Gliese 667 - Planetary System

Planetary System

Two extrasolar planets, Gliese 667 Cb (GJ 667 Cb) and Gliese 667 Cc (GJ 667 Cc), have been confirmed orbiting Gliese 667 C by radial velocity measurements of GJ 667, with an additional two unconfirmed signals none of which and are known to transit. The two confirmed planets have masses of at least 6.0 and 3.9 times the mass of Earth, respectively, (and are thus classified as super-Earths). Planet Cb has an orbital period of approximately one week at a semimajor axis of 0.05 AU, while planet Cc orbits the star every four weeks at a distance of 0.1235 AU.

Planet Cb was first announced by the HARPS group on 19 October 2009, together with 29 other planets, while Cc was first mentioned in a pre-print made public on 21 November 2011, claiming that a discovery paper from the same group was in preparation. However, the announcement of a refereed journal report came on 2 February 2012 by researchers at the Carnegie Institution for Science/University of Göttingen. In this announcement, GJ 667 Cc was described as one of the best candidates yet found to harbor liquid water, and thus, potentially, support life on its surface. A detailed orbital analysis and refined orbital parameters for Gliese 667 Cc were presented. Based on GJ 667 C's bolometric luminosity, GJ 667 Cc should receive 90% of the visible light as Earth does, however much of the electromagnetic radiation it receives would be in the infrared spectrum. Based on black body temperature calculation, GJ 667 Cc would receives more overall electromagnetic radiation (277.4 K), placing it slightly closer to the "hot" edge of the zone than Earth (254.3 K).

Preliminary radial-velocity measurements indicate the presence of an additional super-Earth candidate (Gliese 667 Cd), orbiting in an "extended habitable zone" where large quantities of CO₂ and other greenhouse gases may make life possible (a planet similar to Gliese 581 d).. However, this candidate is less certain due to the similarity of the period to very strong periodicities detected in several activity indices, meaning that the radial velocity signal could be caused by stellar parameters. Its phase sampling is also sparse, causing severe aliasing and potential confusion. Another likely period for this same candidate would be 91 days.

An additional, long-period signal was found in the data. While the trend is largely consistent with the star's orbit around the A/B primary, a minor curvature in the trend suggests that the object may have a shorter period. A preliminary solution of 7100 days was achieved, consistent with a roughly Saturn-mass planet, but a longer time baseline will be needed to differentiate between the two solutions.

The 6 Keplerian signals detected by HARPS for Gliese 667 C is consistent with a system of up to 6 planets with orbital periods of 7.2, 28.1, 30.8, 38.8, 53.2 and 91.3 days. The 7.2 and 28.1 days signals correspond to the orbital periods of two previously known planets around the star. It should be noted that the signal with a period of 53.2 days may not be from a planet since this period also corresponds to the 2nd harmonic of the star's rotation. The five planets detected by HARPS with orbital period, distance and mass in parenthesis are: Gliese 667 C b (7.2 days, 0.049 AU, 5.4 MEarth), Gliese 667 C c (28.1 days, 0.123 AU, 4.8 MEarth), Gliese 667 C d (30.8 days, 0.130 AU, 3.1 MEarth), Gliese 667 C e (38.8 days, 0.152 AU, 2.4 MEarth), Gliese 667 C f (91.3 days, 0.268 AU, 5.4 MEarth).