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.
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.
The road to lower costs outer planet missions has been paved by NASA’s first two New Frontiers missions, the $700M New Horizons mission to Pluto and the $1.1B Juno mission to Jupiter. But can the cost of a mission to the outer solar system be cut to $450M, the limit for a Discovery mission?
Posted by Emily Lakdawalla on 2015/03/23 05:19 CDT
Cassini recently took a long, high-resolution movie of the F ring, catching a view of its ringlets, clumps, and streamers, and two potato-shaped moons, Prometheus and Pandora.
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.