They close their windows and lock their doors and fly past as fast as they can when forced to come anywhere near the planet of the crazies. They're aliens, not idiots. lol

to Fermi la bouche. I don't know if this helps here at all, I'm just repeating what I hear at home.

Most are bereft. Life on such orbs may be beneath the surface. Also the size of each orb may dictate whether to visit another orb or not.

e.g. If we discover earth-like planets or moons that have 5 times our gravity, this is not good for us. The opposite may mean a visitor might have to dwell deep in our planet.

Also mode of transportation. Jut because we do it in flying tin cans does not mean they do.

First is that something like 70% of all stars in our galaxy are red dwarfs. What life might evolve on them would be very different from life on our planet. Keep in mind we have a relatively large moon that affects things like tides. And that those tides were no doubt crucial in the evolution of life on this planet.

So far, no exo-planets we've yet found have our kind of large moon. Okay, so we really have a very long way to go in figuring out if any of those exo-planets are even remotely close to our planet, but we're working on it.

It's also important to know about interstellar distances. If you could actually travel at the speed of light, or some fraction just below it. it would take you about four and a half years to get to the closest star. Which may or may not have a planet capable of Earth-like life.

Another thing to know: cosmic radiation between stars is a real problem. Even travelling at the kinds of speeds we're currently capable of makes the radiation a problem. And the faster you travel, the more and faster that radiation will affect you. Ooops. It is possible that actual travel between stars is truly impossible. Impossible for us, impossible for any other species. Which leads to the possibility that we may have never, ever, been visited by aliens. Think about it.

no one evolves.

He makes it exquisitely clear that interstellar travel will be vastly more dangerous than people realize.

Oh, and Packing for Mars by Mary Roach is another look at how space travel isn't as easy or simple or pleasant as we are generally led to believe.