The Perseverance rover has uncovered a compelling red rock on Mars that contains blobs of green, hinting at the stone’s composition.
The “enigmatic” rock, as NASA described it in a press release, could not be interrogated to the fullest due to the rover’s instruments not having enough room to work in. But the features do hint at how they formed on an ancient, wetter Mars.
Perseverance arrived on Mars in February 2021 with a fundamental goal: investigate a dried-up river delta on the edge of a multi-billion-year-old lake for signs of ancient microbial life. Mars is the only world in our solar system where space agencies have active landers driving around the planet’s surface, imaging and digging up evidence of its ancient past.
Though Mars has much more extreme temperature fluctuations than our planet, and is much more arid, scientists believe it had large lakes of liquid water on its surface billions of years ago. One of those lakes was in Jezero Crater, in which Perseverance landed three years ago.
Since then, Perseverance has trekked across Jezero’s western edge, imaging the planet and scooping up rock cores and some Martian atmosphere that will eventually be shipped to Earth, pending a lot of funding—and even more determination.
The basic idea behind Perseverance’s astrobiological search is that, if life existed on Mars, it would’ve looked like some of the earliest life on Earth: microbes that eked out existence in shallow water. These microbes form sedimentary concretions—layers of rock—as they go about their lives, which then fossilize in warped, Sol Lewitt-like patterns. Those rock fossils are called stromatolites, and they still form on Earth today. Earlier this year, a team of researchers identified the oldest fossilized photosynthetic structures yet, in 1.75-billion-year-old rock in northern Australia—the same neck of the woods where even-more-ancient stromatolites form.
In July, Perseverance found “leopard spots” on Mars in bands of hematite and calcium sulfate, which NASA scientists believe could indicate that the rock was once mud containing organic compounds.
Now, Perseverance has investigated another compelling target: the red rock with green spots. Hardly a smoking-gun for alien life, the stone nevertheless provides a window into Mars’ ironic irony iron-rich past.
The rock’s redness is likely due to oxidized iron, but the Perseverance team wanted to take a closer look. The rover cut a 2-inch-wide (5-centimeter-wide) circular chunk of the rock’s surface using an abrading tool to see the stone underneath, which has not been eroded or otherwise changed by the windswept conditions on the Martian surface.
The green spots in the rock are “relatively common,” according to the NASA release. They occur when water permeates the iron-rich sediment before it turns into rock, oxidizing the metal and turning it green. On Earth, microbes can catalyze that reaction, though it can also happen due to decaying organic matter or interactions between sulfur and iron. Whatever the cause, studying the rock would yield information about Mars’ watery past, potential life on the planet, or how the planet evolved.
Given the possibilities, the green-splotched deposit warranted further investigation. But there wasn’t enough space around the rock sample for Perseverance to unfurl its instruments, so the rock’s composition couldn’t be studied in greater detail.
Hopefully there are more rocks bearing similar features in Perseverance’s near-future. The rover is currently making its way up the rim of Jezero Crater, climbing out of its Martian cradle towards some loftier understanding of our arid next-door neighbor.
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