On Thursday at 02:03 GMT, Comet 67P/Churyumov-Gerasimenko and the European Space Agency's (ESA) Rosetta orbiter reached their closest point (known as perihelion) to the Sun, coming within 186 million km (115 million mi) of our parent star. The event was marked by an increase in activity on the comet, which is expected to continue over the next few weeks as it now heads toward the outer Solar System.

Comet 67P is now 750 million km (466 mi) closer to the Sun than when Rosetta made its rendezvous about a year ago. During the approach, the increasing intensity of the sunlight heated the "dirty snowball" to temperatures tens of degrees above 0° C, causing the various ices to sublimate into gases and blowing out dust particles. These collected around the nucleus and were blown back by the solar winds to form the comet's distinctive coma and tail.

During perihelion, Rosetta took a series of high resolution images, though the dust prevented the spacecraft from approaching closer than 325 km (202 mi). The images show jets of gas and other signs of activity as the comet spewed out 300 kg (660 lb) of water per second, or about as much as two bathtubs, along with 1,000 kg (2,200 lb) of dust. ESA says that this is a thousand times greater than when Rosetta first arrived.

In addition, the space agency says that the comet's southern hemisphere is moving into its 10-month summer, which has revealed four new regions for Rosetta to map, bringing the total to 23. In keeping with agreed convention, the regions were named after the Egyptian gods Anhur, Khonsu, Sobek, and Wosret.

One drawback of the Rosetta mission is that the spacecraft is too close to see the coma and tail of 67P, so earthbound telescopes have been brought in to record images and make measurements of the 120,000 km (75,000 mi) tail.

“Combining these big-picture views from ground-based telescopes with Rosetta’s close-up study of individual jets and outbursts will help us to understand the processes at work on the comet’s surface as it approaches the Sun," says Nicolas Altobelli, acting Rosetta project scientist. “We aim to go back in much closer again after the activity subsides and make a survey of how the comet has changed. We also continue to hope that Philae will be able to resume its scientific operations on the surface and give us a detailed look at changes which may be occurring immediately surrounding its landing site."

As Comet 67P recedes from the Sun, there will eventually be insufficient light available to charge Rosetta’s batteries. Before this happens, mission control in Darmstadt will order the spacecraft to make a controlled landing on the comet’s surface.

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