NASA is investigating mysterious stick figures on Mars that the Curiosity Rover stumbled across while working through the holidays.

The rover transmitted images back to Earth of what look like squiggles left on top of a rock formation, where sand is dusted around. The space agency is looking into how they got there.

“Meanwhile, back on Mars … I’m checking out these stick-like figures,” the rover’s Twitter account wrote Jan. 3. “Maybe they’re crystals? Or they could be minerals that filled spaces where crystals dissolved away. Stay tuned! Science continues.”

Each stick was described as being about a quarter of an inch.

NASA also gave more context to the closeup image when it posted a wider shot of the area.

It was one of several shots the rover took of the area and transmitted back to Earth.

Curiosity arrived on Mars in 2012. It is on a mission from NASA to explore whether Earth’s neighbor has ever been habitable. The rover looks for signs that the planet’s environment could have previously supported alien life — specifically microbes, some of the smallest life forms.

Seeing as Mars is an alien planet, this is not the first time the rover has come across odd features on the Martian landscape. Just last month NASA shared a photo of strange rock formations that looked like cannonballs. The space agency, which has seen these tiny formations on Mars for several years, has dubbed them “blueberries.”

The camera on the Mars Reconnaissance Orbiter that NASA has zipping around the planet has also gotten in on the action. That orbiting camera previously captured what looks like scratches from nails digging into the landscape. The streaks come from chunks of dry ice that formed in the cold but then, when Mars quickly heated up, transformed directly from a solid into a gas and went sliding down sloped terrain, carving the scratches into the ground as they went.

The process by which a material changes from a solid into a gas, skipping the liquid phase of matter, is called sublimation.

mars-russell-crater-dry-ice Dry ice flowed down this sand slope on Mars, leaving behind channels that look like scratch marks. Photo: NASA/JPL-Caltech/Univ. of Arizona