill in the picture of water's role in altering the growing chunks of space rock that would become planets and asteroids.
"These are the early solar system's juices in a bottle," says
Everett Gibson Jr., a senior scientist at NASA's Johnson Space Center in Houston, where the samples are stored.
A report on the discovery, appearing in yesterday's edition of the journal Science, comes at a time when the US space program has placed an increasing emphasis on learning more about the origins of the solar system, and hence, humanity. Water plays a critical role in both, and the earliest years of that history is thought to be recorded in asteroids and comets, debris left over from the construction of the cosmos that's the source of many of the meteors passing through Earth's atmosphere.
Two current space missions to study asteroids and comets up close, Stardust and the Near Earth Asteroid Rendezvous probe, typify NASA's effort.
Until now, inferences about water's role in the early solar system have been drawn from indirect evidence - the mineral content of meteorites. The briny sample from Texas, which fell to Earth last year, "provides the first opportunity to study solar nebula water directly," writes Robert Clayton of the University of Chicago's Enrico Fermi Institute, in a Science commentary.
The Texas meteorite's purple "bottles" are largely identical with common table salt, which mixes readily with water. For that reason, Zolensky of NASA speculates that in its early form, the meteorite's parent body could have harbored a considerable amount of liquid water.
"Salt has a lot of chlorine, which doesn't appear much in rocks, and it takes a lot of water for it to precipitate out," he says, likening the process to evaporating sea water for its salt.
If there was that much liquid water, he continues, "there could have been some organic chemistry going on," forming compounds including those that underlie the formation of life.
Alternately, he says, the water might have come more recently, perhaps a result of a collision with a comet.
In addition, the general make up of the meteorite, researchers add, indicates that it was chipped from a type of stony asteroid long thought to have been formed by processes too hot to allow for the presence of water. "The existence of water-soluble salt in this meteorite is astonishing," Dr. Clayton notes.
The research team, which includes Dr. Gibson, Virginia Tech geologist Robert Bodnar, and three scientists from Lockheed Martin Space Operations Company in Houston, says much can be learned when the water samples' isotopes of hydrogen and oxygen are analyzed. The ratios of different isotopes provides a key to determining the source of the water - from the primal solar nebula itself or from other interstellar sources.
Moreover, the brine's mineral content can reveal much about the processes the parent body underwent as it formed, notes Harry McSween Jr., a meteorite expert at the University of Tennessee at Knoxville.
But such analyses are unlikely to happen until a new generation of instruments that can cope with the teasingly small amounts of water in the Texas meteorite. One such instrument is under construction in Britain and is expected to begin operation in about a year.
In the meantime, the team is analyzing a meteorite from Morocco that appears to harbor similar salt-encased water deposits. Indeed, such "bottles" may be more widespread that many believe, Zolensky holds, but they melt away when exposed to high humidity or traditional methods for slicing samples from meteorites.
With the right preservation techniques, he says, more water samples may emerge, revealing more details about water's role in the early solar system.
(c) Copyright 1999. The Christian Science Publishing Society