Up to six billion Earth-like planets in our galaxy, according to new estimates

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To be considered similar to Earth, a planet must be rocky, about the size of Earth and orbiting the Sun (type G). It must also orbit the habitable zones of its star – the range of distances from a star within which a rocky planet could harbor liquid water, and potentially life, on its surface.

“My calculations place an upper limit of 0.18 Earth-like planets per G-type star,” said UBC researcher Michelle Kunimoto, co-author of the new study in The Astronomical Journal. “Estimating the frequency of different types of planets around different stars can create significant constraints on planet formation and theories of evolution, and help optimize future missions dedicated to the search for exoplanets. ”

According to UBC astronomer Jaymie Matthews: “Our Milky Way has up to 400 billion stars, 7% of which are type G. This means that less than six billion stars can have planets similar to the Earth in our Galaxy. ”

Previous estimates of the frequency of Earth-like planets range from about 0.02 potentially habitable planets per Sun-like star to more than one per Sun-like star.

In general, planets like Earth are more likely to be missed by a planet search than other types, because they are so small and orbit so far from their stars. This means that a catalog of planets represents only a small subset of the planets actually orbiting the desired stars. Kunimoto used a technique known as “advanced modeling” to overcome these challenges.

“I started by simulating the entire population of exoplanets around the stars that Kepler searched for,” she said.

“I marked each planet as” detected “or” missed “based on the probability that my planet search algorithm found them. Next, I compared the detected planets to my actual catalog of planets. If the simulation produced a close match, then the initial population was probably a good representation of the actual population of planets orbiting these stars. ”

Kunimoto’s research has also shed more light on one of the most important questions in exoplanet science today: the planets ’radius’ gap. The radius deviation shows that it is rare for planets with orbital periods of less than 100 days to be between 1.5 and twice the size of Earth. She found that the radius deviation exists over a much narrower range of orbital periods than previously thought. Its observation results may provide constraints on the evolution models of the planet which explain the characteristics of the radius deviation.

Earlier, Kunimoto searched for archival data for 200,000 stars from NASA’s Kepler mission. She discovered 17 new planets outside the solar system, or exoplanets, in addition to recovering thousands of already known planets.

Research paper

Related links

University of British Columbia

Lands Beyond Beyond – Additional Solar Planets – News and Science
Life beyond the earth


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