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Introduction to Planetary Protection
Introduction to Planetary Protection

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4.1.3 Mars sample return

While most of the focus around planetary protection has been on the risks to Mars from terrestrial contamination, missions that might return to Earth from Mars carrying martian materials are already planned. Samples of rocks and soils are being collected by NASA’s Perseverance rover [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] (currently on Mars), stored there, and will be returned to Earth by a future mission, sometime in the 2030s. A sample return mission from Mars would be categorised as Category V ‘Restricted Earth return’.

To prepare for this eventuality, much effort has been put into understanding the harsh martian environment and its potential effect on life and its proliferation. In addition, to reduce the risk to Earth’s biosphere, the samples brought back to Earth would be stored, curated and analysed in a special facility (a Sample Receiving Facility), preventing any material from entering the outside world until it was proven to be safe. In Video 10, the rationale behind such a facility is explained and Figure 27 shows one proposed process by which samples returned from Mars would be delivered through the Earth’s atmosphere to the sample receiving facility.

Download this video clip.Video player: Video 10 Dr Francis McCubbin explains the importance of sample return planetary protection
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Transcript: Video 10 Dr Francis McCubbin explains the importance of sample return planetary protection

Francis Mccubbin
So we need to be able to protect the samples from us and also us from the samples
These samples are precious, They're not contaminated, and we need to do everything we can to make sure they stay uncontaminated, as pristine as the day that they're returned, so that we can continue to use them as a scientific resource.
End transcript: Video 10 Dr Francis McCubbin explains the importance of sample return planetary protection
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Video 10 Dr Francis McCubbin explains the importance of sample return planetary protection
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Figure 27 A proposed process for safely recovering, containing, and transporting Mars samples gathered by NASA's Perseverance Mars rover.
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A multi-part diagram entitled Recovery and containment: Mars rock core samples. It is divided horizontally into two halves. The top half shows the first four steps: 1. bag enclosure, 2. case enclosure; 3 transport to staging; 4 vault enclosure. The bottom half shows the final step, Sample receiving facility.

  1. Bag enclosure reads: Earth entry system (EES) containing orbiting sample (OS) lands in Utah mud flats. EES is bagged. A schematic of a cone-shaped spacecraft with a cylinder in the centre. A downward arrows shows that this is put into a bag.
  2. Case enclosure reads: Bagged EES is stored in case. Landing site cleaned using heat and/or chemical sterilisation. A schematic shows the silhouette of two people in protective clothing spraying something onto the bag, which is now contained in a case.
  3. Transport to staging reads: Case containing EES with sample is transported to staging area. An artists impression of a helicopter is shown carrying the case underneath.
  4. Vault enclosure reads: Case containing EES is placed in a value and transported to Sample Receiving facility (SRF). A photograph of a truck carrying the case is shown and the truck is labelled ‘vault’.
  5. Sample Receiving Facility reads: Vault enclosing case containing EES arrives at Sample Receiving Facility. An artists impression of the truck is shown to the left of a white building. An arrow extends from the truck, to show the case containing the EES passing through the facility. First the vault is disassembled and inspected. Then the EES is removed from the case and bag. Then the OS containing sample tubes is removed from the OS. A sample tube is shown, which is a long cylinder sealed at both ends with Mars core rock in the middle.
Figure 27 A proposed process for safely recovering, containing, and transporting Mars samples gathered by NASA's Perseverance Mars rover.

At the Sample Receiving Facility, the samples would be placed in a cabinet to contain any potentially harmful life, whilst also ensuring that the samples are kept ultra-clean, so that terrestrial life doesn’t contaminate the samples (causing false negative results).

A false positive result is one that indicates the presence of something that is not actually there. In the search for life, contamination might suggest extraterrestrial life is present, but it is in fact from Earth.

A false negative result is one that indicates the absence of something, even though it is present. In the sample receiving facility, terrestrial contamination may be detected and identified but might mask the presence of extraterrestrial life.

These are good reasons for ensuring there is an understanding of potential contamination, but also for developing suitable facilities on Earth for returned samples.

A consortium in the UK (including The Open University) is developing a cabinet that can protect the samples and the Earth environment. The concept is called a ‘double walled isolator’, and it uses positive pressure as a barrier between the laboratory and the samples. That is, the pressure inside the cabinet is higher than around it, preventing anything from entering the chamber (Figure 28).

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Figure 28a) The Double Walled Isolator into which returned samples from Mars could be placed. The arrows indicate the direction of airflow, creating a protective barrier. Figure 28b) An artist’s impression of the cabinet when built.
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Figure 28a) shows a schematic consisting of 5 concentric squares representing different containment boxes of the Isolator. Each box is shown with arrows indicating the direction of airflow. At the centre is the ultra-clean BSCIII double walled isolator (samples) and air flows into this. This is surrounded by high purity inert gas which flows out into the next box, which is a pristine cleanroom with high containment (personnel and select instrumentation). Air flows out of this and into another box, into which air from outside is also flowing. Figure 28b) shows a cleanroom containing a cubic cabinet that has a solid metal base with several digital controls. On top of this is a cabinet with a transparent pane and gloves attached so that whatever is contained within can be reached.

Figure 28a) The Double Walled Isolator into which returned samples from Mars could be placed. The arrows indicate the direction of ...

While the cabinet provides protection for returned samples, it still needs to be operated within a cleanroom environment. As has already been alluded to, cleanrooms are also critical environments for the building of spacecraft as part of contamination mitigation.