Space

Green spots in rocks on Mars intrigue rover scientists

Green sets in rocks: A rock with roundish and oblong flat reddish spots with pink and fuzzy green borders.
View larger. | Enhanced color view of some of the green spots in rocks at Serpentine Rapids at Mars. The Perseverance rover took this image with its SHERLOC WATSON camera on August 15, 2024. The black dots are tiny holes made by a laser, which is part of SHERLOC. Image via NASA/ JPL-Caltech/ Thomas Thomopoulos. Used with permission.
  • A rover on Mars found some red rocks with green spots. The intriguing spots are dark in the middle with fuzzy green rims. The rocks are in the same ancient river valley where other unusual rocks were found.
  • The rocky green spots are similar to those seen on Earth. They might be formed by chemical reactions with water. The exact process isn’t known yet, but on Earth it sometimes involves microbes.
  • Mission scientists are on the lookout for similar rocks. So, what will the rover find next?

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Intriguing green spots in rocks on Mars

As NASA’s Perseverance rover has been making its way from the floor of Jezero crater up to its rim, it keeps finding unusual rocks. These include the leopard spots and zebra rocks. On October 25, 2024, NASA provided an update on some other intriguing rocks: distinctly red rocks with green spots. The rover found them at a location called Serpentine Rapids, within the ancient river valley Neretva Vallis. NASA said the spots were just under the surface of the rocks and are dark in the middle with fuzzy green rims. They likely formed when liquid water altered oxidized iron. On Earth, this process sometimes involves microbes. But what about Mars?

Green spots in rocks on Mars

Perseverance discovered the rocks at a location called Serpentine Rapids. It is within the ancient river valley called Neretva Vallis, which cuts through the rim of Jezero crater. The riverbed ends in a branching delta that is still clearly visible today. The rover came across the rocks about 20 sols (Martian days) after it finished studying the “leopard spots” rocks at Bright Angel, also in the river valley.

Most rocks on Mars appear reddish on their surfaces, due to oxidation and reddish dust – which is everywhere – coating them. But Perseverance spotted some rocks at Serpentine Rapids that were even more distinctly red in color. The rover used the abrading bit on its drill to create a small circular patch on one of the rocks, named Wallace Butte. This revealed what the rock looked like just under the surface. White, black and green colors could be seen.

Interestingly, the abrasion patch also showed something surprising: small roundish and oblong dark spots with fuzzy, green rims. What are they?

Evidence of past liquid water … and perhaps life?

The spots look similar to spots in red rocks on Earth. Scientists call those rocks red beds. The red color comes from oxidized iron, the same found in our blood or rusted metal. And, indeed, green spots are also often found in these rocks. They form when liquid water percolates through sediments. Later, those sediments harden into rock. Consequently, this causes a chemical reaction that changes the iron into a reduced form with a greenish hue.

There are various specific ways this can happen. First, sulfur and iron can interact to create the conditions for the reduced iron to occur. Or, decaying organic matter can also produce a similar result. And – at least on Earth – microbes can also help facilitate the process.

We don’t know which of these scenarios explains the Martian green spots. It is tempting, of course, to think the green color must be a sign of life, but it can occur through other chemical reactions as well.

Tan rock surface with oval dark pink spots surrounded by pink and green borders.
View larger. | A more natural color view of the spots from the top image, seen by Perseverance on August 15, 2024. Image via NASA/ JPL-Caltech.
Tan rocky surface with large circle etched into it and greenish and whitish spots and pebbles.
View larger. | Another view of some of the green spots. This is a nighttime image, with illumination from the rover. The diameter of the abrasion patch – the circular area – is 2 inches (5 centimeters). The large green spot in the upper left of the image is about 2 millimeters (0.08 inch) in diameter. Perseverance took this image on August 19, 2024. Image via NASA/ JPL-Caltech.

Looking for more red and green rocks

Unfortunately, Perseverance wasn’t able to conduct a more in-depth analysis of the spots. As NASA explained it, there wasn’t enough room to place the rover arm directly on top of the tiny spots. That arm contains the SHERLOC and PIXL instruments needed to do the analysis. The rover did zap them with its laser, however, which is part of SHERLOC. The laser looks for organic material and minerals altered by water.

So now the mission team is on the lookout for other similar rocks. The rover is ascending the steep wall of Jezero crater and will ultimately leave the crater. What will it find next?

Bottom line: NASA’s Perseverance rover has found some intriguing green spots in rocks on Mars. The spots are dark in the middle with fuzzy green rims. How did they form?

Via NASA

Read more: Ancient life on Mars? Rover finds intriguing ‘leopard spots’

Read more: A striped ‘zebra rock’ on Mars and a new Mars face

Posted 
November 6, 2024
 in 
Space

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