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There are some planetary protection concerns about backward contamination of Earth by returning samples from Mars, a mission which may well happen around the Earth-Mars opposition of 2025. One of the concerns is that the return capsule could crash during atmospheric entry and landing and spread its content in the atmosphere/ocean/crater.

(How) Could a capsule containing a few kilograms or so samples from Mars be landed without any risk of leakage during the landing process?

A couple of wild suggestions to begin with:

  • The capsule could consist of an ablative heat shield or tungsten shell or something which would survive any atmospheric entry and hard landing scenario, given the return speed from Mars. The capsule would then be fished up or dug up intact. How heavy would such a capsule have to be?

  • Let the return capsule carry a nuclear bomb which can be detonated if the capsule is out of course. Even if in the atmosphere, it would only be about the 1,000th over-the-ground nuclear detonation made. But it of course assumes that the detonator does not fail, which is a challenging assumption in a scenario where something else already has failed. Probably not enough to calm those who worry about Mars bugs.

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We believe so, but a lot of work remains to test and qualify a design to assure containment. These papers outline the approach, which is a simple, extremely robust parachuteless entry vehicle design.

Earth Entry Vehicle cross-section

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The risk of back contamination is quite small, and in fact, most likely happens on a regular basis, via Martian meteorites (At least, according to Robert Zubrin). And in fact, Martian bacteria would be very unlikely to be able to thrive on Earth, making their possibility of disease spread even less likely.

Wikipedia actually has several plausible scenarios on how to make the capsule safely. I suspect the following would happen:

  1. The capsule should be made to survive intact without requiring parachutes. These could be fairly easy to design, terminal velocity on earth is usually around 100 miles/hour or less, which while difficult, could be done.
  2. There should be a vacuum between the sample and the outermost layer of protection, so that any contamination goes inward.
  3. The possibility of a space based experiment center has also been discussed, possibly at the ISS or similar lab.

As for the nuclear option, that seems rather harsh. There are less damaging ways that could be done that should be considered in the event of bad control.

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  • $\begingroup$ 3. An in-space lab to analyze the sample might as well be landed on Mars, saving the return cost. The big benefit of sample return is the access to the best lab's on Earth, now and for decades to come. 2. Could you please reformulate or elaborate that a little bit? A vacuum around the sample should tend to suck it out. Putting the sample inside active carbon maybe helps prevent it from spreading in case of a leak. And yes, a nuke is overkill. A termite reaction which is spontaneously ignited by the heat shield breaking up should do the same job more reliably. $\endgroup$
    – LocalFluff
    Commented Jun 4, 2015 at 15:35
  • $\begingroup$ I tend to agree with you, but it has been discussed. But I generally agree with all of your comments. $\endgroup$
    – PearsonArtPhoto ♦
    Commented Jun 4, 2015 at 17:58
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    $\begingroup$ ISS would actually be less safe than landing it on Earth. It turns out that ISS isn't actually in space. It is in the upper fringes of Earth's atmosphere. If ISS cannot be serviced for several months for whatever reason, it would reenter in an uncontrolled manner with the Mars samples. $\endgroup$
    – Mark Adler
    Commented Jun 5, 2015 at 2:30

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