In the deep reaches of our solar system, 40,000 kms away, orbiting the planet Saturn - exists a moon with a most interesting feature.
Here on Earth, Mt. Everest highest peak is about 9 KM. This ridge is double that size and circles almost the entire planet. If you lived near the ridge, one half of the entire sky would be consumed by this monstrosity!
Author of the 1968 "2001: A Space Odyssey", Arthur C. Clarke, writes about Iapetus. In the final chapters of the book, astronaut Dave Bowman finds an enigmatic alien monolith waiting for him on the surface of Iapetus.
Hello! This is Arthur Clarke, joining you from my home in Colombo, Sri Lanka.
I'm delighted to be part of this event to mark Cassini's flyby of Iapetus.
I send my greetings to all my friends - known and unknown - who are gathered for this important occasion.
I only wish I could be with you, but I'm now completely wheelchaired by Polio and have no plans to leave Sri Lanka again.
Scientists want to know more about the composition of the dark material that coats Iapetus. They also want to learn more about Iapetus' distinctive walnut shape and the chain of mountains along its equator.
The most unique, and perhaps most remarkable feature discovered on Iapetus in Cassini images is a topographic ridge that coincides almost exactly with the geographic equator. The ridge is conspicuous in the picture as an approximately 20-kilometer wide (12 miles) band that extends from the western (left) side of the disc almost to the day/night boundary on the right. On the left horizon, the peak of the ridge reaches at least 13 kilometers (8 miles) above the surrounding terrain. Along the roughly 1,300 kilometer (800 mile) length over which it can be traced in this picture, it remains almost exactly parallel to the equator within a couple of degrees. The physical origin of the ridge has yet to be explained. It is not yet clear whether the ridge is a mountain belt that has folded upward, or an extensional crack in the surface through which material from inside Iapetus erupted onto the surface and accumulated locally, forming the ridge. The origin of Cassini Regio is a long-standing debate among scientists. One theory proposes that its dark material may have erupted onto Iapetus's icy surface from the interior. Another theory holds that the dark material represented accumulated debris ejected by impact events on dark, outer satellites of Saturn. Details of this Cassini image mosaic do not definitively rule out either of the theories. However, they do provide important new insights and constraints.
This flyby was nearly 100 times closer to Iapetus than Cassini's 2004 flyby, bringing the spacecraft to about 1,640 kilometers (1,000 miles) from the surface. The moon's irregular walnut shape, the mountain ridge that lies almost directly on the equator and Iapetus' brightness contrast are among the key mysteries scientists are trying to solve.
Go backstage as scientists watch in real-time as the closest-ever pictures of Saturn's mysterious moon Iapetus are beamed back by NASA's Cassini spacecraft.
This image shows the dark, leading hemisphere of the mysterious moon Iapetus. The dark area is the Cassini region, named for Giovanni Cassini, who discovered the moon in 1672. The diameter of Iapetus is 1,436 kilometers (892 miles).
Cassini noted that he was able to see the moon on one side of its orbit around Saturn, but not on the other side. From this, he correctly deduced that one hemisphere must be dark while the other is much brighter.
N00022350.jpg was taken on October 16, 2004 and received on Earth October 17, 2004. The camera was pointing toward IAPETUS at approximately 1,143,028 kilometers away, and the image was taken using the CL1 and CL2 filters. This image has not been validated or calibrated. A validated/calibrated image will be archived with the NASA Planetary Data System in 2005.
N00007426.jpg was taken on July 20, 2004 and received on Earth July 21, 2004. The camera was pointing toward IAPETUS at approximately 3,263,523 kilometers away, and the image was taken using the CL1 and CL2 filters. This image has not been validated or calibrated. A validated/calibrated image will be archived with the NASA Planetary Data System in 2005.
1. A team of scientists associated with the Cassini mission have argued that the ridge could be a remnant of the oblate shape of the young Iapetus, when it was rotating more rapidly than it does today. The height of the ridge suggests a maximum rotational period of 17 hours. If Iapetus cooled fast enough to preserve the ridge but remain plastic long enough for the tides raised by Saturn to have slowed the rotation to its current tidally locked 79 days, Iapetus must have been heated by the radioactive decay of aluminium-26. This isotope appears to have been abundant in the solar nebula from which Saturn formed, but has since all decayed. The quantities of aluminium-26 needed to heat Iapetus to the required temperature give a tentative date to its formation relative to the rest of the Solar System: Iapetus must have come together earlier than expected, only two million years after the asteroids started to form.
2. The ridge could be icy material that welled up from beneath the surface and then solidified. If it had formed away from the then equator, this hypothesis requires that the rotational axis would have been driven to its current position by the ridge.
3. It has also been suggested that Iapetus could have had a ring system during its formation due to its large Hill sphere, and that the equatorial ridge was then produced by collisional accretion of this ring. However, the ridge appears too solid to be the result of a collapsed ring. Also, recent images show tectonic faults running through the ridge, apparently inconsistent with the collapsed ring hypothesis.