It’s easy to take it for granted, but we’re driving around on freakin’ Mars right now.
We’ve done this a few times before, sure, but it remains one of humankind’s most impressive technological feats. The latest rover to continue our presence on the red planet is Perseverance, the star of the Mars 2020 mission that launched in July of that year and landed in February of 2021.
It has now been busy roving for over two years. News of what we’re discovering—beyond the stream of photos—tends to come in discrete bits that can be hard to connect into a bigger picture if you aren’t following closely. Consider this your wide-angle recap.
Like other rovers, Perseverance is bristling with science instruments. It has cameras of multiple kinds used both for general imagery and spectral analysis that can identify minerals. That latter function is supplemented by an additional X-ray instrument. Perseverance also has a ground-penetrating radar instrument that can reveal layering hidden below the surface. More invasively, there is a drill on the end of the rover’s robotic arm. This is used to grind clean (what geologists call “fresh”) spots for analysis, but it can also core out small cylindrical rock samples—hopefully to be retrieved and returned to Earth by a future mission.
It’s not all about the rocks, though. Perseverance has a weather module tracking atmospheric conditions and airborne dust. And it has a friend—the Ingenuity helicopter has wildly exceeded its pilot-testing goal and is still flying in short hops to keep up with the rover.
This mission set down in Jezero Crater, which was chosen because rocks resembling a river delta are draped over its rim—indicating that flowing water might have met a lake here in the past. It’s the perfect environment to study the history of water on Mars and the possibility of life associated with it. There’s only so much science you can do from orbit. To untangle the forensic clues that remain here, you need to get down on the ground.
First stop: Crater
The first years on Mars were spent investigating the floor of Jezero Crater. The type of rock that would be found here was actually somewhat ambiguous from orbit. There was clearly some igneous rock, either from volcanic magma or a molten pool created by the meteorite impact that formed the crater. But some also expected to see sedimentary rock representing the bottom of a lake that called the crater home.
It turned out to just be igneous basalt under the blanket of wind-blown dust, and any lake-bottom sediments that existed here must have long since eroded away. You might think that’s disappointing—like the pharaoh’s tomb was already cleaned out by grave robbers—but this is actually one of the better looks we’ve gotten at Mars’ igneous bedrock. Missions have often targeted pockets of notable sedimentary rock, with only scattered bits of the much more common igneous rock on display.
The Martian meteorites we’ve found on Earth—chipped off the red planet during large impact events—have only given us literal fragments of the big picture. If we successfully return the eight rock samples collected from the crater floor, this opportunity to cruise around on intact igneous bedrock could answer a lot of questions raised by the meteorites.
In this case, the science team has divided the crater floor rocks they observed into two major layers. The upper one, called the Máaz formation, appears to have formed from lavas. Some portions exhibit a texture like the wrinkled (or “rope-like”) lavas we see in Hawaii. In other areas, the rock happens to stick up through the red dust as flat polygons resembling pavers in a garden, or as taller, boulder-sized blocks.
The lower Séítah formation is distinct in both texture and minerals. It stands out from its surroundings due to its thin layering and visible, closely packed crystals. And while the Máaz rocks contain lots of the mineral feldspar, Séítah’s rocks are dominated by olivine, instead.
This looks like what geologists call “cumulate”—the magmatic equivalent of the gritty dregs in your coffee cup. Because different minerals crystallize at different temperatures (yes, molten rock has a freezing point), minerals like olivine that crystallize early can settle to the bottom of a magma body and accumulate. On Earth, this pattern can be seen in magma chambers that cooled underground or in some sufficiently thick lavas.