The Great Red Spot of Jupiter

The Great Red Spot of Jupiter

To write this article, I was inspired by yesterday’s Astronomy Picture Of the Day (APOD), published by NASA.

The Great Red Spot is certainly one of the most fascinating mysteries of the Solar System. It is a huge anticyclonic storm, located at 22° below the equator of Jupiter which, as far as we know, lasts for at least three centuries. Just think that the Great Red Spot could contain within it three planets like the Earth!

Dimensions and position of the Great Red Spot

The storm rotates counterclockwise with a period of about six Earth days, equivalent to 14 days on Jupiter. Its dimensions are equal to 24,000 – 40,000 km in the east – west direction and 12,000 – 14,000 km in north – south. From the observations recorded over the centuries, we know that the Great Red Spot has changed shape and size. Currently, if the trend remains confirmed, the storm should become circular, even if this fact would be hampered by the very strong jet stream in its immediate vicinity. In particular, the following variations in the width of the Great Red Spot have been observed:

  • At the end of the nineteenth century, however, noted the less sophisticated technology possessed by astronomers, the storm was 41,000 km wide.
  • During the fly-by of the Voyager 2 probe, in 1979, a dimension equal to 23,000 km was measured.
  • In 1995 the Great Red Spot was about 20,000 km wide.
  • In 2014, the Hubble Space Telescope measured a width of 14,000 km.

The Great Red Spot of Jupiter

Jupiter and the Great Red Spot taken from the Voyager 1 probe during its approach to the planet.

Physical characteristics of the Great Red Spot

According to the scientists, the Great Red Spot has a temperature of -113° K, which is lower than the other layers of clouds of the atmosphere of Jupiter, and this causes the storm to be at higher altitudes. In particular, the central layer of the Great Red Spot rises about 8 km from the surrounding layers. The Great Red Spot is confined to the north and south by powerful jet streams. In the outer part of the storm, the winds blow at about 432 km/h while in the central part the situation is much quieter.

It is not clear yet why the storm has this red color, which among other things is not even constant over time: according to some theories, from the point of view of the chemical composition, the Great Red Spot would contain complex organic molecules or compounds of phosphorus or sulfur .

The central part of the Great Red Spot, red – orange, according to the latest studies, would be a slightly warmer region than the rest of the storm, and this slight difference in temperature would be able to trigger a clockwise rotation of the nucleus, compared to the rest of the storm that rotates counter-clockwise.

At this point you may be wondering, why has the storm lasted so long? The answer is that on Jupiter, since there is no solid surface as on the Earth with which there can be friction, the storm tends to maintain its angular moment much more easily and therefore continues in its rotation motion for centuries.

The Great Red Spot of Jupiter

The Great Red Spot of Jupiter taken by the spacecraft Voyager 1 during the fly-by of 1979.

The most recent studies on the Great Red Spot obtained with the Juno probe

Thanks to the Juno probe, launched in 2011 and arrived in the orbit of Jupiter in 2016, it was possible to examine the Great Red Spot very carefully, even in depth. Thanks to the Microwave Radiometer (MWR) on board the spacecraft, astronomers have discovered that the roots of the storm reach up to 300 km deep, far beyond the deepest of the Earth’s oceans.

Andy Ingersoll, professor of planetary science at Caltech, commented:

Juno found that the Great Red Spot’s roots go 50 to 100 times deeper than Earth’s oceans and are warmer at the base than they are at the top. Winds are associated with differences in temperature, and the warmth of the spot’s base explains the ferocious winds we see at the top of the atmosphere.

The Great Red Spot of Jupiter

Data on the Great Red Spot collected by the MWR instrument of the Juno space probe.

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