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.
Now that I have a reasonable-resolution global color view of Pluto, I can drop it into one of my trademark scale image montages, to show you how it fits in with the rest of the similar-sized worlds in the solar system: the major moons and the biggest asteroids.
New Horizons—what will be NASA’s greatest success of 2015—was cancelled multiple times in its early life, and many times before that in its previous incarnations. A mission to Pluto was not inevitable, despite the overwhelming scientific and public excitement.
Over the last several years, engineers at the Jet Propulsion Laboratory and Applied Physics Laboratory have rethought the entire approach to exploring Europa. NASA now has a concept that's affordable.
NASA just announced the science instruments that will be used to understand the enigmatic ocean moon of Europa. The mission is planned to launch sometime in the early 2020s.
I checked out the latest public image release from Cassini and found an awesome panorama across Saturn's rings, as well as some pretty views looking over Titan's north pole.
NASA officials have asked their European counterparts if they would like to propose contributing a small probe to NASA's Europa mission planned for the mid-2020s.
What is the solar system moon with the densest atmosphere? Most space fans know that the answer is Titan. A few of you might know that Triton's is the next densest. But what's the third? Fourth? Do any other moons even have atmospheres? In fact, they do; and one such atmosphere has just been discovered.