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Rosetta Has Arrived, and the View is Astounding

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By Tom Yulsman
Aug 7, 2014 2:46 AMNov 20, 2019 3:51 AM


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This animation comprises 101 images acquired by the Navigation Camera on the European Space Agency's Rosetta spacecraft as it approached comet 67P/C-G. The first image was taken on August 1, 2014, and the last on August 6 at a distance of 110 kilometers, or 68 miles. (Source: ESA/Rosetta/Navcam) It took five loops around the Sun, three gravity-assist fly-bys of Earth and one of Mars, and a journey of 3.97 billion miles lasting 10 years, five months and four days. After all that, the Rosetta spacecraft finally reached it destination today — and made history. Rosetta is the first spacecraft ever to rendezvous with a comet. It is now in quasi-orbit (more about that in a minute) around comet 67P/Churyumov-Gerasimenko. For more than a year, it will take pictures and gather data, and it will also send a lander down to the surface, all in a quest to help us understand the origin and evolution of the solar system. In so doing, it will tell us something of our own origins. The animation above records the final leg of that long and lonesome journey. It consists of 101 images taken by the probe's navigation camera as it approached the comet, the first from Aug. 1 and the last from today.

A close-up of comet 67P/Churyumov-Gerasimenko taken by Rosetta’s OSIRIS narrow-angle camera and downloaded today (Aug. 6). The image was taken when Rosetta was a mere 120 kilometers, or 75 miles, away. (Source: ESA/Rosetta/MPS for OSIRIS Team) Now that Rosetta, a project of the European Space Agency, or ESA, has settled in close to the comet, it will be making roughly triangular loops around it, using its thrusters to maintain the proper trajectory. Technically speaking, this isn't quite an "orbit." But once scientists have a better handle on the comet's gravity, the plan is for Rosetta to attempt a close, near-circular orbit at 30 kilometers, or 18.6 miles, from the surface — and maybe even a bit closer. But even on its current trajectory around the comet, Rosetta is already sending back some spectacular closeup images, including the one above. It shows the comet’s ‘head’ at the left of the frame. This bulbous part of the comet is casting a shadow onto the bright ‘neck’ and ‘body’ to the right. The image resolution is 2.2 meters per pixel, or a little more than 7 feet. That means features equivalent in size to a large boulder are visible. The cometscape is mind boggling — pits, cliffs, crags, and smoother areas (perhaps icy?).

A portrait of the comet taken on Aug. 3 by the OSIRIS narrow-angle camera on Rosetta. (Source: ESA/Rosetta/MPS for OSIRIS Team) You can get a better sense of what the head, neck and body of the comet look like in this image, taken on Aug. 3. From one end to the other, the comet is about 4.5 kilometers long. That's just 2.8 miles. As a runner, I can't help but compare that length to that of a typical race of 5 kilometers. Here on Earth (and at a mile high in Boulder), I can cover that distance in about 20 minutes, plus or minus 10 or so seconds. I mention this not to brag about my running abilities (although I'm pretty fast for a 58-year-old), but simply because it provides a sense of what an absolutely astounding feat it was to send a spacecraft across so much of the solar system and have it arrive so very precisely at an object so small. I should also mention that the resolution of this image is not quite as fine-grained as the previous one — 5.3 meters, or 17 feet, per pixel. So basically, if a big truck were parked on the comet, you'd probably be able to see it at this resolution. This view also provides a good sense of the comet's overall structure — and raises an intriguing question: Why does it consist of two lobes connected by a narrow neck? "Is this double-lobed structure built from two separate comets that came together in the Solar System’s history, or is it one comet that has eroded dramatically and asymmetrically over time?," asks Matt Taylor, ESA's Rosetta project scientist. "Rosetta, by design, is in the best place to study one of these unique objects.” Comets have been described as "dirty snowballs" — basically agglomerations of dust and rock held together by ices consisting of various compounds such as carbon dioxide, water and ammonia. These and other "volatiles" flow off a comet to create its "coma" — the bright envelope of gas that surrounds the nucleus of a comet as it approaches the sun. And that brings me to one last image:

Volatile material streams off comet 67P/Churyumov-Gerasimenko on August 2, 2014, as seen by Rosetta’s OSIRIS wide-angle camera from a distance of 550 kilometers (342 miles). (Source: ESA/Rosetta/MPS for OSIRIS Team) The comet is a very, very long way from the Sun right now — 540 million kilometers, or 340 million miles away, in fact. That's almost as far out from the Sun as Jupiter is. So you'd think it would be really cold out there. And you'd be right. But enough solar energy evidently reaches the comet to melt some of its ice and cause the material to spray out into space. A note of explanation about the image: The exposure time was five and a half minutes — a long time! That's why the nucleus is so bright and no detail is visible. But this long exposure brought out the details of the material streaming off into space, including a big spray of stuff fanning out from the top of the nucleus in this view.

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