The first clear hints of a large multiplanet system around Gliese 667 C emerged last year, through the work of Philip Gregory, an astronomer at the University of British Columbia in Vancouver.
was analyzing public data from the European Southern Observatory's HARPS spectrograph, a world-class planet-hunting instrument in La Silla, Chile.
noticed several previously unreported, potentially planetary wobbles, including one that looked like a 2.5-Earth-mass planet in a 39-day orbit-that is, another rocky planet within the star's habitable zone in addition to the already discovered-Gliese 667 C c. Gregory
wrote up his
findings and submitted them to a journal, but he
stopped just short of claiming that he
had found new planets.
colleagues were also glimpsing the wobbly evidence of Gliese 667 C's wealth of worlds by combining the HARPS measurements with data from two other telescopes.
They analyzed the combined data using two independent and distinct statistical methods.
Both methods strongly supported the presence of the two previously announced planets as well as three "new" planets with orbits and masses essentially identical to what Gregory reported in 2012.
One of the two methods also found tentative evidence for two additional small planets, one in a hot 17-day orbit and another in a frigid 256-day orbit.
Several rounds of further simulations only increased their confidence the planets were real.
praises the group's work as "a very significant step forward," and notes that although his
paper "served to draw attention to the possibility of multiple planets in the habitable zone," the Anglada study contains "more definitive results."