An extrasolar planet is one which isn’t in our Solar system. According to The Extrasolar Planets Encyclopaedia, at the 19th of June 2009, 353 extrasolar plants were discovered.
All of the planets so far confirmed happen to be orbiting round celebrities. Planets not orbiting stars do exist, but discovering them is difficult although at least three possibilities are found.
These are sometimes known as free floating planets. (This upper mass limit is to differentiate them from brown dwarf stars, and is about the mass below that sustained nuclear fusion occurs.) I would also put a lower limit of mass on what we’d think about a Planet.
Naturally, nearly all of the planets so far discovered are much larger than the Earth. This is because larger things are easier to find, and doesn’t imply that Earth sized planets are rare. The array of sizes of extrasolar planets found suggests that there’ll be a lot of Earth sized planets out there.
In 1992, a potential world (Earth: PSR 1257+12 b) was detected which is just somewhat more than a fifth of the mass of the planet, so we can expect increasing numbers of small planets to be discovered.
For all of us, or similar creatures, to live on a world it generally must be orbiting a star in the fairly narrow place where water could be liquid at least portion of the planet, at least portion of the time. A planet also should be large enough to hold a sensible atmosphere.
A world also should not be too large, although there’s been lots of speculation about what type of life could live on gas giants.
Although no Earth sized planets have been found in the habitable zones of different celebrities, about 30 larger planets have.
Earth Sized Planets
Maybe we ought to consider what sized world we can live on. One as little as Mars, if it had sufficient water and was the ideal distance from it celebrity would do, although this is close to the lower limit.
A planet much larger than the Earth might have a tendency to have an uncomfortably significant gravity. But if it had been of lower density which our Earth, it would have a larger diameter and its surface gravity wouldn’t be quite as high. It’s likely that humans may live on some planets with a larger mass than the Earth in addition to a larger surface area for living on.
Based of the limited information we have, we can anticipate that many planets will have moons, and that these are of a enormous array of sizes.
The 30 so large planets in the habitable zones of the celebrities might have Earth sized moons. There’s nothing impossible about a really major planet, like lots of the ones found up to now, having more than one Earth sized moon.
There could be an additional type of habitable moon. If a significant planet was orbiting farther out than the habitable zone of its star, tidal forces could heat its moons sufficient to melt water. This warming effect is clear from the moons of Jupiter.
No definite signs of life have been discovered on any extrasolar planet, but at present our techniques for observing them aren’t good enough to inform. These techniques are rapidly advancing.
We still don’t know if extraterrestrial life exists.