A great extrasolar planet is the one that is not in our Photo voltaic system. Completely long recently been theorized that other actors have planets, but it was only in the latter part of the twentieth century that any were discovered. According to The Extrasolar Planets Encyclopaedia, as of the nineteenth of June 2009, 353 extrasolar plants had recently been discovered. The pace of finding is increasing very swiftly. Carl Kruse Lonely Planet Profile
All the planets so far confirmed have recently been orbiting round stars. Exoplanets not orbiting stars can be found, but uncovering them is difficult although at least three opportunities have been found.
These types of are sometimes called free floating planets. They can be identified in the paper Totally free Floating Planets by Annemarie Hagenaars, Ilja Rosenbrand and Charlotte de Valk as an object that does indeed not orbit a celebrity and has a mass less than 13 times that of Jupiter. (This upper mass limit is to distinguish them from brown dwarf stars, and is roughly the mass below which sustained indivisible fusion occurs. ) We would also create a lower limit of mass on what we would think about a Planet.
Naturally, practically all the planets so far learned are much bigger than our planet. This is because bigger things are much easier to find, and will not suggest that Soil sized planets are unusual. The range of sizes of extrasolar planets learned shows that there will be plenty of Ground sized planets out there.
In 1992, a possible planet (Planet: PSR 1257+12 b) was uncovered which is merely somewhat more than a fifth of the mass of our planet, so we can expect increasing numbers of small exoplanets to be discovered.
For us, or similar creatures, to live on the planet it generally should be orbiting a star in the reasonably narrow region where normal water can be liquid on at least part of the planet, at least part of the time. A planet also needs to be not too young to hold a reasonable atmosphere. For instance, our own Moon is too small.
A planet also should not be too big, although there has recently been plenty of speculation about what sort of life could live on gas giants.
Although no Ground sized planets have recently been uncovered in the usable zones of other actors, about 30 larger exoplanets have. Expect there to also be Earth measured planets.
Earth Sized Exoplanets
I have been using this term loosely. Maybe we should considercarefully what sized planet we could survive. One as small as Mars, whether it got enough water the right distance from it legend would do, although this is near to the lower limit.
A planet much bigger than the Earth might tend to have an uncomfortably high gravity. Nevertheless, if it was of lower density our Ground, it would have a greater diameter and its surface gravity would not be so high. In the limited sample we have available, it appears that the Earth is a higher occurrence planet. It is possible that Humans could survive some planets with a larger mass than the Ground in addition to a larger surface area for living on.
Based of the limited information we have, we can expect that most planets will have moons, which these will be of various kinds of sizes.
The 30 so big planets in the usable zones of their superstars may have Earth measured moons. There is little or nothing impossible about a very big planet, like many of the ones found so far, having more than one Earth measured moon.
There could be another class of usable moon. If a huge globe was orbiting further away than the habitable region of its star, tidal forces could warm it is moons enough to dissolve water. This warming result is apparent in the moons of Jupiter.
Zero definite indications of life have been available on any extrasolar planet, but at present our techniques for observing them are not good enough to tell. These techniques are rapidly improving.