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Europe's Rosetta Probe Reaches Climax of Its Comet-Chasing Mission

After a 10-year, 4 billion-mile trek through deep space, the European Space Agency's Rosetta spacecraft is finally arriving at its comet destination.
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After a 10-year, 4 billion-mile journey through deep space, the European Space Agency's Rosetta probe is finally arriving at its comet destination.

The Rosetta spacecraft is scheduled to rendezvous with Comet 67P/Churyumov-Gerasimenko on Wednesday. If all goes according to plan, Rosetta will become the first probe ever to orbit a comet — and, in November, the first to drop a lander onto the surface of one of these icy wanderers.

"For the first time, we will rendezvous with a comet, for the first time we will escort a comet as it passes through its closet approach to the sun and — the cherry on the top — for the first time, we will deploy a lander," Rosetta project scientist Matt Taylor told via email. "The rendezvous is therefore a key milestone in the mission." [Europe's Rosetta Comet Mission in Pictures]

A long wait

The $1.75 billion (€1.3 billion) Rosetta mission blasted off in March 2004, kicking off a long and circuitous journey through the solar system. The probe has swung around the sun five times and zoomed past Earth on three separate speed-boosting flybys.

The probe was asleep during a decent chunk of its decade-long trip; mission team members woke Rosetta up in January to prepare for the upcoming rendezvous, ending 957 days of hibernation.

Rosetta is homing in on the 2.5-mile-wide (4-kilometer-wide) Comet 67P/Churyumov-Gerasimenko, which takes about 6.5 years to complete one lap around the sun. The comet's elliptical orbit takes it beyond Jupiter at its farthest point from the sun, and between Mars and Earth at its closest point.

The rendezvous operation consists of 10 different maneuvers, which began in early May and will conclude with a final engine burn on Wednesday. These moves will end up slowing Rosetta's speed relative to the comet from 1,790 mph (2,880 kilometers per hour) at the end of the probe's hibernation to 2 mph (3 km/h) — walking speed — at the time of orbital insertion, Taylor said.

"It is challenging; it's never been done before," Taylor said. Earlier comet missions have sped past their target at high speed, coming no closer than 62 miles (100 kilometers). Rosetta's orbital distance will start out at 100 kilometers and eventually drop to 20 to 30 kilometers (12 to 19 miles).

Learning about comets

Rosetta will provide another dose of deep-space drama in November, when the mothership drops a lander called Philae onto the surface of Comet Churyumov-Gerasimenko. Philae will drill into the comet to take samples and transmit images from the surface of the body, ESA officials said.

The Rosetta mothership and Philae will tag along with the comet as it approaches and then swings around the sun. During the trip, readings from the spacecraft will take note of the comet's changes.

Image: Comet
An Aug. 2 image from the Rosetta probe's navigation camera shows Comet Churyumov-Gerasimenko from a distance of about 300 miles (500 kilometers).ESA / Rosetta / NAVCAM

The duo's observations should reveal a great deal about comet composition, which in turn should help researchers better understand solar system evolution. Comets are thought to be the primitive and relatively pristine building blocks left over from the solar system's formation.

Taylor says he and his teammates are looking forward to this "escort phase," which is slated to run from Wednesday through the end of the nominal mission in December 2015.

"All the time we are looking, and sniffing the comet, and with the lander (over a shorter time period) scratching and sniffing," Taylor said. "All this will provide us with an unprecedented view of a comet, its nucleus and coma and how this all works!"

— Mike Wall,

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