A comet nucleus has very low gravity, so the lander relied on harpoons, hold-down thrusters and ice screws to secure itself to the surface. When these mechanisms all failed, the lander bounced back into space for a 1 hour and 50 minute ballistic flight. Due to Comet 67P's low gravity, Philae weighed about the same as a paper clip. On its first rebound, Philae ascended with a speed of 15 inches (38 centimeters) per second. Escape velocity from the comet is 19.7 inches (50 cm) per second.
A grazing collision with rim of crater Hatmehit caused Philae to begin tumbling. The lander's second impact with the comet was followed by about 7 more minutes of drifting.
The closest view taken by Philae, just before its first impact, reveals a granular soil called regolith, littered with blocks up to 16.4 feet (5 meters) in size. Scientists estimate the regolith to be between zero and 6.4 feet (2 m) deep.
Philae's sampler collected material from 6.2 miles (10 km) above the surface and also at its final resting place.
Analysis detected 16 organic compounds including four (methyl isocyanate, acetone, propionaldehyde and acetamide) never before known to exist on comets.
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