And on this memorable day, NASA looks back with satisfaction on the exploration of the ancient river delta, where Perseverance collected dozens of valuable samples along the way.

It is February 18, 2021 when Mars rover Perseverance puts its wheels on the Martian surface for the first time. And since then, the advanced Mars rover has been tirelessly exploring the Jezero crater, with the main goal of discovering evidence of life from a bygone era. But today it is time – literally and figuratively – to stand still. Because Perseverance has already completed 1,000 ‘sols’ on the red planet: an impressive milestone.

A day on Mars, also called a ‘sol’, lasts about 24 hours, 39 minutes and 35 seconds on Earth. This is only a little longer than one day on Earth.

As the Perseverance rover celebrated its 1,000th day on the red planet, it recently completed its exploration of the ancient Jezero River Delta. This delta contains evidence of a lake that filled the crater billions of years ago.

Crater lake
“We decided to choose Jezero Crater as our landing site because images showed it was once filled with water,” said team member Ken Farley. “A lake provides potentially habitable conditions and the delta’s rocks provide an ideal environment for burying evidence of past life, such as fossils. After careful exploration, we have carefully mapped the geological history of the crater, following step by step the different phases of the lake and river, from the very beginning to the end.”

Geological history
The Jezero crater was formed almost four billion years ago by the impact of an asteroid. After Perseverance landed in February 2021, the mission team discovered that the crater floor is composed mainly of igneous rock, created either underground or by volcanic activity on the surface. Later they also discovered sandstone and mudstone, indicating that a river formed several hundred million years after the crater formed. Above these rocks are mudstones with a high salinity, indicating that there was once a shallow lake that slowly evaporated. The team suspects that this lake eventually reached a diameter of up to 35 kilometers and a depth of up to 30 meters. Later, fast-flowing water brought boulders from outside Jezero and scattered them across the delta and other parts of the crater.

Thanks to Perseverance
The fact that we now understand this is largely due to the work of Perseverance, which has been exploring the crater in recent years. “While orbital imagery gave us a general idea of ​​Jezero’s history, getting up close with Perseverance was essential to understand the timeline in detail,” said team member Libby Ives.

Additionally, the advantage of having a roving rover is that Perseverance could collect samples on the spot. To date, the six-wheeled cart has collected 23 samples. To determine which samples to collect, Perseverance first uses a grinder to grind away a piece of rock. It then studies the chemical composition of the rock with precise instruments, including one developed by JPL Planetary Instrument for X-ray Lithochemistry (or PIXL). In this way, Perseverance managed to learn a lot about Mars.

Lefroy Bay
For example, a sample called ‘Lefroy Bay’ contains a lot of fine-grained silica, a substance known on Earth for preserving ancient fossils. “On Earth, this type of fine-grained silica is often found in places that used to be sandy,” says PIXL deputy principal investigator Morgan Cable. “This is a place on Earth where remains of ancient life forms could be preserved and later discovered.” This sample was collected at a spot the researchers call Bills Bay. This site was found to contain carbonates, minerals that form in watery environments and provide favorable conditions for the preservation of organic molecules (organic molecules are formed by both geological and biological processes). The rocks here also contain abundant amounts of silica, a material that is extremely good at preserving organic molecules, including those related to life.

Otis Peak
In contrast, another sample collected, ‘Otis Peak’, contains significantly high levels of phosphate, which is often associated with life as we know it. Phosphate is a building block of DNA and cell membranes in all known life forms on Earth. It is also part of a molecule that helps cells carry energy. The sample was collected at a spot the researchers call “Ouzel Falls.” Here PIXL found iron in combination with phosphate. Both Otis Peak and Lefroy Bay also consist of carbonate, which may contain information about the conditions in which the rocks formed.

Mars Sample Return-missie
The samples Perseverance collects are about the size of a piece of school chalk and are stored in special metal tubes. These tubes are part of the Mars Sample Return mission. Bringing these tubes back to Earth would allow scientists to examine the samples with powerful laboratory equipment too large to send to Mars. read here more about the ambitious Mars Sample Return mission.

Perseverance’s instruments can detect very small, fossil-like structures as well as chemical changes that may have been left behind by ancient microbes. So far, however, the mission team has found no evidence of either. Still, the researchers remain hopeful. “We have a good chance of finding signs of ancient life where we see carbonates and phosphates, which indicate a wetland and habitable environment,” Cable says. “The silica contained can also help preserve organic molecules.”

So Perseverance’s work is still far from finished after 1000 Martian days. During the fourth science phase of the mission, the Mars rover will explore the area on the rim of the Jezero crater, near the entrance to the gorge where a river once flooded the crater floor. Many carbonate deposits have been seen along the edge, which in photos from space look like a ring in a bathtub. In short, there is still plenty to discover about our still mysterious neighboring planet!

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