Juno and the Great Red Spot

Just five days after the Juno spacecraft celebrated the completion of its first year in orbit around Jupiter, it undertook a spectacular mission. On 10 July 2017, Juno conducts its sixth close fly-by of Jupiter, passing just 3,500 kilometres above the cloud tops of Jupiter.

What makes this pass so special is that during this fly-by Juno flies directly above the swirling scarlet clouds of Jupiter’s Great Red Spot. The spacecraft will switch on all its science instruments and peer into the depths of the storm to try to find out what powers the most famous storm in the Solar System.

What is the Great Red Spot?

The Great Red Spot is a huge storm that sits in Jupiter’s southern hemisphere. Small oval storms are common in the turbulent clouds of Jupiter and the other gas giants. However, most of them are small and short lived. This is where the Great Red Spot carves out a niche for itself. Unlike the other storms spotted, the Great Red Spot is enormous and has been around for hundreds of years.

The storm itself is a rotating oval of gas around 40,000 kilometres in diameter. Its volume is estimated to be great enough to fit two or three planet Earths inside. The storm itself takes around six Earth days to rotate as the clouds swirl together.

Investigations of the Great Red Spot have shown that the storm itself is slightly colder than the rest of the clouds on Jupiter. This suggests that the clouds of the storm are higher than the rest. While the clouds are cooler, the atmosphere above the Great Red Spot is much warmer than the rest of Jupiter. This is thought to be part of the mechanism responsible for the storm forming. As these hot gases rise and fall they create swirling eddies in the gas clouds. These eddies stick around rather than disappear as there is little friction due to a lack of a solid surface. The eddies are then free to drift around amongst the clouds and merge forming large storms.

History of the Great Red Spot

First spotted in 1665, the exact history of the Great Red Spot is not quite known. The storm was first observed from 1665 until around 1713 by its discover Giovanni Cassini and others. The spot was observed again in 1830 and has been studied continuously ever since. The gap between the two observations have led some people to question whether they are the same spot or not. Some have suggested that perhaps the spot disappeared and then reformed later. However, the consensus is that this is one continuous storm, which has been around for the last 350 years.

Over its history the Great Red Spot has had various changes.  One of the most noticeable is that the storm has shrunk. Over the last century of detailed study the Great Red Spot’s width has shrunk to half what it used to be. The height has remained the same, leading some scientists to predict that the spot may become circular by 2040. The lifespan of the Great Red Spot is unknown. Perhaps it will continue to shrink until eventually it fizzles out. On the other hand, it may stabilise and continue for much longer.

Juno Mission

The Juno mission to Jupiter left Earth back in 2011 and begun a 5-year journey to rendezvous with the largest planet in the Solar System. In 2016 the spacecraft successfully completed a manoeuvre that put it into orbit around Jupiter. However due to a minor problem with the Juno’s engines, its science orbits were adjusted. Originally the probe was due to reduce its orbit to a position that meant it would fly round Jupiter every 14 days. The engine issues meant that the team responsible for the satellite didn’t want to risk a misfire. This resulted in them keeping the satellite in a 53-day orbit instead. This orbit meant that they would get fewer close approaches of the Jupiter, but ensured they would still be able to collect good science results and that the spacecraft would not be put at any additional risk.

The mission is expected to run for a total of 12 close approaches. This will take the mission into 2018 to complete. At this point the spacecraft will be analysed for electronic damage caused by radiation found in the Jupiter environment. If the spacecraft is in good health, the team will go through a project review and likely apply for an extended mission.

The ultimate end of the mission comes after 37 orbits, if not before. At this point the probe will undergo a controlled deorbit into Jupiter’s atmosphere. The speed the probe will enter at will cause the spacecraft to be burnt up and disintegrated in Jupiter’s atmosphere. This ending is designed to prevent space debris and reduce risks of contamination. This is important to ensure a healthy space environment for us to continue and explore.