Up to 60 BILLION Planets in Our Galaxy May Be Habitable!

Obama needs the inhabitants to sign up for the ACA before they figure out what it is! With 60 billion planets worth, the number of sign-ups could reach triple digits by year's end!

I would think extraterrestrial germs would be at least as big a problem for us as terrestrial ones.

Our immune systems are evolved to attack foreign matter in our bodies and do so pretty well with germs we commonly find in our environment. But would our immune systems have any defense against germs that evolved on a different evolutionary track? I doubt it.

If humans landed on a world that was essentially identical to Earth (mass, temperature, climate, atmosphere, etc.), they would probably be very vulnerable to disease from microbes in the planet's biosphere. Look at what happened to native American populations when they encountered diseases carried by European explorers...

I don't think that that's comparable. Even on a planet identical to earth, the evolution of life would take a course that is completely different. I expect alien life will differ from us at least on the same order that animal life differs from plantlife, or fungi.

The problem with American Indians is that they were confronted with microbes that were spectacularly well evolved specifically at attacking their species, due to the more intensive urban concentrations in Europe - not that they were confronted with something that had never met a human before.

Some diseases can be cross-species, with no need for mutation to occur. They can also infect different species at varying levels of devastation. (Cow pox comes to mind. Somewhat bad for cows, a minor annoyance for humans, but comes with the added bonus of making you immune to small pox.) Fungal infections often don't care what species you are.

Its really an unknowable question until we encounter life that's evolved outside the solar system. Finding life on Mars or Europa that has DNA won't tell us much, because its likely to be difficult to rule out cross-contamination. Finding life on a planet hundreds of lightyears away from the Earth that has DNA will mean that its likely that life can only arise via DNA.

According to Guns, Germs, and Steel, it wasn't just the urban concentrations, it was that for centuries Europeans lived in closer contact with farm animals than did the Native Americans, this allowed the animal diseases to jump from livestock into humans. It may be that alien microbes don't bother humans on the planet at first, but then generations later, people start getting sick from things that never bothered them before.

Yeah, I've read that, I was simplifying a bit.

Cows and humans have a large overlap, genetically. I think you're overestimating the chances of life elsewhere being similar to ours - although neither of us have any data with which to validate our views - obviously!

If life on Europa (I don't think that there's any on Mars, for reasons I'll get to in a bit) doesn't use DNA, then we'll have our answer. If there's life on Europa and it uses DNA, we'll still have questions.

While our sample size of life bearing planets is small, I don't think that its entirely unreasonable to assume that the rules (or at least some of them), which govern life here, won't apply to other planets as well. We've no reason to think that the laws which apply to our corner of the universe don't apply elsewhere. Every kind of life we can find, even the stuff that lives around the undersea vents (which was utterly unexpected until it was discovered), uses DNA or RNA, if not both. Why haven't we discovered something else? It might be that only life can evolve using either of those two things, or it might be that those are the most efficient mechanisms for creating life, and once those two elements develop, they wipe out other competing mechanisms.

Granted, those things are a bit subjective, based on our limited knowledge. There is, however, one element which absolutely cannot be denied, no matter what chemistry drives the formation of life: It must be tenacious, if it is to survive. Not only does it have to be able to survive disease, predation, but the damned cosmos will try to kill it by dropping the odd meteor on the planet. So, it can't simply just cling to the odd rock tucked away in the bowels of some cave, it has to spread out, and in doing so, it will transform the planet it lives on. We used to think that there were barren spots on the Earth, that turns out not to be true. If it is "easy" for life to evolve on a planet, even if it doesn't look like anything we've ever seen on Earth, then why isn't Mars filled with living organisms? Even supposing that the creatures there would be based on iron or silicon, instead of carbon like on Earth, the planet should be crawling with life, if it can crop up just anywhere. Life that's visible to us with our robots running around on the planet and satellites in orbit. Life has a pretty basic law that if you're exploiting a niche no one else is, you're going to do well, so if its there, on Mars, even the thin atmosphere shouldn't prevent it from grabbing hold and putting forth the Martian version of plants, at the very least. They're not there, which means Mars is missing something. Liquid water is a good guess as to what that "something" might be, but it could be other things as well. Lack of a strong magnetic field, certain chemicals being injected via comet collisions, continental plates, whatever it is, its rendered Mars a dead world. Which tells us that life won't crop up just anywhere, but only on certain planets.

Restricting life only to planets that have liquid water opens up more possibilities for life in the universe than saying the planet has to be identical to Earth. But even that may be too generous. I hope not. I'd like for their to be life on Europa, and giant gas bags floating in the atmospheres of Jupiter and Saturn. Otherwise, this is going to be a very lonely galaxy for us.

Obviously? Please elaborate.