Inner and outer planets

Earth is percieved as a rocky planet, what are other planets like? Did you know Mars is cold and that outer planets are really gigantic gas envelopes? What about a liquid planet? Could such a planet exist? And what really defines a planet, anyway? Explore these questions and more on this week’s “SkyTalk.”

Credit: NASA and The Hubble Heritage Team (STScl/AURA)

Listen:[audio: st20090413.mp3]Visit the Skytalk web page for more information.

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