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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.

Towards a Jupiter Weather Forecast

Posted by Leigh Fletcher on 2015/09/24 08:04 CDT

Trying to keep track of the ever-changing face of Jupiter is a pretty big challenge—its a dynamic world that can fascinate and surprise every time we turn our telescopes towards it.

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Checking in on Uranus and Neptune, September 2015 edition

Posted by Emily Lakdawalla on 2015/09/22 01:28 CDT | 5 comments

There are no spacecraft at Uranus or Neptune, and there haven't been for 30 and 25 years, respectively. So we depend on Earth-based astronomers to monitor them, including Damian Peach.

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IceBreaker: The Search for Life on Mars

Posted by Van Kane on 2015/09/08 09:19 CDT | 3 comments

The IceBreaker mission, proposed to NASA's Discovery program for low-cost missions, would seek out life on the northern plains of Mars.

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Galileo's best pictures of Jupiter's ringmoons

Posted by Emily Lakdawalla on 2015/08/24 07:07 CDT | 4 comments

People often ask me to produce one of my scale-comparison montages featuring the small moons of the outer solar system. I'd love to do that, but Galileo's best images of Jupiter's ringmoons lack detail compared to Cassini's images from Saturn.

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Jupiter's changing face, 2009-2015

Posted by Emily Lakdawalla on 2015/07/24 08:46 CDT | 4 comments

Damian Peach's photo-documentation of Jupiter helps us monitor the giant planet's ever-changing patterns of belts, zones, storms, and barges, during a time when no orbiting missions are there to take pictures.

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First look at New Horizons' Pluto and Charon images: "baffling in a very interesting and wonderful way"

Posted by Emily Lakdawalla on 2015/07/15 04:42 CDT | 33 comments

Today's press briefing at the Applied Physics Laboratory in California was preceded by hours of New Horizons team members cryptically dropping hints on Twitter at astonishing details in the seven images downlinked since the flyby. The images are, in fact, astonishing, as well as beautiful, surprising, and puzzling.

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The not-planets

Posted by Emily Lakdawalla on 2015/07/14 12:48 CDT | 37 comments

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.

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NASA Goes First Class for Europa

Posted by Van Kane on 2015/06/10 12:07 CDT | 9 comments

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.

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Here Are the Science Instruments NASA Will Use to Explore Europa

Posted by Casey Dreier on 2015/05/26 01:01 CDT | 8 comments

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.

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Two Months from Pluto!

Posted by Paul Schenk on 2015/05/19 06:12 CDT | 5 comments

Two months. Eight and half weeks. 58 days. It's a concept almost too difficult to grasp: we are on Pluto's doorstep.

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