With the European Space Agency's robotic lander now sitting on a comet hurtling in orbit around the sun, the 10-year trip is over and the real science of the mission has begun.
That means scientists may get valuable clues about the origins of the sun and planets, as well as Earth's oceans and even ourselves.
"We're looking at the big picture here," said Andrew Westphal, a physicist and associate director of the Space Sciences Laboratory at U.C. Berkeley. "The reason why it's so important to study comets is that they're really the building blocks of the solar system. This is a chance to study primitive materials. It could tell us about our own origins.
"It's not just about the origins of the sun and planets but about the origins of us."
On Wednesday, the European Space Agency's Rosetta spacecraft launched a robotic probe, dubbed Philae, onto comet 67P/Churyumov-Gerasimenko. While Rosetta continues in orbit around the comet, Philae will have about two and a half days to study the comet's composition and how it reacts to the approaching heat of the sun.
After that, the probe's battery is expected to run out.
As a result, the scientists behind the mission -- the first to ever land a probe on a comet -- have a short amount of time to learn as much as they can.
The European Space Agency said during a news conference on Thursday that the lander had already begun using its instruments, taking six images for a panoramic view of the comet and collecting magnetic field measurements.
"It has proved that it's working, communicating and making scientific measurements," said Jean-Pierre Bibring, the lander's lead scientist. "A lot of science is getting covered now."
Tonight, the science team will upload the latest instructions to tell the lander what scientific experiments to conduct later at night and Friday, according to Stephan Ulamec, the Philae lander manager. The probe has 10 scientific instruments.
One concern with having the lander deploy its instruments is that it is not securely attached to the comet and scientists are concerned that too much movement or thrust could move Philae or even bounce it off the surface back into space.
Philae had a few problems -- actually a few bounces -- when it touched down on Wednesday morning.
Ulamec reported that when the probe first hit the comet, traveling at about 3 feet per second, the lander's harpoons, which should have grabbed onto the surface, did not deploy. Without its harpoons fastened, the lander bounced about half a mile up into space and traveled about half a mile from its original landing spot before touching down again. After that, it had a second bounce that lasted about 7 minutes.
As of Wednesday afternoon ET, scientists with the space agency were still trying to figure out exactly where Philae was positioned.
"We have a better understanding now of how we got there, though we still don't really know where it is," said Ulamec, noting that scientists must be careful firing up any of Philae's instruments. "We don't know really how we landed and we are not anchored. We just have the weight of the lander, but we are looking to deploy the instruments of the lander."
Now, scientists around the world are waiting to see exactly what those instruments are going to find.
"As a space scientist, this is something you just live for," said Amy Mainzer, an astronomer with NASA's Jet Propulsion Laboratory. "The thing about comets is that they're really time capsules. There isn't really that much left on Earth that we can look at that was in the same shape it was in 4.5 billion years ago. Comets really are our Rosetta Stone for understanding what the solar system was like when it was formed."
She added that studying this comet could help scientists figure out how the planets formed and evolved. They also might get clues as to why comets and asteroids were not swept up to form planets.
"There's a lot we still don't understand," said Mainzer. "This could help us paint a picture.... One of the basic things human beings want to know is where did we come from and how did we get here? Studying these ancient relics starts to tell us how you build a solar system, how you build a planet Earth."
Research into this one comet also could tell scientists a lot about how Earth came to have so much water.
Scientists believe that about 4 billion years ago the Earth, still a relatively young planet, was hit by a huge volley of comets and asteroids. It's believed that during this time, referred to as the Late Heavy Bombardment, comets brought water with them.
By investigating the makeup -- both of minerals and water -- in this particular comet, scientists can see whether the chemical signatures match up to what is here on Earth.
"This is one of the big things people are trying to figure out," said Mainzer. "They're a source of life. How did we get oceans in the first place? Well, they might have come from comets that were packed with water ices?"
Berkeley's Westphal called the mission historic and compared it to the moon landing in 1969.
"It's important to understand the origins of us," he said. "Landing on the moon was important and Apollo moon samples have been telling us a lot about the origins of the moon. But it's pretty dry and not nearly as complicated as the stuff we get from comets. It's of equal scientific importance at least."
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