Bias disclaimer: I think that returning samples from Mars to Earth at a point in time where we also suspect there is a chance that there is microbial life on Mars is ill-advised and arrogant. We are already scared of ancient viruses we don't know about trapped frozen in permafrost here on Earth being released as the climate warms. Even if a microbe doesn't infect humans, all it has to be able to do is to infect something e.g. algae in the ocean, wheat, rice or corn, honey bees, gut bacteria, and the planet or at least humanity is at severe risk. Random examples of news items are shown below.

Sometimes sample return missions go bad and need to be recovered in the desert after they break open.

The capsule broke open on impact, and part of the inner sample capsule was also breached. The damage was less severe than might have been expected given its velocity; it was to some extent cushioned by falling into fairly soft ground.

Genesis crash site scenery

above: Genesis crash site scenery below: What kind of rocket will ESA(?) launch from Mars? Who will build it?

The tubes will be put in a rocket and fired high above Mars

From New York Times Science tweet https://twitter.com/NYTScience/status/1402072048986435585 It survived tens of thousands of years in suspended animation and managed to reproduce once it was thawed out

From New York Times Science tweet

It survived tens of thousands of years in suspended animation and managed to reproduce once it was thawed out

update 7: CNN's August 18, 2023 New study warns against risks of ‘time-traveling pathogens’ outlines the results of recent simulations of the dangers of the release of ancient viruses of Earth origin back into the ecosphere.

update 6: CNN's July 29, 2023 A worm has been revived after 46,000 years in the Siberian permafrost

Scientists have revived a worm that was frozen 46,000 years ago — at a time when woolly mammoths, sabre-toothed tigers and giant elks still roamed the Earth.

The roundworm, of a previously unknown species, survived 40 meters (131.2 feet) below the surface in the Siberian permafrost in a dormant state known as cryptobiosis, according to Teymuras Kurzchalia, professor emeritus at the Max Planck Institute of Molecular Cell Biology and Genetics in Dresden and one of the scientists

[...] Organisms in a cryptobiotic state can endure the complete absence of water or oxygen and withstand high temperatures, as well as freezing or extremely salty conditions. They remain in a state “between death and life,” in which their metabolic rates decrease to an undetectable level, Kurzchalia explained.

“One can halt life and then start it from the beginning. This a major finding,” he said, adding that other organisms previously revived from this state had survived for decades rather than millennia.

One of the researchers, Anastasia Shatilovich, revived two of the worms at the institute by simply rehydrating them with water, before taking around 100 worms to labs in Germany for further analysis, transporting them in her pocket.

update 5: CNN's March 8, 2023 Scientists have revived a ‘zombie’ virus that spent 48,500 years frozen in permafrost begins:

Warmer temperatures in the Arctic are thawing the region’s permafrost — a frozen layer of soil beneath the ground — and potentially stirring viruses that, after lying dormant for tens of thousands of years, could endanger animal and human health.

update 4: From the spaceflight-focused Journal Icarus Recovery and Identification of Viable Bacteria Immured in Glacial Ice

By identifying the features that facilitate microbial survival within terrestrial ice, extrapolations to the likelihood of microorganisms surviving frozen in water ice on Mars, Europa, or within comets will be improved.

See also Polar Research: Abundance, viability and diversity of the indigenous microbialpopulations at different depths of the NEEM Greenland ice core

as well as Glacier ice archives nearly 15,000-year-old microbes and phages Zhong, ZP., Tian, F., Roux, S. et al. Microbiome 9, 160 (2021):

Bacteria of above phyla have been successfully cultured from very old frozen glacier ice [18,19,20,21], including some that were believed to have been preserved for >750,000 years [19] because of the subzero temperatures and low water activities within the ice matrix. Some bacteria were preserved as spores in glacier ice [22, 23]. Although there is currently no direct evidence for in situ activity, some studies have hinted at the possibility of microbial activity in frozen glacier ice based on the detection of some excess gases (e.g., CO2, CH4, and N2O), which may be produced by post-depositional microbial metabolism [24,25,26].

These all discuss survivability of whole bacteria and larger organisms as well. From the BBC's :

But the new study, published in Current Biology on Monday, suggested they could last for thousands of years, if not indefinitely.

"The takeaway is that a multicellular organism can be frozen and stored as such for thousands of years and then return back to life - a dream of many fiction writers," Stas Malavin, of Russia's Institute of Physicochemical and Biological Problems in Soil Science, told the Press Association.

update 3:

“The takeaway is that a multicellular organism can be frozen and stored as such for thousands of years and then return back to life—a dream of many fiction writers,” said (Stas) Malavin. (a co-author of the study)

From Wikipedia's Bdelloidea:

The main characteristics that distinguish bdelloids from related groups of rotifers are exclusively parthenogenetic reproduction and the ability to survive in dry, harsh environments by entering a state of desiccation-induced dormancy (anhydrobiosis) at any life stage. They are often referred to as "ancient asexuals" due to their unique asexual history that spans back to over 25 million years ago through fossil evidence. Bdelloid rotifers are microscopic organisms, typically between 150 and 700 µm in length. Most are slightly too small to be seen with the naked eye, but appear as tiny white dots through even a weak hand lens, especially in bright light.

update 2: See Life on Mars? Scientists Find Mars Has Right Ingredients for Present-Day Microbial Life Beneath Its Surface which links to (paywalled) Earth-like Habitable Environments in the Subsurface of Mars

update 1: See NASA Establishes Board to Initially Review Mars Sample Return Plans:

"NASA stands up these independent boards to help the agency learn from past experiences and uncover subtle issues in space systems that may not have yet received sufficient attention," said David Thompson, retired president of Orbital ATK, who will chair the new board. "This review will give us the chance to focus on overall mission success and to consider potential improvements that can be made early in the program to help ensure that outcome."

Now that's what I'm talkin' about!! Image of the Genesis crash site below illustrates one such "subtle issue." ;-)


Typing "back contamination" in the search box on the main page https://sma.nasa.gov/ returns results that include:

Safeguarding Earth from back contamination is the highest planetary protection priority

from Planetary Protection Knowledge Gaps for Human Extraterrestrial Missions Workshop Report NASA Ames, March 24-26 2015

Safeguarding the Earth from potential back contamination is the highest planetary protection priority in Mars exploration.

From 2nd COSPAR WORKSHOP on: Refining Planetary Protection Requirements for Human Missions May 15-16, 2018 and COSPAR WORK MEETING on Developing Payload Requirements for Addressing PP Gaps on Natural Transport of Contaminants on Mars May 17-18, 20 18 BOX 1: COSPAR Planetary Protection Principles and Implementation Guidelines for Human Missions to Mars


Considering the (small) potential for there to be microbes in Martian samples robotically returned to Earth, what precautions are planned to prevent an accident or anomaly or something else unlikely but not impossible from releasing them into Earth's environment? Will there be hazmat crews ready to go if another Genesis-like land crash happens for example? What if it crashes into water?

Please don't post answers that this is not likely to happen; this is a question about the extent of precautions.

  • 3
    $\begingroup$ Don't add water. imgur.com/vIKrk4w $\endgroup$ Jun 27, 2020 at 17:51
  • 1
    $\begingroup$ NASA was very careful about such matters during the Apollo program with the Apollo 11 & 12 astronauts being quarantined in case there were pathogens on the Moon. I'm not aware of any precautions the Russian took when they obtained lunar samples from the Luna 16 & 20 missions. Likewise for the Japanese asteroid sampling probe Hyabusa that resulted in a sample from Itokawa that landed near Woomera, Australia in 2010. $\endgroup$
    – Fred
    Jul 2, 2020 at 9:29
  • 1
    $\begingroup$ Apparently a sample from Hayabusa 2 will be landing at Woomera in December 2020 $\endgroup$
    – Fred
    Jul 2, 2020 at 9:35
  • 8
    $\begingroup$ Something else to consider: many millions of tons of material has been blasted off Mars and already landed on Earth, and yet we're still here. Why worry about the payload from a small lander? $\endgroup$
    – Snoopy
    Aug 2, 2020 at 2:28
  • 2
    $\begingroup$ mars.nasa.gov/internal_resources/1306 $\endgroup$ Mar 16, 2023 at 2:23

3 Answers 3


Humanity hasn't yet reached a consensus.

Return samples obtained from a Category V body must be curated at facilities rated Biosafety level-4 (BSL-4). Because the existing BSL-4 facilities ... do not have the complex requirements to ensure the preservation and protection of Earth and the sample simultaneously, there are currently at least two proposals to build a BSL-4 facility dedicated to curation of restricted (potentially biohazard) extraterrestrial materials.
-- https://en.wikipedia.org/wiki/Extraterrestrial_sample_curation

More details: https://www.space.com/7625-protect-mars-samples-earth.html

See also https://en.wikipedia.org/wiki/Outer_Space_Treaty.

  • 8
    $\begingroup$ Seems to me like a high earth orbit lab might be a good idea. $\endgroup$
    – ikrase
    Jun 26, 2020 at 9:42
  • $\begingroup$ But "curation" is moot if the spacecraft crashes and breaks open. "...what precautions are planned to prevent an accident or anomaly or something else unlikely but not impossible from releasing them into the environment?" This isn't really an answer yet; does any of the material in your links actually address my question? If so, can you quote a bit of it to demonstrate relevance? $\endgroup$
    – uhoh
    Jun 26, 2020 at 11:45
  • $\begingroup$ @ikrase it’s too expensive in delta v ... $\endgroup$
    – Antzi
    Jun 26, 2020 at 13:05
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    $\begingroup$ @carlwitthoft I understood that the chances of anything coming from Mars are a million to one. But it's ok, they would be slain, after all man's devices had failed, by the humblest things upon the Earth: Bacteria. So, great news! Phew. :-) $\endgroup$
    – SusanW
    Jun 27, 2020 at 1:05
  • 1
    $\begingroup$ @BarrowWight I think the reason it's being brought to Earth for study is that there is not sufficient equipment on Mars to study it, and I'm pretty sure for this mission there will not be any tests for life or for biological safety on Mars by the time it's sent back. $\endgroup$
    – uhoh
    Aug 16, 2020 at 6:35

NASA and the European Space Agency (ESA) have planned a Mars Return Sample (MSR) program. This program would include picking up the geologic and atmospheric samples being gathered by NASA’s Perseverance Mars rover and returning them to Earth in the early 2030s.

The NASA-ESA team is working closely with each agency’s planetary protection leadership to ensure that every spacecraft sent to the Red Planet has been cleaned to prevent Earth organisms from compromising scientific investigations, and to implement numerous steps designed to protect Earth and provide safety assurance by preventing any uncontained, unsterilized Mars material from being delivered to Earth.

Now, whether or not the samples from Mars could present a hazard to Earth’s biosphere has been studied by several different panels of scientific experts from the United States and others over the several decades. The reports from these panels have found an extremely low likelihood that samples collected from areas on Mars like those being explored by Perseverance could possibly contain a biological hazard to Earth's biosphere.

Multiple different sources of scientific evidence contribute to this assessment of the possible biological hazard. The evidence includes the absence of any observed harm to Earth’s environment from Martian rocks that frequently fall to Earth in the form of meteorites, and the fact that the Mars samples being gathered by NASA’s Perseverance Mars rover are from the first few inches of Mars's planetary surface that is very dry and highly irradiated naturally by the Sun, which would sterilize all known active biology. (This is part of why NASA’s science strategy is focused on finding traces of ancient life from long ago, when the Martian environment was wetter and warmer, and not any modern life in these harsh conditions that kills mostly everything).

enter image description here

You can also check out some proposals made by countries around the world for the Mars Return Sample in this Wikipedia link.


Other articles/papers:

  • $\begingroup$ Question asks "What precautions are planned...?" I'm not seeing any effort to describe those precautions. $\endgroup$
    – uhoh
    Aug 21, 2023 at 22:24
  • $\begingroup$ I haven't found any (other than the vessel) , likely because they aren't posted by nasa and due to the low likelihood of contamination @uhoh, neither any descriptions of how the vessel works $\endgroup$
    – DialFrost
    Aug 21, 2023 at 22:39
  • $\begingroup$ Well, in my humble opinion, "I haven't found any" isn't really a good basis for a Stack Exchange answer, especially when there are already other answers that haven't found any either. $\endgroup$
    – uhoh
    Aug 21, 2023 at 22:45
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    $\begingroup$ I just saw this in CNN How NASA has prepared to scoop up an asteroid sample landing in the desert It outlines many precautions that most certainly would apply to future sample return missions as well. I think if you base an answer on these documented precautions it would make for a much better answer than what you have now. $\endgroup$
    – uhoh
    Sep 13, 2023 at 1:23
  • 1
    $\begingroup$ @uhoh Ah thanks so much (sorry I've been inactive in this question I've been busy lately) $\endgroup$
    – DialFrost
    Sep 13, 2023 at 1:34
  1. The samples will have "higher levels of isolation than any mission previously in space flight". This is due to the fact they first sit in an enclosed tube for years on the surface (a very irradiated place). Then they have a 9 month long journey through space (also very irradiated). Therefore is unlikely to be any life forms to escape.
  2. They are using standards similar to those in medicine and aviation to keep them contained. This means that in the event of a crash, they know where it will land and will contain it appropriately.
  3. It has "a container within a container". In other words, there is a fail safe for nearly everything involved here. This means that multiples of everything involved would have to fail upon crashing in order to actually cause a potential problem.

That all being said, don't panic. The entire planetary protection seems to be mostly a show to the public. The steps that I said NASA has taken in no way eliminate this risk. Planetary protection (for Earth) has been extensively looked into, with the general consensus of no. If it were such a risk, NASA would never even consider returning samples from another planet. So, here is why NASA doesn't think it is such a big issue:

  1. Rocks from Mars (basically less sterile samples) fall to Earth all the time. The only difference with what we are doing is that we know were these samples came from and how long it has been exposed to the elements of Earth (should be never).
  2. The samples aren't also that deep. Remember, unlike Earth, Mars has no nice little magnetic field. Therefore it is constantly blasted by the Sun's radiation and solar wind. Not the nicest place for living organisms. It would kill all Earth bacteria. Not to say that Martian bacteria couldn't survive, but a bacteria adapted to that environment might even need the radiation for some reason (ex.it is their energy source). Regardless, the current levels of radiation and solar wind is at least part of the reason that they are mainly looking for past life with the both the rover and the samples, because it would be nearly impossible for there to be any current life on the surface or within a few inches of it.

So, yes, there are really aren't so many effective planetary protection steps for Earth, and little have been taken since the crews of Apollos 11 through 14 had to quarantine (excluding 13 because of that issue). They are unlikely to do so ever again for a robotic mission as it presents no more problem that rocks already coming down from Mars. Also, it would even be unlikely for life to be able to survive in the current surface's conditions.

  • $\begingroup$ Thank you. Fixed. @ErinAnne $\endgroup$ Mar 12, 2023 at 10:39
  • $\begingroup$ Everything here is from that source. We is scientists at NASA. @OrganicMarble $\endgroup$ Mar 12, 2023 at 13:51
  • $\begingroup$ Great point also fixed personal issue @OrganicMarble $\endgroup$ Mar 12, 2023 at 14:01
  • 5
    $\begingroup$ I've asked "What precautions are planned to prevent... crashing and releasing organisms..." Could you help highlight which parts of your answer describe crash-and-release precautions, and support them by linking to authoritative sources? Thanks! (it may be useful to use a search function to locate the sentences in my post that end with a question mark "?" and focus on those. $\endgroup$
    – uhoh
    Mar 12, 2023 at 15:57
  • 6
    $\begingroup$ it's probably being downvoted because you mashed two answers together (one saying that planetary protection won't ever be considered for Earth, another saying all the stuff that NASA has said they'll do to protect Earth during Mars Sample Return), your source is hidden under the word "no," and you haven't made it clear where you're quoting/paraphrasing the source or making your own assertions. $\endgroup$
    – Erin Anne
    Mar 12, 2023 at 21:07

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