Comet and 'Churymoon'

Animated sequence of images obtained by ESA's Rosetta probe at Comet 67P/Churyumov-Gerasimenko on 21 October 2015.

In these images, gathered a couple of months after the comet's closest approach to the Sun along its orbit, or perihelion, depict the nucleus of the comet with an unusual companion: a chunk of orbiting debris (circled). At that time, the spacecraft was at over 400 km away from the comet's centre.

The sizeable chunk in this view was spotted by astrophotographer Jacint Roger from Spain, who mined the Rosetta archive, processed some of the data, and posted the finished images on Twitter as an animated GIF. 

Scientists at ESA and in the OSIRIS instrument team are now looking into this large piece of cometary debris in greater detail. Dubbed a ‘Churyumoon’ by researcher Julia Marín-Yaseli de la Parra, the chunk appears to span just under 4 m in diameter.

Modelling of the Rosetta images indicates that this object spent the first 12 hours after its ejection in an orbital path around 67P/C-G at a distance of between 2.4 and 3.9 km from the comet’s centre. Afterwards, the chunk crossed a portion of the coma, which appears very bright in the images, making it difficult to follow its path precisely; however, later observations on the opposite side of the coma confirm a detection consistent with the orbit of the chunk, providing an indication of its motion around the comet until 23 October 2015.

Scientists have been studying and tracking debris around 67P/C-G since Rosetta’s arrival in 2014. The object pictured in this sequence is likely the largest chunk detected around the comet, and will be subject to further investigations.