Packed star system may have three habitable super-Earths

Washington.edu

The number of potentially habitable planets continues to grow. This week, a team of astronomers provided an update on GJ 667C, a star known to host two super-Earths, based on past observations. Further observations, along with some refined statistical methods, now indicate that there are likely to be at least six planets in the system (and possibly a seventh), all packed in a region that's about half the distance from the Earth to the Sun. Although they're all much closer to the host star, the star is quite a bit dimmer, which also shifts the habitable zone such that two of the planets fall squarely within it.

GJ 667C is part of a three-star system in the direction of the constellation Scorpius. The stars orbit each other at a sufficient distance, however, that GJ 667C's companions don't interfere with the planetary orbits. Initial observations of the star were made with a spectrograph (the HARPS instrument), which detects subtle shifts in the wavelengths of the light emitted by the star. Some of these shifts are changes in the star's activity, but others are caused by its motion towards or away from Earth, which shift the light to higher or lower frequencies, respectively. One of the factors that can cause these shifts is gravitational pull of planets as their orbits take them ever so slightly closer to or further from Earth.

GJ 667C is a type of star called an M-dwarf that is smaller than the Sun. Because of its small size, it's possible to detect even relatively light planets due to their pull on the host star. The ease of detecting planets was one of the reasons that the star was targeted for observations originally, and that paid off with the discovery of the exoplanets GJ 667Cb, a super-Earth close to the star (at 0.05 Astronomical Units) and GJ 667Cc, at about .12 Astronomical Units.