“It could be a lot of things, but without some chemical information to back me up, I’d really hesitate to say what it is,” Aileen Yingst, of the Planetary Science Institute in Tucson, Ariz., told reporters today (Jan. 15).

“I’m not trying to be cagey,” added Yingst, the deputy principal investigator for Curiosity’s Mars Hand Lens Imager, or MAHLI. “I’m just trying to be clear that a light grain could be a lot of different things.”