Thursday, October 2, 2014

Recent Cassini Solstice Mission Photos of Saturn and its Moons

For today's posting I decided to check in with the Cassini Solstice Mission.  As many of you know, I have a fondness for the planet Saturn ever since the museum founder, Axel Niemi, showed me the rings of Saturn through his home made telescope when I was only 10 years old.  As I looked through the telescope and saw Saturn's rings, he said to me:  "Karen, given your eyesight problems, if you can see the rings of Saturn, you can do anything."  That was the first day I believed that to be true, since previous to that I was legally blind.  These photos are from the NASA webpage .

The photo above shows a thin sliver of Saturn's moon, Mimas.   The long shadows show off its many craters, indicators of the moon's violent history. The most famous evidence of a collision on Mimas (246 miles, or 396 kilometers across) is the crater Herschel that gives Mimas its Death Star-like appearance. A photo of the entire moon showing the Herschel crater is below.

The moon, Mimas, is shown in the photo above (bottom left side of planet).  As if trying to get our attention, Mimas is positioned against the shadow of Saturn's rings, bright on dark. As we near summer in Saturn's northern hemisphere, the rings cast ever larger shadows on the planet. With a reflectivity of about 96 percent, Mimas (246 miles, or 396 kilometers across) appears bright against the less-reflective Saturn.

The photo above shows the ring gap caused by Saturn's innermost moon, Pan.  This small moon (17 miles, or 28 kilometers across) maintains the Encke Gap in Saturn's A ring by gravitationally nudging the ring particles back into the rings when they stray in the gap. Scientists think similar processes might be at work as forming planets clear gaps in the circumstellar disks from which they form.

The A Ring gap appears empty from a distance, but the close up image above shows that the ring gap actually has three ringlets threaded through it, two of which are visible here.

Each ringlet has dynamical structure such as the clumps seen in this image. The clumps move about and even appear and disappear, in part due to the gravitational effects of the tiny moon, Pan.

The artist's rendering above shows a cross-section of the surface and subsurface of Saturn's moon Titan, with a possible model for the structure of underground liquid reservoirs there.

Hundreds of lakes and seas are spread across the surface of Titan -- its northern polar region in particular. These lakes are filled with hydrocarbons, a form of organic compound that is also found naturally on Earth and includes methane. While most of the liquid in the lakes is thought to be replenished by rainfall from clouds in Titan's atmosphere, the cycling of liquid between the subsurface, surface and atmosphere is still not well understood.

Scientists have modeled how a subsurface reservoir of liquid hydrocarbons, also called an "alkanofer," once filled with methane rainfall runoff, would diffuse through Titan's porous, icy crust. They found that this diffusion could cause a new reservoir -- formed from clathrates -- to form where the bottom of the original underground reservoir meets layers of non-porous ice. Clathrates are compounds that form a crystal structure with small cages that trap other substances like methane and ethane. Titan's subsurface clathrate reservoirs would interact with and the methane-rich liquid within the original underground hydrocarbon lake, slowly changing its composition. Eventually, subsurface alkanofers that come into contact with the clathrate layer would mainly be composed of either propane or ethane, depending on the type of clathrate that had formed.

Importantly, this process would continue up to Titan's surface. Lakes fed by these propane or ethane subsurface reservoirs would show the same kind of composition, whereas those fed by rainfall would be different and contain methane, nitrogen, and trace amounts of argon and carbon monoxide. In other words, the composition of the lake could indicate what is happening deep underground.

The photo above shows how Saturn reigns supreme, encircled by its retinue of rings. Although all four giant planets have ring systems, Saturn's is by far the most massive and impressive. Scientists are trying to understand why by studying how the rings have formed and how they have evolved over time. Also seen in this image is Saturn's famous north polar vortex and hexagon.

The photo above shows the moon, Pandora (center right).  From the narrow F ring, to the gaps in the A ring, to the Cassini Division, Saturn's rings are a masterpiece of gravitational sculpting by the moons. Pandora (50 miles, or 81 kilometers across), along with its fellow shepherd Prometheus (53 miles, or 86 kilometers across), helps confine the F ring and keep it from spreading.

NASA/JPL-Caltech/Space Science Institute
ESA/ATG medialab

No comments:

Post a Comment