Nobody knows how these mysterious ridges formed on the surface of Mars

Planetary scientists studying photos of Mars's ever-changing landscape have discovered a stunning formation of bedrock ridges near the planet's equator, inside Schiaparelli Crater – but how they formed remains a mystery.

The images you see here come by way of NASA's stunningly powerful HiRISE camera. Researchers were originally drawn to Schiaparelli by the circumferential layers that line its insides. HiRISE – which can image the planet's surface at about 25cm per pixel all the way from orbit – allows researchers to get a good look at these layers and how they change over time.

"This image was targeted to look at potential changes in the distribution of dark sand compared to earlier pictures," writes HiRISE co-investigator Nathan Bridges on the mission's website; and while preliminary investigations have turned up no such changes, they have raised some intriguing new questions:

Nobody knows how these mysterious ridges formed on the surface of Mars

In this image [above], we note something that becomes apparent if we zoom in to many of the areas containing dark sand. Here, the sand is on top of periodic bedrock edges oriented semi-radially from the crater and approximately perpendicular to the layers. How did these ridges form, and what is the relationship to the sand?

Nobody knows how these mysterious ridges formed on the surface of Mars

The answer, Bridges says, is a mystery – though he offers that sand may be somehow "nucleating," or collecting, on the ridges.

"This suggests that some apparent large ripples on Mars are sand nucleation sites on pre-existing topography," he explains. "The extent of such ridges, and their relationship to sand elsewhere on the planet, can be further understood with future HiRISE images in other areas."

[HiRISE]