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Thursday, 19 May 2016

Juno - cracking the mysteries of Jupiter

Above: The planet Jupiter, as seen through a small telescope. Courtesy of mikesastrophotos.
The Juno space probe arrived at Jupiter (July 4th), and it's the first mission to the king of the giant planets since the Galileo probe...

The mission: 
Jupiter is often outshone in the media by its potentially life bearing moon Europa, and the ever violent and changeable Io, but JUNO is actually a mission to Jupiter itself: Jupiter is easily one of the most complex worlds we know of, and has plenty of unsolved mysteries - from simple ones like 'why is the Great Red Spot red', to what makes its storm belts fade away and re-appear, to what causes it's internal heat and how exactly it formed. Juno carries a suite of instruments designed to study deep layers of Jupiter not visible to the naked eye.

Above:The Great Red Spot, a storm the size of Earth - what powers it, why it's red... Juno w try to answer these questions. Courtesy of NASA/JPL.

The giant worlds internal structure, and whether or not it has a rocky core, carries information on how the solar system formed, like a huge 4.5 billion year old fossil.  Jupiter's huge mass and fast rate of spin are expected to warp space-time in a specific way too, letting Juno use it to test general relativity.  The probe will also get the first really good look at the giant planets poles, and hugely powerful aurora.

But to do all this Juno has to survive long enough - Jupiter puts out enough radiation to cook a probe. Once it reaches Jupiter Juno will go into an orbit that will take it to within 5000km of Jupiter's cloud tops and then out over 2 million km. The planned orbit ducks under Jupiter's radiation belts, sparing the craft from the worst effects.

Above: Jupiter, seen by Hubble in infra red light. That heat-glow isn't reflected from the Sun: Something inside Jupiter is still producing energy..... Courtesy of,
The mission will last for one Earth year, and will take in 32 polar orbits of old Jove - a time limit not based on money, but on how, even with the radiation belts avoided and it's main computer shielded, the probe will slowly be eaten away by the radiation.  
Then Juno will be crashed into Jupiter's atmosphere, meeting its end as a flash of plasma. To leave it floating out there would pose a risk of contaminating one of Jupiter's moons with Earth life - a viking funeral for an armoured spacecraft.

The Science:

JUNO's official science objectives are...
  • Measuring the abundance of water in Jupiter, which will help distinguish among prevailing theories linking the gas giant's formation to the Solar System.
  • Measure Jupiter's core mass, which will also help distinguish among prevailing theories linking the gas giant's formation to the Solar System.
  • Map Jupiter's gravitational field to assess the distribution of mass in Jupiter's interior.
  • Precisely map Jupiter's magnetic field to assess the origin and structure of the field and help scientists understand the fundamental physics of dynamo theory.
  • Map the variation in atmospheric composition, temperature, structure, cloud opacity and dynamics to pressures far greater than 100 bars at all latitudes.
  • Explore the three-dimensional structure of Jupiter's polar magnetosphere and its auroras.
  • Measure the orbital frame-dragging, known also as Lense–Thirring precession caused by the angular momentum of Jupiter, and test general relativity effects connected with the Jovian rotation.

The ship:

Above: Double click to see this full sized infographic of Juno, courtesy of NASA.
Juno is built around a radiation hardened hexagonal core, which houses the craft's brain - even though the orbit has been chosen to avoid Jupiter's radiation belts there's  still a lot of high energy particles in Jovian space. Surrounding the core are the sensors and three sets of solar panels -  50% more efficient and radiation resistant than old silicon based designs, which has allowed Juno to break the record for furthest solar powered spacecraft from the Sun. The fore face of the core has the main antenna, which also performs gravity science experiments.
The probes odd shape is partly because Juno is spin stabilised, so it needs to be highly symmetrical along the axis of the spin. The sensors this huge (each solar panel alone is over eight meters long) probe carries are:
  • A gravity/radio science system (Gravity Science)
  • A six-wavelength microwave radiometer for atmospheric sounding and composition (MWR)
  • A vector magnetometer (MAG)
  • Plasma and energetic particle detectors (JADE and JEDI)
  • A radio/plasma wave experiment (Waves)
  • An ultraviolet imager/spectrometer (UVS)
  • An infrared imager/spectrometer (JIRAM)
  • A color camera, called JunoCam, to provide the public with the first detailed glimpse of Jupiter's poles
Juno's engines are simple chemical rockets, and a set of hydrazine RCS navigation thrusters - it's all designed to be simple, robust, and work in one of the most dangerous stretches of space in our solar system

I think that covers the basics - so all that remains is to say: Good luck JUNO, and good luck to her ground control team!

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