One of the most iconic things about Jupiter, as seen through images taken over the years, is the giant red swirling spot on the planet. First seen more than 350 years ago, we are about to get our closest look yet as the Juno spacecraft is about to make a flyby directly over the gas giant’s 16,000 km wide storm – that’s wider than Earth by about 3,000-4,000 km.
Interestingly, the Juno spacecraft entered orbit around Jupiter about a year ago. In fact, on July 5, 8 am IST, Juno will complete exactly one year in orbit around Jupiter. The point at which an orbit, in this case – Juno’s, comes closest to the centre of Jupiter, also known as Perijove, will be encountered on July 11, 7:25 am IST. And about 11 minutes after that, Juno will be directly above the great red swirling clouds – all sensors and images blazing through Junocam.
The storm has been a point of interest for years. Apart from the dimensions, there are several other factors like the composition of the gases in the storm that is of interest. While the duration for which it has been observed is well recorded for the past 350 years, the reason behind the reddish hue itself is still unknown.
Time-lapse sequence from the approach of Voyager 1 to Jupiter, showing the motion of atmospheric bands, and circulation of the Great Red Spot. NASA image.
Why is this a big deal?
It is not easy to observe the giant red swirl on Jupiter, thanks to Jupiter’s gaseous nature. There is no solid ground on the planet to weaken storms, as a result of which the swirl has grown over the years. Any probes sent so far have been limited to observing the upper layers of the atmosphere, which completely obscures the lower layers.
Amy Simon, a planetary atmospheres expert at NASA’s Goddard Space Flight Centre, believes that learning more about Jupiter could help scientists understand Earth’s atmosphere better, since both the planet’s weathers function under the same physics, only millions of miles apart with respect to the Sun. Also, the more we understand the actual compositions of planets in our own solar system, the better we would be able to apply that knowledge to understanding extrasolar planets just by their appearances.
One leading theory agreed to by several experts is that the lower layers of Jupiter’s atmosphere consist of colourless Ammonium Sulphide that reacts with cosmic rays or the sun’s UV rays to give the particular red shade of the spot. Some studies have also suggested that the red spot could be a heat source that is behind the high temperatures of Jupiter’s atmosphere.
The Juno mission has been providing great insights into the gas giant. In one flyby, Juno soared as low as 3,400 km from the planet’s cloud tops, providing NASA a look beneath the mysterious cloud cover and revealing “an intriguingly complex interior structure, energetic polar aurora, and huge polar cyclones” according to NASA.