NASA: 1 Billion ‘Earths’ in Our Galaxy Alone; Estimate, “May Be a Little Low”
July 25th, 2015Via: Washington Post:
During the NASA newser Thursday, I asked whether the latest Kepler data offered any new insight on the abundance of Earth-like planets around sun-like stars (the shorthand for this formulation is “eta-Earth”), and then followed up with an e-mail to NASA. Batalha, an astrophysicist who is the mission scientist for the Kepler telescope, e-mailed her answer:
Previous estimates of eta-Earth suggest that 15-25% of stars host potentially habitable planets. These estimates are based largely on discoveries of planets orbiting the cooler stars called M dwarfs. These new discoveries suggest that the statistics for sun-like stars are roughly in-line with estimates from the cooler M-type stars. So how does that translate to the number of planets in the galaxy? M, K, and G dwarfs comprise about 90% of the stars in the galaxy. Conservatively speaking, if 15% of stars have a planet between 1 and 1.6 times the size of Earth in the Habitable Zone, then you’d expect 15% of 90% of 100 billion stars to have such planets. That’s 14 billion potentially habitable worlds.
M type stars are the most common in the galaxy comprising about 70% of the population of Main Sequence stars. Here’s how the star types break down for the solar neighborhood within 33 light-years:
357 stars total
248 of those are M dwarfs
44 K dwarfs
20 G dwarfs
That means “only” about a billion of the 14 billion I mentioned above are orbiting G stars. Ha!
Thank you, Dr. Batalha! Keep in mind, she is using conservative estimates. So 1 billion may be a little low.
