by APOD Robot » Fri Jan 13, 2012 5:06 am
Saturn's Iapetus: Painted Moon
Explanation: What has happened to Saturn's moon Iapetus? Vast sections of
this strange world are dark as
coal, while others are as bright as ice. The composition of the dark material is unknown, but
infrared spectra indicate that it possibly contains some dark form of
carbon. Iapetus also has an unusual
equatorial ridge that makes it appear like a
walnut. To help better understand this seemingly painted moon,
NASA directed the
robotic Cassini spacecraft orbiting Saturn to swoop
within 2,000 kilometers in 2007.
Pictured above, from about 75,000 kilometers out, Cassini's trajectory allowed unprecedented imaging of the hemisphere of Iapetus that is
always trailing. A huge impact crater seen in the south spans a tremendous 450 kilometers and appears superposed on an
older crater of similar size. The
dark material is seen increasingly coating the easternmost part of
Iapetus, darkening craters and highlands alike.
Close inspection indicates that the dark coating typically faces the moon's equator and is less than a meter thick. A
leading hypothesis is that the dark material is mostly dirt leftover when relatively warm but dirty ice
sublimates. An initial coating of
dark material may have been effectively painted on by the accretion of meteor-liberated debris from other moons. This and other images from Cassini's
Iapetus flyby are being studied for even greater clues.
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[url=http://apod.nasa.gov/apod/ap120113.html][img]http://apod.nasa.gov/apod/calendar/S_120113.jpg[/img] [size=150]Saturn's Iapetus: Painted Moon[/size][/url]
[b] Explanation: [/b] What has happened to Saturn's moon Iapetus? Vast sections of [url=http://en.wikipedia.org/wiki/Iapetus_%28moon%29]this strange world[/url] are dark as [url=http://en.wikipedia.org/wiki/Coal]coal[/url], while others are as bright as ice. The composition of the dark material is unknown, but [url=http://missionscience.nasa.gov/ems/07_infraredwaves.html]infrared[/url] [url=http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html]spectra[/url] indicate that it possibly contains some dark form of [url=http://periodic.lanl.gov/6.shtml]carbon[/url]. Iapetus also has an unusual [url=http://apod.nasa.gov/apod/ap050201.html]equatorial ridge[/url] that makes it appear like a [url=http://www.whfoods.com/genpage.php?tname=foodspice&dbid=99]walnut[/url]. To help better understand this seemingly painted moon, [url=http://www.nasa.gov/about/highlights/index.html]NASA[/url] directed the [url=http://en.wikipedia.org/wiki/Cassini_spacecraft]robotic Cassini spacecraft[/url] orbiting Saturn to swoop [url=http://apod.nasa.gov/apod/ap070919.html]within 2,000 kilometers[/url] in 2007. [url=http://photojournal.jpl.nasa.gov/catalog/PIA08384]Pictured above[/url], from about 75,000 kilometers out, Cassini's trajectory allowed unprecedented imaging of the hemisphere of Iapetus that is [url=http://en.wikipedia.org/wiki/Tidal_locking]always trailing[/url]. A huge impact crater seen in the south spans a tremendous 450 kilometers and appears superposed on an [url=http://apod.nasa.gov/apod/ap060530.html]older crater[/url] of similar size. The [url=http://apod.nasa.gov/apod/ap070914.html]dark material[/url] is seen increasingly coating the easternmost part of [url=http://apod.nasa.gov/apod/ap060103.html]Iapetus[/url], darkening craters and highlands alike. [url=http://micro.magnet.fsu.edu/primer/java/scienceopticsu/powersof10/]Close inspection[/url] indicates that the dark coating typically faces the moon's equator and is less than a meter thick. A [url=http://adsabs.harvard.edu/abs/2005DPS....37.3908S]leading hypothesis[/url] is that the dark material is mostly dirt leftover when relatively warm but dirty ice [url=http://en.wikipedia.org/wiki/Sublimation_(chemistry)]sublimates[/url]. An initial coating of [url=http://www.youtube.com/watch?v=DYvITG_TDfE]dark material[/url] may have been effectively painted on by the accretion of meteor-liberated debris from other moons. This and other images from Cassini's [url=http://www.youtube.com/watch?v=baaGOqIJaFM]Iapetus flyby[/url] are being studied for even greater clues.
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