European and American scientists are working together to uncover the secrets of one of the more mysterious objects in our Solar System. They are currently poring over hundreds of images of Saturn’s third largest moon, Iapetus, sent by the Cassini-Huygens spacecraft, which was developed jointly by the European Space Agency and NASA. Iapetus is best known for its dramatic two-tone colouration: one half is bright, cratered and possibly covered in ice, while the other is ten times darker and covered in a material yet to be identified. ‘The images are really stunning,’ claims Tilmann Denk, Cassini imaging scientist at the Free University in Berlin, Germany. ‘I was most pleased about the images showing huge mountains rising over the horizon.’
The latest dramatic images show a heavily cratered surface and a mountain ridge that runs along the moon’s equator. Many of the close-up observations focus on the curious 20-km high mountain ridge which gives the moon its walnut-shaped appearance. Cassina has flown nearly 100 times closer to Iapetus than in it did in 2004, bringing the spacecraft to a distance of about 1640 km from the surface. ‘Very few places in our solar system are more bizarre than the patchwork of pitch dark and snowy bright we have seen on this moon,’ says Carolyn Porco, Cassini imaging team leader at the Space Station Institute, USA.
|Saturn’s third moon, Iapetus, has two distinct halves.
‘There is never a dull moment on this mission,’ according to Bob Mitchell, Cassini programme manager of NASA’s Jet Propulsion Laboratory. ‘We are very excited about the stunning images being returned. There is plenty here to keep many scientists busy for years.’
The return of images and other data was delayed at one point when the spacecraft was hit by a galactic cosmic ray, which put it into the so-called safe mode. This occurred after the spacecraft had loaded all of the flyby data on its data recorders and had begun sending the data back home. The flow of data was resumed a few hours later. The spacecraft is once again operating normally, and its instruments are expected to resume normal operations shortly.
Cassini’s observations of Iapetus will assist in characterizing the chemical composition of its surface; they will also help in the search for evidence of a faint atmosphere or erupting gas plumes, and map the night-time temperature of the surface. These and other results will be carefully studied in the weeks and months to come, as scientists attempt to make the two-tone moon give up its secrets.