Outer Planets

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.

Iapetus' peerless equatorial ridge

Posted by Emily Lakdawalla on 2012/02/22 01:49 CST

A new paper in the Journal of Geophysical Research - Planets by Dombard, Cheng, McKinnon, and KayI claims to explain how Iapetus' equatorial ridge formed. Cool!�

Checking up on Jupiter and Saturn

Posted by Emily Lakdawalla on 2012/02/10 01:51 CST

It's amateur astronomers, not professionals, who are shouldering the burden of constant monitoring of the weather on Jupiter and Saturn. What's going on these days in the outer solar system?�

Pretty picture: Enceladus, in lovely color

Posted by Emily Lakdawalla on 2012/02/06 02:38 CST

Here's an awesome picture to start off the week. The data came from Cassini's flyby of Enceladus on January 31, 2011; it was part of Cassini's January 2012 data release.�

Parallel planetary processes create semantic headaches

Posted by Emily Lakdawalla on 2012/01/26 03:55 CST

I ran into a semantic problem today: what to call the science of studying liquids on Titan?

Evaporites on Titan

Posted by Emily Lakdawalla on 2012/01/12 04:33 CST

Evaporites form on planetary surfaces when dissolved chemical solids precipitate out of saturated solution as their liquid solvent evaporates and, until recently, were known to exist only on Earth and Mars. This article from the IAG Planetary Geomorphology Working Group describes the third planetary instance of evaporite, discovered on Saturn's moon Titan.

Pretty picture: Saturn, a big moon, and a teeny one

Posted by Emily Lakdawalla on 2012/01/09 11:23 CST

A recent view from Cassini of Saturn with its largest moon (Titan) and one of its small ringmoons, Prometheus.

Pretty pictures from Cassini's recent Dione flyby

Posted by Emily Lakdawalla on 2011/12/22 11:52 CST

Cassini flew close by Dione on December 12 and, as usual, the close pass provided opportunities for lots of dramatic photos, not just of Dione, but of other moons wandering by in the background.

Blink animation between SAR and photo observations of Iapetus

More radar images of icy moons from Cassini: Iapetus, Enceladus, and Rhea

Posted by Emily Lakdawalla on 2011/12/21 12:10 CST

When I posted about the really cool Cassini SAR images of Enceladus a few weeks ago, I initially wrote that this was the first-ever SAR image of an icy moon other than Titan. Several people (some readers and two members of the Cassini science team!) corrected that statement: Cassini has performed SAR imaging of other icy moons (including Enceladus) before.

What do we know about planetary rings? Quite a lot, actually!

Posted by Emily Lakdawalla on 2011/12/15 11:18 CST

A summary of a new article by Matt Tiscareno about planetary ring systems that reviews the known ring systems of the four giant planets and the prospects for ring systems yet to be discovered.