“I could more easily believe that two Yankee professors would lie than that stones would fall from heaven.”

— Thomas Jefferson, 1807


Not known for hyperbole, the magazine Skeptical Inquirer had a headline a few years back, “Earthling Slain by Invader from Mars” which sounds more like a National Enquirer lurid page one teaser. (“GRIFTERS HARRY & MEGHAN FIRED!” we learn from a recent issue.) Skeptical Inquirer, in contrast, typically takes the wilder headlines found in other periodicals and scrutinizes them from a scientific standpoint. Thus, tales about UFOs, crop circles, alien abductions and ghosts are usually shown to have rather prosaic explanations on closer examination. (Mr. And Mrs. Spare may be beyond their purview.)

So what’s with the Martian invader headline? Turns out the Earthling was a dog and the invader was a meteorite. That’s the story, at least. First off, and despite Jefferson’s incredulity, meteorites are indeed stones that fall from the sky. And they do sometimes hit people, as Mrs. Hewlett Hodges, of Sylacauga, Alabama, can testify. She sustained hip and abdominal injuries from a meteorite that crashed through the roof of her house in 1954.

But what about the “from Mars” part of the headline? Meteorites don’t come from Mars, do they? Most don’t, true. But a strong case can be made that a few do. Of all the 75,000-odd meteorites that have been collected and analyzed, nearly 300 are quite different from the rest. They’re known as the SNC group, “snicks” to their friends, after the places where they were originally found: Shergotty in India, Nakhla in Egypt and Chassigny in France. Snicks are different from all other meteorites in that they appear to have crystallized less than a billion years ago, that is, three billion years after the asteroids had cooled. (Virtually all “regular” meteorites originate in asteroids.) Also, snicks are odd because they appear to have formed in a strong gravitational field. Where do you find such a field? Most likely, on the surface of a planet or moon. But which one?

The composition of the snicks eliminates Earth and our moon as potential sources. Venus is ruled out because its thick atmosphere precludes any credible mechanism for ejecting planetary material into orbit, leaving Mars as the prime suspect. And at least one of the known snicks has been found to contain tiny inclusions of gas similar the Martian atmosphere. Finally, they have isotope ratios consistent with rocks found on Mars by Curiosity and the other Mars rovers.

The famous/notorious Martian SNC meteorite, ALH84001 (for Allan Hills in Antarctica, found in 1984), now on display in the Smithsonian. In 1996, claims that it proved there was once life on Mars were immediately countered by more sober scientists who showed that the unusual features could be explained without invoking actual life. Photo: Jstuby at English Wikipedia, CC BY-SA 3.0, via Wikimedia Commons

Electron microscope photo of the interior of ALH84001. Although these structures may look like fossilized life forms, they can (unfortunately) be explained away more prosaically. (NASA)

So the theory is that an ancient meteorite impact on Mars jetted surface material into space where it slowly spiraled sunward. Millions of years later, one chunk of what had been Mars fell to Earth on June 28, 1911 near Alexandria, Egypt. The oft-repeated claim is that a fragment of the “Nakhla” meteorite hit a dog, instantly vaporizing the creature. Although a farmer claimed to have seen this, there were no other witnesses and nothing remained of the dog so…Skeptical Inquirer or National Enquirer material? Your guess is as good as mine.