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Iapetus: Saturn’s Stained Moon

Color image of Iapetus captured by Cassini on March 11, 2017 (NASA/JPL-Caltech/SSI/Jason Major)

Saturn’s “yin-yang” moon Iapetus (pronounced eye-AH-pe-tus) is seen in this image, a color composite made from raw images acquired by Cassini’s narrow-angle camera on March 11, 2017.

The color difference on Iapetus is due to a fine coating of dark material that falls onto its leading hemisphere, sent its way by the distant moon Phoebe traveling within the recently-discovered giant diffuse ring. This dark coating of dust causes that half of Iapetus’ surface to warm up ever-so-slightly-more than the other, making the underlying water ice evaporate and redeposit on the other side. This in turn reinforces the cycle…a positive feedback loop.

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A Northern View of Saturn’s Stained Moon Iapetus

Saturn's moon Iapetus, imaged by Cassini on March 31, 2015 (NASA/JPL-Caltech/SSI)

Saturn’s moon Iapetus, imaged by Cassini on March 31, 2015 (NASA/JPL-Caltech/SSI)

Here’s a raw image of Saturn’s moon Iapetus, looking down on its northern hemisphere from Cassini on March 31, 2015. The moon’s signature two-toned coloration is evident as its bright icy surface is partially coated by dark material, thought to have been ejected from distant neighbor Phoebe.

Iapetus is 914 miles (1,471 km) in diameter, or about as wide as Texas and Louisiana combined. It orbits Saturn at a considerable distance of 2,212,889 miles (3,561,300 km), which is nine times farther than the Moon is from us.

Iapetus’ north pole is located just below and to the left of the centrally-peaked crater south of the brightest region in the image above. (The two prominent craters near image center are Roland and Turpin.)

Learn more about Iapetus here, and for a color version of the above image click here.

A Cosmic Quotation Mark? No, It’s Just Another Moon of Saturn

Saturn's double-colored moon Iapetus

Saturn’s double-colored moon Iapetus

What looks like a single open-quote (or backwards comma) is really Saturn’s two-toned moon Iapetus, seen here in RGB composite color made from raw images acquired by Cassini on Aug. 30 from a distance of about 1.5 million miles.

With a leading side stained a dark reddish hue and a trailing side bright white, the 914-mile-wide Iapetus (eye-AH-peh-tus) is — almost literally — the yin-yang of Saturn’s family of moons.

The color variation on Iapetus is due to the fine coating of dark material that falls onto its leading hemisphere, possibly sent its way by smaller, distant Phoebe. This dark coating of dust causes that half of Iapetus’ surface to warm up ever-so-slightly-more than the other, making the water ice evaporate and redepositing it on the other side. This in turn just reinforces the whole cycle…a positive feedback loop.

Find out more about Iapetus here.

Image: NASA/JPL/Space Science Institute. Composite by Jason Major.

The Curious Central Peaks of Iapetus

The curious, 20-km tall central ridge of Iapetus, a.k.a. the Voyager Mountains

Saturn’s 914-mile (1471-km) -wide Iapetus (pronounced eye-AH-pe-tus) has a particularly curious feature: a chain of 20-kilometer (12-mile) high mountains encircling the moon’s equator. On the anti-Saturnian side of Iapetus, the ridge appears to break up, forming distinct, partially bright mountains. The Voyager I and Voyager II spacecraft provided the first knowledge of the peaks, and they are informally referred to as the Voyager Mountains.

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Look on the Bright Side


Here’s a color-composite image of Saturn’s two-toned moon Iapetus; its Saturn-facing light side is seen here facing to the lower left.

Iapetus is 1,471 km (914 miles) wide.

The raw images were taken by the Cassini spacecraft on June 6, 2011 and received on Earth June 8, 2011. The camera was pointing toward Iapetus from approximately 871,021 kilometers (541,227 miles) away.

Credit: NASA / JPL / SSI / J. Major.

The Light of a Distant Sun

A crescent Iapetus

Since I haven’t posted in a while, I thought I’d put up this image I was playing with last week…it’s a raw image of Saturn’s moon Iapetus combined with a bit of a “glow” from an off-frame Sun and a few stars thrown into the background. Just for curiosity’s sake. 🙂

914-mile-wide Iapetus was discovered in 1671 by Giovanni Cassini, who correctly deduced that the moon has a light side and a dark side when he noticed that the tidally-locked moon could only be seen when on the western side of Saturn. The contrast comes from a coating of darker material on the icy moon’s leading hemisphere, probably ejected off the more distant moon Phoebe, which causes that half to heat up quicker than the other and sending sublimed water vapor to the opposite side, where it refreezes. The dark side, having lost its icy particles, thus becomes darker and the bright side gets brighter, keeping the whole process moving along…a positive-feedback loop.

Raw image credit: NASA/JPL/SSI.

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