A Surface Map of Dione

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This cylindrical projection global map is one of six new color maps of Saturn's midsized icy moons, constructed using 10 years of image data from the Cassini spacecraft. Discovered by Cassini (the astronomer) in 1684, Dione is about 1,120 kilometers across. Based on data extending from infrared to ultraviolet, the full resolution of this latest space-age map is 250 meters per pixel.

Could Titan Be Older Than Saturn?

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The hint comes in the form of a ratio. All elements have a certain number of known isotopes — variants of that element with the same number of protons that differ in their number of neutrons. The ratio of one isotope to another isotope is a crucial diagnostic tool.

In planetary atmospheres and surface materials, the amount of one isotope relative to another isotope is closely tied to the conditions under which materials form. Any change in the ratio will allow scientists to deduce an age for that material...

"When we looked closely at how this ratio could evolve with time, we found that it was impossible for it to change significantly," Mandt said in a press release. "Titan's atmosphere contains so much nitrogen that no process can significantly modify this tracer even given more than four billion years of Solar System history."

It Rains Diamonds on Saturn

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New atmospheric data for the gas giants indicates that carbon is abundant in its dazzling crystal form, they say.

Lightning storms turn methane into soot (carbon) which as it falls hardens into chunks of graphite and then diamond.

These diamond "hail stones" eventually melt into a liquid sea in the planets' hot cores, they told a conference.

The biggest diamonds would likely be about a centimetre in diameter - "big enough to put on a ring, although of course they would be uncut," says Dr Kevin Baines, of the University of Wisconsin-Madison and Nasa's Jet Propulsion Laboratory.