You probably already know that the beginning of this week heralded the arrival of NASA’s Juno probe at Jupiter, where it will be carrying out a range of observations on our solar system’s largest planet. It might also confirm some suspicions we have about Jupiter’s chemistry. So what do we already know about Jupiter from a chemical perspective?

Well, for one, we have a good idea of its general atmospheric composition. In many ways, Jupiter isn’t all that dissimilar from a small star in these terms: it’s atmosphere is composed of a mixture of helium and hydrogen. There are also a small proportion of a range of other gases, such as methane, ammonia, and acetylene.

Juno is going to be examining Jupiter’s atmosphere, and in particular it might be able to answer definitively one of our suppositions – that there might be metallic hydrogen hidden in its atmosphere’s depths. Hydrogen is, of course, a gas at room temperature and pressure. However, studies have shown that it starts behaving pretty weirdly when put under intense pressure.

The intense pressure used in these studies, up to three and a half million times normal atmospheric pressure, turns the hydrogen from a gas into a solid, and packs their atoms closer and closer together. Eventually, it’s theorised that the atoms become so closely packed that their electrons become shared as in a metal – giving us metallic hydrogen.

It’s thought by scientists that the very high pressures in Jupiter’s interior could allow metallic hydrogen to form, and that this could also play a part in Jupiter’s magnetic field. Juno will be examining the composition of Jupiter’s atmosphere, and may be able to help us answer these questions. It’s also going to be looking at how much water is in the atmosphere, to see if it matches up with that predicted by current theories of formation of the solar system.

Another thing that Juno will be examining is Jupiter’s weather. This is dominated, of course, by the Great Red Spot. But what is it that gives the spot its intense orange-red colouration? This is something that scientists have been ruminating on for some time.

Several theories have been proposed for the Great Red Spot’s colour. Some earlier theories suggested that it might be caused by red phosphorus produced from the breakdown of phosphine, or by sulfur-containing compounds rising from the planet’s interior. More recent theories suggest that it might be a type of chemical ‘sunburn’ – molecules such as ammonia and acetylene in the atmosphere and broken down by UV light from the sun, and can react to give products that take on a red-orange hue.

The hope is that Juno’s findings might give us more of an idea of what’s going on in and below Jupiter’s clouds. You can read more about the mission’s goals on the NASA website here.

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