Hundreds of millions of miles from Earth, a European spacecraft made history yesterday by successfully landing on the icy, dusty surface of a speeding comet - an audacious first designed to answer big questions about the universe.
The landing on comet 67P/Churyumov-Gerasimenko required immense precision, as even the slightest error could have resulted in cosmic calamity.
Indications were that the spacecraft touched down almost perfectly, save for an unplanned bounce, said Stephan Ulamec, head of the lander operation.
But thrusters that were meant to push the lander, called Philae, on to the surface, and harpoons that would have anchored it to the comet failed to deploy properly. Initial data from the spacecraft indicated that it lifted off again, turned and then came to rest.
"Today we didn't just land once, we maybe even landed twice," said Ulamac.
The landing team at mission control in Darmstadt first had to sweat through a tense seven-hour countdown that began when Philae dropped from the agency's Rosetta space probe as both it and the comet hurtled through space at 66,000kph.
During the lander's descent, scientists were powerless to do anything but watch, because its vast distance from Earth - 500 million kilometres - made it impossible to send instructions in real time.
Finally, at 16.03 GMT, the agency received a signal that the washing machine-sized lander had touched down on the comet.
While further checks were needed to ascertain the state of the 100km lander, the fact that it was resting on the surface of the comet was already a huge success - the highlight of Rosetta's decade-long mission to study comets and learn more about their origins.
Scientists have likened the trillion or so comets in our solar system to time capsules that are virtually unchanged since the earliest moments of the universe.
"By studying one in enormous detail, we can hope to unlock the puzzle of all of the others," said Mark McCaughrean, a senior scientific adviser to the mission.
The mission will also give researchers the opportunity to test the theory that comets brought organic matter and water to Earth billions of years ago.
Rosetta and Philae will accompany the comet as it races past the sun and becomes increasingly active in the rising temperatures.
Between them, they will use 21 different instruments to collect data that scientists hope will help explain the origins and evolution of celestial bodies - and maybe even life on Earth.
Mission manager Paolo Ferri said there was no time to celebrate, because the lander had only enough battery power to operate for up to 64 hours. After that it will have to recharge, using solar panels to eke out an extra hour of operations each day.
Yesterday's landing capped a 6.4 billion kilometre journey that began a decade ago.
Rosetta, which was launched in 2004, had to slingshot three times around Earth and once around Mars before it could work up enough speed to chase down the comet, which it reached in August.