Diamonds at the core?

These evenings it is hard to miss that bright, starlike object in the southern sky, shining steadily like a lamp. The lack of twinkling tells us that it is not a star; it is a planet: Jupiter, the fifth planet out from the sun.

If you have any sort of telescope or binoculars, get them out to have a look. Binoculars will show a tan-coloured disc with maybe traces of cloud belts. There will be up to four starlike objects forming a line passing through the planet. These are the planet's four largest moons: Io, the closest, and then, going outwards, Europa, Ganymede and Callisto. A telescope, with its higher magnification, will show the disc of the planet, crossed with grey and brown cloud belts.

Jupiter is huge, with a diameter of about 143,000 km. It is big enough to contain over 1,300 Earths. If that planet were a rock ball like the Earth, we would expect its mass to be something like 1,300 times that of the Earth. However, the giant planet is only 320 times more massive than the Earth. This means it must be mostly atmosphere. Saturn, Uranus and Neptune are similar. We call such planets gas giants. When on a long-distance flight, we are above most of the Earth's atmosphere. Jupiter's atmosphere is tens of thousands of kilometres deep. It is made up of a mixture of hydrogen, helium, methane and ammonia, together with a witches brew of organic compounds. These give the planet that tan colour.

Earth's atmosphere started off as more or less the same gaseous mixture as Jupiter's. Under the right conditions the chemicals in this mixture can be persuaded to react, forming aminoacids, an important ingredient for life as we know it. Living creatures here have consumed those chemicals and given us the oxygen atmosphere we have today. The fact we can see these chemicals still there in Jupiter's atmosphere suggests there are no living things there to consume it. However, scientists have fantasized about great blimp creatures floating around in its deep atmosphere. They would have to live in the upper few thousand kilometres because deeper in the atmosphere conditions become more and more extreme.

A few thousand kilometres down into Jupiter's atmosphere the pressure reaches 100-200 million bars, where one bar is the pressure at the Earth's surface. This is where the word "barometer" comes from. As we go downwards, the temperature increases too, so that we eventually reach a point where chemical based life just cannot exist. As we get deeper in towards the centre of the planet, the pressure reaches billions of atmospheres. Under these pressures, gases no longer behave like gases; they are more like liquids or squidgy solids. There might not be a rocky core at all. However, some theories indicate Jupiter might have a very expensive core, a diamond one.

Diamonds are made of carbon. Under extreme temperatures and pressures, carbon atoms do not form the black, sooty stuff we are familiar with; they form diamonds. On Earth, these conditions occur deep underground. They also occur in Jupiter's atmosphere. As we get deeper in that planet's atmosphere, the temperature rises, and under conditions of extreme heat and pressure, methane, which consists of one carbon atom attached to four hydrogen atoms, breaks up. The freed-up carbon atoms diffuse slowly downward, joining together into diamonds, which rain down to the centre of the planet. This might be going on in the cores of the other gas giant planets too. So Jupiter, Saturn, Uranus and Neptune might hold unimaginable riches, but it is extremely unlikely we will ever manage to get our hands on them.


  • Venus lies very low in the sunset glow.
  • Jupiter and Saturn rise in the southeast soon after dark.
  • Sirius, the brightest star in our winter skies, is visible low in the dawn twilight.
  • The moon will reach last quarter on the 30th.

More Skywatching articles

About the Author

Ken Tapping is an astronomer born in the U.K. He has been with the National Research Council since 1975 and moved to the Okanagan in 1990.  

He plays guitar with a couple of local jazz bands and has written weekly astronomy articles since 1992. 

Tapping has a doctorate from the University of Utrecht in The Netherlands.

[email protected]

The views expressed are strictly those of the author and not necessarily those of Castanet. Castanet does not warrant the contents.

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