It’s easy to take this for granted, but we’re riding on fucking Mars right now.
We’ve done it many times before, of course, but it remains one of humanity’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 launched in July of the same year and landed in February 2021.
He has been on the move for over two years now. News of what we discover – beyond the photo stream – tends to come in discrete fragments that can be difficult to connect to the bigger picture if you don’t follow closely. Consider this your wide-angle recap.
Like other rovers, Perseverance is packed with scientific instruments. It has cameras of several types used for both general imaging and spectral analysis to identify minerals. This latter function is complemented by an additional X-ray instrument. Perseverance also has a ground-penetrating radar instrument that can reveal hidden layers beneath the surface. More invasively, there is a drill at the end of the rover’s robotic arm. This is used to grind clean (what geologists call “fresh”) points for analysis, but it can also extract small cylindrical rock samples, which, if all goes well, will be collected and returned to Earth by a future mission.
But it’s not just about rocks. Perseverance has a weather module that tracks atmospheric conditions and airborne dust. And he has a friend: the Ingenuity helicopter has far exceeded its pilot test goal and continues to fly in short hops to follow the rover.
This mission took place in Jezero Crater, which was chosen because rocks resembling a river delta are draped over its rim, indicating that flowing water may have encountered a lake here in the past. It is the ideal environment to study the history of water on Mars and the associated possibility of life. There’s only so much science you can do from orbit. To unravel the forensic clues that remain here, you need to get down on the ground.
First stop: Crater
The first years on Mars were devoted to studying the bottom of Jezero crater. The type of rock that would be found here was actually somewhat ambiguous when viewed from orbit. There was clearly igneous rock, either from volcanic magma or from a molten pool created by the meteorite impact that formed the crater. But some also expected to see sedimentary rocks representing the bottom of a lake that inhabited the crater.
It turned out to be just igneous basalt under the blanket of wind-blown dust, and any lake bottom sediments that existed here must have long ago eroded away. You might think this is disappointing – as if the pharaoh’s tomb had already been cleared by grave robbers – but it’s actually one of the best glimpses we’ve had of Mars’ igneous bedrock. Missions have often targeted pockets of notable sedimentary rocks, with only scattered fragments of much more common igneous rocks exposed.
The Martian meteorites we found on Earth – flaked off the Red Planet during major impacts – have only given us literal fragments of the bigger picture. If we succeed in returning the eight rock samples collected from the crater floor, this opportunity to navigate intact igneous bedrock could answer many of the questions raised by meteorites.
In this case, the scientific team divided the observed crater floor rocks into two main layers. The upper formation, called the Máaz formation, appears to have formed from lavas. Some portions have a texture similar to the wrinkled (or “rope-like”) lavas we see in Hawaii. In other areas, the rock stands out through the red dust as flat polygons resembling cobblestones 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 environment by its thin layer and its visible, tight crystals. And while the Máaz rocks contain a large portion of the mineral feldspar, the Séítah rocks are more dominated by olivine.
This looks like what geologists call “cumulative,” the magmatic equivalent of the grainy dregs in your cup of coffee. Since 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 observed in magma chambers cooled underground or in some sufficiently thick lavas.
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