Will the Mars One mission team be testing samples to know for sure that there are no deadly viruses on Mars?

If there are no viruses, will this pave the way for Mars travel?

What would be the consequences of introducing some of our viruses and bugs to Mars?

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    $\begingroup$ I would think the robotic sample return mission, which has been proposed many times, would be sufficient to infect Earth. $\endgroup$
    – AlanSE
    Dec 16, 2013 at 13:08
  • $\begingroup$ Related question (2 answers): How is equipment sterilized for space missions? $\endgroup$
    – TildalWave
    Dec 16, 2013 at 15:48
  • 10
    $\begingroup$ The title of the question doesn't match the body. Mars One is one-way because of lack of money for the full $\Delta V$ shebang. $\endgroup$ Dec 16, 2013 at 19:18

4 Answers 4


Quarantine was always a standard procedure for the astronauts which landed on the Moon. The Apollo astronauts were kept in quarantine just in case they contracted something on the Moon's surface. This turned out to be unnecessary, but better safe than sorry. But how likely is it that there are deadly pathogens on another planet? I would say it is pretty unlikely.

Infectuous pathogens (viruses, bacteria, parasites, fungi or any other microbiological stuff which makes macrobiological stuff feel sick) evolve to coexist with a particular host. But considering that it is practically impossible that there is higher life on mars right now and that there is currently no hint that it ever existed, there are no hosts for which pathogens could have evolved. When there are microbes on Mars it is unlikely that they evolved to infect and harm other life-forms.

Even when we presume that there once were other higher life-forms on Mars and pathogens evolved to infect them and these pathogens somehow survived millenias and now lie dormant, it is still unlikely that they are harmful to humans. Most diseases on Earth only affect one particular species (they might be carried by more than one, but they are only harmful to one). When they affect more than one species, these are usually closely related. It is very unlikely that a pathogen which evolved in a completely separate ecosphere would be able to infect us.

No, the reason for Mars One being a one way trip is a different one: Money.

A trip between Earth and Mars takes a lot of fuel per kg of payload. When you want to return, you need to carry the fuel for the return-trip with you. To move that fuel you need even more fuel. And you need to carry THAT fuel too. That means a ship for a two-way trip would have to be a lot larger than one for a single voyage. This is referred to as the tyranny of the rocket equation.

And then there are other complexities. Building a capsule which just has to land on Mars is much simpler than one which is equipped with a rocket-engine powerful enough to return into orbit. And it's heavier, which means that even more mass is needed.


There's no need to worry about any viruses from Mars. If there are any, there would also have to be host organisms through which these viruses would multiply and survive (it's still debatable whether viruses even count as life). And host organisms are easier to detect through e.g. their metabolic process byproducts, and also more difficult to contaminate life support of any future colonists due to their size being much larger. And in the eventuality that these theoretical Martian viruses could stay dormant for millennia and endure extreme conditions present there, then they would already have been introduced to the Earth through meteorites originating from Mars.

A common belief that meteorites are on impact glowing hot all the way to their inner core due to heat produced through friction on their fast travel through the atmosphere simply isn't true, and any expert on the subject will tell you that they're at most mildly warm to cold to the touch immediately after impacting on Earth. Or ice, as it is the case in polar regions where a lot of them are collected off the snowy / icy surface since they're easier spotted dark on all white, and the ice or snow under them doesn't melt much at all, icy surface might merely be cracked due to the impact force. This is mostly due to asteroids being cooled to near absolute zero (perhaps at most a few degrees Kelvin, or roughly -450 degrees Fahrenheit) in the vacuum of space before impacting to Earth, and also since they would lose most of the heat generated via friction in the atmosphere through ablation of its outermost layer, then cool again when they slow down in the lower, and still cold atmosphere. All of it lasts perhaps a few seconds, so there simply isn't enough time for their cores to sterilize any hypothetical living microorganisms and viruses in them through extreme heat (i.e. thermal expansion or thermochemical change in levels of free radicals that would disintegrate biological samples).

So there's two options left, either there aren't any, or they're localized to places of local biota which we're still struggling to find. And if there is indigenous life on Mars, chances that any of their viruses would be chemically and, ultimately, genetically compatible with life on Earth as it is, all prerequisites for it to have any effect on us, is extremely remote. And even if they would be, there's not much chance they'd be much of a bother to us because of our better evolved immune system.

You see, viruses can multiply really fast (can go through new generations in hours, some even faster), and with each new generation they can adapt to host organism's defensive mechanisms through natural selection - some mutate and develop new trades that let them survive, and the survivals successfully multiply, preserving the trade that enabled them to survive and creating more resistant, better adapted new generation. Viruses that didn't go through such evolution wouldn't stand a chance, especially from a planet that's not evolving new lifeforms and new, better evolved breeds as fast as here on Earth, i.e. has inferior biodiversity and is less likely to match or adapt pathogen-to-hosts with superior, more diverse biota.

What I'm saying is we're safe from space viruses, because the Earth is the fastest evolving habitat that we know of and viruses already introduced to us have had a chance to adapt through the millions of years of evolution of life and its own natural (and in recent years artificial) defenses. And if we really have to worry about new, yet unknown strains of viruses, then we ought to look no further than under the melting ice of the polar regions here on Earth. And we're safe from higher organisms because our technology is by now sufficiently evolved to detect them even in trace quantities, and we do follow decontamination procedures that are guaranteed to terminate any water-based life compatible with one that strives here on Earth.

The other way, what we call forward-contamination, and planetary protection in general is a bit more interesting though and is lately much discussed in scientific and popular literature. History teaches us that we've caused much sorrow to indigenous population wherever we were discovering and inhabiting new lands and that it is by far more common to introduce a deadly pathogen causing havoc to an isolated, less biodiverse habitat than the other way around. One of the most infamous such examples is the introduction of smallpox, measles and influenza viruses to the indigenous populations of North America, but there are many other similar cases throughout the human history of exploration, which is nicely explained on Wikipedia page on Social history of viruses, but the havoc doesn't stop at microorganisms.

Problem with any such discussions is of course that they might be irrelevant, if it turns out that the planet we're colonizing is indeed a dead rock, but to know that for sure might be nearly impossible without risking contamination first and exploring all of its distinct environment regions. In semi-official capacity, the highest authority on the matter is considered to be the Committee on Space Research (COSPAR) that is preparing recommendations to avoid interplanetary contamination for national space agencies that are members of the International Planetary Data Alliance (IPDA) and including NASA.

But since this is an utterly broad topic and not to beat around the bush too much, I'll just refer you to Wikipedia sections on Containment and quarantine, Decontamination Procedures, and Impact prevention where it's all described in greater detail. It is definitely a hot subject, though. Perhaps worth mentioning too is that we have obviously already managed to forward-contaminate another celestial - the Moon.


First, no that's not the reason it is one way, though it is something that is a matter of concern that has to be thought about.

It's for reasons of cost and technology. Mars is a much harder place to land on and take off from than the Moon. That's because of the rocket equation The delta v to escape from Mars to orbit is 4.1 km / sec. To escape from the Moon is 1.6 km / sec.

That's only 2.5625 times faster. But because of the rocket equation it makes a huge difference. You have to multiply the mass you need, to get into orbit by e^(deltaV/ExhaustV) to get the mass ratio. So if you multiply deltaV by 2.5625, keeping everything else the same, that means the mass ratio is not just multiplied by 2.5625, it's actually taken to the power of 2.5625.

Example, lunar module ascent stage had dry mass of 2.15 tons and including fuel, 4.7 tons. So the ratio was 2.186. For Mars you have to take that to the power 2.5625 so that would be (4.7/2.15)^2.5625 or 7.412 approx. That would make the total including fuel a little short of 16 tons. That's a rough first idea of course. Nothing like as difficult as a Saturn V but much much harder than a lunar module.

Critics of Mars One say their budget to land on Mars is already unrealistically low given the number of new technologies that would need to be developed for the mission. Landing on Mars is far harder than landing anywhere in the solar system - because of the high gravity again. The thin atmosphere lets you slow down from Mach 4 down to Mach 1 but is not enough to get you to a comfortable soft landing, as even with parachutes, at least the largest tested so far, you hit the ground at over 200 mph. That's why you have the need for technologies like the sky crane. It also makes landings far less accurate than they are on the Moon.

So their idea is to make it easier by leaving out the ability to return, but it's not clear that that does reduce the level of technology that significantly as it's landing on the surface safely that's by far the hardest part of a journey to Mars. But it is one less thing to develop.

However - there is indeed significant risk of contamination both ways. Several studies and papers back this up.

Some back contamination issues are:

  1. Pathogens can evolve independently of any higher animal host e.g. as a disease of microbes (as is true for instance for Legionaire's disease - a disease of amoeba that jumped straight to humans quite recently).

  2. DNA of archaea can be shared via gene transfer agents - if those got into the sea, then one study found that almost half the micro-organisms in a sample of ordinary sea water took up the genes in a GTA that conferred antibiotic resistance by the next day, even with no selection advantage to take it up.

  3. A new micro-organism could disrupt natural cycles, displace other microbes in an ecosystem, be a disease of our food, or a disease of other organisms on land or in the sea. So it doesn't need to be a disease of humans to be a problem.

  4. In the most interesting case, independently evolved, it may not be based on DNA. In that case, then the XNA (so called) could be hazardous if it out competes DNA or can occupy niches not occupied by DNA.

  5. Also if it is XNA, then our immune systems and those of other creatures may not recognize the chemicals it produces as the signature of life. This was a concern raised by the Nobel prize winning microbiologist Joshua Lederberg.

In that last case, it could just colonize parts of our bodies, our skin, intestines, or whatever and our bodies only respond to any physical trauma it causes and are not adapted to try to do anything about their cause. It could harm us directly, or it could produce chemicals that are harmful to us as byproducts. It's in the interest of microbes that colonize our bodies to keep us alive, as their host, indeed many eventually adapt to be symbiotes, e.g. the microbes we use to digest food, essential to our survival. So it's not in a microbe's interest to kill us, but could easily do so just because it is not adapted to us, or us to them.

So - life from Mars - could co-exist peacefully, be so harmless we could eat kgs with no harm, could be unable to survive on Earth - but it could also be hazardous to Earth life.

There has been meteorite exchange between Mars and Earth but most of that happened billions of years ago and most microbes probably can't be transmitted between planets on meteorites.

It is believed that some could (though not known for sure if any did) - but there is plenty of room for the possibility that life on Mars is significantly different from Earth life.

The other way - if we introduce Earth life to Mars then we risk contaminating a pristine planet irreversibly. This closes off any future options that might involve a Mars with no Earth life or with different lifeforms there. I would argue strongly that we shouldn't do that until we know very well exactly what Mars is like and have a good idea of the effect of our actions.

It might make any Martian present day life extinct and confuse the study of past life on Mars. Also, it could cause problems for future terraforming or whatever we might decide to do with Mars, if anything.

You can read a lot more about it in my articles on the subject:

Case For Moon - New Positive Future For Humans In Space - Open Ended With Planetary Protection At Its Heart

Need For Caution For An Early Mars Sample Return - Opinion Piece

Trouble with terraforming Mars

and other articles in my column. In forward direction, introducing any life to Mars would hugely confuse attempts at scientific investigation.

See Could Microbes Transferred On Spacecraft Harm Mars Or Earth - Zubrin's Argument Revisted

On searching for life by looking for changes in the environment caused by life - that's okay if life is abundant. But it's no good if it is rare.

Life on Mars is likely to be rarer than life in the Atacama deserts or McMurdo dry valleys - and there - life is so hard to spot that in some places life was only detected for the first time in the last decade.

You are talking about microbes that may have lifetimes of a thousand years or more, slowly metabolizing, hardly making any changes to their environment, just a few of them eeking out a living very much on the edge of what's possible.

We have instruments that can detect life even in such challenging environments as those, and they could work on Mars also - able to detect a single amino acid in a gram of soil for instance, and find its chirality. For that matter the Viking labelled release - updated to take account of the confusing chemistry on Mars - is also exquisitely sensitive able to detect metabolic activity of a few non reproducing microbes.

But could be a long search as there are many places on Mars where we can search, at least four different main types of habitat - the deliquescing salts (within top two cms of soil), the warm seasonal flows (whatever they are, nobody knows for sure but seems pretty convincing is water in some form), the solid state greenhouse effect melting layers of ice - it is same thing that causes the Martian geysers by evaporating dry ice - same thing could also melt ice and may be a habitat and may explain the dark dune spots - and then also life may be able to live using photosynthesis and just the humidity of the night time air even in equatorial regions.

May be life, very low concentration, in many places. Or may be very rare just here and there. And you may have habitats that life could survive in which it just hasn't reached yet, because on Mars it would surely take longer for life to spread to new habitats, and instead of colonizing within weeks or months of habitat formation, may not happen for thousands or even millions of years depending how the life spreads and reproduces and if it can e.g. be spread in the Mars dust storms, say, or needs some other rarer or slower method of transfer.

On reverse contamination

More on reverse contamination

On the general approach of Moon first and taking an open ended approach with planetary protection and reversible biological exploration as core principles.

(edited some more, Robert)

  • 1
    $\begingroup$ Why would a thinner atmosphere be a hindrance to a rocket launch? Also, "Pathogens can evolve independently of any higher animal host". OK, yes, but not with no host whatsoever. No organisms develop dependency without having anything to depend on in the first place. I'm not saying there is no life on Mars, that's yet to be established, what I'm saying is that once you realize this dependency, you might as well try and detect hosts instead, which should be a lot easier. E.g. detect metabolites. If there is life, it has to live of something. So far, we haven't detected any such cycles. $\endgroup$
    – TildalWave
    Jan 6, 2014 at 3:00
  • $\begingroup$ Okay - yes the atmosphere, what it is, actually is a help, because it slows it down from about Mach 5 to Mach 1, but unfortunately parachutes, of the sizes tested so far, don't get you all the way down to a comfortable landing speed so land at over 200 mph, so then within 90 seconds you have to do that + then turn into a lander, retropropulsion etc and land. It doesn't get in the way of a launch much. But the extra gravity, very roughly double Moon, is a big increase in amount of fuel needed because of the rocket equation. So can't carry enough fuel with them to abort to orbit. $\endgroup$ Apr 12, 2016 at 18:35
  • $\begingroup$ Yes that's just one of many options. If it was adapted to a host on Mars we would find that host eventually but it could be microscopic like our amoeba. But if you continue down the list, the other options are that it is just not recognized as life, like some ideas for XNA that could be developed in the laboratory to make implants our body would not recognize as alive. Then you have the possibility that it is just better at Earth life, say at metabolism or photosynthesis, and it's not only humans to think about - there's a lot to it. I'll add links to some of my articles to explain more. $\endgroup$ Apr 12, 2016 at 18:40
  • $\begingroup$ Hi Robert, welcome back. To 'ping' someone, meaning they get a message in their inbox from you, put '@' and then their username - @example. Otherwise it is possible they won't know. I'm going to make some light edits to your post for formatting. Click on edit to see what i've done, or check this guide to Markdown. $\endgroup$
    – kim holder
    Apr 12, 2016 at 19:31
  • $\begingroup$ Hi Kim, okay thanks! @TildalWave just to say I've made an answer, also edited the original answer, hope it helps. $\endgroup$ Apr 14, 2016 at 18:03

Again I can't comment, so I post my 5 cents as an answer.

The one-way direction of flight comes from an expensive budget, but also technology is not advanced enough. Under lack of technology I mean:

  • Solar sail - no working samples at the moment. Definitely it would be noticable if our probes fly there-around in the solar system.
  • Space elevator, no proper carbon nanofibers at the moment. Or some other materials which help to build a space elevator.

But technology is rolling forward, so that "one way" may (or may not) be converted to "Welcome back". Or if they (the cosmonauts) will find 1 cubic km of gold on Mars ...

Some assumed (and argued in answers) probability of biological infestation, like very minor threat - but in a situation where we have near zero information about the Mars environmnent, we can only guessing and preparing ourselves for different scenarios (because any possible scenario may happen). Robert Walker answered and covered much of that question.

Actually, first, it's interesting how our (in human body) microbiological friends (human microflora) will behave in those new circumstances (environment). Second, we have to be over-cautious about XNA. And an XNA may not necessarily consider the human body like a host or target to infect - the human body may just be a package of food for it (for some pretty self-sufficient stuff, like bacteria, etc.). We can be pretty sure - chemistry is the same both on Mars and Earth - "nobody will eat us" - I would not rely on that.

On the Earth: Deep ocean microbiology isn't covered well, also like deep under-earth microbiological stuff, and there can be interesting symbiotic systems, which parts can be not a welcome for us. About Mars ... nobody may be sure what wait us there - be ready.


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