People often ask about Jupiter's surface. Given what we're used to with the Earth - iron core, solid layers in between to the surface and then atmosphere - it's not surprising. But Jupiter is one of the "gas giants" (the others are Saturn, Uranus, and Neptune). The gas planets do not have solid surfaces, their gaseous material simply gets denser with depth - or as we think from the surface of the Earth - less dense with height ("Gee, the air is thin up here").

Jupiter's massive atmosphere creates tremendous pressures as you move closer to the center of the planet (think of how the pressure increases as you dive into deeper water - the more mass above you, the greater the pressure). Extreme pressures and temperatures inside Jupiter make it impossible for us to send a probe deep into Jupiter's interior (learn about the fate of the Galileo Probe). Because of this, much of what we know about the interior and core of Jupiter is in the realm of scientific theory.

The extreme pressure and temperature inside Jupiter leads to exotic chemistry. For example, scientists have reason to believe that the inner layers of hydrogen in Jupiter's atmosphere, under the pressure of the atmosphere above, may have formed into a layer of what is called liquid metallic hydrogen. Not exactly an ocean, not exactly atmosphere, this layer of hydrogen would have properties that stretch our understanding of chemistry. Instead of the simple, free-moving behavior of hydrogen in gas form (as we see in our own atmosphere and on the Sun), liquid metallic hydrogen is a strange matrix capable of conducting huge electrical currents. The persistent radio noise and wildly strong magnetic field of Jupiter could both come from this layer of metallic liquid. Some scientists theorize that beneath this layer there is no solid mass at the center of Jupiter, but that the unique temperature and pressure conditions sustain a core whose density is more like liquid or slush.