Rosetta’s target comet flares to life, grows ‘hair’

A sequence of images showing comet 67P/Churyumov–Gerasimenko moving against a background star field in the constellation Ophiuchus between March 27 and May 4, 2014 as the distance between the spacecraft and comet closed from around 3.1 to 1.2 million miles (5-2 million km). The comet develops a dust coma as the sequence progresses, with clear activity already visible in late April. The globular star cluster M107 is at upper left. Credit: ESA/Rosetta/MPS

This month the Rosetta spacecraft begins braking maneuvers at its target comet 67P/Churyumov-Gerasimenko. By good fortune, the comet has ‘woken up’ at the same time, developing a dusty atmosphere called a coma.

You can create a mini-coma of your own by blowing warm air over a chunk of dry ice. Similarly, as the sun warms the comet’s icy nucleus, dry, water and ammonia ices vaporize, liberating embedded dust particles that form a glowing shell thousands of miles across around the much smaller nucleus.

Coma comes from the Greek word for ‘hair’ and describes a comet’s fuzzy appearance through the telescope. Back in ancient times they were often referred to as ‘hairy stars’. Soon Churyumov-Gerasimenko will have more hair than I do.

During an outburst in 2007, Comet 17P/Holmes grew a spectacularly large coma that expanded to some 869,900 miles (1.4 million km) – larger than the sun! Comas are made of dust and gases boiled off a comet’s nucleus by the sun. Credit: Gil-Estel / Wikipedia

Based on recent photos, 67P/ C-G’s coma now spans over 800 miles (1,300 km) around an irregularly shaped nucleus about 2.5 miles (4 km) wide. The coma will continue to grow as the distance between comet and sun shrinks in the coming months.

It’s amazing to realize that the sun can already work its magic even at the comet’s current distance of 372 million miles (600 million km) or three-quarters the way to Jupiter. Rosetta and the comet will be closest to the sun in August 2015, when the duo will zip along between the orbits of Earth and Mars.

“It’s hard to believe that only a few months from now, Rosetta will be deep inside this cloud of dust and en route to the origin of the comet’s activity,” said Holger Sierks, principal investigator for OSIRIS, the Optical, Spectroscopic and Infrared Remote Imaging System used to take the photos for the sequence above. Rosetta will begin orbiting the comet this August and land a small probe on its surface November 11.

Interactive visualization of the Rosetta mission to Comet Churyumov-Gerasimenko. Go ahead and hit play – it’s live.

Besides showing an increase in activity, scientists tracking periodic changes in the brightness of 67P have nailed down its rate of spin at 12.4 hours. One day on the comet equals half a day back on Earth. Follow along with Rosetta as its travels ever closer to its target by clicking and dragging on the live simulator.

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