Why (and how) have we sent a space probe on a five year journey to Jupiter?

On 4th July 2016, NASA’s Juno spacecraft entered Jupiter’s orbit after a five year journey. The mission, so far, has been declared a roaring success, but why has NASA sent a spacecraft to orbit the giant planet? How will a planet 588 million kilometers from Earth be able to help us understand the birth of the solar system?

How did Juno manage to orbit Jupiter?


The Juno spacecraft was launched from Cape Canaveral on 5th August 2011. Since then, it has been on a 588 million kilometer trajectory towards the Red Planet whilst constantly being monitored by the New Frontiers Program. Upon the final approach to Jupiter, the attitude of the Juno probe was changed so that the main engine of the probe would point in the right direction and its rotation rate was increased to 2 rpm to 5 rpm, in order to stabilise the probe. The velocity of probe was also decreased to 1,212 mph in order for it to enter Jupiter’s orbit. Data collection from the Juno probe will begin in October this year with the help of nine different instruments carried by the probe.

What are the main instruments on board Juno?


The main piece of equipment on board is the Jupiter Energetic Particle Detector Instrument or JEDI. JEDI is able to measured charged particles which are accelerated to high energies within the magnetosphere of Jupiter. It does this by having three shoebox sized detectors viewing a 120 by 12 degree section of the sky around Jupiter each. These detectors are able to pick up data from charged particles with between 30-1000 keV of energy that envelops Jupiter and creates auroras which circle the polar regions. JEDI is able to detect neutral atoms, protons, helium, oxygen and sulfur by simultaneously measuring incoming particles from many different directions. This data, which is effectively speed and energy, can be analysed to find the mass composition of incoming particles. We are then able to find out where the particles that surround Jupiter actually come from, how they are energised and how energy from these particles are released?

The Juno probe can also measure lower energies of particles for the same aurora process mentioned above with the JADE instrument. It can measure Jupiter’s 3D magnetic field with MAG and the Wave instrument can measure the radio and plasma waves in Jupiter’s magnetosphere. The upstream of ions can also be measured to discover how Jupiter’s auroras are formed and whether their formations are affected by solar wind. Normally in a solar wind, sulfur is present but in Jupiter’s atmosphere sulfur is not found. Instead, high energy electrons are produced which can be seen at great distances from Jupiter. Hence, the origin of the solar winds around Jupiter can be determined by detecting the amount of sulfur present. If sulfur is present, then the probe will be outside of Jupiter’s solar wind and hence, out with Jupiter’s planetary influence in terms of orbit and gravity. The probe will then be able to push upstream against the solar wind in order to find its origin and the composition of particles at this area.

However, it’s all very good having these complex instruments to find out complex answers to complex problems, but why is this mission going ahead?

What’s the point in Juno’s five year journey?


There are many different aims that the NASA team will try to achieve. The ultimate aim is to comprehend the origin and evolution of Jupiter itself. Understanding this processes in Jupiter’s birth will help understand the steps and conditions that were needed for our solar system to come into existence. The Juno spacecraft will do accomplish this goal by achieving the following ‘mini-goals’:

  • Determine whether a solid planetary core exists – As this will give an origin for the creation of Jupiter.
  • Map Jupiter’s magnetosphere – Under the pressure of Jupiter’s atmosphere, hydrogen gas is pushed into a fluid of metallic hydrogen which acts like a conducting metal. This creates a magnetic environment which creates auroras. Understanding how the magnetosphere and auroras function will assist in understanding of the evolution of young stars, which was essential in the formation of the solar system.
  • How Jupiter formed and the role of giant planets in putting together a solar system – This will be done by finding the composition of Jupiter by tracing the planet’s history using instruments to measure water and ammonia levels, and gravitational and magnetic fields. This should, hopefully, reveal whether the planet started with an unstable collapse inside a nebula or was a massive planetary core formed with gravity helping to capture the gases which make up the planet.

No matter what the results of the these ‘mini-goals’ are, we will gain critical knowledge of how planetary systems are formed.

What are your views on the Juno space mission? Will the instruments on board Juno be of any use to NASA scientists and do you think it is important for us to understand the evolution of the solar system? Feel free to share your opinions.


Johns Hopkins University Applied Physics Laboratory. “NASA’s Juno and JEDI: Ready to unlock mysteries of Jupiter.” ScienceDaily. http://www.sciencedaily.com/releases/2016/07/160701100109.htm (accessed July 7, 2016)

NASA/Jet Propulsion Laboratory. “NASA’s Juno spacecraft in orbit around mighty Jupiter.” ScienceDaily. http://www.sciencedaily.com/releases/2016/07/160705084023.htm (accessed July 13, 2016)

NASA. “Juno Overview” https://www.nasa.gov/mission_pages/juno/overview/index.html (accessed July 12 2016)


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