I guess those movie & TV aliens look like that so human actors can play the part.
I bet we've enjoyed some of the same books.
From JPL - http://planetquest.jpl.nasa.gov/news/ssu_images.cfm
Wednesday 25th April, 2007
First habitable Earth like planet outside Solar System discovered
...this planet takes only 13 days to complete one orbit round its star. It is also 14 times closer to its star than the Earth is from the Sun.
However, since its host star, the red dwarf Gliese 581, is smaller and colder than the Sun - and thus less luminous - the planet lies in the habitable zone, the region around a star where water could be liquid!
"We have estimated that the mean temperature of this super-Earth lies between 0 and 40 degrees Celsius, and water would thus be liquid," said Stiphane Udry from the Geneva Observatory, Switzerland and lead-author of the paper in the journal Astronomy and Astrophysics.
"Moreover, its radius should be only 1.5 times the Earth's radius, and models predict that the planet should be either rocky - like our Earth - or covered with oceans," he said.
"Liquid water is critical to life as we know it and because of its temperature and relative proximity, this planet will most probably be a very important target of the future space missions dedicated to the search for extra-terrestrial life. On the treasure map of the Universe, one would be tempted to mark this planet with an X," added Xavier Delfosse, a member of the team from Grenoble University, France....