No trumpet sounded to mark the historic event -- instead, it was a hollow, springy plop which heralded last week's landing by the comet probe Philae.

Scientists at the German space agency DLR on Thursday said they had recorded vibrations from sensors on Philae's three legs as the robot lab touched down on Comet 67P/Churyumov-Gerasimenko.

There is no sound in space, so the team transcribed the two-second signal into its acoustic equivalent. The clip can be heard on http://www.dlr.de/dlr/presse/en/desktopdefault.aspx/tabid-10172/213_read-12221/year-all/#/gallery/17248.

Even though it is fleeting, the sound has yielded a nugget of knowledge about the comet's surface, said DLR scientist Klaus Seidensticker.

"The Philae lander came into contact with a soft layer several centimetres (a couple of inches) thick. Then, just milliseconds later, the feet encountered a hard, perhaps icy layer," he said.

Laden with 10 instruments, Philae was sent down on November 12 by its mother ship, Rosetta, after a 10-year race around the Solar System to catch up with "67P."

Harpoons designed to anchor it to the surface failed to fire. The 100-kilo (220-pound) probe bounced up after landing, came back down some distance away, bounced again and on its third contact finally settled.

But it found itself at an angle and in the shadow of a cliff, crimping its ability to harvest sunlight to recharge its battery.

It went into standby mode after nearly 60 hours' work, but was able to send back precious data in time.

The Rosetta mission, approved in 1993, aims at exploring the composition of comets, believed to be primordial clusters of ice and dust left from the building of the Solar System 4.6 billion years ago.