With all the private companies launching satellites and manned missions to space these days, one can dream that it's only a matter of time before the human race is zipping across our star system, colonising inhabitable planets. And while that's a definite projection, and the eventual end-game, it might not be within our lifetime.

Renowned theoretical physicist Stephen Hawking has now said, as reported by the Guardian, that human colonisation of other planets could take a while, so we should be taking more active care of Earth. “We will not establish self-sustaining colonies in space for at least the next hundred years, so we have to be very careful in this period,” he implored. It's not the first time Hawking has cautioned against the dangers we face on Earth. In 2012, he said that an extinction-level disaster, like a nuclear war, is likely to befall us in the next thousand years, and that possibility increases the closer we get to that deadline.

So why does colonisation of other planets have to take that long? We're already landing rovers on comets, finding water on Mars, and even sending observational satellites out of our solar system. You see, even before we start to address what steps we have to take to make a planet livable, we have to question whether we should.

As Elon Musk once said, the first hurdle to colonising Mars is that we have to warm it up. And that, of course, takes time. He did suggest, however, that there's a fast way to do that. Skip to 1:30 for the diabolical plan.

Now, even leaving aside having to deal with all that pesky radiation once the planet is warm enough, there's another thing to consider; what are we doing to a possibly existing ecosystem? You see, scientists have just about discovered the evidence of flowing water on Mars. The discovery was made by Georgia University graduate student Lujendra Ojha, lead author of the paper detailing the findings his team unearthed. And just that discovery could mean a breakthrough for space exploration. But the fact of the matter is, we still don't know if that water on Mars supports life, only that there's a high probability it does. And if there IS life on the red planet, we don't want to destroy it.

The reason such a monumental discovery has taken us so long, despite the Curiosity rover making it's landing on Mars in August 2012, is that there's some places it's just not allowed to go. Scientists don't know where they might find life on a celestial body, so they're unwilling to take rovers (and possibly Earth contaminants), to places they aren't absolutely sure are dead zones. And this may be a slightly lesser known detail, but there are governing bodies to make sure this never happens. NASA's equivalent is the Office of Planetary Protection, which lays down guidelines for where manned-missions can land, where rovers can go, and the like. On a more global scale is the Committee on Space Research (COSPAR) which, under supervision from the International Council for Science (ICSU), makes sure national space research organisations share their findings, and also, according to their charter, looks to "ensure that nations capable of planetary exploration protect these pristine environments from human contamination".

We don't want any Earthly contamination to destroy a Martian ecosystem the moment we find it, and we certainly don't want any extraterrestrial viruses, or the like, to reach Earth. As Ojha himself mentioned to us in a chat at TEDx last year, "We don't know how feasible (Musk's) idea is yet. We don't want to nuke the poles, only to arrive and find out there was life there we've now eradicated". So there goes that super-villainy "nuke Mars" plan. And unfortunately, there also go our chances of nailing down a "Home Sweet Home" sign on the planet anytime soon. It's more likely our grandchildren or great-grandchildren will see the red planet's surface in person; that is, once we're done greenhouse gassing, cloud seeding, and generally terra-forming it to make it habitable for human life.