Jack Lissauer, planetary scientist and a Kepler science team member, said: "The Kepler-11 planetary system is amazing. It’s amazingly compact, it’s amazingly flat, there’s an amazingly large number of big planets orbiting close to their star – we didn’t know such systems could even exist."
By "flat", Lissauer means that Kepler-11's planets orbit in pretty much the same plane, as do the planets in our own solar system. Keplers b to f have orbital periods between 10 and 47 days, while the outermost world circles in a rather more tardy 118 days.
All of the Kepler planets are less dense than Earth, leading scientists to suspect that while "their surfaces could be rocky or a combination of rock and ice", they may "also have a lot of gas because their densities are so low", as Kepler astronomer Eric Ford of the University of Florida put it.
Specifically, Kepler-11d, Kepler-11e and Kepler-11f "have a significant amount of light gas, which Lissauer says indicates that at least these three planets formed early in the history of the planetary system, within a few million years".
NASA explains that such bodies form from a star's protoplanetary disc "relatively quickly in order to obtain gases before the disk disperses". It elaborates: "Protoplanetary disks can be seen around most stars that are less than a million years old, but few stars more than five million years old have them."
Kepler will continue to eye Kepler-11 with a view to providing further insights into the system. Lissauer said: "These data will enable us to calculate more precise estimates of the planet sizes and masses, and could allow us to detect more planets orbiting the Kepler-11 star.
"Perhaps we could find a seventh planet in the system, either because of its transits or from the gravitational tugs it exerts on the six planets that we already see. We’re going to learn a fantastic amount about the diversity of planets out there, around stars within our galaxy."
The Kepler-11 findings are published in today's issue of Nature.
NASA, meanwhile, is hailing even more Kepler planetary revelations, including the "first candidates in the habitable zone, a region where liquid water could exist on a planet's surface".
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