Source: Science News

In February, NASA’s Perseverance rover touched down on Mars and went to work. The rover has seen the first flight of a Martian robot, gotten its drill bit dirty and begun traversing the floor of Jezero crater, thought to be the remains of an ancient lake.

And what Perseverance is finding isn’t exactly what scientists expected. “The crater floor is super interesting,” says planetary scientist Briony Horgan of Purdue University in West Lafayette, Ind., one of the mission’s long-term science planners. “We didn’t really know what we were getting into from orbit.”

Perseverance is getting views of enormous boulders that may have been transported by ancient floods, fine rock layers that look like they settled in calm waters, and rocks with large crystals that look volcanic. The rover’s landing site may include a volcanic lava flow from long ago, or signs of an earlier episode of water — or something else.

“It’s not as obvious as we thought,” Horgan says. “Whatever it is, it’s cool.”

Here are some of the image highlights from the rover so far.

Taking the long view

Before the rover landed, the Perseverance team knew that Jezero crater looked like the dry basin of an ancient lake, with a river delta flowing into it. The prospect of finding preserved lake floor sediments made the site good for searching for past life, one of the mission’s primary goals.

Perseverance took this snapshot March 17 of a steep slope in a part of Jezero’s delta, from more than two kilometers away. The rover probably won’t reach that spot until sometime next year. But already, the rover’s Remote Microscopic Imager camera is uncovering details that could reveal new insight into the crater’s watery past.

For example, the tilted layers of sedimentary rock and cementlike mixtures of coarse sand and pebbles in this rock feature, nicknamed “Delta Scarp,” confirm the delta’s wet history. There are also individual large boulders cemented into the front of the scarp, suggesting that the region saw high floods, says Perseverance deputy project scientist Katie Stack Morgan of NASA’s Jet Propulsion Lab in Pasadena, Calif.

Closer to home

Even eroded outcrops close to Perseverance’s landing site look like they had a watery history. This image of a remnant of part of the delta rising out of the crater floor was taken with Perseverance’s Mastcam-Z camera February 22.

“Many of us expected these outcrops to be quite uninteresting, based on orbital data,” Stack Morgan says. But images from the ground showed beautiful layers, just like what you would find in a deep-lake deposit.

“We weren’t expecting to find them here, but maybe they’re right next door to our landing site,” she says. These outcrops could be remnants of the edge of the lake that used to fill Jezero crater or could represent an even older lake that was replaced.

Even closer

Perseverance is taking close-ups of the rocks around it too. This closeup image of a rock nicknamed “Foux” was taken July 11 using the WATSON camera on the end of the rover’s robotic arm. The area in the image is only about 4 centimeters by 3 centimeters.

The textures in this image are fascinating, as are the “crazy red coatings” that are more purple than typical Mars dust, Horgan says. “What rocks are these?” The coatings probably imply alteration by water, and the purple color suggests that they contain some iron, she adds.

Volcanic grains?

Perseverance has also found evidence of igneous, or volcanic, rocks on Jezero’s crater floor. That wasn’t surprising — observations from orbit suggested that volcanic rocks should be there, and scientists hoped to pick up some to help researchers back on Earth figure out the rocks’ absolute ages. Right now, the timing of past events on Mars is based on the sizes of craters and the ages of rocks from the moon, and it’s not extremely precise.

Igneous rocks on Mars tend to be old and preserve a record of their ages well. “If you want to figure out when things happened on Mars, you want an igneous rock,” Stack Morgan says.

On the ground, though, things are a little more complicated. This rock was the first that Perseverance cleared dust from in preparation for taking a sample. The image shows mysterious holes, which could have been formed by erosion or by air bubbles trapped in lava as it cooled. And the surface is divided into light and dark patches that could be individual crystals, or cemented grains.

If they’re crystals, that suggests volcanic activity, Stack Morgan says — but these crystals are bigger than expected for lava that would have cooled at the planet’s surface. Similar crystals form deep in the subsurface of Earth, where magma solidifies slowly. When lava cools at Earth’s surface, the crystals “don’t have time to grow big,” Stack Morgan says. The next step, she says, is “thinking through how rocks like this could have formed here, if they are indeed igneous or volcanic rocks. How would we get a rock that looks like this?” Maybe this rock formed underground and was transported to the surface, but it’s not clear how.

First sample attempt

That same rock carried more surprises when the rover team tried to drill into it August 6. The drill worked perfectly, to the team’s elation. “One of the most complex robotic systems ever designed and executed worked perfectly with no faults the first time,” Stack Morgan says. “We were like ‘Oh my god, this is amazing.’”

But when they looked inside the tube that was meant to capture the rock sample, it was empty.

“It’s been a bit of an emotional roller coaster,” Stack Morgan says.

The team thinks that the rock was more crumbly than expected, and essentially turned to dust. “The rock was not able to keep its act together,” Stack Morgan says. The drill is designed to sweep the small grains produced in the drilling process, called cuttings, up and out of the sample tube. Stack Morgan thinks the entire sample was treated as cuttings and ended up in a pile of dust on the ground.

There is a silver lining: Now the rover has a sealed sample of Martian atmosphere. And the rover will attempt to take another sample of a hardier rock sometime soon, Stack Morgan says.

In the wind

Mars may have had lakes and rivers in its past, but today the dry, dusty landscape is shaped mostly by wind. Perseverance has seen a number of dust devils and windstorms sweep through Jezero crater as a beautiful reminder of how environments are always changing, even on a dried-up planet like Mars.

“We often think of Mars as this barren wasteland where not much happens today,” Stack Morgan says. “But when you see these dust devils move across the images, you’re kind of reminded that Mars, even though not Earthlike, is its own very active planet still.”

Source: Science News