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.
A newly published paper confirms a subsurface ocean at Ganymede. An ocean there was already suspected from its magnetic field and predicted by geophysics; new Hubble data confirms it, and even says it is in the same place we thought it was before. Such consistency is rare enough in planetary science to be worth celebration.
At last! Cassini is orbiting in Saturn's ring plane again. I do enjoy the dramatic photographs of Saturn's open ring system that Cassini can get from an inclined orbit, and we won't be getting those again for another year. But with an orbit close to the ring plane, Cassini can repeatedly encounter Saturn's icy moons, and icy moon flybys are my favorite thing about the Cassini mission.
Our own Dr. Bruce Betts is once again teaching his Introduction to Planetary Science and Astronomy college course online. Come join him.
NASA's 2016 budget request increases the space agency's budget by $519 million, starts a new mission to Europa, increases funds to Commercial Crew, and threatens some long-running planetary missions.
Last week's Dawn images of Ceres were just slightly less detailed than Hubble's best. This week's are just slightly better.
The landing of Huygens on Titan was a significant moment for planetary science and a great accomplishment for Europe. But the Huygens landing also stimulated the development of the international community of amateur image processors that does such great work with space images today. I was in the midst of it all at the European Space Operations Centre in Darmstadt.