One answer to my previous question Is there any demonstrated or even proposed technology that can sterilize a spacecraft with 100% certainty and yet leave it electronically functional? asserts:

Absolute 100% sterilization is impossible.

See also Who decided that a <1 in 10,000 probability of contaminating the europan ocean by a viable Earth microorganism was legally and ethically sufficient?

I understand that penetration of sterilizing chemicals into nooks and crannies is imperfect and the effects of sterilizing radiation is statistical, but raising a spacecraft up to some temperature $T$ (baking it) may be sufficient to kill all known Earthbound life forms and inactivate their spores.

See for example these in Biology SE:

Answers to Would it be possible to build a probe that could operate at about 480 °C (900F degrees) without insulation? indicate that it may be quite feasible to build spacecraft components that could even operate at 480 °C but that wouldn't be necessary.

After launch and exit from Earth's atmosphere and entrance into a deep space trajectory toward a subsurface ocean world, the spacecraft, still encased in an "oven", could be incubated at say circa 500 °C or some other temperature known to be sufficient.

Question: Are any space agencies working on an (essentially) 100% reliable sterilization technique for spacecraft bound for subsurface ocean worlds? Are they perhaps looking for some temperature sufficient to bake a spacecraft in deep space such that no living organisms nor any viable bacterial spores remain?

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    $\begingroup$ Achievability in engineering and 100% reliability are contradictory concepts. $\endgroup$ Commented Nov 15, 2021 at 23:40

1 Answer 1


“100% reliable” may be unattainable, but “Dang close” is already routine in hospitals. Dry heat sterilization is possible, but requires long exposure times which can damage many materials.

Etylene oxide is the gold standard for cold sterilization. It is routinely used for surgical instruments which contain electronics, paper, rubber, plastics and optics. https://www.cdc.gov/infectioncontrol/guidelines/disinfection/sterilization/ethylene-oxide.html

Ethylene Oxide is flammable and poisonous, but widely used in industrial chemical synthesis, so methods for handling it are routine. https://www.who.int/ipcs/publications/cicad/en/cicad54.pdf

Death rate curves of bacterial spores using Ethylene oxide have been extensively investigated. Standards for sterilization of medical devices have been developed by the FDA https://www.fda.gov/medical-devices/general-hospital-devices-and-supplies/ethylene-oxide-sterilization-medical-devices

The COSPAR Planetary Protection standards are primarily concerned with preventing Back Contamination (bringing bugs to earth) and contaminating extraterestial life experiments rather than preventing Forward Contamination (taking Earth bugs to celestial bodies).

For instance, InSight’s “mole” probe penetrated the Mars surface 0.5m. The mission is Category IVa (not investigating life) so the spacecraft is “allowed” to have 300,000 viable bacterial spores on its surface. Spores are the hardiest dormant form of bacteria in terms of resisting extremes of heat, UV and desiccation. They are formed by the organisms which cause Botulism, Gangrene, Tetanus and Anthrax. It is possible that InSight introduced spores into the warm(er), moist(er), low(er) UV subsoil where they could germinate and reproduce. InSight could have been sterilized to a higher standard, but it was not.

NASA’s protocols are primarily concerned with preventing Earth biochemicals from confusing life-detecting experiments, rather than preventing contamination of new celestial bodies.

The problem is not lack of sterilization techniques. It is the standards for applying those techniques.

Since ethylene oxide sterilization is available, affordable and safe, it should be used for all spacecraft contacting celestial bodies that are not obviously lethal to Earth microbes (Son, Mercury, Venus).

  • $\begingroup$ This is potentially a good answer to the question I've linked to in the first sentence Is there any demonstrated or even proposed technology that can sterilize a spacecraft with 100% certainty and yet leave it electronically functional? but it does not answer the current question as asked: "Are any space agencies working on a...?" You might consider deleting it here and posting it there instead. Thanks! $\endgroup$
    – uhoh
    Commented Nov 14, 2021 at 8:43
  • $\begingroup$ I find this distracting as it answers a question I didn't ask and doesn't even try to answer the question I have. $\endgroup$
    – uhoh
    Commented Nov 15, 2021 at 0:55
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    $\begingroup$ It would be a bit ironic if future Martian colonists ended up contracting anthrax from spores delivered by an earlier probe. $\endgroup$
    – DrMcCleod
    Commented Nov 20, 2021 at 10:45
  • $\begingroup$ @DrMcCleod if it hasn't been done before, please write that short story and submit it somewhere! $\endgroup$
    – uhoh
    Commented Nov 24, 2021 at 1:08

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