New science planning for martian samples for return to Earth has been published in the October edition of the Astrobiology journal.

By ESA planetary scientist Elliot Sefton-Nash

Four papers are the result of several years of work by NASA-ESA teams set up to study how to return samples collected by the Perseverance rover at Jezero crater.

A measurement definition team was formed in 2023 to describe the measurements that would be done in a Sample Receiving Facility – the Earth-based lab to which the sealed Mars samples would be first transported after landing on Earth.

Martian inventory

Their task was first to elaborate on what measurements are needed to achieve the scientific objectives of Mars Sample Return. Then, they worked together with experts on planetary protection and curation to come up with a master plan that combines the science measurements with all the other steps would be needed to properly handle the samples.

A martian horizon. Credits: ESA/A. Brancaccio

The plan needed to account for how to document the samples, firstly when they arrive at the facility in sealed tubes, and after the tubes are opened and the material from Mars is extracted. These first basic characterisation steps would help generate the sample catalogue, a detailed inventory to keep track of exactly what has been returned from Mars.

Pristine samples

The samples that have been collected at Jezero crater hold enormous scientific value, but they are expected to be biologically benign. The rules regarding planetary protection are set by the Committee on Space Research (COSPAR) and are strictly followed by ESA and NASA. The rules require that for places where there is evidence of past or present habitability, returned samples must be kept in containment until it is confirmed that they pose no risk to Earth’s biosphere.

Organic molecules, such as those containing carbon and hydrogen, or carbon and carbon, bonded together, form easily in the Universe, and they occur naturally on planets, comets and asteroids, even without the presence of life.

Artistic impression of a scientist processing martian samples in a laboratory on Earth. Credits: ESA/A. Brancaccio

This was shown spectacularly in results from the Rosetta mission, where ingredients for life were found in comet Churyumov-Gerasimenko (67/P). Knowing what organic background to expect in the samples from Mars, and how to measure it, is therefore essential to test for the presence of molecules formed by life that might be above this background level.

To do this, a team was set up to work on a Sample Safety Assessment Protocol (SSAP). Their findings about the organic background that is not due to life, also called abiotic, and how to measure it in samples returned from Mars are also published in this body of work, as an essential element of planning for the Sample Receiving Facility.

Protect me from what I want

The final piece of this puzzle on how to handle returned samples from Mars is about how to keep them safe… from us!  The scientific information in a sample returned to Earth from elsewhere in the Solar System is best preserved when the sample stays pristine, in other words, when it is not contaminated by Earth’s chemistry.

This applies especially because life on Earth is abundant and could produce false positives of life detection in returned samples. When working with samples in a lab, we need to take special care to protect the samples from our own biology to retain the chance to answer questions about life and habitability on Mars.

Artistic impression of a scientist using remote sensing tools to process martian samples. Credits: ESA/A. Brancaccio

This ‘contamination control’ is also relevant for science questions that are not about the search for life. Some measurements that are planned on Mars samples rely on trace amounts of certain elements, but metals or plastics in lab equipment could very easily drown the real signal in the samples.

Carefully designed lab-setups and sample handling procedures can help keep the samples clean and maximise the science we can do with them.

Work by another team in the effort, the Sample Contamination Panel, proposes ways to carefully deal with this.

Perseverance paving the way

The final paper in this issue of Astrobiology maps the science objectives of Mars Sample Return to the individual samples that have been collected by Perseverance.

The sample collection has great scientific potential because it is diverse, and allows us to address a broad range of outstanding science questions about Mars; from its planet-wide evolution and habitability over billions of years up to the specifics of processes happening today on its surface and  atmosphere.

Crucially,  this mapping of science objectives to samples allows to plan the specific set of measurements that would be prioritised to be done on each sample in the receiving facility.

Phew!

These studies are an essential and important step forward, paving the way for the next level of even more detailed planning to get the best possible science out of the precious samples.