Lee Billings, writing for Scientific American:
From its position 22 light-years away in the constellation of Scorpius, the red M dwarf star Gliese 667 C doesn’t look like much. Its dim light is lost to the naked eye, washed out by two brighter companion stars. Yet this tiny, exceedingly average star could play a crucial role in establishing that small, potentially Earth-like planets are common throughout our galaxy. Researchers have announced that seven planets orbit that star—and, if their mathematical analyses are correct, three of them could be habitable.
Astronomers previously knew of two planets that circle Gliese 667C. One named Gliese 667C c is a super-Earth—a planet slightly larger than Earth but much smaller than Uranus, which is about 14.5 times the size of Earth—and resides in the habitable zone, the distance from the star where liquid water can exist on the planet’s surface.
But now they have identified three to five additional planets orbiting Gliese 667C, two of which are super-Earths (Gliese 667C f and Gliese 667C e) that may reside in the habitable zone. All but one of these orbit very close to Gliese 667C—about the distance between the Sun and Mercury. But because Gliese 667C is smaller than our sun, its habitable zone is closer.
Like other exoplanets, these newest were discovered by detecting the slight pull they have on their star as they orbit. Some scientists are skeptical of the data, citing the problems with trusting weak signals amongst noisy data. But others are excited about the possibilities, in part because this type of star system is the most common found in the Milky Way.