There’s no greater mystery than a mystery cropping up somewhere you thought you understood. In the case of the Martian plain Hesperia Planum, it was filed under “Region on Mars. Not Particularly Interesting. No Further Study Needed.” Now, in typical Mars fashion, it appears Hesperia Planum has been hiding some secrets.
Hesperia Planum is known for, well, being unremarkable. But it is important nonetheless.
It’s an ancient lava-filled plain that has been used by scientists to characterize the base of a Martian geologic epoch, the aptly named “Hesperian” that spanned 3.7 to 3.1 billion years ago.
But as it’s a plain, it’s always been assumed that “what you see is what you get.” It’s a plain plain. “Most scientists don’t want to work on the flat things,” said geologist Tracy Gregg of The University at Buffalo, State University of New York, in a Geological Society of America press release.
But now we have an armada of satellites orbiting the Red Planet — NASA’s Mars Reconnaissance Orbiter and Mars Odyssey plus ESA’s Mars Express — scientists have access to an unprecedented amount of high-resolution imagery.
So, during a study led by Gregg and her student Carolyn Roberts focusing on this “classic” Martian lava plain with modern data, the assumptions about Hesperia Planum started to break down.
For starters, the pair of researchers noticed a small volcano (as one would expect to find in an ancient lava-filled plain) and yet there is no evidence of other associated features like vents and… wait for it… lava flows.
The explanation may be fairly straight forward: “A likely cause of this trouble is the thick dust that blankets Hesperia Planum,” said Gregg. “It covers everywhere like a snowfall.”
But this is where things start to get a little weird. When they turned their attention to sinuous rilles — the long, snaking veins in the Martian surface tunneled-out by lava flows — it appears they have no source and no destination.
These rilles are basically tubes, sometimes empty tunnels, where ancient lava used to flow when Mars was a volcanically active world. Since tectonic activity shut down, these features were left behind. Sometimes the hardened roofs collapse, revealing a sunken cavern that are often eyed by Mars colonization advocates as potential shelter for the first Mars settlements.
However, the rille features Gregg and Roberts are studying don’t appear to be connected with volcanic activity at all! In fact, something entirely different may have formed them: Could it have been water?
“Everybody assumed these were huge lava flows,” said Gregg. “But if it turns out to be a lake deposit, it’s a very different picture of what Mars was doing at that time.”
The next thing they intend to do is to compare the sinuous rilles on Mars with the ones on the moon. After all, the ones on the moon were definitely caused by volcanic activity. Should lunar rilles’ plumbing be as dodgy as the Martian ones, then perhaps the water explanation, well, isn’t going to hold water.
But if water is a possibility, then Hesperia Planum suddenly became a lot more interesting. Evidence for a watery past plus ancient volcanism may have provided the ideal environment to incubate life.
Image: A Rille To Nowhere? Credit: NASA/GSFC/Arizona State University