Comparable, in what sense? - Scientists have discovered over a thousand planets outside our Solar System; most of these are much larger than Earth (since those are easier to discover), but several have been found that have a mass comoparable to Earth.
The first planet discovered besides Earth is Uranus. It was discovered by William Herschel in 1781.
It was actualy not too long ago. Scientists discovered it Wednesday morning, December 7th 2011.
Scientists
The earth as planet was discovered by some of the ancient astronomers. Nicolaus Copernicus and Ptolemy are credited with provision of the initial information of the earth as a planet in relation to the solar system.
on planet earth
Scientists in the Antarctic study the health of planet earth.
The planet that has enough density to support the weight of a colony is Mars. Scientists have discovered that Mars is relatively similar to the conditions on Earth.
The perturbations in the bowels of the planet earth.
earth
Earth...
Yes, this is possible. Some would argue that whether or not we find such life, it is nearly impossible that it does not exist somewhere.
The planet human being's can possibly live on besides-planet earth, Well scientists don't know for sure because scientists are not always correct no offense to scientists though. Well that's my answer!