This graphic is taken from the paper “Characterizing the Cool KOIs IV: Kepler-32 as a prototype for the formation of compact planetary systems throughout the Galaxy”, by Johnson, Swift, et al. Drawing on data from NASA’s Kepler exoplanet-hunting satellite, the team identified the signals of five planets orbiting Kepler-32, a M1V red dwarf with a bit more than half the Sun’s mass but only 5% of its luminosity a bit more than three thousand light years away.
Some days ago, I noted at my blog, via an article by Phys.org’s Marcus Woo, the recent claim by a team of astronomers at Caltech that red dwarf stars, the least massive and dimmest yet by far most common sort of star, are likely to have relatively extensive planetary systems.
Discussion at Centauri Dreams about the Kepler-32 system emphasizes the extent to which this very compact system–five planets orbit this star within 0.13 AU, a mere third of the distance of Mercury from the Sun!–centers on speculation as to the frequency of Earth-mass planets orbiting within the habitable zone of red dwarfs. Preliminary data suggests that Earth-mass planets orbit these dim stars far too closely to be habitable. Even the most distant planet in this system, a commenter suggests, might receive three times as much radiation as the Earth does from its star.