What Is Our Martian Quarantine Protocol?

If you somehow haven’t read or watched War of the Worlds, here’s a spoiler alert. The Martians are brought down by the common cold. You can argue if alien biology would be susceptible to human pathogens, but if they were, it wouldn’t be surprising if aliens had little defense against our bugs. The worrisome part of that is the reverse. Could an astronaut or a space probe bring back something that would ravage the Earth with some disease? This is not science fiction, it is both a historically serious question and one we’ll face in the near future. If we send people to Mars are they going to come back with something harmful?

A Bit of News: Methane Gas Fluctuations on Mars

What got me thinking about this was the mounting evidence that there could be life on Mars. Not a little green man with a death ray, but perhaps microbe-like life forms. In a recent press release, NASA revealed that they not only found old organic material in rocks, but they also found that methane gas is present on Mars and the amount varies based on the season with more methane occurring in the summer months. There’s some dispute about possible inorganic reasons for this, but it is at least possible that the variation is due to increased biological activity during the summer.

These aren’t the first potential signs of life on Mars, either. In 1996, David McKay, Everett Gibson, and Kathie Thomas-Keprta from the Johnson Space Center announced they had found microbial fossils in a piece of meteorite that originated on Mars (see picture, below). The scientific community came up with a lot of alternative explanations, but to this day we don’t know conclusively if it is evidence of Martian life or just an inorganic process.

History Repeats

So far, there’s nothing really worrisome about Martian microbes because they are far away. But we have had contact with one other extraterrestrial body already: the moon. If you think the moon landing was fake, you’ve clearly overestimated the ability of the government to keep a secret. In 1969, two astronauts who had walked on the moon returned to Earth. Would they go down in history as modern-day typhoid Mary’s?

There was a very low chance that the moon harbored any sort of dangerous microbes, but there was a chance. And the price to pay for being wrong could have been very high, so NASA erred on the side of caution. That’s how the Mobile Quarantine Facility (MQF) came into being.

Chillin’ in an RV

If you have ever seen an Airstream trailer, you’d recognize the MQF. It was a 35-foot trailer that had no wheels but did have an elaborate air filtering system. Once the Apollo capsule landed in the ocean, the recovery crew threw down isolation suits the crew put on until they were brought to USS Hornet where they were installed in the MQF.

Although 35 feet doesn’t sound very big for three men, it was spacious compared to the lunar capsule they’d been in. Actually, there were five men inside — an engineer and a doctor were sealed in with the crew for the 65-hour observation period. Carried by airplane and truck, the MQF made its way to Pearl Harbor and then Houston. Once in Houston, the space travelers were released for two more weeks of isolation in the Lunar Receiving Lab.

The same procedure was in place until Apollo 15. Of course, Apollo 13 didn’t reach the moon, so it didn’t use the MQF either. Looking back on it, it seems almost silly that there was so much concern.

Now There’s Mars

It might seem silly now, but back then the logic was sound. First and foremost, if there was any chance at all, you had to be sure. Being wrong would have been devastating — possibly even killing everyone on Earth. Second, this was a well-funded and highly-visible government project so there was some political need to look cautious and a lot of money available to do so.

Mars may be a different story. NASA isn’t funded like it used to be. Elon Musk’s company may get there first, or maybe another country will go. We are at a time when people aren’t as careful as they used to be, in a lot of areas. Will we take precautions against a Martian plague?

Even if you think native Martian life is not likely (or not likely to want to feast on humans and other Earth creatures), there’s another concern. In fact, it may be more likely and more likely to be deadly. It turns out that despite NASA’s unwillingness to go out on a limb and say there is life on Mars, we know that there is almost certainly some life on Mars. We know that because we brought it there ourselves.

Every spacecraft we send to the red planet — or anywhere — will have some amount of Earth life within it. The process even has a name: forward contamination. NASA has a planetary protection officer that ensures the Committee on Space Research (COSPAR) standards are met. This international standard requires that all space exploring nations limit the chance of contamination to 1 in 1,000 total. It even goes as far as to allocate that total to different nations. The US is allowed a 1 in 40,000 chance.

The initial Viking probes were baked almost sterile, but after discovering the harsh environment on the Martian surface, future probes were given more latitude. However, more recent research has shown that on Earth, microbes can live under some hellish conditions, so there is some likelihood we’ve already contaminated Mars.

Don’t think the microbes would survive the ride to Mars? Think again. Experiments on the International Space Station confirm that the cleaning done by NASA leaves only the hardiest strains of bacteria and it appears that at least some could hibernate until they found the right conditions for life. In fact, under current COSPAR rules, if NASA’s Curiosity probe finds water, it can’t get near it because it is not clean enough.

Double Threat

So there are really two threats. Native Martian microbes hitching a ride to Earth, or mutated Earth organisms catching a lift back to their home planet. Either way could have serious consequences. The same COSPAR group that dictates how many microbes you can take to Mars and other planets also specifies how to quarantine things coming back. The United States actually had the “Extra-Terrestrial Exposure Law” at the time of the moon landings, but that was removed in 1991. So it isn’t clear if a private entity like Musk would be required to follow any such procedure.

Of course, this is Hackaday, so what’s the hacker angle to all this? In my opinion, part of the problem here is defining life. What’s alive and what’s not? Like Justice Potter Stewart said about pornography, “I know it when I see it.” On Star Trek it was easy to “scan” a planet and announce you’d found life forms. But what does that mean exactly? There have been cases found of inorganic matter self-organizing. There are macromolecular systems that self-replicate. There is no assurance that alien life would be based on the carbon chemistry we associate with life.

A few decades of scientists haven’t figured that out yet. Maybe its time we took a crack at it. How can you detect life? For safety, how much life do you need to detect? Microbial life? Is it possible that inorganic life (e.g., silicon-based life) would not be harmful to people? Are we sure? Even just determining Earth-like life — preferably over at least a short distance — would be a great benefit to science.  If you want some reading on that topic, stop off at NASA’s astrobiology web site.

All the images in this post are from NASA, as you might expect. If you want to see more about the MQF, Airstream has an interesting video with a few internal details of the facility’s construction. You can see that video, below.


89 thoughts on “What Is Our Martian Quarantine Protocol?

      1. In fact, the Martian “fossils” may have been organisms that drifted from Earth via Solar Wind to a prehistoric watery Mars. Or, due to asteroid/comet action, life from Mars may have colonized primordial Earth!

  1. It’s easy to envision a plague or other catastrophic event, but any invasive species can become a huge problem. We see this in different parts of the world. I live near the great lakes and we’re trying to keep asian carp out using electric barriers, also trying to mitigate zebra mussels brought in with ballast from ocean going vessels. I hear starlings are bug problem in Australia and New Zealand. And of course kudzu is snuffing out native vegetation in North America (and I think it’s a problem in Europe too?).

    Even if it’s unlikely, having quarantine procedures in mind seems like the right idea.

    1. 24(?) English Starlings were introduced to the United States by a Shakespeare appreciation society, that wanted to have all the animals Shakespeare wrote about introduced to the US. They are now a huge pest in the US and Canada.

    2. “any invasive species can become a huge problem. We see this in different parts of the world.”

      Yes we do. We see this problem in the world, that’s world; singular. We have similar water and soil everywhere. Our temperature may vary by latitude enough to give us bands where certain species can thrive but those bands go all the way around the planet. Many isolated areas have compatible climates where people can spread invasive life and once it arrives it finds a climate nearly identical to the one it is naturally adapted for.

      Martian life on the other hand? Given enough travel between Earth and Mars maybe the bacteria that live under glaciers and in the dry valleys of Antarctica might be in danger. Or.. maybe martian life will be in danger from them.

      Will anyone even notice?

    3. Here’s my idea for thinning out the Asian carp. Take a fast boat and put a sloped front on it, with thick polycarbonate windows so the person steering can see forward. Have a lot of retractable spikes poking through the slope and a basket across the bottom.

      Zip along at high speed and when the carp jump they get impaled on the spikes. When the spikes are full, retract them so the carp slide down to the basket.

      Have a fleet of these boats running parallel, shore to shore, staggered formation so their paths overlap. Run up and down the river until the carp stop jumping.

    4. Mike Szczys – My idea is to reintroduce a prehistoric monster fish to the Asian Carp (aka Black Carp) to the affected areas. The monster fish is huge and quite scary looking to humans but seems to have a taste for specifically for Asian Carp, which also tend to be large fish, but almost impossible to fish for traditionally. Making it the natural predator of Asian Carp. Reintroducing this monster fish is not an ecological problem as this living fossil (maybe on the endangered species list too) already inhabits Louisiana, Mississippi, Texas and other US water ways probably for thousands of years. Its probably the most scariest thing you’ve ever seen in a Louisiana Bayou – teeth galore, huge body, big eyes, and a temperament to be watchful of.


  2. Nope Nope Nope! This should not be a serious concern.

    Just ask someone who designs medical implants. Our immune systems don’t just fight off pathogens that they ‘recognize’. They fight off anything that they don’t recognize. Attacking any and every foreign thing in our bodies is the default reaction.

    Earth born successful infections agents succeed only because they have evolved the ability to fool our immune systems into ‘thinking’ that they are not foreign. This evolution has been going on for billions of years right alongside our immune systems’ evolution which is constantly finding new ways to recognize them.

    Any alien organism attempting to attack a life form from Earth would be an absolute newcomer. The odds that an Earth immune system would see it as anything but foreign are to small to be considered. The immune system would have the contaminant identified, surrounded and removed long before it had a chance to begin reproducing.

    It is true that having previous exposure to a virus helps as we can already have antibodies which instantly serve as templates for creating more antibodies if the virus comes back. This is an extra defense however which helps us against viri that are already well adapted to evade our immune systems specifically. We would not need this extra advantage against an alien pathogen that is not already adapted to our physiology.

    1. I’m not much of a biologist, but I think the whole thing turns into a risk calculation. The basic idea behind risk management is to look at the likelihood AND the consequence. So while a plane crashing is statistically unlikely, the consequence is very high. So you take extra measures to mitigate that risk. We’ve talked before about how crashing a car is way more likely, but the overall consequence is usually less, so there are not so many measures taken. I think the most likely possibility is that truly alien life will look at us and go “meh” — as we would it. Kind of like how Spock was always immune to whatever the threat of the week was because the bugs didn’t like his green blood.

      But… if something does come in that turns out to be harmful… maybe even something we can’t imagine now…. the consequence could be HORRIBLE. Plus there is the political aspect of it. Even if it makes zero sense, you don’t want Joe Q. Public wondering why we aren’t protecting him from alien bugs.

      Of course, an interesting related question is if we find life on Mars will it really be alien? Is it possible that organics on some cloud of meteors seeded both Earth and Mars with some common ancestor microbial life? Maybe the planet that is now the asteroid belt was Atlantis. Or maybe Elon Musk went back in his time machine and started life on both planets making a huge time loop.

      1. “The basic idea behind risk management is to look at the likelihood AND the consequence”

        Sure, low likelihood events can be worth considering if they have extremely high consequences. However, even then I think that to use that as a reason to lose any sleep over “alien bugs” is to extremely overestimate the likelihood that they could be a problem for us.

        The probability that an alien organism would somehow be well adapted to our immune systems is beyond low likelihood. It’s not like worrying that an asteroid might hit us tomorrow. It’s like worrying that ALL the asteroids might hit us tomorrow. It’s something that just isn’t going to happen!

        1. Well, as I pointed out do you know for sure there isn’t a common origin for life on Earth and Mars? And I think some of it may very well boil down to how confident are we in our knowledge of exobiology? We don’t really have a great sample set to draw on.

          1. Nope! But it doesn’t matter.

            When a new plague hits us it is a minor variation of something that already infected either our own species or one close to our own. Most of the time our illnesses don’t even transfer between ourselves and our mammalian pets!

            Even if some ancient comet carried life from Mars to Earth or from Earth to Mars back in the beginning that life is now billions of years removed from us. It is far more removed from ourselves than anything found here on Earth.

        2. Well you are clearly very interested in this and I’m not the right person to argue with you, so I won’t. However, science or not, we did take steps from the moon and that was VERY unlikely. So it will surprise me if a government-sponsored mission doesn’t do something similar. If it isn’t government-sponsored then I’ll hope your exobiology is correct.

    2. What if the life that comes back isn’t infectious per se, but rather something that out competes Earth life? Something microbial that eats more efficiently or reproduces more rapidly on Earth than do are native microbes. They could end up starving portions of our biosphere leading to a very slow collapse.

      1. If we ever find a truly earthlike planet with life on it that is made of/consumes the same chemistry as our life then this could be an issue. When mixed the life of one might out compete the other.

        Life from Mars would be adapted to a different environment from us. Earth life has billions of years of a head start in adapting to Earth’s environment. Martian life if it exists is adapted to Mars. Perhaps, if brought to Earth some martian microbes might manage to survive in some niche environment but It will not out compete us on our own planet.

    3. You make a fair point about exobiological infections but what about the more likely issue of terrestrial microorganisms which may have survived the sterilization process?

    4. The simplest solution is don’t send people and don’t bring anything back. Next is don’t bring anybody or anything back. If you simply must go and return, seed Mars with Earth microbes fist and see if they get attacked.

      There is no point in avoiding contamination. It will happen soon or later.

      1. >There is no point in avoiding contamination. It will happen soon or later.

        I feel like there’s a decent point to avoiding contamination, at least until what the contamination will kill has been found, documented, and preserved.

      1. We work with heavy metal ores and other toxic rocks all the time. Wear gloves, N95, and wash your hands.
        A GC or XRD should sort out any organophosphate compounds. So that deals with most nerve agents that affect humans.

    1. As far as I know they were not in the ocean. They put on the decom suits before leaving. If you ever come to Houston and go to Space Center Houston and can navigate beyond the Squarebob Spongepants exhibits or whatever they have that week, you can see one of the suits along with some other really cool hardware.

        1. Well they were able to put on and off spacesuits…

          From here: https://www.jsc.nasa.gov/history/oral_histories/McCollumGW_BogardD/ApolloLQP.pdf — There are some pictures and details about the LRL I didn’t share either, so if you are really interested, this is a good doc to checkout.

          Biological isolation garments were used in Apollo 11 to isolate the
          crew from the Earth’s environment and from contact with recovery
          personnel. These garments were constructed from a fabric which
          effectively isolated microorganisms from the crewman’s body. The
          garment was donned in the spacecraft before the helicopter hoist
          operation and was worn until the crew entered the MQF aboard the
          primary recovery ship. The suit was fabricated of nylon. A respirator
          was worn with the garment. It featured an air-inlet flapper valve
          and high efficiency air-outlet filter to biologically filter expired gas.
          The Apollo 11 crew used a heavier biological isolation garment, but
          this was discarded as an unnecessary precaution after the initial
          lunar landing flight. On later missions, a lightweight overgarment
          was used when transferring from the Command Module to the

      1. I didn’t know about the biological isolation garments, thank you for taking the time to explain it.

        The whole extraction looks very wet and messy. By watching the entire footage of the Apollo 11 astronauts extraction, it is hard to believe that the risk of Earth contamination was 100% mitigated.

        Even so, it totally makes sense to wear sterile suits in order to minimize the risks.


        At 1:42 they mention throwing the ‘Biological Isolation Garments’ inside the capsule.

    2. So the astronauts were put in the decom suits before leaving the capsule, but what about the capsule it’s self. The interior was exposed to the astronauts for the entire trip back from the moon, providing ample time for any bugs to hide, and later infect Earth, sort of like the smallpox infected blankets.

  3. When I took a college level biology class about a decade ago, I was surprised to find out that virii are not defined as “life”.
    It is a strand of DNA/RNA in a protein capsule that is replicated by the host organism.

  4. Can’t we just wait until we have teleporter beam with biofilter comes around to filter out anything so we won’t need to deal with quarantine or vaccinations.

  5. You all are way too late, the protocol was broken by a nasa contractor when the last probe was launched. The probe is protected from any earth based contamination, however, prior to launch a concern developed about what if the drill system failed to load a bit, it was decided one bit should be inserted prior to launch, In violation of all rules a person entered the clean room with no suit and using bare hands installed a bit into the drill, totally contaminating mars, so there is zero reason to be concerned about protocols anymore, a drill bit penis infected with earth native elements has been inserted into mars repeatedly for years.

  6. Can’t the return trip itself be used as a quarantine period? The astronauts are already isolated in a spaceship for at least a couple of months on the way back to earth and they will probably already have a doctor and the required medical equipment on board. So if everything goes well, there is probably no need for an additional quarantine time after arriving back on earth.

    There could still be some interesting ethical questions on whether/when they can return to earth if one (or several) of the astronauts gets seriously ill for unknown reasons.

  7. What happens when an earth extremophile is taken out of it extreme environment and placed in an hospitable environment, dose it grow rapidly or die? If is now life on Mars it did not evolve to live in the current conditions of Mars. It evolved in a much more hospitable environment and is now just barley living or it is just the extremophiles that are left living. My point is that I think earth will present an hospitable environment for theses thing to grow in and we need to be concerned about it.

  8. Martians have been to Earth lots of times and for many, many years. So they have already figured out any precautions they need to take in order not be affected by Earth viruses/bacteria. They themselves are quite disease free, so they won’t be bringing anything here.
    See http://ufocoverup.org

  9. The airstream used to be displayed in the hangar on the USS Hornet in Alameda, CA. I think it’s been moved to some air and space museum now. It looks just like a late sixties airstream. My wife used to know the captain of the Hornet at the time of the moon landings (Carl Seiberlich) and he said that Nixon wanted them taken out so he could be photographed with them. Capt. Seiberlich told Nixon they couldn’t come out because of “Moon Germs”. https://commons.wikimedia.org/wiki/File:President_Nixon_welcomes_the_Apollo_11_astronauts_aboard_the_U.S.S._Hornet.jpg

  10. >>A few decades of scientists haven’t figured that out yet. Maybe its time we took a crack at it. How can you detect life?
    You don’t.
    Look for signs of life like the Redfield ratio (https://en.wikipedia.org/wiki/Redfield_ratio) which while developed around phytoplankton can be loosely extended to other Earthcentric biology. It’s easier to find footprints than the animal that left them.

    >>Is it possible that inorganic life (e.g., silicon-based life) would not be harmful to people?
    While there doesn’t seem to be a hard law of nature that limits life to be based around carbon, you would almost certainly need very similar properties to carbon in order to have complex life. Silicon is a popular alternative but the galactic prevalence of carbon (4th most abundant) makes it a whole lot more likely.
    As to the harm, without any idea of the exact structure it’s hard to say. I would be surprised if it weren’t to some degree though. Think about how many organisms on Earth interfere with metabolism of other organisms. Once we get some understanding of their ‘DNA’ it would be easier to model any harmful effects.

  11. I just looked it up . Pathfinder and sojourner launched in 96. Spirit and opportunity in 2003. Why are we just now hearing about this methane?

    I’m pretty sure captain Kirk was not worried about alien germs. Right Al?

    1. Because not everybody reads science news on a regular basis!

      Many of us are not hearing about this just now, we’re just hearing that more analysis has been completed.

  12. Well if invading aliens exist or even desire to make close encounter, they will come in their version of a haz-mat suit. So rhinoviruses are not an issue for them. However, what about this little “alien” that has been on Earth for a long while? Impervious to EVERYTHING – but no space suit.


    Also what about cephlapods. Are they really aliens? They sure seem like it to scientists.

      1. Leithoa – Because I have a feeling that “if” corporeal advanced life forms out there exist and capable of space travel, they probably share key biological similarities with Earth life forms.Its just a feeling, nothing concrete nor empirical… (i.e. an intuitive hunch).

        However the WATER BEAR I posted here yesterday (as a microscopic image) baffles me. Scientists even have a diagram of it’s internal organs on the Internet. How can it be impervious to just about anything we can throw at it? It can even withstand exposure to outer space! I guess the same thing applies to cephlapods who can withstand the crushing pressure of deep oceans and yet can come to the surface with no ill effects. We humans, not so much…

  13. If free to wander exoplanets in the Goldilocks zones of the milky way looking for a habitable planet, it would either have life on it with the potential oxygen atmosphere, or not have life, which would require altering a planet’s atmosphere.
    If a planet has multicellular organisms, logically it would have single cell organisms, that could take a long time to learn if they could effect ours.
    But just as we would want to avoid planets with life to not be effected/infected by it, I can understand why other life from other worlds would avoid contact.
    The answer to, if intelligent life exists, why haven’t they made contact, could logically be answered,
    because they are intelligent.
    I hope we go to Mars for many reasons, one being humans learning to improve their environment to improve their lives. Instead of destroying their own environment and calling it progress.
    Rather like destroying wilderness is destroying the very environment responsible for the evolution of our intelligence…..
    I don’t think 1000 light year away planets are out of reach, only that we might not know how, yet.

    Those who say “it can’t be done”, haven’t met many hackers.

  14. Actually, Gulfstream or no Gulfstream, the lunar pathogen protocol was breached the moment they opened the capsule hatch in the ocean. Sure the MQF protected against anything the astronauts themselves might be incubating, but what about airborne contaminants in the capsule itself? As Sagan complained in “The Cosmic Connection”:

    “The one clear lesson… is that mission controllers are unwilling to risk the certain discomfort of an astronaut–never mind his death–against the remote possibility of a global pandemic. When Apollo 11, the first successful manned lunar lander, returned to Earth–it was a spaceworthy, but not a very seaworthy, vessel–the agreed-upon quarantine protocol was immediately breached. It was adjudged better to open the Apollo 11 hatch to the air of the Pacific Ocean and, for all we then knew, expose the Earth to lunar pathogens, than to risk three seasick astronauts. So little concern was paid to quarantine that the aircraft-carrier crane scheduled to lift the command module unopened out of the Pacific was discovered at the last moment to be unsafe. Exit from Apollo 11 was required in the open sea.”

    1. >> the lunar pathogen protocol was breached the moment they opened the capsule hatch in the ocean.

      Technically it was the north equitorial current with thousands of miles to the nearest landfall via drift (850nm from hawaii but that’s up current). We dispose of compounds far more dangerous than space germs far closer to land than that with no ill effects to human populations, fisheries not so much.
      Spray down the ship with 10% calcium hypochlorite (better than sodium based house hold bleach) & everything’s fine.

      1. Just curious: At what point is the astronaut or the capsule EVER exposed to alleged Lunar Pathogens? I mean the astronaut is ALWAYS in his EVA suit from Hamilton/Sunstrand the entire time. The capsule is flooded with O2. There is no O2 on the lunar surface so the shock of NASA’s bottled O2 would be daunting to a foreign pathogen. How could a pathogen survive the lunar surface anyway? No O2, constant solar radiation bombardment, temperature extremes, etc. (Of course the WATER BEAR – aka Tardigrade, could take it though – what a creepy thing that thing is).

        Then the astronauts remain in their suits the entire ride home. The capsule exterior is exposed to the high heat of re-entry killing off anything riding along (except maybe Water Bears). The interior still exposed to O2 and maybe even UV lamps too. I just think NASA may have been over reacting on quarantines. But hey, an ounce of prevention may stop a pandemic.We had one on Earth once that mysteriously started and then mysteriously ended back in early 20th century.

        The Tardigrade may be the reason why we need to worry about hard to kill tiny things. Also there are very dangerous things to us that are NOT even life forms at all but act like life forms like Viruses and Prions. There’s too many unknown unknowns for man to be exploring space without advanced robots. I unofficially vote (as a US taxpayer) that NASA’s Valkyrie take over all future manned missions. We can just leave her out there. No more quarantines.

    1. Steve – Percival Lowell, Dr. Giovanni Schiaparelli, and the Royal Observatory of London all eye-witnessed “artificiality” on Mars via sophisticated telescopes at the turn of the 20th century. Nikola Tesla “claimed” to be in electronic contact with the denizens via his infamous “Tesla Scope”. Of course Tesla was actually listening to Morse Code EMF emanating from local Colorado very long telegraph lines. But the others were actually looking at something inexplicable on Mars. Other scientists have seen flashing or beams of light from near Olympus Mons (I think), around the same time period (but flashing lights continue up until 2014 seen by NASA’s Curiosity). NASA found water all over Mars. I think whatever biological influence on Earth from Mars is “past tense”. I don’t think there is any life on Mars today. I have no theories either so don’t ask…

      1. That’s a nice thought, but no; these experiments have been done and redone for decades, placing hardy microbes that live inside rocks into radiation chambers to simulate thousands of years floating in space, and then heating them to simulate entry.

        A notable percent of some species would be expected to survive. If the rock didn’t totally burn up, if there is some remnant to land on the Earth as a meteorite, then it _would_be_ expected to have survivors.

        They survive simulations of the whole series of conditions, the impact that tears their home apart and thrusts it into space, floating in space, and then returning to a planet, maybe even a different one.

        Not only that, but high in atmosphere, in part we would normally refer to as space, there are living microbes that get blown up that high. Remember, probability + statistics + very large numbers of microbial individuals means that they do manage to get blown up to the top of the atmosphere, and even out into space, even without an impact to toss whole rocks up! The numbers of individual microbes really throws a wrench in the (completely natural, but misguided) ability to intuitively understand what is reasonable, likely, or even possible. Without rocks for shielding, they don’t live vary long, probably not more than a few thousand years, but they might also manage to drift back down into atmosphere without burning up. So Mars Earth might reasonably happen all the time at a low rate. But it certainly has happened repeatedly; something like the impact that coincided with the extinction of the dinosaurs would have dumped a whole bunch of Earth microbes onto Mars. We can’t know how many or how many would survive, but the probabilities and number of individuals involved make it appear that non-zero answers are the most likely.

  15. I think it would be safer to limit humans on mars to one way trips, and not bring back mars samples in protected containers that skip any natural sterilization physics of entering earth atmosphere the same way that’s been going on hundreds of millions of years.
    Humans live and travel isolated from their environment as if already living on another planet so they seem already acclimated, as if we could take the cities and roads and put them on mars, were they seem to belong, more than on earth.
    I think it would help the earth and these people if we could come up with an earth friendly way to reach escape velocity.
    Earth, love it or leave it.

    Powered by almost 40 year old solar panels and wind turbines made from what I took out of the landfill. You don’t have to go back to stone tools to live with the earth. Yes I’m working in the garden today, but also spending more than a few hours today taking apart printers and scanners for stepper motors and sensors and electronics to connect them to Arduinos and Raspberry Pi’s
    I’m a high tech caveman, longing for the day, those who don’t love earth, can leave it in peace.
    Humans (and space travel) have their ugly problems,
    but it’s the solutions that can be as awesome and inspiring as they are beautiful.
    If humans learn to live in peace with mars maybe they can do the same here,
    Until we learn to live in peace with the earth we won’t have peace,
    we’ll be to busy fighting each other over the earth.
    I think it’s in our nature to travel to the stars, but as this article points out, protecting earth environment from those who return, should be a very clear part of that plan.

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