If you're like me, every time NASA scientists announce something about the possibility of life, or even just water, on Mars, you're like: Send a probe to look for life there! Send it there! Why aren't you sending it there? (Video via NASA)
The answer is that NASA is actually constrained by law from doing that. The agency sends a lot of stuff to the red planet, but it has to follow strict rules about how close unsterilized equipment can get to areas where life might be possible. (Video via NASA)
It's not a frivolous decision. The U.S. and most other countries have ratified a U.N. agreement dubbed the Outer Space Treaty, which, among many other rules, says countries must "conduct exploration of [celestial bodies] so as to avoid their harmful contamination."
Contaminating Mars with Earth life is a real concern because there's no way to be sure the equipment we send to the planet is sterile. Over the past few decades, we've learned that microbes can survive where we never would have thought, like in extreme heat or cold, or even in acid. (Video via NASA)
So even though NASA builds its probes in a clean environment, some hardy microbe is already bound to have slipped past the defenses and wound up on Mars. (Video via NASA)
"We know that there's life on Mars because we sent it there," NASA's John Grunsfeld said.
That's why it's so tricky to go look for life in those water flows. For one, we don't want to send microbial alien invaders that might wipe out existing Mars life. (Video via National Science Foundation)
And also, simply having Earth microbes around makes it that much harder to tell whether any life we find is actually Martian.
"You can't do a do-over on releasing organisms into the Mars environment. Once they're there, they will be there. ... We really want to understand what's there at Mars and not see the stuff we brought with us," NASA's planetary protection officer Catharine Conley said.
There's some debate among scientists about how strict the rules are, though. A 2013 paper in Nature Geoscience caused a stir by calling Mars planetary protection efforts a waste of time and money, saying, "If Earth microorganisms can thrive on Mars, they almost certainly already do; and if they cannot, the [transfer] of Earth life to Mars should be of no concern." (Video via NASA)
And those efforts are undeniably expensive. Baking a spacecraft, like NASA did with the Viking mission, costs around $100 million.
Other scientists argue that there's no way to prevent Mars contamination, anyway, since every year asteroid strikes kick up clouds of rocks that float back and forth between the two planets, potentially carrying life. (Video via NASA)
So far, these suggestions haven't swayed the international community toward turning Mars into a microbe free-for-all. So for now, NASA will continue its slow, careful, almost tedious exploration. (Video via C-SPAN)
This video includes images from NASA and William Waterway / CC BY SA 3.0.
