With highlights such as the incredible images and science results obtained by the Cassini and New Horizons missions to the Saturn and Pluto systems respectively, the last few years have been very exciting for outer solar system exploration.
Now it’s the turn of Jupiter, and NASA's space probe ‘Juno’, which has been orbiting our largest neighbour for over 2 years now, has not disappointed. Junocam, the spacecraft’s visual telescope and camera has produced some stunning images, often of regions and features of Jupiter never before imaged, such as these chaotic northern hemisphere storms.
Juno's mission
Impressive as Junocam’s images are, the mission’s goals reach far beyond visible imaging, and its suite of scientific instruments are designed to study many features of the giant planet.
For example, scientists are keen to learn more about Jupiter's turbulent atmosphere, including the iconic Great Red Spot, its largest storm feature – how deep does the turbulence extend? what causes it? what is the atmosphere actually composed of? how much water and ammonia does it contain?
Jupiter's polar aurorae are also intriguing - much stronger than Earth's aurorae, they are visible manifestations of the planet’s powerful magnetic field. Due to its massü Jupiter's gravitational field is also incredibly strong. Scientists hope to learn more about the strength and distribution of these fields, which in turn should provide insights into what’s inside the planet – does it have a solid core? and what’s the source of the planet's internal heat?
Jupiter has belts of extremely strong radiation, which caused a headache for the mission planners – to minimise damage and the instruments had to be enclosed in a shielded vault, and the spacecraft uses an unusual, highly elliptical orbit that swoops over the poles, to avoid the radiation belts as much as possible.
Origin of the solar system?
Fascinating as it may be, gaining a deeper understanding of Jupiter is much more than an end in itself. Because Jupiter is made up mainly of hydrogen and helium, just like the Sun, scientists believe that it formed early in the history of the solar system and has remained virtually unchanged ever since. Consequently, studying Jupiter should help us to understand the process by which the solar system itself was formed – and the process of planet formation in general.
So, what has Juno found so far? Some of the results have been intriguing and unexpected.
Juno has measured the Great Red Spot to be at least 300 km deep, with powerful winds at the cloud tops caused by temperature differences between the surface and the depths. But the atmosphere as a whole extends much deeper, to 3000km or more. Jupiter’s weather system appears to be ammonia-based, with ammonia playing a similar role to that of water vapour on Earth. Beneath this, observations suggest that the interior is rotating as a solid body, in contrast to the atmosphere which rotates in bands of alternating direction and different speeds.
In addition, Juno has discovered new and totally unexpected radiation belts around Jupiter.
But the most fascinating finding for me is that the most powerful Jovian aurorae appear to be formed by a totally different process from those on Earth, a turbulent acceleration of energetic particles that is not yet fully understood. It seems that Jupiter is turning out to be a laboratory for physics that may work differently from on Earth – a lab that is likely to be very valuable in understanding physics in planetary systems beyond our own.
1. NASA/JPL-Caltech/SwRI/MSSS/John Landino https://www.nasa.gov/image-feature/jpl/pia21972/jupiter-blues
2 .NASA/JPL-Caltech/SwRI/JHUAPL www.jpl.nasa.gov/spaceimages/details.php?id=PIA22179
3. NASA/JPL-Caltech/SwRI h www.jpl.nasa.gov/spaceimages/details.php?id=PIA21938