The Curiosity rover has been getting all sorts of attention lately, and no wonder: it’s by far the most sophisticated robotic explorer that has ever set down on another planet. The Mars Science Laboratory — Curiosity’s formal name — is armed with a suite of instruments that can analyze the Red Planet’s rocks and soil at a level of detail never before possible. There’s every reason to believe the rover, still just at the beginning of its mission, will ultimately reveal all sorts of secrets about Mars’ geologic, and perhaps even biologic, history.
Back here on Earth, however, a chunk of rock known as NWA 7034 is answering at least some of those questions already. The prosaically named bit of rubble is an artifact of Mars that was blasted off the surface eons ago, made the long, cold journey to Earth and eventually slammed into the Sahara Desert as a meteorite. And as a new report in Science makes clear, it’s got a remarkable story to tell. “We know that Mars may have been warm and wet very early in its history,” says lead author Carl Agee, of the University of New Mexico. “But this sample suggests the water may have lingered much longer than anyone realized.”
(Photos: Window on Infinity: Pictures from Space)
The fact that bits of Mars fall to Earth every so often is well known to planetary scientists. NASA has cataloged nearly three dozen pieces of the Red Planet so far, presumably flung into space by one of the asteroids that whacks Mars every so often. It’s not as hard for Earth to intercept so many of these space rocks as it seems. For one thing, Mars has produced a lot of the stuff over time, especially since its tenuously thin atmosphere makes it more vulnerable to asteroid hits than the well-swaddled Earth is. Mars’ lower gravity also makes it easier for any rubble that’s kicked up to escape into space. Once that happens, one of these rocks may, over time, make millions of orbital passes by Earth, eventually getting drawn in by our planet’s gravity. Scientists can confirm a meteorite’s Martian origin by comparing its mineralogy and trace atmospheric content to what they know of Mars’ makeup. The best-known Mars rock so far: ALH84001, which made headlines in 1996 when scientists claimed — wrongly, most now believe — that it contained evidence of ancient Martian bacteria.
But while the excitement about ALH84001 has long since faded, scientific interest in Martian meteorites hasn’t at all. So when a meteorite collector handed NWA 7034 over to Agee back in 2011, it was immediately clear that even among Mars rocks, this one was special. “I’d never seen anything like it,” says Agee. Most meteorites are black on the outside, thanks to their superheated passage through Earth’s atmosphere, but NWA 7034 was black on the inside as well. “It also had other colors — patches of white, and so on. Just a very unusual texture. It sat on my shelf for a month while I scratched my head, wondering, ‘What is that thing?’”
It took more than a year of analysis by labs across the U.S. and in China before Agee and his co-authors could really say. As they explain in Science, while NWA 7034 is different in composition from any other Mars meteorite ever seen, it turns out to be quite similar to the chunks Curiosity has been finding. “All the other meteorites,” says Agee, “are thought to be from just two or three places on the Martian surface.” The reason those spots are overrepresented is that even with Mars’ higher rate of asteroid bombardment, it’s still not easy for a rock to be launched on just the right trajectory to reach Earth. That would be fine if the two or three places that have donated meteorites to Earth were typical of the rest of Mars, but they appear not to be.
Instead, it’s the crustal region that produced NWA 7034 that seems a better representative of the rest of Mars and thus holds more information about the planet’s history. The most exciting finding so far: while the rock is extremely dry, it still has about 10 times the water content of other Martian meteorites. “It suggests,” says Agee, “that when it formed, there was water permeating and interacting with it.” Yet radioactive dating showed NWA 7034 is a mere 2.1 billion years old, which places it in an era long after the water was supposed to have vanished.
This sample, says Agee, may therefore be telling us that the loss of Martian surface water happened much more gradually than has been believed. “There could be other interpretations as well,” he cautions. NWA 7034 is volcanic, and it’s possible it formed near a hydrothermal vent, where deep subsurface water — much less surprising than surface water would be, and possibly present on Mars to this day — was heated and forced up from below. “There’s always more than one way to explain something like this,” he says.
This and other questions about NWA 7034 could still be resolved, however: the Science paper is only the first volley in what will likely be a barrage of findings. “We’ve got 10 labs working on this meteorite right now,” says Agee. “This was just NWA 7034’s debut.”
(Photos: Seeing Red: 40 Years of Exploration on Mars)
(From the Magazine: Aliens Among Us)