Jupiter. Saturn. Uranus. Neptune. Each of these giant planets is the center of its own miniature solar system. Each is spectacularly beautiful and scientifically fascinating, which are reasons enough to explore them. But by studying the giant planets and their rings and moons, we can also learn about the forces that operated during the formation of our own solar system, as well as the origins of the hundreds of new extrasolar planetary systems that we discover every year.
And their moons are worlds in their own right. There are at least 16 outer planetary moons that would be called dwarf planets if they orbited the Sun rather than a planet. Two (Jupiter's Ganymede and Saturn's Titan) are larger than the planet Mercury, and one (Triton) is probably a captured Kuiper belt object.
But it is challenging and expensive to explore the outer planets, and missions to the outer planets take a very long time to develop, fly, and operate. Cassini will be orbiting Saturn until 2017, and Juno will operate at Jupiter from 2016 to 2017. After that, it's not clear if anyone will be sending a followup mission to Saturn or Jupiter or its moons, or an orbiter to survey the Uranus or Neptune systems. And there is a critical shortage of the isotope of plutonium that is needed to generate power for outer planetary missions.
In honor of the 25th anniversary of the Voyager 2 flyby of Neptune, image magician Björn Jónsson has produced two new global mosaics of the distant ice giant, the highest-resolution ever made.
Jason Perry brings us a report on recent ground-based observations that shed new light on the most powerful of Io’s volcanic eruptions.
For the last four weeks, the name of the game for Curiosity has been driving. But these weeks of driving have been more challenging than they used to be.
In 1979, the Voyager 1 probe took a stunning series of images on its final approach to Jupiter. Thirty-five years later, almost to the day, a group of seven Swedish amateur astronomers set out to replicate this odyssey, but with images taken with their own ground-based telescopes.
As Cassini celebrates 10 years at Saturn, we're beginning to see its long-term observations of Saturnian moons bear fruit. A surprising new result: While Prometheus exerts control over the F ring and Atlas, Pandora -- long thought to be a shepherd of the F ring -- does not.