Comet-Chaser Spacecraft to Be Visible Tonight

Stefan Lovgren
National Geographic News

Updated March 4, 2005

Space fans, get your telescopes ready.

Tonight the Rosetta spacecraft will make a flyby of Earth on its way to Comet 67P/Churyumov-Gerasimenko. Space watchers should be able to see the "comet chaser" with telescopes or binoculars if the sky is clear.

Rosetta, launched by the European Space Agency in February 2004, will reach the comet in 2014 and deliver a lander, Philae, to the surface. It is to be the first mission ever to orbit and land on a comet.

With the mission, scientists hope to learn not only how comets work but also about the evolution of our solar system.

Comets are composed of ice, gas, and dust—primitive debris from the formation of our solar system about 4.5 billion years ago. Many scientists also believe comets are the source of most of the water and organic material that was long ago delivered to some planets.

"By looking back into the infancy of the solar system … at the material out of which planets formed … [we can] study some of the pieces of the puzzle that we try to put together to understand how life formed on Earth," said Gerhard Schwehm, project scientist for the Rosetta mission.

Slingshot Effect

Rosetta is approaching Earth from an area in space between the constellations Leo and Sextans. The spacecraft will make its closest approach to Earth tonight (March 4) at about 11:10 p.m. central European time (5:10 p.m. ET), when it will come within 1,200 miles (1,900 kilometers) of Earth, passing over Mexico.

After sunset in Europe, the spacecraft will appear to travel from southeast to southwest, moving from the constellation Sextans toward the setting sun, crossing the sky, according to the ESA's Rosetta Web site.

It will be visible almost all night from the Northern Hemisphere and most of the Southern Hemisphere.

The flyby maneuver will swing the spacecraft around our planet and out toward Mars. It is the first of four planet flybys (three times with Earth, once with Mars) that Rosetta will carry out in its long journey to the comet.

This type of flyby is used to accelerate spacecraft, using the gravity of a planet, in this case Earth, to gain orbital velocity.

"It's basically a trick to save fuel and to reach targets that are not accessible even with the most powerful launchers currently available," Schwehm said.

After its gravity-assists, Rosetta will fly through our system's asteroid belt on its way to the comet. After releasing the small lander onto the comet's icy nucleus, Rosetta will spend the next two years orbiting the comet as it heads toward the sun.

"Rosetta is truly a key mission to understand primitive objects—composition, physical properties—in our solar system, which is important to understand the evolution of our planets out of [interstellar gas and dust clouds]," Schwehm said.

Delivering Life?

Comets are chunks of rock and ice surrounded by glowing clouds of gas and dust that come from the outer edge of our solar system. Asteroids are fragments of metal or rocks that orbit the sun, largely between Jupiter and Mars.

There could be a trillion or more comets in the deep cold beyond the fringes of our solar system. Because they are so far away, comets are believed to preserve the original gas and dust left over from the formation of our system 4.5 billion years ago.

Scientists, therefore, believe that comets could answer basic questions about how the solar system was created.

Many scientists also believe that comets could be the source of organic material that was delivered to Earth during its formation. The icy nature of the comets almost certainly contributed to the water that now exists in Earth's oceans.

By studying Comet 67P/Churyumov-Gerasimenko, Rosetta will produce a full inventory of organic chemicals in that comet. In particular, it will search for molecules known as left-handed amino acids—building blocks with which all proteins on Earth are built.

"By studying the isotopic ratios of the elements, we can also get some insight into where, or through which processes, these elements were formed," Schwehm said.

Rosetta Up Close

Although dimmer than a typical faint star, and thus not readily apparent to the eye, Rosetta should be visible, weather permitting, during its flyby to people using small telescopes or even binoculars.

Amateur astronomers using video or photo-imaging with telescopes may even be able to see Rosetta's solar panels, which extend over 35 yards (32 meters).

The ESA is hosting a "Rosetta Up Close" photography contest, in which sky-watchers everywhere are invited to submit their photos of Rosetta passing Earth. (Please see related link on the right side of this page.)

The photo contest is the latest in a series of interactive science competitions organized around the mission.

"We have come to realize that the space-interested public is willing not only to passively read articles about our missions, but also to actively think about and debate such cutting edge space missions," said Bernhard von Weyhe, a spokesperson for ESA in Darmstadt, Germany.

"This is reflected not only in numerous e-mails we receive around all mission milestones but also in independent Web-discussion forums on space," he said.

"Winning an exclusive ESA prize for it is another level of participation in the fascinating adventure of discovering our universe and using space technology on Earth."

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