Regarding Germs

There is an amazing opportunity waiting for us on Mars:  The chance to escape, once and for all, from disease.  However, is it really an opportunity?  Or is it a temptation best avoided?

At first glance, Mars with it's completely sterile environment, devoid of all life, and therefore all germs, viruses, and the like, seems like a boon to humanity.  We can go live there, and as long as the colonists are detoxed before flight, they will never again catch a cold, a flu, or indeed any other dangerous germ borne illness.  When we move to Mars, we can simply leave germs behind, for the most part.   Of course, no antibacterial soap is perfect, and no matter what, humans and their livestock will carry some pathogens into space, however, a short term quarantine before flight should allow the astronauts immune systems to finish off anything that they were carrying, and avoid picking up anything new.

When they get on board ship, their bodies will already be accustomed to defeating all the diseases they carry with them.  By the end of their journey to Mars, some of those strains may have died out completely in the absence of new, defenseless hosts.  Any strains that do remain are benign, and have lost the ability to hurt us without mutation.

Mutation is possible, but is a matter of odds.  On Earth, bacteria populations are estimated to be 5*10^30, or 5,000,000,000,000,000,000,000,000,000,000,000.   That's a lot.  A whole, whole, lot.  Of course this is an estimate (found here: http://www.sdearthtimes.com/et0998/et0998s8.html ), but the obvious thing is that with so many bacteria the odds of a mutation are very, very high, probably happening every second or so.   Some of those mutations make deadly diseases, others might create new, useful medicinal treatments.  But, now consider Mars.  Presumed bacteria population: 0.  How much will we bring with us?

An average human has roughly 10^14 bacteria living in and on their body (so says wikipedia here: http://en.wikipedia.org/wiki/Human_microbiome ), about 1000 species.  We need these bacteria to live, so getting rid of them completely is out of the question.  If we assume at least 100 people are going to Mars (I'd rather have a thousand, but that's rather unlikely), that means 10^16 bacteria.  Let's double that number, to include livestock (rabbits, perhaps, and goats, maybe a few cattle), and then double it again to account for topsoil traveling with the plants on board ship (roughly a trillion bacteria per kg of soil, and I expect they will need to carry at least 20 tonnes of topsoil to create a ground layer that can grow crops for 100 people), and we can estimate 4x10^16 bacteria on board our colony ship.  That means that a mutation with good odds of happening once every second on Earth will probably only happen once every five million years in our Mars colony.

That's a very big deal, because it means that Mars will probably have roughly the same strains of bacteria for the first few thousand years after colonization, since population growth after landing will be limited to the size of human settlements, and even at a very high rate of settlement, it is not likely that we will ever reach Earth-like microorganism populations.  Humans will almost certainly adapt to beat all of them, and then will almost certainly not need to adapt any more, which is a problem.  See, if we don't adapt, it is like our immune systems using outdated software.  Imagine if you didn't update any of your computer's software for five thousand years, and then plugged into the internet.  Your computer would explode.  That's what it would be like for humans who live on Mars their whole lives, always exposed to the same bacteria and viruses, and then come back to Earth.  They will suffer extreme immune deficiencies, which could make any Earth tourism very dangerous.

This is why I said that the lure of a disease-free Mars is a temptation.  While it is true that we could solve a lot problems for individuals by eliminating disease on Mars, we would lose the ability to return safely to Earth in two generations or so.  Longevity and health on Mars would come at the cost of isolation.  Soon, even trading with Earth would become risky, because there is no knowing when some chance germ will ride along against which the Martian humans have no immunity.  An epidemic could easily cripple the young colonies, where every person will be necessary, and one death might mean that suddenly nobody on the planet knows how to fix the air purifiers.

To some extent, this separation is unavoidable, and will almost certainly occur.  There is simply no way that the Mars biosphere can keep up with the robustness of the Earth biosphere.  And for some diseases, there is absolutely no reason to let them travel to Mars.  For example, simple screening can completely eliminate all sexually transmitted diseases from the Martian population.  AIDS will be a non-issue on Mars.  Depending on how many people are willing to go, it may even be possible to be selective and create a population devoid of most genetic risk factors.  Similarly, parasites and certain diseases can be done away with.  For example, there is no reason to bring malaria to Mars, or any disease for which a vaccine is available, since Earth can simply send the vaccine instead and immunity can be achieved without an outbreak taking place.

But, if Mars and Earth mean to be in contact with each other, it will be necessary to intentionally expose Mars to at least the more mild Earth germs.  Martian children will still need to be immunized against Earth illnesses, like tuberculosis and tetanus, and for these diseases a simple vaccine should solve the problem.  The really unfortunate part is that Martian humans will also need to be exposed to incurable but common diseases as well, so that if they ever return to the home world they aren't at a physical disadvantage.  The flu, the cold, and perhaps the occasional stomach bug will all be necessary ailments to make sure that Martian immune systems stay up to date.  In essence, there will need to be annual germ deliveries from Earth to make sure that Mars gets sick.

And now, I am certain that my name will be cursed forever on Mars, as the one who suggested an annual "Disease Day."  It's sort of a holiday.  Like Christmas, except that instead of presents, you get the flu.