About the Mars Samples
Sample Caching
The Perseverance rover is collecting a set of samples of rock, soil, dust and atmosphere from Mars that will, for the first time, be brought back to Earth. Analysis of the samples in state-of-the-art laboratories will provide unprecedented scientific insights about Mars.
Perseverance carries 38 identical tubes that are designed to hold the samples. The process of collecting, storing and depositing samples on the martian surface is called ‘caching’.
Collecting and Storing Samples
The sample tubes are designed to contain small amounts of martian rock, soil, and atmosphere. Each sample tube is around 15 centimetres long and can hold up to 15 grams of martian material.
Perseverance uses a drill located in its robotic arm to cut cylindrical sections (cores) from the interior of rocks and place them directly into a sample tube. The drill can penetrate about 5 cm into the selected rock. For soil samples, a special drill-bit is used to collect the loose material and deposit it into a sample tube.
Once a sample has been collected, the rover’s cameras take images of the colour and texture of the sample itself and document the area from which it has been taken. Next, Perseverance caps the sample tube and creates an airtight (hermetic) seal. The tube is then placed in a storage rack located in the belly of the rover.
To avoid bringing any Earth contaminants to Mars, Perseverance was required to meet exceptionally high cleanliness standards before launch. Scientists also put measures in place to limit contamination of the martian samples by the rover itself. Alongside the sample tubes, Perseverance carries 5 ‘witness tubes’ that contain materials designed to detect any terrestrial material that may have arrived on Mars with the spacecraft, such as chemicals from the landing system, or gases released by materials on the rover.
Perseverance opens a witness tube and exposes its contents to the local environment at designated sample sites. The witness tubes are sealed like the sample tubes and will be returned to Earth. This will help scientists determine which materials in the samples may be of terrestrial origin.
Perseverance is collecting two sets of samples:
- One stays onboard the rover
- The other is deposited in a cache on the martian surface.
Perseverance will deliver the onboard set of sample tubes to the Sample Retrieval Lander in the next step of the Mars Sample Return campaign. If Perseverance cannot reach the lander, the cached samples will be collected by two Sample Recovery Helicopters.
Deep Dive: The Sample Tubes
The sample tubes will contain the first samples brought back to Earth from another planet.
Perseverance was sent to Mars with a total of 43 sample tubes stored in its belly. Of these, 38 tubes will hold samples of martian material collected by the rover. The other five are ‘witness tubes’ that Perseverance will use to check for contamination.
The sample tubes, made mostly from titanium, weigh around 57 grams and are 15 centimetres long. Each sample tube has been laser-etched with a unique serial number to help scientists identify the tubes, and samples they contain, upon their return to Earth.
The sample tubes need to be robust enough to protect the valuable samples during their multistage journey from Mars to Earth and clean enough to avoid contamination of the samples with terrestrial material.
The tubes were constructed in a ‘hyper-clean’ environment (essentially a cleanroom within a cleanroom). During their assembly, the tubes were cleaned with filtered air blasts, placed in ultrasonic baths with acetone and isopropyl alcohol, rinsed with deionised water, and heated to remove any Earth contaminants, including organic, inorganic or biological material.
These precautions mean that scientists can be sure that any detections of life in the samples genuinely relate to Mars and are not false indications resulting from terrestrial contamination.
The First Martian Depot
Three Forks was chosen as the location for the first martian depot. It is a flat terrain, with no large rocks, where vehicles can move around without risk of disturbing the cached sample tubes. Perseverance is depositing a set of sample tubes at the depot as a backup measure in case it is unable to deliver the samples it carries in its belly to the Sample Retrieval Lander.
On 21 December 2022, Perseverance deposited the first sample in the Three Forks cache. Over the following two months, 10 sample tubes were deposited, including:
- Seven rock cores (four from igneous rocks and three from sedimentary rocks)
- One tube containing martian soil (regolith)
- One tube containing martian atmosphere
- One witness sample.
Deep Dive into some of the Samples Collected by Perseverance
About the Samples Collected by Perseverance
Perseverance is collecting a diverse set of rocks, regolith, and atmospheric gases. The different sample types will give a range of insights into the geology and evolution of Mars. For example:
- Igneous rocks can be radiometrically dated in the laboratory to give the crystallisation age of the samples and provide exact timings for when the rocks formed on Mars.
- Sedimentary rocks contain sulphates, carbonates, organics, and clays that are good at preserving biosignatures of past life. These samples are crucial to return to Earth for analysis, as they may contain evidence that Mars was once habitable and contained life.
- The soil samples (regolith) collected by Perseverance will help scientists understand how the surface of Mars has been shaped over time. Regolith samples will also help inform the design of future missions and equipment that will operate on the martian surface.
Montagnac and its paired sample, Montdenier, were the first rock cores collected by Perseverance. The samples are igneous cores collected from the Artuby Ridge region of the crater floor. The Mars 2020 mission team only expected to see sedimentary rocks and lake sediments on the crater floor; instead, they found a diverse range of igneous rocks. The scientists have determined that two distinct geological formations are present at the sample site. The formations have been named ‘Máaz’ (after the Navajo name for Mars) and ‘Séítah’ (Navajo for ‘amidst the sands’). Máaz is thought to have formed through a series of lava flows and Séítah is thought to have been formed by a slow cooling melt or magma body. The samples were cored from a rock that displayed a pitted texture, suggesting that it had experienced extensive alteration from water. Montagnac, the larger sample, was kept onboard Perseverance and Montedenier was deposited in the Three Forks depot.
Salette
Salette and its paired sample, Coulette, are igneous cores collected from an outcrop called Brac in the South Séítah region of the crater floor. The samples are of particular interest as they contain sulfates – small white minerals that indicate water alteration – and also have a strong carbonate signal. Carbonates provide a record of a rock’s interaction with water and are indicators of habitable environments, since they form in pH neutral conditions. The samples also show signs of hydration, meaning they contain minerals, such as phosphates, that trap water into the rock’s structure. The samples will, thus, provide information on the aqueous history of Mars. Salette was kept onboard Perseverance and Coulette was deposited in the Three Forks depot.
Robine
Robine and its paired sample, Malay, are igneous cores collected from a rock named ‘Issole’ in the South Séítah region of the crater floor. The rock contains large sulfate crystals. Sulfates are evidence of alteration by water and, on Earth, are capable of preserving biosignatures. Astrobiologists are particularly excited by the opportunity analyse samples from Issole, as the rock had a strong organic signal. Organics are the building blocks of life and are also a sign of potential habitability. Robine was kept onboard Perseverance and Malay was deposited in the Three Forks depot.
Ha’ahóni
Ha’ahóni (meaning ‘perseverance’ in Navajo) and its paired sample, Atsá (meaning ‘eagle’ in Navajo), are igneous cores collected near the Perseverance landing site, ‘Octavia E. Butler’, in the crater floor. The samples were cored from a rock named ‘Sid’ in the Máaz formation. Sid is thought to be the most pristine igneous rock sampled by Perseverance to date, showing less evidence of alteration by liquid water than the other samples. Ha’ahóni was kept onboard Perseverance and Atsá was cached at Three Forks, as the latter experienced some delays between the drilling and sealing process.
Swift Run
Swift Run and its paired sample, Skyland, were the first sedimentary cores collected by Perseverance. The samples were collected from Skinner Ridge in the front of the delta, an ideal place to search for evidence of past life. On Earth, deltas provide multiple habitats, host a diverse range of life, and contain minerals that help preserve organics and biosignatures. The rock from which the samples were cored is richer in carbonates than the other samples collected. Carbonates provide evidence of water alteration and are a good indicator of habitability. Swift Run was chosen to remain onboard Perseverance and Skyland was deposited in the Three Forks depot.
Hazeltop
Hazeltop and its paired sample, Bearwallow, were collected from Wildcat Ridge in the delta front. The sedimentary cores are fine-grained mudstones that were deposited in an ancient lake. Fine-grained sediments are compact and are, therefore, better at protecting signs of past life from changes in the external environment. The Hazeltop core appears to include mineral veins and part of a ‘concretion’, a hard mass that forms when minerals precipitate in cracks in sedimentary rocks. Concretions are direct evidence of interaction with water. Hazeltop was kept onboard Perseverance and Bearwallow was deposited in the Three Forks depot.
Shuyak
Shuyak and its paired sample, Mageik, were collected from a rock named Amalik in the delta front. Amalik is a fine-grained rock that contains clay. On Earth, this type of rock is very good at preserving biosignatures and fossils. Scientists believe these cores have a particularly high chance of containing organic molecules and signs of past life. Shuyak was kept onboard Perseverance and Mageik was deposited at the Three Fork depot.
Kukaklek
Kukaklek is a sedimentary core collected from the Hidden Harbor feature in the delta front. The sample contains a lot of different textures and colours of sulfate minerals, indicating that it may have experienced interactions with water at several different times. Kukaklek is onboard Perseverance and has no pair sample.
Atmo Mountain
Atmo Mountain and its paired sample, Crosswind Lake, were the first regolith samples collected by Perseverance. Regolith is a mix of broken rock and dust found on the martian surface. The samples were collected at Observation Mountain in the delta front, from a ‘mega-ripple’ feature of wind-blown sand that is similar to sand dunes found on Earth. Studies of martian regolith on Earth will enhance our understanding of how the surface of Mars has been shaped over time and inform the design of future missions and equipment that will operate on the martian surface. Atmo Mountain was kept onboard Perseverance and Crosswind Lake was deposited in the Three Forks depot.
Melyn
Melyn was collected from an outcrop called Berea in the upper fan of the delta. The sedimentary core is the first sample collected from the river part of the ancient delta system, compared to the other samples that were taken from lake deposits at the delta front. It is a carbonate-rich rock. Melyn is onboard Perseverance and has no paired sample.
Otis Peak
Otis Peak was collected from Emerald Rock in the upper fan of the delta. It is the first sample of a conglomerate rock, which consists of pebbles cemented together. The pebbles were carried by the ancient river from a wide area beyond Jezero crater, so give insights into a region around the crater that Perseverance will not explore directly. Otis Peak is onboard Perseverance and has no paired sample.
Planetary Protection
Planetary Protection is a very important aspect of sample return missions that:
- Prevents terrestrial contamination of astrobiologically significant targets in our Solar System (like Mars)
- Protects the Earth from extra-terrestrial contamination.
For each stage of the mission, from sending Perseverance to collect the samples on the martian surface to their return to Earth, a safety-first approach has been developed to ensure the protection of the martian environment, the martian samples, and planet Earth.
ESA’s Earth Return Orbiter will land at the Utah Test and Training Range. The Earth Entry System, containing the Orbiting Sample, will be bagged and stored in a case. The landing site will then be sterilised using a chemical or heat to avoid any contamination brought from Mars to Earth. The case will be transported to a Sample Receiving Facility where characterisation of the samples can begin.
Sample Receiving & Sample Curation Facilities
The Mars Sample Return campaign is classified as ‘restricted’ due to the possibility that the returned samples will hold martian life.
Although there is a minimal chance that any of the samples will contain a living organism, they must be protected from terrestrial contamination, and the Earth’s biosphere must be protected from exposure to the samples until they are deemed safe. A dedicated Sample Receiving Facility will be constructed to provide a pristine and isolated environment for the returned samples. As the samples will land in Utah, it is likely that the initial Sample Receiving Facility will be set up in the US.
The Sample Receiving Facility will be built using similar designs and technologies to Biosafety Level 4 laboratories, which allow scientists to safely handle and store some of the world’s most hazardous biological agents.
The samples will be characterised and undergo rigours tests at the Sample Receiving Facility to determine if they pose any hazards. If the samples are deemed safe, they will be prepared, sterilised and packaged for distribution to the wider planetary science community, who will carry out the analysis.
To support the long-term storage of samples, a Sample Curation Facility will be set up. The Sample Curation Facility will oversee the handling, documentation, preparation, preservation, and allocation of the samples for research in the long-term.
Deep Dive into Planetary Protection and Sample Curation
Planetary Protection and Sample Curation
Missions have returned samples from the Moon (Apollo, Luna 24 and Chang’e-5), asteroids (e.g. OSIRIS-Rex, Hayabusa and Hayabusa 2), comets (e.g. Stardust), the solar wind (e.g. Genesis), and now plan to bring back samples from Mars and its moons (the Mars Sample Return campaign, Tianwen-3 and MMX).
Meeting planetary protection constraints is a legal obligation that has been agreed by all space agencies. The Committee on Space Research (COSPAR) has created a planetary protection policy that complies with the United Nations Outer Space Treaty. Sample return missions have the strictest planetary protection requirements. Depending on the origin of the returned samples, these missions can either be ‘unrestricted’ or ‘restricted’.
- Unrestricted missions have no special requirements as they contain samples that, based on scientific opinion, cannot contain life. These missions include sample return from bodies such as the Moon and asteroids.
- Restricted missions contain samples where the scientific community are unsure about the possibility of life, such as from Mars. These missions must follow specific restrictions on the containment of all hardware and samples.
Some curation facilities for samples collected from space already exist, such as the Astromaterials Acquisition and Curation Office at NASA’s Johnson Space Centre in the US and the Planetary Material Sample Curation Facility at the Japan Aerospace Exploration Agency (JAXA), Japan.
In 2015, the European Curation of Astromaterials Returned from Exploration of Space (EURO-CARES) project was established to outline the requirements for a European Sample Curation Facility for samples of material returned from asteroids, comets, the Moon, and Mars.
EURO-CARES focused on six key themes:
- Planetary Protection
- Curation of extra-terrestrial materials
- Infrastructure requirements
- Instruments and methods for sample handling, preparation, and analysis
- Analogue samples as proxies for extra-terrestrial materials
- Technologies for sample reception and transport
The recommendations of EURO-CARES fed into a roadmap and ongoing planning to develop a European Sample Curation Facility.
References
References:
Williams, N. R., Golombek, M. P., Do, S., Claef, F., Lethcoe, H., Cameron, M., Trussell, A., Brooks, C., Russo, F., Deahn, M., Morris, M., Hibbard, S., Heverly, M., Spencer, D., Fosse, E. and Maki, J. (2023). Mars Sample Return “Three Forks” Landing and Depot Site Selections. 54th Lunar and Planetary Science Conference, Abstract # 2618.
Maki, J. N., Farley, K., Stack, K., Calef, F., Williams, N., Bell, J. F., Herd, C. D. K., Wadhwa, M. and Brown, A. (2023). The Mars 2020 Three Forks Sample Depot. 54th Lunar and Planetary Science Conference, Abstract # 2875.
https://mars.nasa.gov/resources/27268/perseverances-three-forks-sample-depot-map/
https://www.nasa.gov/feature/jpl/nasa-s-perseverance-rover-shows-off-collection-of-mars-samples
https://www.jpl.nasa.gov/news/nasas-perseverance-rover-shows-off-collection-of-mars-samples
NASA’s Perseverance Rover Deposits First Sample on Mars Surface – NASA Mars Exploration
Mars Rock Samples – NASA Mars Exploration
References: Return to Earth
Sample Retrieval Lander – NASA Mars
Sample Recovery Helicopters – NASA Mars
Mars Ascent Vehicle – NASA Mars
Earth Return Orbiter – ESA – NASA Mars
https://www.jpl.nasa.gov/missions/mars-sample-return-msr
https://mars.nasa.gov/msr/#Sample-Retrieval
https://mars.nasa.gov/resources/26895/mars-sample-return-concept-illustration/
https://mars.nasa.gov/internal_resources/1305/
