A geological postcard from Australia to Mars on NASA Perseverance
Associate Professor Patrice Rey has sent a chert rock from the Pilbara to Mars via NASA. Photo: Chris Angwin
On 19 February at 7.55am, Sydney time, NASA is scheduled to land the Perseverance rover on Mars. A little-known fact is that a piece of the Australian continent is part of this mission to the Red Planet.
NASA’s Mission to Mars 2020 targets the Jezero crater on the western edge of the Isidi Basin at latitude 18º38’ north of the Martian equator. Jezero is a crater of Noachian age (4.1 to 3.7 billion years ago) of about 50 kilometres in diameter.
In the Late Noachian to Early Hesperian (3.7 to 3.0 billion years ago), this crater hosted a lake in which water-borne sediments eroded from the basaltic crust were deposited, before being blanketed by volcanic activity around 3.5 billion years ago.
This environment is considered to be a geological analogue to conditions on Earth 4.0 to 3.5 billion years ago, when microbial life was taking hold on our planet. Whether or not life was also emerging on Mars at the same time is the focus of Mission to Mars 2020, building on the legacy of the 2003-2018 Mars Opportunity mission.
Perseverance is carrying seven miniature laboratories and the drone Ingenuity. The aim of this remote sensing facility is to scan, probe and analyse the surface and sub-surface of the red planet, to search for life-related organic compounds, and to prepare rock samples that will be brought back to Earth in a future mission.
Where is the Pilbara rock hidden?
Arrow points to the Pilbara chert in the SuperCam device that is onboard Perseverance.
SuperCam is one of the seven miniature laboratories attached to Perseverance. It is a remote sensing multi-instrument device able to analyse tiny samples within a distance of up to seven metres from the rover. SuperCam relies on a powerful laser to blast tiny spots of rocks and analyse the ejected cloud of dust to map its mineralogy and search for organic molecules.
SuperCam is the product of an International collaboration involving research and engineers from the University of Lyon, University of Toulouse, University of Valladolid and NASA.
Key to the accuracy and precision of these analyses is a periodic calibration of the SuperCam’s instruments on a set of known targets attached to it. One of these 22 calibration targets is a tiny piece of the Australian continent, a fine-grained sedimentary rock called chert, a rock commonly found in formations from about 2.5 to 4 billion years ago.
Where does it come from?
Dr Claire Mallard (left) and Professor Nicolas Coltice at the site where the chert was excavated in the Pilbara. Photo: Patrice Rey
In 2015, Associate Professor Patrice Rey (School of Geosciences, University of Sydney), Professor Nicolas Coltice (ENS Paris) and then PhD candidate Claire Mallard (now post-doctoral researcher at ARC-ITRH Basin Genesis Hub, University of Sydney) went on a field expedition to the Pilbara in Western Australia on the traditional land of the Nyamal people, in search of the perfect sample for the Mars 2020 mission.
Together, they carefully removed from its place of origin the sample of red chert which is now about to land on Mars. The outcrop, conveniently located near the Iron Clad pub in Marble Bar, is a well-known geological site where travellers and scientists alike are welcome to collect chert specimens.
What is the sample's significance?
In 2003, this site was selected as one of the four drill holes of the Archean Biosphere Drilling Project (ABDP), an International project involving researchers from Australia, Japan, France and the USA searching for ancient life on Earth. This colourful outcrop is part of the Marble Bar Chert Member, a rock formation that was deposited in a deep undersea fan, the oldest documented deep-sea fan on Earth (Olivier et al., 2012).
The Marble Bar Chert (MBC) sits at the top of the volcaniclastic Duffer Formation whose uppermost volcanic unit is dated at 3.459 billion years ago. The Marble Bar Chert is itself overlain by the Apex basalt underneath the 3.449-billion-year-old Panorama Formation. Hence, the age of the Marble Bar Chert is constrained between 3.459 and 3.449 billion years ago, which fits well with the estimated age of the rock formations where Perseverance will land this week.
The very low uranium concentration of the Marble Bar Chert, as well as the presence of grains of pyrite, points to an oxygen-free environment of deposition. However, the red cherts of the MBC contain a few percent of hematite, an oxidised form of iron oxide, which suggests that some oxygen was already available 3.46 billion years ago.
There is debate on origin of the hematite and its significance for the oxygenation of the Earth. This hematite could have formed in-situ in a deep oxygenated body of water. Alternatively, it could have been formed in shallow pools where oxygen-producing cyanobacteria where thriving, before being transported into deeper oxygen-free water.
Lastly, it could have formed well after the deposition of the chert via the oxidation of much older ferrous oxide. Regardless of the solution to this debate, the Australian sample used to calibrate SuperCam holds the secret of an ancient geological environment that was common to both Earth and Mars 3.5 billion years ago.
Mission to Mars 2020 will eventually bring back to Earth rock specimens from Mars. In the meantime, a remarkable piece of Australia will now play its role discovering whether there has been life on Mars.
Authors: Patrice Rey, Nicolas Coltice, Claire Mallard