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| Size and number of Kepler Planet Candidates |
So, how many Earth-size planets exist? Well, to start with, small terrestrial planets drastically outnumber larger Earth-size and Jupiter-size planets. That being the case, recent observations suggest that Earth-size planets are fairly common around Sun-like stars.[003] There are so many such planets, the 2013 study Prevalence of Earth-size planets orbiting Sun-like stars states that (given certain circumstances),
The number of Sun-like stars in the Milky Way Galaxy is said to be about 10%.* The number total stars is a matter of debate, but it often stated as 100 billion stars.[006] 10% of that is 10 billion stars. Therefore, 22% of 10 billion is 2.2 billion stars. With that determined, how common are planets that are so similar to Earth that events naturally occur in the right sequence to spark and nurture life? How likely is that life to evolve to develop the human-level expression of intelligence and curiosity? What is the likelihood of any of species developing in the same timeframe as us? Are other species close enough to us to communicate with us? Should we really trying to reach out to these others? Some of these questions will be addressed in further articles.
*10% is stated by multiple tertiary sources for "sun-like" stars, and 7.5% is stated for "g-type" stars, but I could not verify these percentages from any original sources.
Primary reference:
E.A. Petigura, A.W. Howard, G.W. Marcya, Proceedings of the National Academy of Sciences of the United States of America, 110 no. 48, (Nov., 2013), 19273-19278, 10.1073/pnas.1319909110, Prevalence of Earth-size planets orbiting Sun-like stars
Response:
Voat.co (backup link)
Reddit
...the nearest such planet is expected to orbit a star that is less than 12 light-years from Earth and can be seen by the unaided eye.[003]That's not only a lot of planets, 12 light-years is a distance that seems at least somewhat reachable with technology that is currently being investigated. Recently, such a planet seems to have been discovered around the closest star to our own, Proxima Centauri.[004] Technically, Proxima Centauri cannot be seen with the unaided eye on its own, but rather as part triple star system that appears as one the dot in the Southern Hemisphere sky called Alpha Centauri, but close enough (literally).[005]
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| Kepler's Small Habitable Zone Planets |
Overall based on Kepler space observatory results, it is calculated that about 22% of all Sun-like stars have an Earth-size planet within its Habitable Zone. Prevalence of Earth-size planets orbiting Sun-like stars seems well informed in its conclusion (2013),
Future instrumentation to image and take spectra of these Earths need only observe a few dozen nearby stars to detect a sample of Earth-size planets residing in the Habitable Zones of their host stars.[003]
*10% is stated by multiple tertiary sources for "sun-like" stars, and 7.5% is stated for "g-type" stars, but I could not verify these percentages from any original sources.
Primary reference:
E.A. Petigura, A.W. Howard, G.W. Marcya, Proceedings of the National Academy of Sciences of the United States of America, 110 no. 48, (Nov., 2013), 19273-19278, 10.1073/pnas.1319909110, Prevalence of Earth-size planets orbiting Sun-like stars
Response:
Voat.co (backup link)
Article Series:
- Limited lifespan of Habitable Zones around other stars [and a loosely held secret finally revealed about me]
- Small stars may have stable Habitable Zones, but habitable planets might not be common there
- Habitable Planets around White Dwarfs
- Habitable Worlds Around Binary Star Systems might not match Sci-fi
- How many Earth-like planets are orbiting Sun-like stars?
- First round of life in the Universe might have been possible extremely early
- Factors a planet needs for suitability of life; perhaps
- "Goldilocks zone of metallicity" on a galactic scale
- Maybe we are the first
