A space rover discards its suit as it gets closer to the Red Planet

An illustration depicting Perseverance casting off its spacecraft's cruise stage just before entering the Martian atmosphere © NASA

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How to collect rocks on Mars

NASA's most sophisticated rover, Perseverance will be collecting rock samples from Jezero crater. This momentous occasion is one of many steps to finding life on Mars and understanding the early solar system.

On 6 August, Perseverance made its first attempt to collect a rock sample, except all did not go to plan. While the rover seemingly managed to take a rock sample, the tube in which it was meant to be deposited remains empty. 

Perseverance, landed on Mars on 18 February 2021 as part of the Mars 2020 mission.

Since then, the rover has been exploring the cold, barren landscape within Jezero Crater - a 45 kilometre wide basin found in the Martian northern hemisphere.

Around 3.5 billion years ago, a large river flowed into a lake in the crater, depositing sediments in a fan shape known as a delta.

Scientists think the ancient river delta and its deposits could have collected and preserved organic molecules and potentially, signs of fossilised microbial life.

Keyron Hickman-Lewis, a palaeontologist at the Museum is a member of the Science Team. He is also a Returned Sample Science Participating Scientists (RSS-PS), one of 15 people who inform and guide on the sampling procedures using images sent by Perseverance to ensure the best rocks are collected.

'We chose to land at Jezero crater as it reflects the most ancient part of Mars' history and once contained water,' says Keyron.

'We know that all life on Earth requires water to live and, because Mars hosted water in its distant past, there may also have been life on the planet at some time.

'As RSS-PS, we must ensure ideal samples are chosen because when they are returned to Earth, they will be very precious materials and should be able to answer a planet's worth of questions.'

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On the left, an image from the rover shows the hole from which the sample was taken, with the image on the right showing a close-up composite image of the first-ever borehole on Mars ©NASA/JPL-Caltech/MSSS  

The first-ever sampling attempt on Mars 

On Friday 6 August, Perseverance made its historic first sampling attempt.

The rover drilled down into the Martian rocks as over 90 scientists and engineers held their breath awaiting the data. At first, the information sent back to Earth confirmed that a sampled had been taken, as pictures showed a near perfectly hole bored into the planet's surface.

The rover confirmed that a sampling tube had been successfully sealed and transferred from the Corer to the storage component on the rover. But all was not as it seemed.

When the data for the weight of the sample arrived, it was clear that the sampling tube was empty.

What happened between Perseverance taking the sample and depositing it in the tube is still not known, but the scientists suspect that it might have something to do with the specific properties of the rock that was being sampled.

The science team have now regathered, and have decided to try again at the next scheduled sampling location where they expect the rock type to be more similar to that which the rover's technology was tested with on Earth. 

But how do they know which rocks to sample in the first place?

A black and white ariel view of the landing site on Mars

The green dot shows where Perseverance landed within Jezero crater on Mars on 18 February 2021. The image was taken by an orbiter previously ejected into space. © NASA. 

Choosing rock samples to bring back to Earth

Perseverance has transported 43 tubes to Mars, most of which will hold one rock sample. Each rock will be several centimetres long and about 1.5 centimetres across in diameter. They will include sedimentary and igneous rocks, including basalt, sandstone and mudstone.

'There are many fine-grained sedimentary rocks in the crater that have a high potential for preserving organic material and potentially fossils,' explains Keyron.

'Here on Earth, fine-grain sedimentary rocks are the place to search for organic material and fossils so hopefully, we can expect to find a similarly high degree of preservation in similar rocks on Mars.'

A few tubes will be used to collect Martian soil called regolith, while a couple will remain empty so scientists can understand the degree of ongoing contamination that may affect the collected samples. The amount of material returned should total around half a kilogramme.

Rocks that look like they have been altered since their formation are usually avoided. However, in this case, some may be collected as they can help scientists understand the alteration process in pristine samples.

Such alterations can be seen by major differences in colour of rocks or disruptions in their fabric. For example, a straight line going across the body of a carbonate rock probably did not occur during its formation, but tens of millions of years later.

Alteration in rocks is often identified by applying various image treatments to the photos sent back to Keyron and his colleagues by Perseverance. This process stretches the contrast between certain colours or chemistries of rocks and allows scientists to see finer details that are not obvious in the original images.

'We can see the rocks on the surface of Mars from satellite observations, but of course, we have a very different view from the surface,' explains Keyron. 'It's like comparing something you see on Google Earth against something you see on the street. You can see approximately where you are going but not to the scale of a few centimetres.

'As we approach these localities, we will start taking closer images of the probable sampling sites and begin focussed science discussions amongst team members in order to better understand the precise mechanics of the sampling.

'We must be certain where we take the samples, and ensure not only the best sample for that particular rock type but also the most appropriate sample within the context of the crater.' 

A rover roams the desert landscape of Mars

An illustration depicting Perseverance exploring Jezero crater. The Martian terrain consists of mountains, volcanoes, craters and dunes. © NASA.

What can Martian rocks tell us about Earth and the solar system?

Previous exploration of Mars has shown the conditions were similar to Earth about 3.5 billion years ago. At that time, Earth already hosted microbial life so it is possible Mars may have done so.

While Earth experienced many environmental changes, such as the movement of tectonic plates and weathering which has led to the alteration of many rocks, Mars' geology has remained relatively constant since its early history.

Martian rocks are some of the oldest and best-preserved rocks in the solar system that we can obtain.

'These samples can tell us much about the chemistry of the early solar system,' says Keyron. 'For example, we can find out the elemental compositions of Martian rocks at that time and compare them to the earliest rocks on Earth.

'They may also help us understand more about the magnetic field on Mars. The magnetic field on Earth is a big factor in sustaining the atmosphere, but Mars no longer has a magnetic field. There may, however, be a record of a previous magnetic field in the rocks we sample.'

Looking for the similarities and differences between rocks on Mars and Earth will help shed light on whether life on Earth is a unique phenomenon.

'I view Mars as an opportunity to explore that concept for Earth and the solar system more broadly,' explains Keyron. 'While we are using Earth as a tool to understand Mars, in the future we will hopefully have the opportunity to use Mars as a tool to understand the early Earth.'

Mars 2020 is an invaluable endeavour that can potentially offer us a wealth of information about early life on both Mars and Earth, as well as the solar system as a whole.

An ariel view of the Jezero Crater where the ancient river flowed into a lake

An image of the ancient delta taken by High Resolution Stereo Camera aboard the European Space Agency (ESA) Mars Express orbiter © ESA/SLR/FU-Berlin

The next steps for Mars 2020

Perseverance is expected to function for at least several years, storing samples it will collect during the mission in its body.

These samples will be cached at the surface of Mars where they will await a second rover, called Sample Fetch to make its way to Mars in the coming years. The sole aim of Sample Fetch is to collect the tubes deposited by Perseverance and help bring them back to Earth.

'Mars Sample Return is a challenging endeavour. It will involve multiple stages and be a real international collaboration,' Keyron adds.

The team responsible for the sample return mission is made up of scientists from all across the globe. These scientists have diverse scientific backgrounds and will bring a rich variety of knowledge and working styles.

In addition to collecting samples, Mars 2020 aims to learn about the climate and geology of Mars, and if all goes well, prepare for human exploration in the coming decades.