Twin tails

Amateur and professional astronomers alike have been monitoring changes in Comet 67P/Churyumov-Gerasimenko’s tail, which, since December, has been exhibiting two prominent structures. “Current indications from the data we’re collecting of Comet 67P/C-G is that both features are dust structures,” says professional astronomer Alan Fitzsimmons, who has recently spent time observing the comet with the Isaac Newton Telescope in La Palma. Multiple tail structures are not uncommon in comets, and indeed have been observed during previous apparitions of Comet 67P/C-G. The two portions of the tail are attributed to different populations of dust grains swept away from the comet’s nucleus by the radiation pressure of the Sun over the course of its 6.5 year orbit around the Sun. In the image above, taken with the 2.5m Isaac Newton Telescope on La Palma, the upper ‘streamer’ is precisely aligned along the projected orbit of the comet, implying it is made of large and/or old dust grains moving slowly along the orbit of comet. This part is called a comet dust trail because it is formed from the particles trailing along the path of a comet. This dust trail of Comet 67P/C-G has been seen several times before by both ground-based telescopes and space-based infrared observatories. The lower portion of the dust tail exhibits a thin central core and resembles a feature called a neckline structure. This is formed from dust grains released on the “opposite side” of the orbit from the time of the observation, and all lining up as seen from Earth. This has also been seen before in previous returns of Comet 67P/C-G. “We need to do more calculations and modelling, but if our interpretation is correct, then the dust grains forming the neckline in December 2015 were ejected from the comet nucleus around March last year, prior to perihelion,” […]

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