After a few weeks of limited communication with ground controllers, NASA's Curiosity rover is back online and doing some science.

The rover has resumed its exploration of a Martian valley that hosts a rock-layer contact zone. The contact zone, where two types of bedrock abut each other, is located near Marias Pass on Mount Sharp.

Curiosity discovered the contact zone while exploring the geological features of Mount Sharp. The zone features contact between a paler mudstone and a darker, fine-grained sandstone. The rover has also identified an intermediary layer of sandstone made up of a variety of grain sizes and colors.

Rock layers and their transitions can tell scientists a lot about the terrain's geological history and evolution. Contact zones typically mark changes in the environmental conditions that produced each layer of bedrock.

"This site has exactly what we were looking for, and perhaps something extra," Ashwin Vasavada, Curiosity project scientist at NASA's Jet Propulsion Laboratory, said in a press release. "Right at the contact between the Pahrump-like mudstone and the Stimson sandstone, there appears to be a thin band of coarser-grained rock that's different from either of them."

The transition layer features a diversity of rock samples which may explain the transition from sandstone to mudstone.

"The roundedness of some of the grains suggests they traveled long distances, but others are angular, perhaps meaning that they came from close by," Vasavada said. "Some grains are dark, others much lighter, which indicates that their composition varies. The grains are more diverse than in other sandstone we've examined with Curiosity."

After a period of limited communication, researchers plan to keep Curiosity busy at Marias Pass for the next couple weeks. The rover and its managers weren't able to speak to each other for most of June as Mars passed almost directly behind the sun, limiting radio wave contact. It's a phenomenon that happens every 26 months.