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.

Jupiter on July 12, 2011 (with bonus Ganymede)

Jupiter's southern belt is coming back

Posted by Emily Lakdawalla on 2011/08/01 09:34 CDT

In a story that I've been following for quite a while, Jupiter's southern equatorial belt, having faded to white in 2009, is now well on its way back to its former red glory.

Pretty movie: Everything in the Saturn system is in motion!

Posted by Emily Lakdawalla on 2011/07/26 06:28 CDT

Pretty movie: Everything in the Saturn system is in motion!

Crescents Dione and Rhea (contrast stretched)

Cassini animations: Rhea and Dione and Titan

Posted by Emily Lakdawalla on 2011/06/28 04:12 CDT

I've been mucking about in the Cassini data archives (as I often do when procrastinating) and unearthed a neat, if short, mutual event sequence of two crescent moons passing by each other.

Cassini finally catches Helene

Posted by Emily Lakdawalla on 2011/06/20 04:41 CDT

Cassini finally catches Helene

Europa on the ropes

Posted by James Wray on 2011/06/11 01:10 CDT

For now, Mars continues to eclipse Jupiter's moon Europa (shown here to scale) in NASA's flagship mission plans, but not in its appeal to many planetary scientists.

Galileo's still producing discoveries: A magma ocean within Io!

Posted by Jason Perry on 2011/05/13 11:44 CDT

A fresh report was published online yesterday in Science Express on the discovery of a magma ocean beneath the surface of Io. Big news! This is a paper I've been looking forward to seeing for more than year and half.

Evidence for rain on Titan

Posted by Emily Lakdawalla on 2011/03/22 04:40 CDT

Last week, Zibi Turtle and Jason Perry and a dozen other coauthors published a paper in Science discussing evidence for rain on Titan.

Some recent pictures of Saturn's northern storm

Posted by Emily Lakdawalla on 2011/02/07 04:35 CST

There is a huge storm that's spreading across so much of Saturn that it's been readily visible even from Earth-based telescopes. Over the past couple of days a couple of new images of Saturn have appeared that show just how enormous the storm is today.

Io and Jupiter from Voyager 1

Posted by Emily Lakdawalla on 2011/01/31 03:14 CST

Here's an image I've been meaning to post for months, a new mosaic from Voyager 1 by Ted Stryk of Io crossing Jupiter's terminator as it neared closest approach.

Jupiter's outbreak is spreading

Posted by Emily Lakdawalla on 2010/11/22 11:03 CST

Jupiter, always a pretty sight in the sky, is now worth visiting every day; the "outbreak" that heralds the return of Jupiter's formerly red, now fadedsouth equatorial belt is expanding and multiplying.