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European Spacecraft Pulls Alongside Comet European Spacecraft Pulls Alongside Comet
(about 3 hours later)
After 10 years and a journey of four billion miles, the European Space Agency’s Rosetta spacecraft arrived at its destination on Wednesday for the first extended, close examination of a comet.After 10 years and a journey of four billion miles, the European Space Agency’s Rosetta spacecraft arrived at its destination on Wednesday for the first extended, close examination of a comet.
A six-minute thruster firing beginning at 5 a.m. Eastern time, the last in a series of 10 over the past few months, slowed Rosetta to the pace of a person walking, about two miles per hour relative to the speed of its target, Comet 67P/Churyumov-Gerasimenk. A six-minute thruster firing at 5 a.m. Eastern time, the last in a series of 10 over the past few months, slowed Rosetta to the pace of a person walking, about two miles per hour relative to the speed of its target, Comet 67P/Churyumov-Gerasimenko.
Over the coming months, Rosetta and its comet, called C-G for short, will plunge together toward the sun. In November, a small 220-pound lander is to leave the spacecraft, set down on the comet and harpoon itself to the surface. “It is like driving a car or a bus on a motorway for 10 years,” said Andrea Accomazzo, the flight director, at a post-rendezvous news conference. “Now we’ve entered downtown. We’re downtown and we have to start orienting ourselves. We don’t know the town yet, so we have to discover it first.”
That will be the first time a spacecraft has gently landed on a comet. “It’s really going to get down and scratch the surface to get the most pristine material that we can from the surface of the comet,” said Matthew Taylor, the mission’s project scientist. Over the coming months, Rosetta and its comet, called C-G for short, will plunge together toward the sun.
At this point, the comet and its shadowing spacecraft are more than 330 million miles from the sun (more than three times as far out as Earth), traveling at 35,000 miles per hour. With the firing of the final thruster, Rosetta was a mere 60 miles from the comet’s surface. In November, a small 220-pound lander is to leave the spacecraft, set down on the comet and harpoon itself to the surface, the first time a spacecraft has gently landed on a comet.
“The key thing is we’re rendezvousing and escorting right in alongside the comet for an extended period, for over a year,” Dr. Taylor said. At this point, the comet and its shadowing spacecraft are more than 330 million miles from the sun (more than three times as far out as Earth), traveling at 35,000 miles per hour. With the final firing of the thruster, Rosetta was a mere 60 miles from the comet’s surface.
Comets, made of ice, dust and rock, are frozen leftovers from the formation of the solar system. Rosetta is named after the Rosetta Stone, the engraved block that was crucial in deciphering Egyptian hieroglyphics, and scientists hope that the spacecraft’s observations will offer important clues to how the solar system came together 4.5 billion years ago. (Rosetta’s lander, Philae, is named after the island in the River Nile where the Rosetta Stone was found.) “This morning, we hit a milestone, an important milestone of this mission,” said Laurence O’Rourke, a member of its science team.
Photographs have revealed a surprisingly irregular shape for the 2.5-mile-wide comet, possibly an amalgamation of two icy bodies or a result of uneven weathering during previous trips to the inner solar system. From a distance, the blurry blob initially looked somewhat like a rubber duck. As the details came into focus, it began to bear a closer resemblance to a knob of ginger flying through space. “But this mission isn’t just about arriving at a comet,” he went on. “It’s about studying the comet. It’s about placing a lander on a comet, but again the mission does not end there. The science continues. We’re trying to follow this comet all around its orbit.”
In June, the spacecraft measured the flow of water vapor streaming off the comet at a rate of about two cups a second, which would fill an Olympic-size swimming pool in about 100 days. As the comet accelerates toward the sun, its surface will warm, and the trickle will grow to a torrent of hundreds of pounds a second, forming the long tail that is characteristic of comets. Rosetta is still not close enough to be captured by the comet’s gravity, but instead will be flying a triangular path in front of the comet as it maps the surface. It will eventually move within 6.2 miles of the surface and enter orbit around the comet.
Measurements in July put the surface temperature at minus 94 degrees Fahrenheit, or minus 70 Celsius. That was warm enough to indicate that the surface was not exclusively ice and that some parts were dusty and darker, absorbing more heat from the sun. Comets, made of ice, dust and rock, are frozen leftovers from the formation of the solar system. Rosetta is named after the Rosetta Stone, the engraved block that was crucial in deciphering Egyptian hieroglyphics, and scientists hope that the spacecraft’s observations will offer important clues to how the solar system came together 4.5 billion years ago. (Rosetta’s lander, Philae, is named after the island in the Nile River where the Rosetta Stone was found.)
Photographs have revealed a surprisingly irregular shape for the two-and-a-half-mile-wide comet, possibly an amalgamation of two icy bodies or a result of uneven weathering during previous trips to the inner solar system. From a distance, the blurry blob looked something like a rubber duck; as the details came into focus, it began to bear a closer resemblance to a knob of ginger flying through space.
At the news conference, Holger Sierks, the principal investigator for Rosetta’s high-resolution camera, revealed the latest images, pointing to cliffs, deep shadows and also flat areas with boulders sitting on the surface. “We’ll learn in the coming months what this is telling us,” he said.
The spacecraft had earlier measured the flow of water vapor streaming off the comet at a rate of about two cups a second, which would fill an Olympic-size swimming pool in about 100 days. As the comet accelerates toward the sun, its surface will warm, and the trickle will grow to a torrent of hundreds of pounds a second, forming the long tail that is characteristic of comets.
Measurements in July put the average surface temperature at minus 94 degrees Fahrenheit, or minus 70 Celsius. That was warm enough to indicate that the surface was not exclusively ice and that some parts were dusty and darker, absorbing more heat from the sun.
An unsolved mystery of Earth is where the water in the oceans came from; some suggest it came from comets. The water in comets from the distant Oort Cloud, far beyond Pluto, does not match the water on Earth, but the water in nearer comets may.
C-G is one of the nearer comets: Its orbit extends not far beyond Jupiter. Scientists should now be able to get a better idea of its composition by measuring temperatures at its surface and a few inches below, and in the gases streaming off the comet, along with the weight of water molecules streaming off it.
Much of the work in the next three months is to find a safe place for Philae to land. Once released from Rosetta, the lander will be pulled down by the comet’s gravity and it will strike its surface at a couple of miles per hour, like someone walking into a wall. “It’s hurting but it doesn’t kill you,” said Stephan Ulamec, head of the consortium that built the lander.
The harpoons and a thruster will help keep it from bouncing off, although Dr. Ulamec said recent photographs suggested a dusty surface more like cigarette ash or newly fallen snow than hard ice. “But actually we do not know it yet,” he said. “We will only find out when we land there.”
Designed to operate through 2015, Rosetta and Philae will make observations as the comet makes its nearest approach to the sun a little more than a year from now, at 115 million miles, still outside the orbit of Earth. The comet will remain too dim to be seen by the naked eye.Designed to operate through 2015, Rosetta and Philae will make observations as the comet makes its nearest approach to the sun a little more than a year from now, at 115 million miles, still outside the orbit of Earth. The comet will remain too dim to be seen by the naked eye.
Other missions to comets have made brief flybys, beginning with the International Sun-Earth Explorer-3 in September 1985. NASA’s Deep Impact slammed into a comet in 2005, and another mission, Stardust, has collected particles of dust and returned them to Earth for study.Other missions to comets have made brief flybys, beginning with the International Sun-Earth Explorer-3 in September 1985. NASA’s Deep Impact slammed into a comet in 2005, and another mission, Stardust, has collected particles of dust and returned them to Earth for study.
(ISEE-3 is back in the news, because the spacecraft, still largely working, will zip past Earth again on Sunday.)(ISEE-3 is back in the news, because the spacecraft, still largely working, will zip past Earth again on Sunday.)
The $1.7 billion Rosetta mission will provide a much longer, much closer look at one comet. Instead of taking a brief snapshot, Rosetta will observe as the comet goes from a quiescent ball of ice and rock to an active comet spewing out dust and gas and then make before-and-after comparisons. “We’ll observe how this occurs, how this activity is onset, how it fluctuates, really how a comet works over a long time period,” Dr. Taylor said. “That’s really the difference between this and anything that’s been done before.” The $1.7 billion Rosetta mission will provide a much longer, much closer look at one comet. Instead of taking a brief snapshot, the spacecraft will observe C-G going from a quiescent ball of ice and rock to an active comet spewing out dust and gas and then make before-and-after comparisons.
Launched in March 2004, it followed a circuitous route through the solar system, using flybys of the Earth and Mars to fling itself into the same orbital path as Comet C-G. In January, it successfully emerged from a hibernation of two and a half years and began its final approach. Launched in March 2004, Rosetta followed a circuitous route through the solar system, using flybys of the Earth and Mars to fling itself into the same orbital path as Comet C-G. In January, it emerged from a hibernation of two and a half years and began its final approach.