Yes they could. First, planetary protection is only done on basis of probabilities. Target for Mars was a chance of 1 in 10,000 of contaminating Mars for each mission, with a 1 in 1000 chance of contaminating it during the exploration period. This is a figure chosen by Carl Sagan I think. It is arbitrary - you can't come up with a reasoning to some particular figure like that. But you have to choose some figure because it is impossible to sterilize our spacecraft totally of microbes with present day technology. This is the method used for instance for Viking 1 and 2 on Mars.
There are several phases to the sterilization. So starts with assembly in a clean room, with hardly any microbes in the atmosphere, and using clean wipes and other methods to keep it clean. In case of Viking they added a heat sterilization phase, basically baking it in a slow oven for many hours.
Then the microbes are reduced further during the journey to the destination, in this case Mars, by vacuum and cosmic radiation and UV. Then reduced further on landing on Mars and continue to be reduced as long as the spacecraft remains on Mars. So all of that was allowed for in the calculations.
Later on, this is for Mars only, they dropped the Viking final heat sterilization phase, because Viking found that conditions on the surface of Mars are so hostile to life that they thought this added the equivalent of several more decimal reductions, that roughly the harshness on Mars compensated for the lack of a heat sterilization phase, and dropped the requirement of a detailed per mission probability assessment in favour of a spore count of the spacecraft before launch, depending on how sensitive the target is.
So you can question if that was a wise decision. Some think a 1 in 1000 chance of contaminating Mars is a low enough probability. If you want certainty, well we couldn't yet send any rovers to Mars as we don't have the technology needed to achieve more or less complete certainty here.
And it's known from experiments on the ISS, for sure, that many microbes would be able to survive the trip to Mars in dormant form on our spacecraft and would revive after that trip if they met suitable conditions there.
And many extermophiles have been found in spacecraft assembly facilities and on the spacecraft themselves, analysing swabs of the spacecraft after cleaning.
As well as that we have had several crashes on Mars. The early Russian spacecraft as you say. The Russians say they sterilized them thoroughly, but the US are doubtful about their claims here.
Then the Mars polar lander, crashed into the ice cap, a sensitive place for life. And the Climate Orbiter - not sterilized adequately for the surface - this is the one that crashed due to mixup of imperial and metric units used by different teams of researchers.
Also I'd add Phoenix. It discovered possibilities of conditions for life where it landed, which was not expected, and was only sterilized for a landing in a place totally hostile to life. And it's particularly vulnerable because it got crushed by a layer of dry ice a meter or so thick as winter progressed (they knew this would happen and it was only designed to last until the winter came) - which broke off its solar panels and you can see from orbital images that it has been damaged.
In case of Venus, it is less likely, because the surface of Venus is totally hostile to Earth life. The Venera balloon probes spent some time in the upper atmosphere of Venus. However the high levels of sulfuric acid in the cloud droplets there make it next to impossible that they contaminated Mars. That's because we don't yet know of any Earth lifeforms able to withstand such high concentrations of sulfuric acid - though it is not far off the upper range of some extremophiles we do have. Chances that something able to survive there was on the Venera balloon envelopes and transferred to the clouds is surely minute.
There just possibly might be life there, some indirect but inconclusive findings (detection of OCS which on Earth always means life but sadly, some non biological processes can also produce it in the Venus atmosphere, and detection of non spherical particles just the right size for microbes - that's the only suggested evidence so far as far as I know). Most I think would say it is unlikely. But not at all likely that we have contaminated the clouds yet, if Earth life is possible there at all.
In future if we send spacecraft to Europa we need to rethink this and most of the scientists in the workshop report for Europa planetary protection said that we need to protect it not just for an exploratory period - but for all future time (until we know what's there at least).
But at present Mars is the only one we need to worry about. We sent life to the Moon but there is no chance, according to modern understanding, that it was able to reproduce there.
In case of Mars there is a chance. And I think myself that as a matter of some urgency we should send a spacecraft to one of the earlier landers or crashes on Mars to see if any of the life they brought has survived and if any has started to reproduce. If they have, is a chance, given the harsh conditions there and how slowly life would spread at first, slow long lifetimes of microbes - especially if the life started a bit below the surface not carried everywhere in dust storms - perhaps we can stop it in its tracks.
Phoenix would be an ideal target there, as we know where it is, and know what conditions are like from ground measurements made by Phoenix itself. And it is also an interesting location for both past and present day search for life. So you could send a rover there that would do in situ searches for life past and present - land a fair bit away from Phoenix so as not to be confused by any contamination in the case that Phoenix has brought any to Mars - and then visit Phoenix for a close up inspection. We have many very sensitive biological instruments we could send to Mars that would have no trouble detecting Earth life if it is present - as well as being useful for search for Mars life.
And could do the same for the crashed Soviet probes and the Mars polar lander, once we get to the situation where it is easy to send many lander missions to Mars.
Actually personally I think that Phoenix is more likely to be an issue than the Soviet probes, unless there are conditions for surface life prevalent on the surface of Mars almost anywhere. That's because it would be a long distance for the dust storms to carry any microbes from the crashed probes to somewhere where they could reproduce and many opportunities for them to die due to cosmic radiation and UV light.
Conditions are so hostile on Mars for life, with only a few potential microhabitats if they exist, of a few mms of liquid here and there - and most of our spacecraft landed in the almost totally dry equatorial regions. So - I think most scientists believe that life is unlikely to have reproduced there yet.
However, perhaps the chance is a bit higher though than the target 1 in 1000 that we have contaminated Mars with life that has started to reproduce there. It would be good to have some ground truth from Mars to find out how well our planetary protection measures have worked to date.
There are several phases to the sterilization. So starts with assembly in a clean room, with hardly any microbes in the atmosphere, and using clean wipes and other methods to keep it clean. In case of Viking they added a heat sterilization phase, basically baking it in a slow oven for many hours.
Then the microbes are reduced further during the journey to the destination, in this case Mars, by vacuum and cosmic radiation and UV. Then reduced further on landing on Mars and continue to be reduced as long as the spacecraft remains on Mars. So all of that was allowed for in the calculations.
Later on, this is for Mars only, they dropped the Viking final heat sterilization phase, because Viking found that conditions on the surface of Mars are so hostile to life that they thought this added the equivalent of several more decimal reductions, that roughly the harshness on Mars compensated for the lack of a heat sterilization phase, and dropped the requirement of a detailed per mission probability assessment in favour of a spore count of the spacecraft before launch, depending on how sensitive the target is.
So you can question if that was a wise decision. Some think a 1 in 1000 chance of contaminating Mars is a low enough probability. If you want certainty, well we couldn't yet send any rovers to Mars as we don't have the technology needed to achieve more or less complete certainty here.
And it's known from experiments on the ISS, for sure, that many microbes would be able to survive the trip to Mars in dormant form on our spacecraft and would revive after that trip if they met suitable conditions there.
And many extermophiles have been found in spacecraft assembly facilities and on the spacecraft themselves, analysing swabs of the spacecraft after cleaning.
As well as that we have had several crashes on Mars. The early Russian spacecraft as you say. The Russians say they sterilized them thoroughly, but the US are doubtful about their claims here.
Then the Mars polar lander, crashed into the ice cap, a sensitive place for life. And the Climate Orbiter - not sterilized adequately for the surface - this is the one that crashed due to mixup of imperial and metric units used by different teams of researchers.
Also I'd add Phoenix. It discovered possibilities of conditions for life where it landed, which was not expected, and was only sterilized for a landing in a place totally hostile to life. And it's particularly vulnerable because it got crushed by a layer of dry ice a meter or so thick as winter progressed (they knew this would happen and it was only designed to last until the winter came) - which broke off its solar panels and you can see from orbital images that it has been damaged.
Before and after image of Phoenix from orbit showing how it was damaged by the winter time meters thick dry ice layers that covered it in between the two images. Phoenix Mars Lander is Silent, New Image Shows Damage
Droplets of what may be salty brine on the legs of Phoenix. One hypothesis is that they formed due to ice and salt mixed together that landed on its legs during the landing - and then formed liquid. If this can happen on the Phoenix legs, it may well also happen naturally on the surface when conditions are right. If so then that means Phoenix landed in a sensitive area on Mars where life could flourish, which wasn't known before its launch.
And conceivably life from Earth could have reproduced inside those droplets also. They would be very salty if the theory is right, so most Earth life would not be able to reproduce there. And may have been far too cold for life. But there are microbes that could reproduce there if not too salty and warm enough, and some of those have been detected in spacecraft assembly clean rooms. So not totally impossible I think, But at the same time given that the spacecraft are thoroughly cleaned before launch, and the sterilization on the way there etc, reasonable chance that nothing happened.
In case of Venus, it is less likely, because the surface of Venus is totally hostile to Earth life. The Venera balloon probes spent some time in the upper atmosphere of Venus. However the high levels of sulfuric acid in the cloud droplets there make it next to impossible that they contaminated Mars. That's because we don't yet know of any Earth lifeforms able to withstand such high concentrations of sulfuric acid - though it is not far off the upper range of some extremophiles we do have. Chances that something able to survive there was on the Venera balloon envelopes and transferred to the clouds is surely minute.
There just possibly might be life there, some indirect but inconclusive findings (detection of OCS which on Earth always means life but sadly, some non biological processes can also produce it in the Venus atmosphere, and detection of non spherical particles just the right size for microbes - that's the only suggested evidence so far as far as I know). Most I think would say it is unlikely. But not at all likely that we have contaminated the clouds yet, if Earth life is possible there at all.
In future if we send spacecraft to Europa we need to rethink this and most of the scientists in the workshop report for Europa planetary protection said that we need to protect it not just for an exploratory period - but for all future time (until we know what's there at least).
But at present Mars is the only one we need to worry about. We sent life to the Moon but there is no chance, according to modern understanding, that it was able to reproduce there.
In case of Mars there is a chance. And I think myself that as a matter of some urgency we should send a spacecraft to one of the earlier landers or crashes on Mars to see if any of the life they brought has survived and if any has started to reproduce. If they have, is a chance, given the harsh conditions there and how slowly life would spread at first, slow long lifetimes of microbes - especially if the life started a bit below the surface not carried everywhere in dust storms - perhaps we can stop it in its tracks.
Phoenix would be an ideal target there, as we know where it is, and know what conditions are like from ground measurements made by Phoenix itself. And it is also an interesting location for both past and present day search for life. So you could send a rover there that would do in situ searches for life past and present - land a fair bit away from Phoenix so as not to be confused by any contamination in the case that Phoenix has brought any to Mars - and then visit Phoenix for a close up inspection. We have many very sensitive biological instruments we could send to Mars that would have no trouble detecting Earth life if it is present - as well as being useful for search for Mars life.
And could do the same for the crashed Soviet probes and the Mars polar lander, once we get to the situation where it is easy to send many lander missions to Mars.
Actually personally I think that Phoenix is more likely to be an issue than the Soviet probes, unless there are conditions for surface life prevalent on the surface of Mars almost anywhere. That's because it would be a long distance for the dust storms to carry any microbes from the crashed probes to somewhere where they could reproduce and many opportunities for them to die due to cosmic radiation and UV light.
Conditions are so hostile on Mars for life, with only a few potential microhabitats if they exist, of a few mms of liquid here and there - and most of our spacecraft landed in the almost totally dry equatorial regions. So - I think most scientists believe that life is unlikely to have reproduced there yet.
However, perhaps the chance is a bit higher though than the target 1 in 1000 that we have contaminated Mars with life that has started to reproduce there. It would be good to have some ground truth from Mars to find out how well our planetary protection measures have worked to date.
About the Author
Robert Walker
Writer of articles on Mars and Space issues - Software Developer of Tune Smithy, Bounce Metronome etc.Studied at Wolfson College, Oxford
Lives in Isle of Mull
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