The spot where a spacecraft will attempt the first landing on a comet has been unveiled by officials at the European Space Agency (ESA).
The Rosetta probe plans to drop its 100kg robotic lander, Philae, onto the surface of comet 67P/Churyumov-Gerasimenko on Nov. 11.
At a press conference in Paris on Monday, mission scientists named primary and backup landing sites selected from five provisional spots on the comet, whose double-lobed shape resembles a giant rubber duck. The primary landing site is on the smaller “head” of the comet, while the backup is on the “body.”
Photo: AFP
The awkward shape of the 4km comet makes it incredibly difficult to land on and success is far from guaranteed. The ground at the primary landing site has slopes and ridges, and boulders are scattered across the surface. There is more rough terrain at the backup landing spot.
None of the sites met all of the criteria that the ESA had set for touchdown, but the chosen spot won the unanimous vote of the mission scientists. Uncertainties in the landing procedure mean that Philae’s final resting place can only be predicted within a few hundred meters.
“Originally, we were all thinking that we’d get to some rounded, potato-shaped comet,” said Fred Jansen, Rosetta mission manager.
Based on that simpler shape, researchers calculated the chances of a successful landing at 70 percent to 75 percent. The more complex rubber-duck shape makes the landing much tougher.
Rosetta blasted off from French Guiana more than 10 years ago. Last month, it caught up with the comet, which is hurtling toward the sun at 55,000kph. Rosetta is flying around the comet at a distance of 30km.
Over the next two months, mission scientists will pore over images from Rosetta’s scanners to learn more about the primary landing site. The patch of comet, known simply as Site J in ESA discussions, will be renamed in a public competition.
Before the attempted landing Rosetta will move closer. From an altitude of about 20km the Philae lander will be pushed away from its mothership, starting a descent that will take about seven hours at walking speed.
With a force of gravity many times less than that on Earth, Philae will weigh almost nothing on the surface. To stop itself from falling off, the lander will fire harpoons and drive ice screws into the ground as it touches down.
ESA officials arrived at their decision after assessing a square kilometer of land at five different sites. At Site J most of the slopes are less than 30 degrees, which reduces the odds of the lander tipping over when it lands. It seems to have fewer boulders than other spots and receives enough daylight for Philae to recharge its batteries.
“It’s not as perfectly flat an area as we’d have hoped for a landing site,” said Stephan Ulamec, Philae lander manager.
If observations in the coming weeks reveal major new hazards at the primary landing site, the team will switch to the backup option. In that case, an attempt to touch down could be delayed by up to 28 days.
“We cannot predict the activity of the comet between now and landing. A sudden increase in activity could affect the position of Rosetta in its orbit at the moment of deployment and in turn the exact location where Philae will land, and that’s what makes this a risky operation,” flight director Andrea Accomazzo said.
The Rosetta mission has already captured breathtaking images of the comet, but researchers hope that sensors on board Rosetta and the lander will help them build an unprecedented picture of the body.
“No one has ever attempted to land on a comet before, so it is a real challenge,” Jansen said. “The risks are worth taking to have the chance of making the first ever soft landing on a comet.”
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