new six-planet extra-solar planetary system!

Dan Foreman-Mackey showed up for a couple of days of hacking. He has been searching for single (isolated) transits (that is, very long-period planets) in the 4-year Kepler data. He has found a few great outer planets! When the stellar properties are well known for the host star (especially the density of the host star, it turns out), the period and eccentricity of the long-period planet are (jointly) constrained fairly well from the transit duration.

Foreman-Mackey's search is super-conservative, as it must be, because the best way to find planets is through their periodicity in the data, and these long-period planets are (by construction of the problem) not periodic inside the Kepler time window. He finds candidates in the time stream and then does a set of probabilistic hypothesis tests against various kinds of data-artifact models. Finally, he rejects systems that induce what are known as “centroid shifts” in the Kepler imaging. These are blends (and therefore the planetary inferences are wrong).

One system he rejected that way, we figured out today, is the sixth planet in a known five-planet system with a set of five closely packed short-period planets. It has a small centroid shift associated with the single transit, but that centroid shift (it turns out) is quantitatively consistent with a small amount of contamination from a fainter star that is within one Kepler pixel angular separation of the target star. That is, the contamination is small and the planetary inferences are not very wrong (and this conclusion applies both to the short-period planets and to the long-period outer planet). Hence: A new six-planet system! You heard it here first, folks! Question for Foreman-Mackey: Why wasn't this announcement made by a twitter (tm) bot?

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