Tomorrow, at 7:36pm PDT (10:36pm EDT), the Cassini-Huygens probe, a joint NASA/ESA/ASI mission, will make its orbital insertion burn to slow down and enter Saturn's orbit. Launched October 15, 1997, it's the most expensive unmanned mission yet -- and probably the last of its kind for awhile. If all goes smoothly (and, so far, all has gone smoothly with Cassini-Huygens), the craft will spend the next four years studying Saturn, orbiting around the planet more than 70 times. The pictures (and the science) should be incredible.
But the real excitement will come in January of next year, when the Huygens probe separates from Cassini, dropping into the thick, cold atmosphere of Titan, the second largest moon in the solar system. Nobody is entirely certain what Huygens will find; Titan's atmosphere is actually thicker than that of Earth's, and is an opaque soup of nitrogen, methane, and other fairly unpleasant gases. The ESA developers don't actually expect Huygens to survive the landing, but are hoping to get abundant data from the six different instruments on the probe.
Contact with Cassini-Huygens will be cut off, briefly, as it passes through the outer edges of Saturn's ring system, by far the riskiest part of the whole mission. The probe will send back its "here's how things went" data around midnight, California time. The first pictures will be sent received around 7:30 in the morning PDT on Wednesday.
Among the mysteries the joint research teams hope to solve: why does Saturn appear to be rotating six minutes slower than it did when Voyager 1 & 2 passed through in 1977? (That story also includes a link to an audio file of Saturn's radio signal...)
Listening in or watching mission control during the insertion will probably be very memorable (the Mars rover landing certainly was!). NASA will be webcasting, if you don't have NASA TV.
My gosh, has it really been seven years? Man, that sure seemed like a long time to wait.