According to a new study quoted in Space.com, the Milky Way Galaxy may have as many as 4.5 billion Earthlike planets, some within a close distance of Earth, as interstellar gulfs go, within 13 light-years.
Earth-like planets circle red dwarf stars
Space.com reports that the study, to be published in The Astrophysical Journal, is based on analysis of data derived from the Kepler Space Telescope. Kepler, which is dedicated to discovering exoplanets, has found 2,740 candidates for planets circling other stars since March 2009. The study suggests that red dwarf stars that Kepler has examined are smaller and cooler than previously thought. Worlds that had previously been thought to be too large and too hot to maintain life have been "downsized" to a degree that many of them are now considered rocky worlds of the approximate size of Earth. Also since their parent stars are considered cooler, many exoplanets thought to be circling too close to such stars may now be in the habitable zone where liquid water can exist and thus life may be present.
4.5 billion Earths in our galaxy
Space.com goes further to state that according to the data from Kepler, roughly 60 percent of red dwarves have planets smaller than Neptune, the smallest gas giant in our solar system. It was determined that roughly 6 percent of the red dwarves in the Milky Way Galaxy have Earth-like planets, hence the figure of 4.5 billion.
Red dwarves
According to Universe Today, a red dwarf star ranges from less than half to 7.5 percent of the mass of the sun. A red dwarf puts out between 10 percent and 1/10000 the energy of the sun. Red dwarves consume themselves at far less the rate of a yellow star such as the sun and therefore a considerably older. Thus the habitable zone for such a star is much closer to it than that of the sun, where Earth is located. The closest star to Earth besides the sun is a red dwarf, Proxima Centauri.
Visiting Earth-like worlds
The idea that another Earth might be within 13 light-years is beguiling to scientists. Thus far, no technology exists that could propel a probe to any star system outside our own for any amount of time less than centuries. However Space.com reports that NASA has embarked on a research and development program that might, some decades hence, create something resembling warp drive as depicted in science fiction such as "Star Trek." It could be that people alive today will see one or more of these new Earths with their own eyes.