Europe · ESAfirstrobotic
November 12, 2014
Philae lands on comet 67P/Churyumov–Gerasimenko
On the morning of 12 November 2014, in the control room of ESA's operations centre in Darmstadt, Germany, flight controllers sent the command they had waited a decade to give. Five hundred and ten million kilometres away, the washing-machine-sized Philae lander detached from its Rosetta mothership and began a seven-hour free fall toward comet 67P/Churyumov-Gerasimenko. There was no engine to fire and no joystick to grab; radio signals took 28 minutes to cross the gulf. Whatever happened next, the people who had built Philae, ten years and 6.4 billion kilometres after leaving Earth, could only watch.
Confirmation of touchdown reached Earth at 16:03 GMT, and lander manager Stephan Ulamec announced that Philae's anchoring harpoons had fired and rewound. Telemetry soon told a more dangerous story: the harpoons had never fired at all, and a hold-down thruster had failed overnight. In gravity roughly one hundred-thousandth of Earth's, the 100-kilogram lander bounced. The first rebound lasted nearly two hours and arced about a kilometre above the surface. Philae touched the comet three times, at 15:34, 17:25 and 17:32 GMT, before lodging against a cliff at a shadowed spot later named Abydos.
Tilted, anchorless and starved of sunlight, Philae raced its dying batteries. For roughly 57 hours the lander worked through its entire first science sequence, hammering, drilling, imaging its alien surroundings and detecting organic molecules at the surface. On 15 November, with the primary battery exhausted and its solar panels in shadow, Philae fell silent. Engineers had squeezed nearly every planned measurement out of a landing that had gone wrong three times over.
The story had two codas. On 13 June 2015, as the comet neared the Sun and light finally reached the lander's panels, Philae unexpectedly called home after seven months of silence. Then, on 2 September 2016, weeks before the mission's end, Rosetta's high-resolution camera spotted the lost lander wedged in a dark crack with one leg thrust toward the sky. When Rosetta itself was set down on the comet on 30 September 2016, the two travellers ended the mission together.
“We are extremely relieved to be safely on the surface of the comet, especially given the extra challenges that we faced with the health of the lander.”
Mission Data
Launch (aboard Rosetta)
2 Mar 2004
Landing
12 Nov 2014
Lander mass
~100 kg
Descent duration
7 hours
Distance from Earth
510 million km
Surface science
~57 hours on primary battery
Key Facts
Philae's harpoons never fired and its hold-down thruster had failed; it survived two uncontrolled bounces, the first lasting nearly two hours in gravity so weak the 100 kg lander pressed down with about the force of a gram.
The triumphant first announcement, "Philae is talking to us," celebrated harpoons that telemetry later showed had never deployed at all.
Despite landing in shadow on its side, Philae completed nearly its entire first science sequence and detected organic molecules at the comet's surface, several never previously identified at a comet.
Philae was lost for 22 months; Rosetta's camera finally found it on 2 September 2016, wedged in a crevice at Abydos with one leg in the air, just weeks before the mission ended.
Confirmation of the landing needed 28 minutes to reach Earth at the speed of light, so by the time controllers celebrated the first touchdown, Philae was already bouncing back into space.
Why It Mattered
Philae proved that a soft landing on a comet was possible, and its near-disaster showed just how unforgiving small-body gravity can be, lessons absorbed by every asteroid and comet lander designed since. Its measurements of organic molecules and an unexpectedly hard, dusty crust reshaped comet science, while the Rosetta mission's broader findings on the comet's water chemistry fed directly into debates about the origin of Earth's oceans. Just as significantly, the little lander's drama, hibernation and rediscovery became a global cultural moment that re-energized European planetary exploration and demonstrated that robotic missions could command Apollo-scale public attention.
ESA/Rosetta/NAVCAM, CC BY-SA 3.0 IGO
Official source
