Today’s factismal: The Cassini probe has been orbiting Saturn since June 30, 2004.
Sending a robotic probe to a planet is never easy. It can take ten years to get the plan approved, another decade to build (and fund!) the probe, and then the real terror begins. There’s the possibility that the rocket launching the probe will blow up on the launching pad, the way that NASA’s Vanguard TV3 did. There’s the possibility that someone made a mistake in programming the probe’s computer, as happened with ESA’s Arianne 5. And then there’s the wait as your probe goes from planet to planet in an attempt to gain enough speed to make it to its goal. For probes to the Moon, the trip time is just a few days or weeks at most. For probes to Mars, it typically takes about two years for the trip. But for probes to the outer planets, like Jupiter and Saturn, the trip can take even longer!
Take the Cassini probe. The Cassini probe to Saturn was proposed in 1982, launched on October 15, 1997, and arrived in orbit around Saturn on June 30, 2004. As trip times go, it was relatively short and sweet; the probe worked beautifully from the first power up. And as probes go, it was (and is) a beauty. The probe carried another, smaller probe along piggy-back style; named Huygens, the smaller probe was dropped into Titan’s atmosphere on January 14, 2005. After that, Cassini started cruising the Saturnian system, going from moon to moon and returning scads of spectacular images.
And that’s what we’ve got here. It is a view of the moon Rhea as it passes behind Saturn (what astronomers call an “occultation” which means “got hidden”). Cassini is on the far side of Saturn, with the Sun at the left of the image and Rhea passing between Cassini and Saturn. If you look carefully, you can see a thin bit of Rhea is lit up like the crescent moon (mainly because that’s what it is). And that thin line cutting the picture in half? That’s the rings, seen almost edge on.
If you’d like to see more pictures of awesome splendor, then head on over to NASA’s Astronomy Picture of The Day (APOD) website. For more than two decades now (or about the length of a typical planetological program), this website has been providing the public with amazing images and clear explanations. To visit it, go to: