A trans-Neptunian object (TNO) is any object in the Solar System that orbits the Sun at a greater distance on average than Neptune. The Kuiper belt, scattered disk, and Oort cloud are three divisions of this volume of space.[1]
The first trans-Neptunian object to be discovered was Pluto in 1930. It took more than 60 years to discover, in 1992, a second trans-Neptunian object, (15760) 1992 QB1, with only the discovery of Pluto's moon Charon before that in 1978. Since then however, over 1,000 trans-Neptunian objects have been discovered, differing in sizes, orbits, and surface composition. 197 of these (as of March, 2009) have their orbit well enough determined that they are given a permanent minor planet designation.[2][3]
The largest known trans-Neptunian object is Eris (discovered in 2005), followed by Pluto, Makemake and Haumea.
http://www.iop.org/EJ/article/1538-4357/605/1/L65/18164.text.html
The possible existence of life on other planets is of central interest in modern astronomy. A standard working hypothesis is that liquid water is required for life; here we describe an observational signature of evolved oceans on extrasolar terrestrial planets.
Astronomers have found more than 300 alien (extrasolar) worlds so far. Most of these are gas giants like Jupiter, and are either too hot (too close to their star) or too cold (too far away) to support life as we know it.
Sometime in the near future, however, astronomers will probably find one that's just right – a planet with a solid surface that's the right distance for a temperature that allows liquid water -- an essential ingredient in the recipe for life.
Still of EPOXI video showing Earth and the Moon.These two videos from EPOXI show the moon transiting (passing in front of) Earth. They are observed at different light wavelengths, which is why differences in details are visible. The first version uses a red-green-blue filter; the second, an infrared-green-blue. The first pictures of an Earth-like extrasolar planet will not be this detailed. Instead, the images will be more like the Voyager picture of Earth as a single point of light (below).
But the first picture of this world will be just a speck of light. How can we find out if it might have liquid water on its surface? If it has lots of water – oceans – we are in luck.
http://www.centauri-dreams.org/?p=1115
If you want to put the hunt for planets around other stars in perspective, consider this. For almost all of our species’ time on this planet, we have looked at the planets in our own Solar System as unresolved points of light that seemed to move upon a celestial sphere. The brief time that we have been able to see more is measured since the invention of the telescope, a tiny window compared to the millennia that went before.
We are now working hard to see extrasolar planets as unresolved, moving points of light. In doing so, we’re looking at ways to image these planets that would yield the greatest scientific return. Recall former NASA administrator Dan Goldin’s wish to actually see the surfaces of distant exoplanets — he talked to putting such images on the walls of our schools. One day, starshade technologies coupled with space-borne telescopes may make that possible. For now, though, there is the real potential of something closer: identifying exoplanets with oceans.
The beauty of such an identification, writes Peter McCullough (Space Telescope Science Institute) is that we don’t actually need to resolve the planet to find out whether it has an atmosphere and an ocean. Here the scientist writes about what we can do with near-term technologies:
