June 17, 2016 | David F. Coppedge

How Long Can Comets Bust Up and Re-form?

If comets repeatedly break up and re-coagulate, how long could that recur?

A new paper in Nature from the Rosetta team suggests a strange new theory about comets. Their Comet 67P has two prominent lobes, like a dumbbell, but it’s not unique. Four other comet nuclei also have a bilobed appearance. This suggests a new theory of how they got that way:

Here, we study the structure and dynamics of 67P’s nucleus. We find that sublimation torques have caused the nucleus to spin up in the past to form the large cracks observed on its neck. However, the chaotic evolution of its spin state has so far forestalled its splitting, although it should eventually reach a rapid enough spin rate to do so. Once this occurs, the separated components will be unable to escape each other; they will orbit each other for a time, ultimately undergoing a low-speed merger that will result in a new bilobate configuration. The components of four other imaged bilobate nuclei have volume ratios that are consistent with a similar reconfiguration cycle, pointing to such cycles as a fundamental process in the evolution of short-period comet nuclei. It has been shown that comets were not strong contributors to the so-called late heavy bombardment about 4 billion years ago. The reconfiguration process suggested here would preferentially decimate comet nuclei during migration to the inner solar system, perhaps explaining this lack of a substantial cometary flux.

It’s a destructive process, in other words. How long could that go on?

This is grist for someone’s research mill – someone open to the idea that billions of years are neither necessary nor empirically tenable.


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