JUNO closes in on Jupiter

On Monday 4 July we'll begin to further understand our own solar system. That's when NASA's JUNO spacecraft reaches Jupiter and completes the first stage of a mission that began in 2011. 

Dr Christian Schröder, lecturer in biological and environmental sciences at the University of Stirling, explains what will happen next...

JUNO's Mission

To those unfamiliar with Roman mythology, Juno was the chief goddess married to chief god, Jupiter. Far from being a faithful husband, Jupiter tried to hide his mischievous undertakings below a veil of clouds. This was not enough to hide from a powerful goddess wife, of course, who was able to peer through the clouds and discover Jupiter’s true nature. 

NASA’s latest mission to the giant planet Jupiter aims to do the same: peer underneath its cloud bands and uncover its secrets. And therefore, although the acronym is slightly strained, JUNO – which stands for JUpiter Near-polar Orbiter – is a fitting name for this mission.

JUNO was launched on 5 August, 2011 from Cape Canaveral in Florida and will reach Jupiter after a five-year cruise on 4 July. JUNO will be only the second spacecraft to orbit Jupiter after the Galileo probe (http://solarsystem.nasa.gov/galileo/), which orbited the gas giant from 1995 to 2003. 
The Galileo probe was named after Italian polymath Galileo Galilei (1564 – 1642), and JUNO also carries a plaque in honour of Galilei. The plaque was provided by the Italian Space Agency who also provided one of JUNO’s nine science instruments. 

Galilei was one of the first to use the then newly invented telescope to study the planets. He discovered Jupiter’s four largest moons - Ganymede, Callisto, Io, and Europa – since known as the Galilean moons.


What is so special about Jupiter?

Jupiter, with more than double the mass of all other planets combined, is by far the largest planet in our solar system. It boasts a total of 67 moons discovered to date and its own (albeit faint) ring system. 

The larger moons are interesting worlds in their own right. Io, for example, is the most volcanically active body in our solar system. Europa has a planet-spanning ocean of liquid water underneath a many kilometres thick ice sheet. 

Water is obviously the most important prerequisite of life meaning that Europa is a hotspot for the search of potential life outside Earth (we are talking about microorganisms here, let’s not get carried away).

Jupiter was probably the first planet that formed in our solar system and none of the primordial material it formed from has since escaped its strong gravitational pull. 

It is not clear whether Jupiter formed at its current distance from the Sun or whether it formed closer to the Sun and subsequently migrated outward. Jupiter is a gas giant made up mainly of hydrogen and helium. It is unknown, however, whether Jupiter contains a rocky core or not. 

Jupiter produces a strong magnetic field but its origins are not well understood. By studying Jupiter’s composition and internal structure, it provides fundamental new insights into the origins and evolution of our own and other solar systems, planetary formation processes, and the physics behind magnetic field generation.

How will JUNO carry out its mission?

JUNO will use microwaves and infrared light to look ~500 kilometres deep into the atmosphere to study its composition cloud movements. It will measure the abundance of water molecules, which provides a clue how far from the Sun Jupiter formed. 

In the early solar system, water molecules would have been more abundant further away from the hot Sun. 


To look deeper inside the 140,000 kilometres diameter planet and to learn more about its internal structure, JUNO will study its gravitational and magnetic fields. Is there a rocky core? Mapping the magnetic field lines reveals how deep within Jupiter the magnetic field is generated. 

Earth’s magnetic field is thought to be generated by a dynamo effect where the liquid electrically conducting outer part of the iron core revolves around the solid part. Hydrogen at high pressure can enter a metallic state where it becomes electrically conducting. 

Pressure towards Jupiter’s interior are thought to produce this state of hydrogen, which might circulate a solid (rocky?) core generating a magnetic field in a dynamo effect similar to Earth’s.

Earth’s magnetic field channels charged particles emitted by the Sun towards the poles where they interact with the atmosphere and produce a light phenomenon known as aurora borealis or australis. 

The same happens on Jupiter on an impressive scale. Studying the aurorae as a light phenomenon as well as tracking the movement of charged particles helps to understand its magnetic field and its influence on Jupiter’s atmosphere.

JUNO future after completion

JUNO will orbit Jupiter for approximately one year before it will plunge itself into its atmosphere ending the mission. This is precautionary to avoid an uncontrollable spacecraft from colliding with one of Jupiter’s moons such as Europa and potentially spreading hardy microbes from Earth. We can look forward to new discoveries once JUNO has rendezvoused with Jupiter.

If you're interested in finding out even more about JUNO's mission then you can visit the links below:


So what do you think will be found beneath the clouds of Jupiter? Will there be a groundbreaking discovery? Does space fascinate you or do you see exploration of it as a waste of time? Share your thoughts below!