A great article by Miriam Kramer in Mashable brings up something that has bugged me for a while. After billions of dollars and many years of study, we still can't definitively say if there is any kind of life on Mars or not. "Earth-like planet" makes for a great headline, but does it mean what one might reasonably think it means?
Mars is roughly 50 million miles from Earth. And yet, we have a lot of stories in the last couple of years on Earth-like planets being discovered by super-duper space telescopes - but these discoveries are light years away from Earth. One light year is 5,878,499,810,000 miles.
Read that number again. That's ONE light year; and that's not a big distance in terms of the visible universe.
Once you get past the "Earth-like planet" headline, you will inevitably find that these probable planets are usually several light years away, and the detection of these planets is mostly through inference and supposition - we can't directly "see" an Earth-sized body several light years away.
When observers say "Earth-like", they tend to mean it orbits a suitable star (not too big or too small, too young or too old) at a distance where it won't be scorched or completely frozen.
They don't mean they can tell us that the (inferred) planet has an atmosphere, or vegetation, or animals, or anything like that. So while it's fascinating that we can apparently detect other solar systems in deep space, let's not get carried away quite yet. These are not "M-class" planets by the Star Trek definition.