An international team working on an unprecedented mission to orbit and land on a comet will attempt a touchdown on the smaller of the comet's two lobes, a site tentatively named "J", Rosetta scientists announced on Monday.
Landing, targeted for Nov. 11, is by no means assured. Engineers, expecting the comet would be a potato-shaped, ice-covered body, put the odds of success at 70 percent.
But after a decade of travel, the Rosetta spacecraft in August reached the twin-lobed Comet 67P/Churyumov-Gerasimenko, which turned out to be part icy, part dusty, part dry and topographically diverse, complicating landing.
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Mission managers declined to offer new predictions for a successful touchdown, but they say landing on "J" is the best shot at success.
"This is not an easy task," Stephan Ulamec, manager for Rosetta's Philae lander, told reporters during a webcast press conference.
"There are flat areas, but there is also rough terrain. There are some cliffs, there are some boulders ... It's not a perfectly flat area as we probably would have hoped for a safe landing site," he said.
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Landing on the comet would set the stage for a scientific bonanza on top of an already successful and unprecedented mission to study a comet at close range. The Rosetta spacecraft is currently orbiting about 18 miles, or 29 kilometers, above the comet and will continue to do so for at least the next 15 months.
Rosetta's Philae lander is equipped with a drill to retrieve pristine samples from beneath the comet's surface. Scientists want to learn more about the basic chemistry and mineralogy of comets, which are believed to be leftover frozen remains from the formation of the solar system more than 4 billion years ago.
"We're in the middle of a revolution of our thinking of how planets evolved, why do we have such a huge diversity, when you compare Earth to Mars to Venus to Jupiter ... although we know that essentially all the planets originate from a single solar nebula," said Philae lead scientist Jean-Pierre Bibring.
"It's even worse when you compare the solar system to the solar systems we see elsewhere," he added.
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Scientists are specifically interested in learning if Earth and the solar system are unique in some way, or if the same processes could have been replicated elsewhere. The studies also have a direct tie to the prospects of life beyond Earth since comets are suspected of delivering not only Earth's water but also organic materials that may have eventually led to life.
"The question of whether or not we are alone in the universe is directly connected to what we are looking for here," Bibring said.
The European Space Agency plans a public outreach to rename the landing site. As a backup, scientists also will continue to look at a backup landing site, designated "C" on the comet's big lobe.