Said the Native Americans to Columbus....

On another note... If you listen to ToySoldier; Any extra-terrestrial visitors will also be human anyway so the Earth will seem perfect to them

Assuming they have hands. I think they will be very strange. They may live on a planet that doesn't rotate. No night or day. They may live on a high density atmosphere, and float instead of walk. They may "sun" themselves for a period of time rather than eat. They may communicate by changing "skin" colors. Water may cause them to melt. They may find 120º F bone chilling cold. Our atmospheric pressure may cause them to pop. Think weird. Maybe they are so advanced, they can have probes the size of atoms. The universe is big, and almost everything is possible.

Now that you mention it... I think I have met some of these folks...

Yeah, the point was missed. The "biological needs" refers to biochemistry, an assumption that A) they would be similar to terrestrial life (if asteroidal amino acids are any guide); and, 2) they would want to colonize terrestrial "goldilocks" planets around g-type stars if they decide to do so beyond their native system. The operating assumption for the scenario is that they do come here (for their own reasons) and find us here.

The "tendencies" refers to colonizing behavior and basic curiosity and level of technology. They might sit and wait to see if they ever discover superluminal transportation technology before they venture beyond their native system, but would we? Assuming we might use subluminal vehicles, we can assume that they might as well.

__________________
"What you think you thought you saw you did not see." Agent J, MiB - Manhatten Bureau

The ones that pop, or the ones that melt?

In my opinion, it's still more likely they'll send probes to explore first. It's just more efficient.

If they have not managed to invent some form of faster-than-light travel,
they might still be surprised by our presence, of course.

Their probes might have sent back pictures of Neanderthals (or dinosaurs) as the most advanced life forms

So that's where the Wicked Witch of the West came from! Space!

__________________
"If you think the LHC will create black holes, you might as well believe Hobbits are at the bottom of your garden."- Dr. Mike Inglis
Rovers forever! - ToSeek
"Carl Sagan sent a message to ET,
Neil Armstrong walked in the Sea of Tranquility
Steve Squyers built Spirit and Opportunity
Dan Haylen upchucked in zero gravity." -Brent Simon, The Space Camp Song

Not the same situation. To make it analagous, Columbus would have to have sailed past dozens to hundreds of other continents before reaching this one.

Well, that goes without saying.

__________________
"If this were play'd upon a stage now, I could condemn it as an improbable fiction."
Shakespeare, Twelfth Night
Illuminati's Razor-The most complicatedly evil answer is usually the most correct answer. - Fazor
"Every book is a children's book if the kid can read." - Mitch Hedberg
"Distance doesn’t matter much in space, where if you just start a thing off with the right kind of shove, sooner or later it will get where you want it to go." -Frederik Pohl, Mining the Oort

Not if they chose this site specifically.

OR even stumbled on us by blind luck.

Yes, but my point is why would they do so? Nothing special or unique here (again, except for life, which is hard to detect from a distance). And bypassing plenty of other star systems with situations no better or worse than here.

As for "stumbling on us by accident", that's only possible if they left home without a specific goal. Refugees fleeing a disaster or persecution might wander at random, stopping only for supplies, and if so they might head into any system. But they're not going to invade us. More likely refugees would avoid alien contact altogether. If they do stop here even after discovering a potentially hostile, violent race like us, it'll probably be because they're in such desperate need of assistance that their need overrides whatever drove them to abandon their homes.

__________________
"If this were play'd upon a stage now, I could condemn it as an improbable fiction."
Shakespeare, Twelfth Night
Illuminati's Razor-The most complicatedly evil answer is usually the most correct answer. - Fazor
"Every book is a children's book if the kid can read." - Mitch Hedberg
"Distance doesn’t matter much in space, where if you just start a thing off with the right kind of shove, sooner or later it will get where you want it to go." -Frederik Pohl, Mining the Oort

There is a Lot of Water.
Mars, Venus (Earth) may present the appearance- at a distance- of planets that can be terraformed or support biodomes.

Assuming similar biochemistry, and an intent to terraform, yes (well, not Venus). There's also a whole universe of other planets. No doubt many of them also look fairly good from a distance. Again, what makes ours a uniquely desirable goal? One worth the massive effort of crossing light-years of space for?

__________________
"If this were play'd upon a stage now, I could condemn it as an improbable fiction."
Shakespeare, Twelfth Night
Illuminati's Razor-The most complicatedly evil answer is usually the most correct answer. - Fazor
"Every book is a children's book if the kid can read." - Mitch Hedberg
"Distance doesn’t matter much in space, where if you just start a thing off with the right kind of shove, sooner or later it will get where you want it to go." -Frederik Pohl, Mining the Oort

Frankly, as Far As We Currently Know
Our solar system could be the only one with habitable planets over quite a large area.
3 at least and several moons.

Saturn, incidentally, is a rarity with it's rings. I'm willing to bet it is Quite Unique ( I may be working with outdated information on this one though).

ETA: You are assuming many habitable- we can as easily assume not many are around here.

You could tell that from the atmospheric mix. There should be space telescopes before too long that could detect that sort of thing if in a nearby system. See the Darwin Mission for example:

http://en.wikipedia.org/wiki/Darwin_%28ESA%29

Quoting:

For planet detection, the telescopes would operate in an imaging mode. To detect an Earth-like planet would require about 10 hours of observation in total, spread out over several months. Once a planet is detected, a more detailed study of its atmosphere would be made by taking an infrared spectrum of the planet. By analysing this spectrum, the chemistry of the atmosphere could be determined, and this could provide evidence for life on the planet. The presence of oxygen along with water vapor in the atmosphere would be evidence for life, as water vapor is extremely effective in reducing oxygen back to other gases. If nevertheless large amounts of oxygen exist in the atmosphere, it must be continually reproduced "artificially", i.e. via biological photosynthesis. The presence of oxygen alone could not be seen as evidence. Numerical simulations showed that under proper conditions it is possible to build up an oxygen atmosphere via photolysis of carbon dioxide.

I expect that any species that could build interstellar spacecraft would know a lot about other solar systems before they bothered to go there. However, I also expect that any species with the technology to go to other star systems wouldn't bother with planets with existing ecosystems if they just want some place to live. It would be much cheaper and safer to build habitats anywhere there were resources.

__________________
I say there is an invisible elf in my backyard. How do you prove that I am wrong?

Disclaimer: Avatar is not an official NASA image and does not imply any specific interplanetary or interstellar capability.

The Leif Ericson Cruiser

Nahh.. Slave Labor. We're doomed.

There is one known world habitable to us. To live anywhere else in the solar system would require heavy technological intervention, whether that is a surface or space habitat. Either way, we would have become very good at making small, efficient closed ecologies. Terraforming would be far more difficult yet (the resource requirements for Mars are huge, and for Venus it is even worse).

If we find a cheap and easy space drive that lets us travel cheaply much faster than light, and if we find planets with essentially identical ecologies, then it might make sense to go with the "Star Trek" model of planetary habitation. But, assuming known physics, the energy requirements to send big ships to other star systems would be huge, and would take many years even for nearby stars. So, to do that, we would need large energy resources and be able to build great closed cycle ecologies. Under those circumstances, if we want to expand, we would start by developing the solar system (and there is much more construction room off of the surfaces of worlds), then go to any nearby systems with useful worlds (anything with resources we could use).

Saturn has the most impressive rings in the solar system, but it isn't the only planet with rings:

http://en.wikipedia.org/wiki/Rings_of_Jupiter

http://en.wikipedia.org/wiki/Rings_of_Uranus

http://en.wikipedia.org/wiki/Rings_of_Neptune

And there might even be a moon with rings:

http://saturn.jpl.nasa.gov/news/pres...cfm?newsID=820

__________________
I say there is an invisible elf in my backyard. How do you prove that I am wrong?

Disclaimer: Avatar is not an official NASA image and does not imply any specific interplanetary or interstellar capability.

The Leif Ericson Cruiser