Contaminating space

In April, 2019, Israel’s Beresheet spacecraft landed on crashed into the Moon.

It later emerged that it was secretly carrying a supply of live tardigrades — microscopic creatures known for their hardiness.

Naturally, many observers, joking or not, brought up the idea of accidentally contaminating the Moon with destructive Earth life.

I worry about a lot of things, but accidentally contaminating other celestial bodies with invasive Earth life just isn’t one of them.

NASA and other space agencies aren’t actually worried about contaminating the Moon. It’s obvious that the Moon is lifeless and inhospitable. But they do have some concern about other celestial bodies, particularly those that may have liquid water. How concerned they really are is hard to say. The experts don’t all agree.

They did go to the trouble of crashing the Cassini spacecraft into Saturn at the end of its mission, and they plan to do the same with Juno and Jupiter. They seem to make a big deal of the fact that this is done to prevent possible contamination of the icy moons. Okay, I guess. It’s good to clean up your space junk, anyway. But spacecraft can fail at any time, making it impossible to crash them as planned. Apparently, that was an acceptable level of risk.

I don’t want this post to get lost in the weeds of official procedures and risk formulas and international agreements. My non-expert, long-story-short prediction is that even if we’re as reckless as can be, contamination is exceedingly unlikely. A lot of miracles would have to occur, piled on top of one another.

But maybe a more important thing is that if contamination is possible, I don’t think there’s any way we could prevent it. Assuming humanity beats the odds and remains a space-faring species for a few hundred more years, we’ll probably contaminate every contaminable world, no matter how hard we try not to. It might be an unlikely accident, or someone goes rogue and deliberately contaminates a world.

I hesitate to bring this up, but if we’re absolutely sure that a world is lifeless, it isn’t necessarily objectively bad to contaminate it. That’s a matter of opinion. The problem is, we can never be completely sure that the world was in fact lifeless.

Back to the likelihood of contamination, I think we are too enamored with the idea of life being incredibly resilient and versatile, creatively finding ways to live in every available environment. I put some of the blame on the movie Jurassic Park, with its silly “Life finds a way” line. I would point out that there are parts of the Atacama Desert that no life at all has colonized. And the Atacama Desert is in Chile, on Earth. Life may be resilient, but it has its limits.

Fundamentally, being alive is a highly unnatural thing. There are many more ways of being not alive than there are of being alive.

Suppose you’re in room whose air temperature is 22°C (72°F), and your body temperature is a steady 37°C (98°F). That’s just wrong. Your body is violating the laws of thermodynamics!

Of course it’s not really violating the laws of thermodynamics, but it has to constantly battle against them. It shouldn’t be surprising that, one way or another, it will eventually lose.

Body temperature is a way to illustrate the point, but it’s not really about that. Even if you’re one of our secret cold-blooded reptilian overlords in disguise, the laws of thermodynamics are still trying to make you not alive, in ways that are only slightly harder to understand. All life requires energy gradients of some sort, and the universe is working to get rid of those gradients.

So, all things considered, contaminating extraterrestrial worlds is not one of my top things to worry about.

Of course, with my luck, it will be the one thing I should have worried about. The Moon Tardigrades will Find a Way, mutate, develop a space program, and I guess we know what happens next.


  • All images are from Encyclopedia Britannica, 11th Edition.
  • I won’t link to any specific articles. Just search the web for “tardigrades on the moon”.

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