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Rosetta Spacecraft: To Catch a Comet

Rosetta Spacecraft Deploying Philae Lander on Comet Artist Impression
An artist's impression of the Rosetta orbiter deploying the Philae lander to comet 67P/Churyumov–Gerasimenko in 2014.
Credit: ESA–C. Carreau/ATG medialab

Rosetta is a spacecraft on a 10-year mission to catch a comet. Launched in 2004, the spacecraft will soon make its rendezvous with Comet 67P/Churyumov-Gerasimenko.

Rosetta will be the first spacecraft to accompany a comet as it enters the inner solar system. After meeting up with the comet, it will begin a two-year study of the comet's nucleus and environment, observing how a frozen comet changes as it approaches the heat of the sun. Rosetta will also deploy a robot to make the first controlled landing on a comet. [Photos: Europe's Rosetta Comet Mission in Pictures]

Rosetta is named for the Rosetta Stone, a block of black basalt that was inscribed with a royal decree in three languages — Egyptian hieroglyphics, Egyptian Demotic and Greek. The spacecraft's robotic lander is called Philae, named after a similarly inscribed obelisk found on an island in the Nile River. Both the stone and the obelisk were key to deciphering ancient Egyptian hieroglyphs. Scientists hope the mission will provide a key to many questions about the origins of the solar system and, perhaps, life on Earth.

Side missions

Rosetta was set to launch in 2003 to rendezvous with Comet 46P/Wirtanen. However, due to rocket failure, the mission was postponed, and the target was changed to Comet 67P/Churyumov-Gerasimenko. [Best Close Encounters of the Comet Kind]

Rosetta launched on March 2, 2004, aboard an Ariane 5 rocket. It made four slingshot flybys to boost its speed — one around Mars and three around Earth. On its journey, it passed and photographed asteroids, studied other comets and provided information about the atmospheres of Venus and Mars.

Scientists at the European Space Agency put Rosetta into hibernation mode in June 2011 for its 373-million-mile (600 million kilometers) journey. After awakening in January 2014, the spacecraft still has four more months to travel until it reaches its target just inside Jupiter's orbit.

An artist's illustration of the European Space Agency's comet-chasing Rosetta spacecraft.
An artist's illustration of the European Space Agency's comet-chasing Rosetta spacecraft. Rosetta will explore Comet 67-P/Churyumov-Gerasimenko when it arrives at the object in August 2014.
Credit: ESA - C. Carreau

Jupiter Family comet

Comet 67P/Churyumov-Gerasimenko was first observed in 1969 by Klim Churyumov and Svetlana Gerasimenko, astronomers from Kiev, Ukraine, who were working at the Alma-Ata Astrophysical Institute in the area that is now Kazakhstan. Churyumov was studying photographs of Comet 32P/Comas Solá, taken by Gerasimenko, when he thought he saw another cometlike object. After returning to Kiev, he examined the photograph more closely and determined that it was a new comet.

The comet — whose name is sometimes shortened to Comet 67P and sometimes to Comet C-G — makes regular visits to the inner solar system, as it orbits the sun every 6.5 years between the orbits of Earth and Jupiter. It is among several short-period comets that have orbital periods of less than 20 years and a low orbital inclination. Because Jupiter's gravity controls their orbits, they are called Jupiter Family comets.

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Comet Quiz: Test Your Cosmic Knowledge
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These comets are thought to originate in the Kuiper Belt, a region of space beyond Neptune's orbit filled with icy bodies. As these bodies collide, some are knocked out of the Kuiper Belt and fall toward the sun. Jupiter, with its massive gravitational pull, grabs some of them and changes their orbit.

Scientists say Comet 67P's perihelion — its closest approach to the sun — used to be 4 AU (Earth-sun distances), or 373 million miles. Close encounters with Jupiter over time have decreased the comet's perihelion to 1.24 AU, or 116 million miles (186 million km).

Most of the time, Comet C-G is very faint and hard to find with Earth-based telescopes. The comet has been observed by ground-based telescopes seven times: in 1969, 1976, 1982, 1989, 1996, 2002 and 2009. The Hubble Space Telescope also photographed the comet in 2003, which enabled scientists to estimate that the comet is about 2 miles wide and 3 miles long (3 km by 5 km).

Rosetta orbiter

Rosetta is an aluminum box with two solar panels that extend out like wings. The box, which weighs about 6,600 lbs. (3,000 kilograms), measures about 9 by 6.8 by 6.5 feet (2.8 by 2.1 by 2 meters). The solar panels have a total span of about 105 feet (32 m). Rosetta is the first spacecraft to rely solely on solar cells to generate power.

Rosetta's payload includes 11 instruments that will provide information about how the comet develops its coma and tails, and how its chemicals interact with one another and with radiation and the solar wind. Other instruments will analyze the comet's composition and atmosphere.

Rosetta is expected to start mapping Comet 67P in August 2014.

Rosetta lander

In November 2014, after the orbiter is aligned correctly, it will launch a 220-lb. (100 kg) lander, named Philae. It will touch down and then fire a harpoon to anchor itself and prevent it from escaping the comet's weak gravity. Philae carries nine instruments, including a drill to take samples of subsurface material.

Solar escort

Rosetta and Philae will accompany Comet 67P to its perihelion in August 2015 and travel with the comet around the sun and back into deep space until the mission ends in December 2015.

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Tim Sharp, Reference Editor

Tim Sharp

Tim was a Technology Editor at nytimes.com and the Online Editor at the Des Moines Register, where he helped launch that newspaper's website. He was also a copy editor at several newspapers. Before joining TechMediaNetwork as Reference Editor, Tim was the Online Content Editor at the Hazelden Foundation. He has a journalism degree from the University of Kansas. Tim is also a self-proclaimed nerd and has won several trivia contests. To find out what his latest project is, you can follow Tim on .
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