Sometimes a pile of data and an eye for detail are all you need to make an amazing discovery. Several months back, Spanish astrophotographer Jacint Roger spotted an object orbiting comet 67P/Churyumov-Gerasimenko while mining the Rosetta image archive. In case you forgot, Rosetta was the European mission that rendezvoused with the comet in August 2014 and remained in orbit for closeup studies until September 2016.
He found the comet moon in a sequence of images taken by Rosetta on Oct. 21, 2015 when the spacecraft hovered 248 miles (400 km) from the comet’s center. After processing the images he assembled them into a short video and posted it on his Twitter. Scientists at the European Space Agency and spacecraft camera team are now studying this chunk of cometary debris in greater detail. They’ve even given it a name — Churymoon. Spanning just under 13 feet (4 meters) you’d hardly consider it a moon, but because it orbits the 4-kilometer-wide “mothership” it’s as much a moon as some of the tiny moons that orbit a modest number of asteroids.
Modelling done using the images indicate that after it broke away from the comet, Churymoon spent its first 12 hours orbiting at a distance of just 1.5 to 2.4 miles (2.4-3.9 km) from 67P/C-G’s center. Later, the chunk crossed a portion of the coma — that’s the fluffy cloud of gas and dust surrounding the comet’s icy nucleus — and appeared on the opposite side of the comet, confirming its orbit at least through Oct. 23.
Scientists have been studying and tracking debris around 67P/C-G since Rosetta’s arrival in 2014. The object pictured in this view is likely the largest chunk detected around the comet, and is still being investigated.
Like many comets, 67P/C-G’s ices are embedded with dust. The closer a comet gets to the sun, the more ice is vaporized and the more dust released. As it neared its closest approach to the Sun in late July and August 2015, instruments on Rosetta recorded a huge amount of dust enshrouding the comet, much of it spat into space by geyser-like jets. This disturbed, ejected material forms the coma, a temporary atmosphere of gas and dust that envelopes the comet’s nucleus. Often, some of that material is pushed back by sunlight to form a beautiful tail, a comet’s defining characteristic in the public eye.
Comet 67P/C-G is currently in the outer solar system between the orbits of Mars and Jupiter. Orbiting the sun every 6.5 years, its next closest approach is in 2021.