Rosetta Spacecraft: To Catch a Comet
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 and land a probe on it. Launched in 2004, the spacecraft arrived at its target, Comet 67P/Churyumov-Gerasimenko, on Aug. 6, 2014. The lander, named Philae, made contact on Nov. 12, 2014.

Scientists at the European Space Agency said Philae unexpectedly bounced twice before landing on the comet when the probe's anchor-like harpoon system failed to fire. Philae ended up in shadow near a cliff face on the head of the 2.5-mile-wide (4 kilometers) comet, which scientists say is shaped like giant rubber duck. The probe fell silent on Nov. 14, possibly forever, as its solar batteries ran out of power.

For complete coverage on the mission, read more here: Rosetta Mission's Historic Comet Landing: Full Coverage.

Rosetta is the first spacecraft to accompany a comet as it enters the inner solar system. After meeting up with the comet, it began 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.  [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, Philae, is 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.

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.

Philae, the 220-lb. (100 kg) lander, about the size of a washing machine, touched down at 1600 GMT (11 a.m. EST, Nov. 11). Philae carries 10 instruments, including a drill to take samples of subsurface material.

The planned landing site, called Agilkia after an island in the Nile River in Egypt, is located on the "head" of the comet, the smaller of the two lobes that make up Comet 67P/C-G. Mission controllers at the European Space Agency also chose a secondary landing site for Philae. Site J is a sunny area, but it is also rocky, potentially making it a dangerous place to land.

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 had 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. Rosetta will explore Comet 67-P/Churyumov-Gerasimenko when it arrives at the object in August 2014.
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

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.

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 (600 million km). 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 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.