The Tangled Orbits of Saturn's Moons

NASA plans three more closeup passes at Enceladus, the moon of Saturn that has been mysteriously venting organic compounds into the space around it.

Good Friday morning.  An update to yesterday's post:

Tom Carnesi, you asked three good questions, and I'll try my best at them. 

--How to get closer to Enceladus?  I think this was the closest they cared to come--Cassini did wind up probably colliding with material from the geysers near the little moon's south pole.  The plan is for the ship to make flybys of as many moons as possible, but it's complicated, not something you can just make happen without using all the fuel left on board. 

Three more Enceladus flybys are in the extended mission plan--if they get the funding.  (That's a big if.  Alan Stern, NASA's head of space science, resigned this week.   He gave no explanation, but he's also been caught in the middle of NASA's budget wars.)

--Getting close to Saturn: the limiting factor is not the planet's gravity, but its atmosphere.  (Jupiter emits large amounts of radiation, so approach with caution.)  Since the Moon has virtually no atmosphere, Apollo flights often orbited only nine miles above the surface--with astronauts joking about that uncharted ten-mile-high mountain dead ahead.

--Pictures of the Sun: Actually, I think it's still plenty bright, even from Saturn's distance.  But here's the next best thing: Saturn, as seen so that it blocks the Sun out.  This image by Cassini dates from 2006; here's a previous POST of mine about it.

Two things to note about the picture:

1) See how the night side isn't all dark?  That's sunlight bouncing off the rings and lighting the whole planet.

2) Click on the picture to enlarge -- it's worth it.  To the left and slightly above the planet, right inside the second of those very filmy rings, look for a bright dot.  That's Earth--all six billion of us, in our own orbit around the Sun.

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