Wobbling Huygens Probe Reveals Nature of Titan's Surface

The European Space Agency's Huygens probe bounced, slid and wobbled in ten seconds after landing on Saturn's Titan moon, suggests a new analysis.

The Huygens probe carried by NASA's Cassini spacecraft touched down on Titan in January 2005. Titan is the largest of all Saturn's moons. It is the second largest moon in the solar system after Jupiter's moon Ganymede.

Scientists reconstructed the chain of events after Huygens probe's landing on Titan. They used data from Huygens instruments and compared it with results from computer simulations and drop test with a model of Huygens.

They found that the Huygens probe made a dent of 4.7 inches deep after touching down on the flat surface of Titan. It then slid 12 to 16 inches and wobbled back and forth five times in 10 seconds. Each wobble was about half as large the previous wobble, the researchers said.

The probe's sensors detected small vibrations until its movement stopped. "A spike in the acceleration data suggests that during the first wobble, the probe likely encountered a pebble protruding by around an inch from the surface of Titan, and may have even pushed it into the ground, suggesting that the surface had a consistency of soft, damp sand," lead author Stefan Schröder, of the Max Planck Institute for Solar System Research in Germany, said in a statement.

Earlier studies have suggested that the Titan's surface is soft. The new analysis shows that Titan's surface is not only soft with wet sand, but also has a crust like frozen snow on top.

"It is like snow that has been frozen on top. If you walk carefully, you can walk as on a solid surface, but if you step on the snow a little too hard, you break in very deeply," co-author of the study Erich Karkoschka, from the University of Arizona, Tucson, was quoted as saying by space.com.

Further analysis of Huygens' landing data evidence shows dust-like material from Titan's atmosphere being thrown up and suspended for about four seconds after the landing impact. 

The dust was so easily lifted that researchers suggest that the dust was dry. It could mean that liquid methane or ethane that periodically falls as rain hadn't fallen for sometime before Huygens' landing.

The findings of the study are published in the journal Planetary and Space Science.