There may be as many as a planet similar to the Earth, and all the five stars like the Sun in the Milky Way Galaxy, according to new estimates from the University of british Columbia, astronomers using data NASA’s Kepler of the mission.
To be considered, such as the Earth, a planet must be rocky, about the size of Earth and orbiting the Sun-like (G-type) stars. It also has to orbit in the habitable land area of its star—the range of distances from a star in which a rocky planet could host liquid water and possibly life, on its surface.
The estimate of the frequency of different types of planets around stars can provide important constraints on planet formation and evolution theories.
“My calculations place an upper limit of 0.18 for Earth-like planets by G-type star,” says UBC researcher Michelle Kunimoto, co-author of the new study in The Astronomical Journal. “Estimation of the frequency of the different types of planets around stars can provide important constraints on the formation of planets and the evolution of theories, and help to optimize future missions dedicated to the search for exoplanets.”
According to UBC astronomer Jaymie Matthews: “Our Milky Way has 400 billion stars, with seven per cent of G-type. This means that less than six billion stars have Earth-like planets in our Galaxy.”
The previous estimates of the frequency of Earth-like planets in the range of about 0.02 potentially habitable planets per solar-type star, more than one per solar-type star.
Generally, the Earth-like planets are more likely to be missed by a search for planets of other types, as they are so small and orbit so far from their star. That means that a planet catalogue represents only a small subset of planets that are in orbit around the stars looking for. Kunimoto used a technique called forward modeling ” to overcome these challenges.
“I started with the simulation of the full population of exoplanets around stars Kepler sought-after,” she explained. “I’ve marked each planet as “detected” or “missed” depending on how likely it was to my planet-searching algorithm would have found. Then, I compared the detection of planets in my catalog of planets. If the simulation has produced a close match, so that the initial population was probably a good representation of the actual population of the planets orbiting these stars.”
Kunimoto research also shed light on one of the most of the outstanding issues exoplanet the science today: the radius of the gap’ of the planets. The radius of the gap demonstrates that it is rare for planets with orbital periods under 100 days to have a size of between 1.5 and two times that of the Earth. It has been found that the radius of the gap there is a lot of tightening of the range of orbital periods than previously thought. His observation of the results can provide constraints on planet evolution models that explain the radius of the deviation of its characteristics.
Previously, Kunimoto searched archival data of over 200,000 stars NASA’s Kepler mission. She has discovered 17 new planets outside the Solar System, or exoplanets, in addition to the recovery of thousands of already known planets.
Reference: “the Search of the Entirety of the Data of Kepler. II. The frequency of occurrence Estimates for FGK Stars” by Michelle Kunimoto and Jaymie M. Matthews, May 4, 2020, The Astronomical Journal.