I’m an space engineer not an astronomer but news like this get’s me excited. Building spacecraft is a pleasure of it’s own but deep down I hope it will one day bring us to planets like these. Becoming a mulitplanetary species is awesome in it’s own right, but if you read the Elon Musk interview you know that is also a way to alleviate the stress we put on our planet. Considering the impact we are having on our planet right now, this is not a frivolous luxury.
In short, to have chance of harboring life a planet must at least be rocky and have liquid water on it’s surface. To have liquid water, surface temperatures have to be above 0 and below 100 degrees Celsius. The surface temperature on a planet is primarily dependent on the distance to it’s parent star and the brightness of that star. The distance from the parent star where the temperature is neither to hot, nor to cold, but ‘just right’ is called the Goldilocks zone, named after the fairytale. There are however many more criteria. The gravity needs to be similar, it needs a proper atmostphere and a magnetosphere to shield it from cosmisc radiation and preferably a giant (gas) planet in it’s starsystem that shields it against meteors. The latest models include 200 parameters a planet must have to be comparable to Earth. And although this may sound depressing, considering the astronomical number of stars in our universe of which most have planets, scientists are actually very optimistic about finding habitable planets.
The Keppler spacecraft was launched in 2009 and has found 1000 Earth-like planets, so far 8 of these might be able to harbor life. Two recent discoveries Keppler-442b and Keppler-438b are confirmed to be in the habitable zone and have >70% of being rocky, the most exciting results so far. The sad news is that they are 1100 and 470 lightyears away, so we won’t visit them any time soon.