Chronos said:Earth sized planets are very difficult to detect, largely due to instrument limitations. NASA's Kepler mission is the most recent entry into this field:
http://kepler.nasa.gov/
An Earth-sized planet is a planet that has a similar size and mass to Earth. It typically has a solid surface and is capable of supporting liquid water, making it potentially habitable for life as we know it.
According to current estimates, there may be billions of Earth-sized planets in our galaxy alone. With the vast number of stars in the universe, it is likely that there are many more Earth-sized planets in other galaxies as well.
While Earth-sized planets may have a similar size and mass to Earth, they can vary greatly in terms of their characteristics. Some may have a similar atmosphere and composition, while others may have vastly different environments due to their distance from their star, composition, and other factors.
The potential for an Earth-sized planet to support life depends on a variety of factors, including its distance from its star, composition, atmosphere, and other conditions. While some may be habitable, others may not be able to support life as we know it.
Scientists use a variety of methods to discover and study Earth-sized planets. This includes using telescopes to observe the transit method, where the planet passes in front of its star and causes a dip in the star's brightness. Scientists also use the radial velocity method, which measures the slight wobble of a star caused by the gravitational pull of an orbiting planet.