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It's been a while since I've posted a breathtaking Cassini Saturn photo. To make up for that, I have something special today.
First, a brief background. On August 11, 2009, it was Saturn's vernal equinox: the point on its orbit when the sun was directly above Saturn's equator. This means that the sun shone exactly on the rings of Saturn. Why is it important? Well, because lighting it counts!
The rings are composed of innumerable chunks of almost pure water ice, some tiny, some of several meters in diameter. The way the light passes through them changes in appearance – when it is not the equinox and the sun shines on one side of the rings, they look different from the illuminated side to that of the "below", the non enlightened. Indeed, the light reflected by the rings (seen from above, sunny side) is much more powerful than the light that passes through it. This radically changes their appearance and we can learn a lot about their composition in this way.
Seeing them at the equinox, when the sun shines perfectly in their plane, offers a third option. But also, at the equinox, any deviation from the rings being flat is much more obvious, because something coming out of the rings will cast a shadow on the rings themselves. Think of a small rock on the ground at noon, projecting a small shadow, as opposed to sunset when the shadow is very long, longer than the rock itself.
The rings of Saturn are strangely flat. But no Perfectly so. Due to the influence of moons in orbit around the planet, some ice particles from the ring can be extracted from the plane. This gives spectacular images of ice towers seen due to the low angle of the sun, which would be invisible at other times of the year of Saturn. Thus, Cassini officials took zillions of images of the rings during this time, both before and after the exact day of the equinox, to capture these long shadows.
Enter Kevin M. Gill, a software engineer who also processes the images. He has frequently reprocessed Cassini's raw images into high quality works of art and has made an amazing video here. He took a stack of images taken on July 26, 2009 just before the equinox, sewed them into 3D and remapped them in a cylindrical projection, creating an animation that gives the impression you fly above the rings at the equinox, follow them around Saturn for 250,000 kilometers!
Watch:
Whoaaaaaaaa. In this animation, you fly over the outer edge of the B ring. Saturn is about 175,000 kilometers to the right, the sun about 1,5 km. billion kilometers on the left. More immediately, on the left side of the screen is the inner edge of the Cassini division, a huge rift in the rings of Saturn (you can even see it in small telescopes of the Earth). This part of the division is particularly devoid of ring particles and is called Huygens Gap.
A little more than a minute after the start of the animation, you start to see irregularities in the B ring, which get bigger as you travel, then 2 minutes later, they dominate the ring up to 3 km high! These are probably caused by small ring B glasses that interact by gravitation with the particles of the ring, which throws them into these huge arrows.
Note that as you travel 250,000 km around the rings here, it's still only about a third of the way! The rings of Saturn are immense. Despite everything, they are fragile and thin, composed of innumerable billions of small grains of ice.
How wonderful would it be to make such a trip in reality? I sincerely and sincerely hope that humanity will eventually have the chance to make a trip like this.
P.S. You can follow Gill on Twitter and see all his amazing images as he does them.
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