Sciency Words: Planetary Protection

Sciency Words PHYS copy

Today’s post is part of a special series here on Planet Pailly called Sciency Words. Each week, we take a closer look at an interesting science or science-related term to help us all expand our scientific vocabularies together. Today’s word is:


I swear this isn’t science fiction. The Office of Planetary Protection is a real department at NASA which follows the guidelines set by COSPAR, an international council with jurisdiction over the safe and responsible exploration of space.

The three core tenets of planetary protection are:

  • Don’t contaminate other worlds (we don’t want to harm alien life, if it exists).
  • Seriously, don’t contaminate other worlds (it would suck if the “alien life” we discover on Mars turns out to be E. coli).
  • While you’re at it, don’t contaminate Earth either (have you seen the Andromeda Strain?).

Under COSPAR rules, different mission categories require different levels of planetary protection. Categories I, II, and III require only minimal precautions. Nobody cares if we contaminate Venus. Nothing lives on Venus (probably). Category VI covers missions on the surfaces of worlds that could theoretically support life, and category V is for sample return missions that could theoretically bring alien organisms back to Earth.

Until recently, planetary protection has been a fairly esoteric concern. But now we know there’s water on Mars, and scientists really, really want to get a closer look at that!

Ja07 Curiosity on Mars 1

The Curiosity rover is currently located near a potential recurring slope line (RSL) site, meaning it’s only a few kilometers from what appears to be actively flowing water. But NASA won’t allow Curiosity to investigate.

First off, I should mention there is a logistical concern. Remember the slope part of recurring slope linea. The slope may be too steep for Curiosity to climb.

But the bigger issue is planetary protection (I mean, we could let Curiosity at least try to climb that hill). Under current planetary protection rules, the exploration of an RSL zone is a category IV mission. Specifically, it’s a category IVc. Curiosity is only rated for category IVb, because at the time of launch no one knew there was water on the surface of Mars. So there is a chance—a remote chance, but a chance nonetheless—that it is carrying live bacteria from Earth.

In my opinion, Curiosity should be allowed to investigate the RSL site anyway. It would be a miracle if any microorganism from Earth could survive on Mars. There’s too much radiation, and the water is brimming with toxic perchlorate salts. And the idea that organisms from cushy, comfortable Earth might outcompete native Martian life forms—life forms that are perfectly adapted to the harsh environment found on Mars—sounds 100% preposterous to me.

Ja07 Curiosity on Mars 2

At the same time, I know any evidence of life Curiosity might find would be justifiably suspect. We could never rule out the possibility of a contaminated sample.

So what do you think? Should Curiosity keep its distance from potential RSLs, or are COSPAR and the Office of Planetary Protection being over-precautious?


The Office of Planetary Protection (official website).

COSPAR Planetary Protection Policy from COSPAR and the IAU.

Water on Mars: NASA Faces Contamination Dilemma over Future Investigations from The Guardian.

5 thoughts on “Sciency Words: Planetary Protection

  1. Excellent art work!

    I have no idea whether or not it’s safe to have a category IVb robot explore a category IVc area. I suspect those making the decision would rather risk going down in history as the people who were too cautious rather than the people who accidentally poisoned the Martian biosphere. Although if the water is coming from humidity in the atmosphere, it seems like any damage might already have happened.

    Liked by 1 person

    1. You bring up a fair point. I’m no expert, but I’m under the impression that the distinction between category IVb and IVc is fairly minor. Of course if there is a big difference between them, I’d be more convinced that Curiosity should keep its distance.

      Liked by 1 person

  2. As eager as I am to have the RSLs explored, I’m of the opinion Curiosity should stay away. Think of it as a (valid) excuse to send an even bigger, badder rover to Mars in the near future.

    Liked by 1 person

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