Silica is a crystalline structure made of silicon and oxygen that can be found in quartz, glass and sand. Hydrated silica holds water within its crystal structure. On Earth, hydrated silica can form in a variety of environments, like in volcanic glass and on the ocean floor.

The oldest evidence definitive evidence of microfossils that we have on Earth are usually found in silica, said Jesse Tarnas, a planetary scientist at Brown University and one of the authors of the paper.

The researchers found evidence for hydrated silica in Jezero Crater when data from the Mars Reconnaissance Orbiter spacecraft matched up with similar measurements taken of hydrated silica in the lab. Once the rover lands in 2021, scientists will be able to study the minerals up close and figure out how they formed and whether they might contain signs of past life.

Jezero Crater was once home to rivers that carved a delta into the planets surface. Its possible that the hydrated silica formed in these deltas, Tarnas said. Other possibilities are that it formed in volcanoes or rocks upriver, and that wind or water carried it into the delta. Some of these scenarios are more promising for preserving signs of life than others.

The Mars 2020 rover is scheduled to launch in July 2020 and land on Mars in February 2021. Once its there, the rover's instruments can carefully analyze the chemistry of the hydrated silica and surrounding rocks. These observations will let scientists figure out how the hydrated silica formed and if they contain complex organic molecules.

If the rovers on-site analysis looks promising, it can pack samples that a future Mars mission could try to bring back. Scientists would likely need to study the samples in person, Tarnas said, to confirm or deny whether they contain signs of life.

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Mars 2020's landing site could be a good place to hunt for fossils - Astronomy Magazine