Every now and then, one of the robots on Mars sends back a picture of an unusual rock it has found on its journeys. After all, that’s one of the reasons we sent them there.
These can range from the interesting (such as the donut-shaped rock which may not be from the planet) to the silly (hello, avocado rock. What’s up, big pile of “bones” on Mars?). NASA’s Perseverance rover is on a particularly good streak of finding the interesting kind of rocks as it slowly climbs the Jezero Crater rim. Fresh from finding an unusual “zebra” rock, it has now found mysterious green spots on the particularly red rocks of the “Serpentine Rapids” in the Neretva Vallis region of Mars.
The rover is equipped with a percussive drill which can be used to abrade rocks for further analysis, and created a small smooth surface about 5 centimeters (2 inches) in diameter.
“The newly drilled abrasion is full of cuttings – the dust generated by drilling. The cuttings hide what the scientists are interested in seeing: the color and shape of individual grains in the abrasion. Perseverance removes the cuttings using another tool on the turret called the Gaseous Dust Removal Tool (GDRT),” NASA explains. “The GDRT has a tank of nitrogen gas and uses four short puffs to blow the cuttings away and reveal the fresh rock surface underneath.”
Within the red rock at Serpentine Rapids, Perseverance found unusual patches of dark and drab green, which drew NASA’s attention.
“Green spots like those observed in the Wallace Butte abrasion are common in ancient ‘red beds’ on Earth and form when liquid water percolates through the sediment before it hardens to rock, kicking off a chemical reaction that transforms oxidized iron to its reduced (Fe2+) form, resulting in a greenish hue,” NASA explained in a statement. “On Earth, microbes are sometimes involved in this iron reduction reaction. However, green spots can also result from decaying organic matter that creates localized reducing conditions. Interactions between sulfur and iron can also create iron-reducing conditions without the involvement of microbial life.”
Unfortunately, Perseverance was unable to get a closer look at these green spots as there wasn’t enough room to maneuver its instruments into position. Nevertheless, there will likely be other interesting rocks to find as the plucky rover heads up the rim of the crater which has been its home for the past two years.
