Does life exist beyond Earth? That's arguably the biggest question the modern science community faces. There's very good reason to believe it does. Life in the Cosmos seems statistically inevitable, but aside from the "weirdest star in the galaxy," KIC 8462852, we have yet to detect any semblance of intelligent civilization within a relative shouting distance around Earth.
On a broader scale, the challenge astronomers face is finding any life at all, anywhere in outer space. That means life forms as small as microbes and bacteria, which are known to survive even in Earth's most hostile environments, from the subfreezing regions in Antarctica, to the boiling-hot vents at the bottom of the ocean. So many scientists think microbes could be living in the Martian soil--or better yet, the water. There's only one problem:
NASA forbids sending the Mars rovers to analyze the water.
More specifically, there's an international treaty forbidding it. It refers to planetary protection, which is "the practice of protecting solar system bodies from contamination by Earth life, and protecting Earth from possible life forms that may be returned from other solar system bodies" [Source: NASA].
At a glance, this seems like a reasonable law to make. For purposes of remotely exploring other planets, namely Mars, you don't want to contaminate the planet and make a false discovery of life. On the flipside, when rockets start traveling back to Earth from Mars and elsewhere, you don't want to bring back a microbe/bacteria/virus that's going to kill off humans and other species.
But that raises a question: how can humans hope to explore the solar system if these threats and sanctions are ever-present?
While it's admirable to want to preserve the so-called pristine environments of other worlds, we must also accept the inevitable fact that if we want to live beyond Earth, we will have to contaminate Mars, and it's better to do it sooner rather than later.
Finding extraterrestrial life will be an amazing moment in science. There's no doubt about that. But for the long run, we need to think about human exploration and humans inhabiting other planets. We need to accept the reality that Mars simply does not have any enduring surface ecosystems--environments that we would need to worry about destroying. If there were trees and grass and other animals that didn't share our biology, and our contamination, or mere presence there ended up killing those life forms, that would be a big problem. But until we find a functioning, obvious ecosystem, I say we go forth.
Why would introducing Earth life (microbes, bacteria, etc) be good for us inhabiting planets? And why would it be good to start early? Simple: to prepare the way. To begin creating an environment we can survive in and spread Earth life to. It would be one of the first steps of terraforming planets like Mars: nourishing the soil.
Bacteria and microbes, we know, are capable of adapting to hostile environments, and can do so very quickly. And another thing microscopic organisms are good at doing is multiplying very, very fast. Growing colonies of microbial life and introducing them into the Martian soil would allow plants to grow. There's plenty of carbon-dioxide on Mars, so with incremental exposure, there would be no trouble growing plants--and thus changing the composition of Mars' atmosphere to a breathable one (Mars' atmosphere is currently composed of approximately 95.3% CO2, but it's very thin and, as a result, doesn't trap heat well, compared with CO2's effects on Earth and Venus).
Along with the introduction of microbial colonies and imported chemicals and greenhouse gases, and eventually plants, the Martian soil would release trapped gas. On a large scale, this would thicken Mars' atmosphere to a sustainable pressure and temperature, and life would explode--in a good way. Under those conditions, Earth life would need only take root, and we could turn Mars into a second Earth. Water would condense out of the soil, forming lakes and streams and possibly oceans, allowing for even more diversity to flourish.
Some would argue that humans going to another planet would just spell destruction for that planet, that humans are a disease that needs to be extinguished. This is the most pessimistic thing anybody can say, really, but it's a sad reality that our society has seen science take a backseat in the world's priorities to the point where people literally think going to Mars would "kill the planet."
This simply isn't true. We learn from our mistakes, and as society and science advances, so does our appreciation for nature and the universe. Humanity's recent history is a lesson in progress, and the more we develop, the more careful and precise we will be. We wouldn't be killing Mars; we'd be developing a world where life as we know it could survive. A second inhabited world on which to preserve life. It is our duty as an intelligent, cognisant species to spread life wherever it can take root.
The window of opportunity to spread life is opening wider, and we must take it while we can. We cannot hold back. We must carry life to those far off, distant worlds.