Science Interviews


Mon, 18th Jul 2016

Jupiter: The weird planet

Dr Marc Rayman, NASA's Jet Propulsion Lab

Listen Now    Download as mp3 from the show Jupiter: King of the Planets

With its strong radiation belts, polar auroras and red spot, Jupiter is a bit of an Jupiter's red spotenigma, as Graihagh Jackson discovers with Heather and Marc Rayman...

Marc - Although some planets seem to be gassy, they aren't like the light, airy, and substantial gas we generally think of. On Earth, the weight of the air above you pulled down by our planetís gravity creates a modest pressure. This is about 1 kilogram per square centimetre. Thatís the mass of a big book, like a dictionary if you remember those from the 20th century, pushing down on an area about the size of a single Lego brick. We conveniently call it 1 bar.

Heather - That's Earth, but what about Jupiter?

Marc - In contrast to our planet, gas planets are composed mostly of gas. They're also gigantic and the weight of all that gas is tremendous. For example, Jupiter is mostly hydrogen and it is enormous, 11 times the diameter of Earth and over 300 times the mass. It may have a rocky core thatís more than 10 times the mass of Earth. All that mass causes intense gravity, pulling downward on the gas which compresses it and creates fantastically high pressure.

Heather - More pressure than one dictionary, how many though? A hundred? A thousand? Ten thousand?

Marc - If you ever tried to land on a gassy planet, you would be subjected to pressure beyond anything you can imagine. As you descended below the colourful gas clouds, the pressure would grow and grow, rising to 1 million bar, at a depth of about 10,000 kilometres.

Heather - One million dictionaries.

Marc - You would be immersed in a sea of hydrogen so dense that itís more like liquid than gas. At 20,000 kilometres, the pressure is around 2 million bars. Thatís 2,000 times greater than the highest pressure found on Earth in the Mariana Trench in the deepest part of the Pacific Ocean.

Heather - Two million dictionaries.

Marc - The hydrogen is compressed so hard that the electrons are squeezed off. The strange condition makes the hydrogen metallic, but going still deeper, the pressure would continue to skyrocket, exceeding perhaps 40 million bars at the rocky core, more than 60,000 kilometres deep.

Heather - Forty million dictionaries.

Marc - If you ever tried to land on a gassy planet, you would not even make it to a few hundred kilometres. Your spacecraft,and you, would be utterly destroyed, squashed by the crushing atmospheric pressure, long before you found the core. So, you might sink to the core, but only in the form of squished atoms.


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