Image: The fraction of Sun-like stars having planets of different sizes, orbiting within 1/4 of the Earth-Sun distance (0.25 AU) of the host star. The graph shows that planets as small as Earth (far left) are relatively common compared to planets 8.0x the size of Earth (similar to Jupiter). For example, 7.9% of Sun-like stars harbor a planet with a size of 1.0-1.4 times the size of Earth, orbiting inward of 1/4 the Earth-Sun distance (closer than Mercury’s distance from the Sun). There are increasing numbers of planets from 8x the size of Earth down to 2.8x Earth. Remarkably, the number of planets smaller than 2.8x Earth is approximately constant with planet size, down to the size of our Earth. The gray indicates the planets discovered in this study, and the orange represents the correction applied to account for planets the TERRA software would miss statistically, typically about 20%. Credit: Image by Erik Petigura and Geoff Marcy, UC Berkeley, and Andrew Howard, Institute for Astronomy, University of Hawaii.

Earth-Sized Planets Widespread in Galaxy


Plenty of interesting news is coming out of the American Astronomical Society meeting in Long Beach CA, enough that I’ll want to spread our look at it out over the next few days. I want to start with Geoff Marcy’s investigations with grad student Erik Petigura at UC-Berkeley, the two working in tandem with Andrew Howard (University of Hawaii) on the question of Earth-sized planets and their distribution in the galaxy. But I can’t help noting before I begin how science fictional all these exoplanets are starting to seem as each day brings a new paper or announcement.

For me, science fiction has always been as much about landscape as it is about science, and exoplanets are the ultimate exercise in imagining exotic places. When exoplanet announcements were still new and we had only a small catalog of these worlds, I would find myself pondering each and thinking about what it would be like to orbit one, or stand on it. Now we’re getting hard data on potentially habitable places that evoke the compelling artwork on the covers of SF magazines I’ve read over the years. People gripe about not having flying cars or humans in the outer system, but to me the future I’ve lived into is every bit as provocative as the one that used to be portrayed in the pages of Astounding or Galaxy.

Read more: Earth-Sized Planets Widespread in Galaxy — Centauri Dreams.

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