PONTE VEDRA, Florida — Europe’s Rosetta comet-chaser satellite on Aug. 6 arrived at its destination — a comet some 405 million kilometers from Earth — and began returning surprising images and data as it begins an 18-month in-depth study of the comet on its annual approach toward the sun.
Nearly 10.5 years after its launch and more than six months after it was reawakened following a 31-month hibernation, Rosetta closed to its planned 100-kilometer distance from Comet 67P/Churyumov-Gerasimenko and immediately began to send images and data from inside the still-modest gas and dust cloud being thrown off by the comet.
It took the 20-nation European Space Agency’s European Space Operations Centre in Darmstadt, Germany, several hours to process the images sent by the 35-kilogram, 4-megapixel Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) camera. The data flow was no more than 70 kilobits per second over 405 million kilometers.
Early assessments: Comet 67P, measuring 3 by 5 kilometers, is spewing out water vapor at a rate of about one-third of a liter — two glasses — per second. This rate will increase 100 to 1,000 times as the comet approaches the sun.
The first images taken from the 100-kilometer distance had a 2.5-meter resolution and showed what Holger Sierks, principal investigator for the OSIRIS camera, called a “village of boulders,” some as large as houses — plus 100-meter-tall cliffs and a gorge between the two main bodies of what ESA officials variously described as two potatoes stuck together, or a rubber duck.
“For 10 years we’ve been in the car on the way to scientific Disneyland,” said Mark McCaughrean, senior science adviser in ESA’s science directorate. “We’re there. We’ve arrived. Look out the window and see.”
Rosetta will maneuver in a series triangle-shaped paths to stay mainly in front of Comet 67P on its way to the sun, the better to keep the comet — whose color is pitch-black — illuminated.
Its distance from the comet will gradually decrease to as close as 10 kilometers as its 11 onboard instruments analyze the composition of the comet’s coma — the envelope of gas and dust that is thrown off — and map its terrain to find a suitable landing spot for the small Philae lander.
Philae carries its own suite of instruments, including a drill to penetrate as much as 23 centimeters beneath the surface, that will deploy once the lander has safely attached itself to Comet 67P, whose weak gravitational pull will require the lander to attach itself to the surface with harpoons.
Comets — whose role in delivering water to Earth is still a subject of debate — have been described as “dirty snowballs,” but Rosetta’s discoveries are likely to force that description into retirement. Comet 67P looks to have a lot more dirt and rock than ice on its surface.
Philae’s landing and attachment to Comet 67P carries multiple risks; the lander could bounce off the surface, or sink into what may be a surprisingly soft surface.
Officials here stressed that even getting to the point at which Philae can be released will signal a victory given the amount of data likely to have been collected by then.
One of the striking features of the comet’s shape is what looks like a gorge. That will be one more thing to study as Rosetta gets as close as 10 kilometers from the comet, all the while dodging the rising amount of material thrown off as temperatures increase as it nears the sun.
Andrea Accomazzo, Rosetta flight director at ESA, warned the program’s many science teams not to get overly ambitious: “Don’t ask us to fly through the gorge,” he told them. “I know you!”
Rosetta cost ESA and its participating member states some 1.3 billion euros ($1.75 billion), a figure that includes the Airbus Defence and Space-built satellite, the Philae lander, launch aboard a European Ariane rocket and its planned operations to the end of 2015.
At the comet-arrival event at the European Space Operations Centre on Aug. 6, representatives from three of ESA’s biggest contributors — Germany, France and Italy — stood up to say Rosetta is an example of money well spent.
Brigitte Zypries, Germany’s aerospace coordinator — her job makes her Germany’s space minister — said the German contribution of 300 million euros was an excellent investment. She particularly praised ESA for its use of social media to encourage interest in Rosetta by young people.
Jean-Yves Le Gall, president of the French space agency, CNES, said France’s 250 million euros was “one of the best investments ever made by France in space.”
Roberto Battiston, president of the Italian Space Agency, ASI, said Italy contributed 100 million euros and views Rosetta as an example of what Europe can do on its own even without the support of the United States.
It was a demonstration of unity-in-spending that is in sharp contrast to these three nations’ difficult negotiations, continuing this week, over the way forward in launch vehicles and with respect to the international space station. They need to decide both issues by a ministerial conference scheduled for Dec. 2 in Luxembourg.
