In our galaxy alone, the Milky Way, there are tens of billions of planets similar to Earth scattered all over. Many of them orbit around stars similar to our Sun.
Previous studies suggested that these rocky, or terrestrial, planets were orbiting around small stars, rather than stars similar to our Sun. However, new data from the Kepler NASA mission, launched in 2009, have given different results. According to the study presented at the annual meeting of the Astronomical Society of the United States, in California, astronomer François Fressin of the Harvard Smithsonian Center for Astrophysics in Cambridge, Massachusetts, had to say that “they have found that the presence of small planets around big stars has been underestimated.”
To locate new planets, the Kepler telescope is focused on a part of the sky of the constellation Cygnus, consisting of some 150 thousand stars. Space telescopes detect planets by revealing potential traces of light that are created when planets pass in front of their stars. Using his own independent software to analyze the planets detected by Kepler. Fressin and his team estimated that about 17 percent of the “sunlike” stars in the Milky Way harbor a rocky planet orbiting around them, even closer than Mercury’s location to the Sun.
Given that in the Milky Way there are about 100 billion stars, we could draw the conclusion that there are at least 17 billion terrestrial planets out there. When Fressin’s team extended the research to orbits similar to that of Earth, they discovered that half the Sun-like stars can harbor rocky planets. Fressin said that “almost all the stars we see on a starry night feature a planetary system.”
However, the rocky planets represent only a portion of the total number of planets present in the Milky Way. A study on the possible number of planets classified as red dwarfs spectral type M suggests that our galaxy could hold at least 100 billion planets in total.