This is a very spiffy website: http://phl.upr.edu/projects/habitable-exoplanets-catalog/results This could be a very useful thing for the astronomically curious as well as SF authors looking for someplace to put that next alien race or colony.
They found planets around Tau Ceti? I didn't even know that! I'm behind the times! Although I checked SolStation and it seems to say the identification is still tentative.
I think we still have to keep an open mind on this stuff, the goldilocks zone might be a little too perfect. NASA has still to yet rule out if Mars and if Jupiter's Moon Europa are dead worlds. Forms of life have been found miles deep in the colds of Antarctica, found in hot thermal vents under extreme pressure at the bottom of the ocean and forms of life have been found in decaying Russian nuclear radioactive submarines.
The other thing of note is that MARS has a 64% rating of being Earth like. So is this scale logarithmic or something because what does 50% mean, their gas planets? I would also state that Earth's orbit and stability isn't really that friendly to life either and as you said it may be possible that just because a planet is in the habitable zone it is really habitable.
Lots of interesting information in that link! I like that chart further down that classifies potentially habitable planets based on their temperature: Thermoplanet (slightly hotter) - Class T Psychroplanet (slightly colder) - Class P Mesoplanet (similar to Earth) - Class M (!)
The only thing meant by habitable zone is that temperatures are such that liquid water may exist. That does not mean liquid water is in fact present, that life exists there, nor that life cannot exist elsewhere. But as a beginning point, it makes a lot of sense to start here since soon we will be able to analyse the atmosphere of some of these planets. We do not have a game plan to be able to do things like look under the ice of moons outside of this solar system.
^Right. Science isn't about making absolute statements about everything that can ever exist anywhere. It's about making conclusions and predictions about what we can observe and measure. Although, granted, calling it a "habitable zone" instead of a "liquid water zone," say, is a bit misleading. Then again, when they say "habitable," they don't mean habitable to humans, just potentially habitable for some kind of life as we know it, even microbes.
^ Fourth picture up from the bottom in the OP's link, in the section titled "Current and Pending Potential Habitable Exoplanets".
So here's a question. Let's say we find a planet that has its own carbon-based life. Even if it was within the habitable range for humans, could humans ever live on that planet? Or would the threat of microbial nasties that we had no immunity to make that possible? Or would our presence inevitably disrupt the existing ecosystem there? Would it be possible for us to live there without bringing our own microbial nasties? I've never really thought about that--I've always assumed that landing on an "M-class" planet wouldn't quite as cavalier as Star Trek, but that humans would more or less be able to survive there. Is this a foolish assumption?
That depends. We probably wouldn't be in danger from their viruses, since they might have a different genetic medium than DNA, or at least one following a different protein-coding "language." But bacteria could be a problem if our biochemistry is compatible enough with theirs that they could thrive in our bodies. And that's pretty much a given if we could thrive in the planet's environment. The safer we are from a planet's bacteria, the less suitable the planet would be for us to inhabit at all.
So what's our best bet if we're looking for a planet to colonize? Something that's in the Goldilocks zone but has no life?
I think they'll be experimenting on animals till they're absolutely sure of the process and then there will be a line of space cadets waiting to be tested. Of course it helps if the subjects get paid in medical experiments. People will do just about anything if the money's good.
I might have added any moons from this system to the list: http://en.wikipedia.org/wiki/47_Ursae_Majoris http://en.wikipedia.org/wiki/Stars_and_planetary_systems_in_fiction#47_Ursae_Majoris The star has a gas giant 2-3 times Jupiter mass orbiting its star about where our asteroid belt is in relation to our own sun. The star there is also slightly brighter than our sun, and with a big gas giant reflecting light, its effective insolation distance might be that of our Mars--thus any Europa type moon will probably have some liquid water.