Rosetta mission: Five questions about the comet landing

A EUROPEAN spacecraft has made history with a successful landing on a comet, but what answers are scientists actually seeking?

This image was taken with the lander's CIVA-P imaging system and captures one of Rosetta's 14 metre-long solar arrays. Picture: ESA

THE European Space Agency has achieved a historic first: landing a washing machine-sized spacecraft on a comet speeding through our solar system at 66,000kph.

The mission is an audacious attempt to answer the big questions about the universe — but what happens next? Here are five questions about the space mission.

How difficult was it to land on a comet?

Nothing like Wednesday’s landing had ever been attempted before.

NASA landed a probe on an asteroid in 2001, but comets are much more volatile destinations because they continually release dust and gas that can harm a spacecraft. Also, because this landing was taking place 500 million kilometres from the Earth, the Rosetta spacecraft and the Philae lander it carried were both designed to perform the landing autonomously. Once they received the go-ahead, there was nothing scientists at mission control in Darmstadt, Germany could do to adjust the lander’s course.

Philae’s separation from Rosetta also had to be extremely precise. An error of just two centimetres during separation could have put the lander 250 metres off target on the comet named 67P/Churyumov-Gerasimenko. But Paolo Ferri, head of mission operations for the space agency, said Philae’s landing was almost perfectly on target — save for one unplanned bounce.

INTERACTIVE: Rosetta’s comet rendezvous

This image was taken with the lander's CIVA-P imaging system and captures one of Rosetta's 14 metre-long solar arrays. Picture: ESA

Where there any problems with the landing?

Several.

First, the lander failed to wake up properly on Tuesday. Scientists fixed that with a trick familiar to anyone who has used a computer. They rebooted it.

After the separation from Rosetta it became clear that there was a problem with Philae’s downward thrusters. They were designed to press the lander onto the surface during the final touchdown, to help it get a grip using harpoons and screws. The thruster failure wouldn’t have been so dramatic if the harpoons had fired, but they didn’t. So Philae bounced, once, before coming to rest again on the comet.

Scientists are also trying to resolve intermittent communication problems with the lander, but those shouldn’t interfere too badly with the mission.

This image shows comet 67P/CG acquired by the ROLIS instrument on the Philae lander during descent from a distance of approximately 3km from the surface. Picture: ESA

What data are scientists seeking?

Scientists have likened the trillion or so comets in our solar system to time capsules that remain virtually unchanged since the earliest moments of the universe. One of the things they are most excited about is the possibility that the mission might help confirm that comets brought the building blocks of life — organic matter and water — to Earth. They already know that comets contain amino acids, a key component of cells. Finding the right kind of amino acids and water would be an important hint that life on Earth did come from space.

A scientist celebrates in the main control room at the European Space Agency after the first unmanned spacecraft Philae landed on the comet 67P/Churyumov-Gerasimenko, at the control centre in Darmstadt.

How will the lander collect data?

“The science starts the minute we get down to the ground,” said Mark McCaughrean, a senior scientific adviser on the mission. Philae has ten instruments on board — including devices to measure light, electrical magnetism and heat — and flying up above the comet the Rosetta spacecraft has another 11 instruments. The Philae lander will provide plenty of images of a world no human has ever seen close up and will drill below the surface to extract a sample of the comet that will be analysed on-board.

The lander’s batteries are expected to last just 64 hours but that should be enough for scientists to gather a huge wealth of data. In addition, the lander has a solar panel that should provide an hour’s worth of battery life per day for up to five months.

An artist’s impression of the European probe Philae separating from its mother ship Rosetta. Picture: ESA/ATG MEDIALAB

What challenges lie ahead?

The comet is on a six-and-a-half-elliptical orbit around the sun. At the moment it is getting closer to our star. This makes for great science, since Philae and Rosetta will be able to observe the comet becoming more active.

As 67P approaches the sun, the amount of matter it sheds will greatly increase, posing a potential risk to the lander and even to the Rosetta spacecraft flying in tandem with the comet. As the comet reaches perihelion, the closest point to the sun, the rising temperatures could also damage Philae. But the lander should remain stuck to the comet forever, even after its systems have shut down. Rosetta will continue to fly alongside the comet until the end of its useful lifetime in about two years. Scientists have suggested that a fitting end would be for it, too, to land on the comet and reunite with the lander once more.