Thus far, the main candidate for life elsewhere than in our own solar system has been Gliese 581 C, a world around the red dwarf star Gliese 581, about 20.4 light years distant from us. This world has a diameter about 1.4 times that of Earth but since its orbit isn't transitory that is just an estimation.
Gliese 581 C's orbit lies in what is called the green zone, where the average surface temperature of a planet like Earth is not cold enough to freeze water nor hot enough to boil it. As a matter of fact, if it were Earth-like its mean temperature would be around 23C but astronomers think that it is subject to a runaway greenhouse effect because of what we know thus far about its atmospheric makeup.
We must consider the unique nature of its red sun so that the planetary composition and the intensity of solar radiation are still mostly speculative and that these factors should be considered only outside of our own relative context. Additionally, there could be a moon orbiting it which is large enough and which contains all the necessary ingredients for life much as we know it. It is a compelling and tempting notion. Once must consider the odds for the emergence of life there to be better than even in light of Anthropocentric Universe Theory.
Let's stop and think for a moment what unique characteristics life on 581C around the red dwarf sun Gliese 581 might possess. If we are looking for strangeness we needn't look past our own world to find it, so we may presume that even if the rules of life dictate that a certain pattern of progression in evolution is mandated no matter where we look for it, then we would necessarily find in it adaptations to those environments unlike our own, which should make alien humans different from us and in some radical ways.
For one thing, humans evolving in the light of a red sun means that the cones and rods in the retinas of their eyes are tuned toward the infra-red end of the spectrum, and in all likelihood their brains interpret images from heat radiation as a portion of the range of frequencies which they deem to fall in the visible optical spectrum. In the entire optical spectrum, our range of visible frequencies is somewhat shifted to the left in the direction of the ultraviolet with respect to what Gilesians would consider their visible range.
Things being relative, that would not necessarily present a great obstacle to vision for them or us if we were to visit each other's worlds. It's a little brighter here for them and a little darker there for us but not so much that we would need to compensate, but they will require protection from our sun's intensity. Gliese 581 is much cooler and dimmer than Sol. But then again, they are so close to their sun that their year is not even two weeks long.
It is tempting to think that we have been visited in the past by people from Gliese 581 C. One might even stretch one's imagination a bit and decide that the artifacts found on the plains of Nazca, in Peru, were etched by those same visitors, people who knew flight, because those etchings can only be seen from the air.
It is possible that Gliesians require a high altitude because their air must be more rarified due to the limited oxygen production of plants thriving under the light of a red sun. Furthermore, the amount of neural processing that must be required to decode the "night-vision" visual information from that part of the optical spectrum that accounts for their visible range of frequencies no doubt far exceeds ours, which wiuld account for the dolicocephaloid appearance of the occipital cortex in the elongated skulls that were discovered there, and which can be viewed in the Museo De National in Lima. Their occipital cortex requires more neurons to decode their visual information into the same level of detail that we see on our own world.
Sweet and hot peppers, kidney and lima beans, tomatoes; all came originally from Peru. Gliese 581 C might very well some day provide the answers to these and other mysteries of Peru.