Nov. 20--Listen to this! When the Rosetta spacecraft's Philae lander landed on the surface of a comet last week, it actually recorded the sound of its feet meeting the comet for the first time -- and now you can hear it too.
The two-second impact recording may sound like a mere moment in the long drama of the European Space Agency mission's Nov. 12 landing on comet 67P/Churyumov-Gerasimenko. But there's loads of information that scientists say they have pulled from that simple crunchy thud.
The three-legged lander's ears are in its feet: The sound was recorded by the Cometary Acoustic Surface Sounding Experiment (CASSE), which uses sensors at the ends of Philae's legs to determine the mechanical properties of the surface and its layers below. CASSE is part of the Surface Electrical, Seismic and Acoustic Monitoring Experiment (SESAME), which includes two other instruments.
"The Philae lander came into contact with a soft layer several centimeters thick. Then, just milliseconds later, the feet encountered a hard, perhaps icy layer on 67P/Churyumov-Gerasimenko," German Aerospace Center researcher Klaus Seidensticker, lead scientist for the SESAME instrument suite, said in a statement.
Of course, while the audio recording documents Philae's first touchdown -- an historic first -- this touchdown wasn't the last: The lander actually "bounced" because the harpoons meant to anchor it in place didn't deploy, forcing it to attempt two more landings before it stuck the third, near the edge of a crater.
CASSE wasn't the only instrument learning from the landing: SESAME's two other instruments sent back fresh data until Philae's primary battery ran out roughly 60 hours later. SESAME's Dust Impact Monitor didn't detect dust moving in the area, so Philae's current landing spot probably isn't geologically active. The Permittivity Probe sent an electrical current through the surface, and discovered a vast amount of ice beneath the surface.
Comets are dusty iceballs left over from the formation of the early solar system, when such rocky fragments joined together to form the planets. These leftovers, rich in water and organic compounds, could shed light on the solar system's building blocks -- and how the basic ingredients for life arrived on Earth.
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