What In The World Just Happened To Comet 67P?

19 February 2016 was going to be just another day on Comet 67P — until suddenly, the icy space rock lit up in a blaze of glory, as if suddenly slapped by an angry angel. Rosetta's wide angle camera captured this outburst from Comet 67P on February 19. Image: ESA/Rosetta/MPS

The strange astronomical event would have gone unnoticed by the seven billion people living right down the cosmic street, except that lucky for us, we had a spacecraft in orbit around that sucker. Rosetta caught all the action, and scientists on Earth have now reconstructed a detailed sequence of events that may have been triggered by a landslide.

The analysis, led by Eberhard Grün of the Max-Planck-Institute for Nuclear Physics, has been accepted for publication in Monthly Notices of the Royal Astronomical Society.

"By happy coincidence, we were pointing the majority of instruments at the comet at this time, and having these simultaneous measurements provides us with the most complete set of data on an outburst ever collected," ESA Rosetta project scientist Matt Taylor said in a statement.

Timeline on Comet 67P's recent outburst, as witnessed by Rosetta's cameras, dust collectors, gas and plasma analysers. Image: ESA/Rosetta/MPS

The action began around 9:40 GMT, when Rosetta's detectors noted a strong brightening in the coma, the halo of airborne water vapour and dust surrounding Comet 67P. Over the next few hours, the UV brightness of sunlight reflected off the coma increased sixfold, while the amount of sunlight scattered off dust grew by a factor of 10. Meanwhile, temperatures in the gas rose some 30C.

Then, Rosetta was blasted by dust, its sensors registering almost 200 individual particles in just three hours, compared with an average of three to 10 particles per day. By mid afternoon, the comet had settled back down.

Location of the Atum region, where Comet 67P's recent outburst likely originated. Image: ESA/Rosetta/NavCam

By putting all of their data together, scientists believe they have identified the cause of the commotion: A steep slope on the comet's larger lobe, in what's known as the Atum region. The outburst started just after this region emerged from shadow, suggesting that heat from the sun's rays may have vaporised a patch of exposed water ice and triggered a landslide.

I'd like to pose an alternate hypothesis: Comet 67P is a Pokemon GO gym. Hey, it explains why the Philae lander never calls us any more.

[European Space Agency]

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