The ‘fire ring’ named Tappers (arrow) indicates where a sediment pipe may have developed at the head of Moonlight Valley in Gale Crater. The feature (also seen in close-up at right) suggests the presence of one or more layers of evaporites buried below the surface, clues to Gale’s ancient climate history. The yellow square at right marks the area analyzed by the ChemCam laser instrument. (Figure from abstract.)
The Curiosity rover has imaged a number of roughly circular features with thick walls along its traverse in Gale Crater. These features may indicate the existence of evaporite beds below the surface sediments, reports (PDF) Roger Wiens (Los Alamos National Laboratory) at the 46th Lunar and Planetary Science Conference in The Woodlands, Texas. Wiens is the lead author on the report, which has about two dozen co-authors.
The scientists have dubbed the features “fire rings” for their resemblence to the rock fire circles typically seen at camp sites. Previous landers have not seen these features anywhere on Mars before.
Wiens says, “The largest of these round features is the Tappers ‘fire ring’ seen on Sol 527, near the head of Moonlight Valley, just above Dingo Gap Dune.” The object is about 60 centimeters (2 feet) in diameter, while its rim rises about 7 cm (3 inches) and is several inches thick.
“We observed several other features possibly related to Tappers farther down the valley,” Wiens adds. “They’re similar in appearance but smaller in size.”
While the origin of these features is uncertain, Wiens suggests that they may be sediment pipes. “In sedimentary regions containing layers of evaporites such as gypsum and anhydrite, if the buried evaporite layer is dissolved in places, the overlying layer may partially collapse,” he explains.
“Cylindrical pipes may develop where sediments have flowed downward after the subsurface support goes away,” Wiens says. Such features would have important implications for Gale’s past climate history.
“An evaporite layer would imply an epoch in which at least part of the crater lake dried up, followed by wetter periods that would have deposited the overlying sandstones.”