21. The Volcanoes of Io hot lava from Tvashtar Catena Pele plume to 300 km, fallout size of France Galileo image 50 km
22. Europa - Ice Over a Vast Ocean Voyager image Galileo image 5 km
23. Ganymede and Callisto Voyager Galileo Galileo Voyager/Galileo torn comet, 200 km scar 15 km
24. Saturn and Titan dense, nitrogen-methane atmosphere for Titan complex rings, many diverse moons ring “spokes” chemistry may resemble early Earth
25. Uranus and Miranda tilted, featureless, ringed, and 10 new moons discovered smashed and reassembled, or upwelling? diameter 472 km
26. Neptune and Triton geyser-like eruptions fast winds, Great Dark Spot, faint rings, 6 new moons retrograde, likely captured object
Notes de l'éditeur
After having been on a journey exploration for more than 26 years, the Voyagers continue to return suprises about our world. Even as Voyager 1 surpasses 90 AU, the discoveries continue. I know many of you know what an AU - astronomical unit - is, but since you may hear it a lot tonight, I thought I should briefly define it.
An AU is simplly the average distance between the Earth and the Sun, which is about 93 million miles or the distance light travels in slightly more than 8 minutes. There is a lot of history behind the Voyager missions, and I’ll tell you later how to find more information. But for this overview, I will begin with the Mariner Jupiter Saturn mission
The MJS mission was designed as a less expensive alternative to the original Grand Tour mission which was deemed not affordable and canceled. Using two spacecraft the objectives were to explore Jupiter, Saturn, their largest moon and rings of Saturn. As the spacecraft flew by Jupiter, they would get a gravitational assist which would slingshot them on to Saturn.
The Voyager spacecraft is characterized by 4 major features: A 3.7 meter hi-gain antenna which is continually pointing tward Earth. This is used to communicate with the spacecraft 3 RTGs which provide electrical power by converting the heat from the natural decay of plutonium A 13 meter long magnetometer boom which distances the magnetometers from the radioactive environment of the RTGs And a scan platform upon which the imaging instruments were mounted and which pointed the instruments The spacecraft were launched in August and September 1977. Voyager 2 was launched first but Voyager 1 was launched on a faster flight path and actually reached Jupiter and Saturn before Voyager 2.
This graphic depicts the paths taken by the spacecraft. Voyager 1 flew by Jupiter and was then slung on to Saturn and then on a northerly path toward interstellar space. After passing Jupiter and Saturn, Voyager 2 was routed on to Uranus and then Neptune and then on a southerly path toward interstellar space
Though the original mission objectives only included the exploration of Jupiter and Saturn, Voyager 2 was sent on a path that would allow it to proceed to Uranus and then Neptune, taking advantage of an alignment of the planets that only occur every 176 years. Once the original mission objectives were completed, the spacecraft was in good health and enough power and attitude control gas remained to continue on to Uranus. NASA approved the Uranaus mission and, eventually the mission to Neptune, completing the Grand Tour.
After Voyager 1 passed the orbit of Neptune, it turned around and took a series of pictures which is called the Portrait of the Solar System. It was the first - and only - time the planets had been imaged from outside the planetary system. At about 40 AU Earth appeared - as Carl Sagan called it - a pale blue dot. He observed that in our planetary system all the intelligence as we know it exists on that tiny little speck - and this portion of space is only one of many specks. Perhaps somewhere out there in the vastness of space there is other intelligent life.
Today, Voyager 1 is 90 AU from the Sun and it takes more than a day for us to communicate with it and get a response Voyager 2 is headed south and is slighly more than 70 AU from the Sun.
Enough electrical power is available to operate the science instruments and communicate with Earth until approx 2020. But, even after we are no longer to talk to the spacecraft they will wander the Milky Way, never really coming very close to a currently know object. In 40,000 years Voyager 1 will come within about 1.6 light years of a little known star which will then be within one light year of the Sun.
Just in case there are other intelligent beings in all that expanse, each Voyager carries a message from Earth. These phonograph recors and their covers contain information that reveals from whence the spacecraft came, when they were launched and pictures, music, greeting and sounds that would provide an extraterresttrial information about the beings that built and sent the Voyagers into interstellar space.