Although the Perseverance rover has only been on the planet for 10 months, it has already made an unexpected finding. The rover's latest discovery shows that the bedrock it has been driving over since landing was previously formed by volcanic lava flows, which mission scientists describe as "completely unexpected." They previously assumed the layered rocks seen by Perseverance were sedimentary.
Perseverance's rocks have also indicated that they had interacted with water several times, and that some of them contain organic molecules. These findings could aid scientists in constructing a precise timeframe for events that occurred in Jezero Crater, the site of an ancient lake, and have broader implications for our understanding of Mars.
The discovery was presented at the American Geophysical Union's Fall Meeting in New Orleans on Wednesday.
In February, Perseverance dropped into Jezero Crater. This deep depression was picked as the destination because satellite images revealed the presence of a delta - a structure formed by the silt and sand dumped by a river as it enters a larger body of water, such as a lake.
It's the kind of geological formation that could hold evidence of past microbial life on Mars billions of years ago. The rover did not land on the delta proper, but rather on the surrounding topography, on the crater floor. The robot has discovered its baseline rocks here.
Perseverance was ordered to investigate two large areas, one termed "Fractured Rough" and the other "Séítah" (meaning "amidst the sand" in the Navajo language).
The scientists' first impression of the latter was that its rocks were sedimentary in nature, meaning that they were formed by the compacted accumulation of mineral particles deposited in water or by the wind. The visible layering just added to this impression.
When Perseverance began drilling into Séítah and investigating its geochemistry in detail, the mission team was taken aback. Many olivine crystals were consumed and surrounded by the mineral pyroxene, as per instruments.
According to Kelsey Moore of the California Institute of Technology, geologists characterize Perseverance's vision as a cumulate texture.
"And the reason that that's important is that a cumulate texture is very indicative of a specific type of igneous rock that forms as a very thick magma body is cooling, and the olivine crystals crystallize and sink, and then the pyroxene forms around those olivine crystals," she explained.
Perseverance's rock fragments drilled in Séítah and the Fractured Rough will also be returned to Earth in the near future. Their ages will be determined by examining their radioactive content.
