In a previous article (check it out here) we had written about the spacecraft Juno, fully equipped with the greatest scientific equipment, on its mission to find out about Jupiter’s atmosphere and its history of formation. On July 10th 2017, during one of its 37 orbits of Jupiter, Juno flew directly over the famous Great Red Spot, at a height of just 9000 km above the cloud tops of the storm. To put that into perspective, the radius of Jupiter is around 70,000 km. When this happened, JunoCam, the visible light camera, took pictures of the Spot, the likes of which man has never seen before! Seen here is an enhanced colour image, prepared by Jason Major, a citizen scientist, from images captured during the fly by.
Although the first confirmed observation of the Great Red Spot was around the 1830s, there have been observations regarding similar spots which go back up to 350 years. An example of this is the 1711 painting by Italian artist Donato Cretiz, which depicts what looks like a red spot on Jupiter.
So what is it about this storm that has captured the attention of so many people, and what do we hope Juno can help uncover about it?
The Great Red Spot is basically an anticyclone that is located at around 22 degrees south of Jupiter’s equator. Being nearly twice the size of the Earth, its gigantic size makes it an instantly recognizable feature of Jupiter. The storm rotates once in six earth-days, and it has been observed that the storm is reducing in size, and may lose its oval shape to become circular by as early as 2040.
An ordinary cyclone has a central region of low pressure, with winds rushing into it, anti-clockwise in the northern hemisphere and clockwise in the southern hemisphere. Instead, in an anticyclone, the central region is at a higher pressure than its surroundings, and the direction of the motion of the winds is reversed in both hemispheres.
While most cyclones on earth do not last very long, the ones on Jupiter can go on for decades at a time. Jupiter, along with Saturn, is a gas giant. They are mainly composed of hydrogen and helium. In fact, due to the high pressures, hydrogen is present in a liquid form known as ‘Metallic Hydrogen’, which makes it a good conductor. This forms a liquid layer around the core. This is a probable cause for the strong magnetic fields which are found around Jupiter. Another implication of this layer is that the lack of a solid planetary surface offers a lesser resistance to the storm, making them last long.
Previously ignored by scientists, the vertical flows inside the storm may be another contributing factor to the longevity of the Great Red Spot. These flows carry hot and cold gases in and out of the storm, and restoring its energy. The storms on Jupiter are always changing, both in shape as well as in colour. The great red spot is often faint red or even white.
Another great mystery which we hope Juno will be able to resolve during its mission is the reason behind the reddish hues of Jupiter’s storm. Scientists do have many theories for this, but only concrete data from Jupiter will help us understand this better. For the first time, with Juno we will be able to explore beneath one of Jupiter’s cloud layers.
With Juno, we hope to confirm theories on formation of planets and study how the strong magnetic field affects Jupiter’s atmosphere.
– Asavari Limaye
Final Year, CS&E