- NEW: Controllers say the probe's anchoring harpoons failed, craft may have bounced
- NASA scientist calls the comet the most "bizarre, wonderful thing I have ever seen"
- The probe tweets: "Touchdown! My new address: 67P!"
- Philae has 9 experiments including drill to sample the surface, onboard oven
London (CNN) -- Imagination became reality Wednesday when a mechanical space traveler called the Philae probe plunked down on its target, a comet with a much less romantic name -- 67P -- some 310 million miles from Earth.
European Space Agency scientists and executives high-fived and hugged each other when the landing was confirmed. Spacecraft have crashed into comets before, but this is the first soft, or controlled landing, in history.
Later, ESA said there was a glitch.
After leaving the mother ship Rosetta and descending, Philae may have bounced, rather than gently settled, on the surface of the comet, ESA scientists said at a news conference. Comet 67P has a very weak gravity, so anchoring harpoons were designed to shoot into the comet to fix the spacecraft to the surface. They failed to fire and Philae is not firmly secure, ESA said.
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"So maybe we didn't land once -- we landed twice," Philae lander manager Stephan Ulamec said. "Did we land in a soft sandbox or is there something else happening? We don't fully understand what happened."
Ulamec said scientists hope to know more on Thursday. In the meantime ESA isn't letting that problem ruin its big day.
'A place in the history books'
"Our ambitious Rosetta mission has secured a place in the history books: not only is it the first to rendezvous with and orbit a comet, but it is now also the first to deliver a lander to a comet's surface," Jean-Jacques Dordain, ESA's director general, said in an article posted on the ESA website.
Many people, and not just the ones who work for ESA, are excited about what kind of information Philae will deliver.
"Rosetta is trying to answer the very big questions about the history of our solar system," Matt Taylor, ESA Rosetta project scientist, said in the article on the ESA website. "What were the conditions like at its infancy and how did it evolve? What role did comets play in this evolution? How do comets work?"
And science fiction writer Alastair Reynolds said: "This is science fiction made real in terms of the achievement of the mission itself, but Rosetta is also taking us a step closer to answering science fiction's grandest question of all: Are we alone?"
Rosetta took off from Earth 10 years ago carrying Philae and traveled 6.4 billion miles before arriving in early August at the comet.
The Philae lander separated from the orbiting Rosetta around 3:30 a.m. ET Wednesday and landed on the comet seven hours later.
ESA lander system engineer Laurence O'Rourke told CNN that the orbiter Rosetta had to be in the right position to allow the lander craft, which had no thrusters, to "free fall" on the correct trajectory so it landed on the comet.
The lander weighs about 220 pounds and is the size of a domestic washing machine. The target comet is only four kilometers, or 2.5 miles, in diameter.
Named after Rosetta Stone
Shortly after landing was confirmed, the probe tweeted: "Touchdown! My new address: 67P!" Later, it tweeted again: "I'm on the surface but my harpoons did not fire."
What can we learn from comet landing?
The mission has historic allusions.
The spaceship is named after the Rosetta Stone, an inscribed piece of volcanic rock found in Egypt in 1799 that allowed scientists to decipher hieroglyphics and thus understand the ancient Egyptian culture, ESA said. The lander is named after an island in the Nile River where an obelisk was found that helped decipher the Rosetta Stone, ESA said.
Led by ESA with a consortium of partners including NASA, scientists on the Rosetta comet-chasing mission hope to learn more about the composition of comets and how they interact with the solar wind: high energy particles blasted into space by the sun.
The comet is currently 500 million kilometers (310 million miles) from Earth and pictures from the Rosetta mission to track it on its orbit around the sun have amazed scientists.
An array of experiments
We can land on a comet, but we can't...
Philae is equipped with an array of experiments to photograph and test the surface of Comet 67P as well as to find out what happens when the roasting effect of the sun drives off gas and dust.
Built by a European consortium, led by the German Aerospace Research Institute, the landing probe has 10 instruments.
According to details on ESA's Rosetta website, sensors on the lander will measure the density and thermal properties of the surface, gas analyzers will help detect and identify any complex organic chemicals that might be present, while other tests will measure the magnetic field and interaction between the comet and solar wind.
What is a comet and what will Rosetta discover
Philae also carries a drill that can drive 20 centimeters (8 inches) into the comet and deliver material to its onboard ovens for testing.
Scientists are already pleased with progress of the mission, and they're wowed by what's already been accomplished.
ESA project scientist Matt Taylor said: "The orbiter will remain alongside the comet for over a year, watching it grow in activity as it approaches the sun, getting to within 180 million kilometers (112 million miles) in summer next year, when the comet will be expelling hundreds of kilograms of material every second."
Daniel Brown, an astronomy expert at Nottingham Trent University in the United Kingdom, said: "Apart from the amazing scientific results, the sheer challenge and ambition of such a mission is outstanding and illustrates how our space exploration of the solar system has become more advanced and successful. It gives us much to hope for in future missions."
"It's got an awesome profile -- the adventure of the decade-long journey necessary to capture its prey, flying past the Earth, Mars and two asteroids on the way," NASA's chief scientist, Ellen Stofan, told CNN: "No one has ever gotten data like Rosetta has gotten. No one has ever been able to land on a comet the way Philae just did."
How comet mission helps search for alien life
CNN's Dave Gilbert contributed to this report.
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