Are not the chances considerable that the crash landing of the Schiaparelli lander has contaminated the subsurface of Mars with microbes ?

For Mars there are 3 categories of Planetary Protection missions, for instance Curiosity has the IVa criteria, a mission not intended to seek for life.

Missions like that are not allowed to come into contact with places where liquid water can occasionally occur, and that is valid also for the Beagle 2 and Schiaparelli landers.

Thus far there have been no missions with the IVb and IVc criteria, which may look for life, because sterilization was to expensive.

Because the crash landings may have brought components into contact with subsurface water, is it not evident then that the IVa criteria for protection have been broken ?

See also Wikipedia for these issues

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    $\begingroup$ Why do you think crash landings break them? $\endgroup$
    – Rory Alsop
    Apr 20, 2018 at 13:21
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    $\begingroup$ What I'm saying is why do you think that crash landings would violate those conditions? I don't see any reason why they should. $\endgroup$
    – Rory Alsop
    Apr 20, 2018 at 14:04
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    $\begingroup$ I still don't see why you think there would be contaminants brought to the surface. The rules are reasonably strict to help ensure contaminants are not taken to Mars orbit, let alone re-entry. From that perspective it doesn't matter if the craft crashes - there is nothing to contaminate the surface with. $\endgroup$
    – Rory Alsop
    Apr 20, 2018 at 14:41
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    $\begingroup$ IVa, IVb and IVc are just variations depending on mission type. And you have still not articulated why you think one crashing is going to introduce contaminants into underground water. What contaminants do you think it will bring, and how do you think they will mess up future missions? $\endgroup$
    – Rory Alsop
    Apr 20, 2018 at 15:13
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    $\begingroup$ This isn't a bad question. Compare Why is Curiosity not heading for Peace Vallis? - had Curiosity crashed into Peace Vallis, it would definitely "enter" it as per IVc, probably ruining it for future missions. $\endgroup$
    – SF.
    Apr 20, 2018 at 17:17

2 Answers 2



If there is a crash landing, then the Planetary Protection Officer (ESA's in the case of Schiaparelli) documents the crash location and the organic and biological material that was likely dispersed. This is available to all of the agency Planetary Protection Officers in order to provide information and advice for future missions to consider how that contamination could impact their experiments.

The mission needs to provide an assessment before launch of the probability of a crash landing. However for Category IVa there is no requirement on that probability, and it is most certainly not expected to be zero. Instead the mission is required to provide before launch an inventory of the organic materials in the spacecraft, so that if it does crash, the degree of contamination can be estimated for future missions to Mars. You would expect that a future life or organic material detection mission would not go near a previous crash site.

Category IVa missions must clean the outside surfaces of the spacecraft to constrain the biological burden that Mars would be exposed to on a normal landing. However there are many parts inside the spacecraft that are not so cleaned because they are not expected to be exposed, unless the landing fails dramatically. A simple example is the Inertial Measurement Unit, which is a sealed device that was built with no biological cleanliness requirements. If that thing breaks open on landing, then there will be more biological contamination of the impact site than for a normal landing.

There is no evidence that any of the crashes have brought components into contact with subsurface water. IVa missions cannot target environments that are considered likely to have near-surface subsurface water. These are called "special regions".

From the Planetary Protection Provisions for Robotic Extraterrestrial Missions:

Special Regions are defined as areas or volumes within which sufficient water activity AND sufficiently warm temperatures to permit replication of Earth organisms may exist.

Missions to such locations are deemed Category IVc (whether or not they are looking for evidence of life), which require much more stringent sterilization. The surface bioburden requirement is four orders of magnitude lower than for IVa. If the probability of a crash landing is assessed to be more than 1%, then the innards have a bioburden requirement as well, though not as stringent. (At this point, I would consider it very unlikely that any project planning to land something on Mars would be able to successfully defend a claim that their probability of a crash landing is 1% or less.)

The only Mars missions' landers that has been subject to such sterilization to date is Viking, which subjected the entire lander systems to a dry heat sterilization process and encapsulated the whole thing to prevent recontamination before launch. Some parts of Beagle 2 were sterilized, but not the whole thing. Some parts of Mars 2020 will be sterilized and encapsulated, mainly the parts that will be in contact with collected samples.

None of the requirements are zero. There can and likely will be some potentially viable bacterial spores on the surface of lander targeted even to a special region, and many inside.

From the reference, the project is required to document at end of mission, for any category, whether the landing was successful or not:

(6) An inventory of bulk constituent organics that includes:

(a) Parts lists, material lists, and other program documentation containing data relevant to organic material identification that are prepared by a flight project to specify and control the materials that are included in a vehicle destined for planetary landing.

(b) The locations of landings and impact points (determined and defined as accurately as mission constraints permit) of major components of space vehicles on the planet surface,

(c) Estimates of the condition of each landed spacecraft to assist in calculating the spread of organic materials.

If the lander crashes, The PPO documents the crash location along with an estimate of the biological contamination of the site.

Here are the specific IVa requirements: Category IVa. Lander systems not carrying instruments for the investigations of extant martian life shall be restricted to a surface biological burden level of ≤ 3 x 105 spores, and an average of ≤ 300 spores per square meter.

a. An assessment of the probability of a non-nominal landing (including EDL) shall be provided.

The keys there are "surface" and "non-nominal landing". The non-nominal landing is NASA terminology for a crash landing. Only the surfaces need to be cleaned for IVa, and the project needs to tell the Planetary Protection officer what they think the probability of a crash landing is.


The main concern is a lander (looking for life on Mars) bringing life to Mars and its instruments then detecting that life in a false positive. A crash landing makes that a non-issue: the instruments are no longer functional.

Broadly, these are the goals of NASA's planetary protection rules:

  1. Preserving our ability to study other worlds as they exist in their natural states;

  2. Avoiding the biological contamination of explored environments that may obscure our ability to find life elsewhere – if it exists;

  3. To ensure that we take prudent precautions to protect Earth’s biosphere in case life does exist elsewhere.

You seem to think a crash-landing can bring life to Mars and then spread it all over the planet. That is not a realistic scenario. The worst case we're looking at is local contamination making the crash site unsuitable for further missions. Mars is large enough that that is not an issue.

  • $\begingroup$ Do you mean detecting martian life as a false positive ? $\endgroup$
    – Cornelis
    Apr 20, 2018 at 12:58
  • $\begingroup$ So bringing earth life with a crash landing is a minor concern ? $\endgroup$
    – Cornelis
    Apr 20, 2018 at 13:13
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    $\begingroup$ Why does a crash landing make it a non-issue? $\endgroup$
    – TylerH
    Apr 20, 2018 at 16:15
  • $\begingroup$ It does not matter what i think, missions that are not IVb or IVc category are not allowed to come into contact with liiqiud water. $\endgroup$
    – Cornelis
    Apr 20, 2018 at 16:57
  • $\begingroup$ The instruments on THAT CRAFT becoming non-functional is completely moot as the instruments were insufficient to perform the kind of analysis the contamination makes impossible in the first place. The problem is the contaminated site becomes useless for future missions. $\endgroup$
    – SF.
    Apr 20, 2018 at 21:15

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