Posted on September 21, 2017
Today's historical anniversary is quite appropriate:
On this date in 2003, the spacecraft named Galileo ended its mission by entering Jupiter's atmosphere - to be crushed and to burn up.
Why did I say it was appropriate? Because this year (2017), on September 15 (about a week ago), the spacecraft named Cassini ended ITS mission by entering Saturn's atmosphere - to break apart and burn up.
These "death dives" were conceived to make sure that the planets' moons, which might possibly be homes to some primitive lifeforms, will not be contaminated with Earth organisms (bacteria, etc.). There is no way for the gas giants themselves to have any sort of life-as-we-know-it, and the extreme heat as the spacecraft burn up in the atmospheres would ensure that the remaining materials would be sterilized.
But the death dives are more than just a handy way to avoid contamination. These dives give us a bit more data to go along with all the data the probes already provided during their lifetimes. Scientists are pretty sure they know many aspects of the atmospheres and other conditions on the gas giants, and so they are able to make predictions of the conditions the spacecraft will encounter on their suicidal dives. The spacecraft keep transmitting until they break up, or are crushed, so we are able to compare the predictions with the actual measurements taken and with the behavior of the spacecraft.
Here are some comparison stats of the two spacecraft:
Galileo - October 18, 1989
Cassini - October 15, 1997
Planned mission lengths, including travel time:
Cassini - about 10 years
Galileo - almost 14 years!
Cassini - almost 21 years!
Galileo lasted six years longer than planned, and Cassini lasted more than a full decade longer than planned! Wow!
Here are a few highlights of Galileo's findings:
Discovered the first asteroid moon
First direct measurement of Jupiter's atmosphere
First asteroid flyby
Observed Comet Shoemaker-Levy 9's collision with Jupiter
Observed volcanoes erupting on Io (a moon)
Observed Io's interaction with Jupiter's atmosphere
Theory of liquid ocean under moon's ice supported (but not yet confirmed) - Europa
Probable liquid saltwater layers under moons' ice - Ganymede and Callisto
Magnetosphere detected on Ganymede
Exosphere detected around three large moons
Faint ring system detected around Jupiter