Fluxgate Magnets, Gravity Science and LEGO: A look into the things on board NASA’s Juno

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Artist’s rendering of the invisible lines of Jupiter’s magnetic field. Credit: NASA//JPL-Caltech

JUNO ORBITS JUPITER. After a five-year journey through space, NASA’s space-probe Juno arrived last week at planet Jupiter, the gas-giant, the largest planet in our solar system.

NASA’s Mission Juno surveys the northern and southern lights of Jupiter, the planet’s magnetic field, radiation, as well as the secrets that lie beneath Jupiter’s thick swirl of milky orange clouds.

“Today, there remain major unanswered questions about this giant planet and the origins of our solar system hidden beneath the clouds and massive storms of Jupiter’s upper atmosphere,” says the team behind NASA’s Mission Juno.

“An understanding of the origin and evolution of Jupiter, as the archetype of giant planets, can provide the knowledge needed to help us understand the origin of our solar system and planetary systems around other stars.”

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Juno’s Science Instruments. Credit: NASA

Juno gets its name from Roman mythology. Jupiter, king of the gods—the Roman’s version of Zeus, with all the same thunder and with an appetite for debauchery. Jupiter was known to be unfaithful to his wife, Juno. One evening he’s getting cosy with Io, the fair and beautiful river nymph, so he summons up a bit of cloud cover to keep the mischief just between them. But nothing gets past Juno.

Half as saucy, NASA’s Juno story is just as exciting. The spacecraft Juno has eyes to pierce the clouds of Jupiter, instruments that rival the clairvoyance of a Roman god. The science gets pulpy, but we’ve squeezed the juice for you.

Here’s a look into some of the equipment (and passengers!) aboard Juno:

The Magnetometer

Two of them, actually. Two “fluxgate magnetometers” are mounted on the end of a specialised boom, which is the triangular frame you can see attached to the end of one of Juno’s three solar panels. Inside the fluxgate magnetometers is a specialised, highly sensitive magnetic compass. But what does a spinning compass on a spinning Juno achieve?

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Technicians test Juno’s solar arrays in preparation for launch at NASA’s Kennedy Space Center. Credit: NASA

First, think of Jupiter itself as an enormous magnet. Of the eight planets in our solar system Jupiter has a magnetic field that is by far the most powerful. Scientists believe this may have something to do with the element hydrogen.

Jupiter, the gas-giant, is mostly made up of hydrogen—the lightest of all elements, a colourless, odourless, tasteless, nontoxic but highly flammable gas. Hydrogen is in fact the most abundant element in the universe. It’s probably too the first element to ever exist, long before the fusion reactions inside stars were able to create the heavier elements that make up you and me (yes, we are made up of the remnants of dead stars).

Far down in the depths of Jupiter, the pressure isn’t enough to elicit a fusion reaction, but it is enough to condense hydrogen down into a dense liquid state known as “metallic hydrogen”. At such tremendous pressures, these oceans of metallic hydrogen act as enormous electrical conductors running through the interior of the planet. This is thought to be responsible for Jupiter’s magnetic field, as well as its bright polar auroras.

From the sun, electrical solar winds blow out across space, and they eddy and curl against the intense magnetism of Jupiter. As charged particles precipitate down into the Jovian atmosphere, the polar regions are lit up with the brightest ribbons of aurora in our solar system.


This image combines an image taken with the NASA/ESA Hubble Space Telescope in the optical, and observations of the Jovian aurora in the ultraviolet. Credit: NASA/ESA

Two devices, the Jovian Aural Distributions Experiment and the Jovian Energetic Particle Detector Instrument (or, the JADE and the JEDI), can witness the aurora of Jupiter in ultraviolet light.

But the Magnetometer sees deeper. Inside this device runs a stream of particles called electrons. The electrons twist and jiggle against the magnetic lines of Jupiter and from these patterns scientists can begin to deduce and map out the planet’s metallic hydrogen innards.

Even on Earth there’s still much we don’t know about aurora and the magnetic field of planets. But because Jupiter lacks a rocky crust or continents that complicate the picture as they do on Earth, Juno’s observations could be the most detailed look we’ve ever had at such effects.

Gravity Science—or the ‘GS’

Simply, the GS device broadcasts radio waves back to Earth. With some clever thinking and fiddly physics, a radio broadcast can actually sense for varying regions of mass beneath Jupiter’s atmosphere. The way this works is indeed fiddly, but it is bloody fascinating.

Scientists believe that beneath the gaseous atmosphere there may be patches of higher or lower density—such as that of liquids and solids. Varying density across the planet would make the gravitational pull of Jupiter slightly uneven. And wobbly gravity will in turn have an ever so slight effect on the velocity of Juno’s orbit.

Juno broadcasts radio waves back to Earth. These radio waves will actually vary in frequency depending on the spacecraft’s speed.

You may have heard of the Doppler effect—if not, chances are you’ve experienced it in everyday life. Say you’re standing on the side of the road: a car approaches and as it does the sound, as well as becoming louder, will also increase in pitch—“vvvRRR…”

Then as soon as the car has passed the sound drops to a lower frequency, “…rruhhmmm”


The Doppler effect: Sound waves compress as their source, the car, moves towards Jim, resulting in a higher frequency sound. As the car moves away from Annie, the sound waves dilate, resulting in a lower frequency sound.

Sound, as you may know, travels in waves. What’s happening here is that the wavelengths of sound squeeze in tighter as the source they’re coming from hurtles forward towards your ear. When the source passes, the sound waves are dragged off and stretched out. Larger wavelengths means less frequent wavelengths. And less frequent wavelengths means a lower frequency.

Radio waves, which are actually a form of unseeable light, work in the same way. The minute dilations and contractions of these waves coming from Juno implies changes in its speed, which implies changes in Jupiter’s gravity, from which scientists can deduce inconsistencies in planetary mass.

Lego passengers

There are several other scientific instruments on board Juno, each with their own flavour and means of probing the gas-giant. Juno is a feat in science, certainly. For many of us, including the scientists, the sentimental value of getting to know another planet in our solar neighbourhood is just as strong.

So what would the trip be without passengers! Yes, across space and all the way to Jupiter, Juno has carried with it three beautiful Lego people. They’re made from tough-knitted aluminium, to survive Jupiter’s fierce radiation.

The touch of Lego is part a joint outreach and educational program developed as part of the partnership between NASA and the LEGO Group to inspire children to explore science, technology, engineering and mathematics.
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The Juno LEGO figures, from left to right: Galileo, Juno and Jupiter. Credit: NASA/JPL-Caltech/LEGO

The Lego people on board are to the likeness of the Roman god Jupiter, god of the sky, storms and thunder; of Juno, with her magnifying glass, whose insight will lead us into the depths of understanding Jupiter and the creation of planets; and Galileo Galilei, the Italian scientist, persecuted by the Catholic Church until his death, but from whose work bloomed modern physics and observational astronomy. Albert Einstein called him the father of modern science. Galileo was overjoyed when he discovered that moons orbit Jupiter—named Io, Europa, Ganymede and Callisto—and he’d probably be very pleased that a Lego figure in his likeness orbits the planet today.

Scientists believe that beneath their icy crust, there many be oceans of flowing water inside these moons, bubbling against the volleys of volcanic activity. Heat and water happen to be the key ingredients of life. That’s why at the end of its mission, Juno is programmed to launch its rockets one last time—flying directly into the perilous storms of Jupiter, so that no stray biotic material from Earth might end up contaminating one of the potentially life-harbouring moons. Along with Juno and all its equipment, the Lego people will fall into the darkness of Jupiter, to be sliced apart and obliterated by the swells of millions of tonnes of pressure.

…or will they?

Perhaps they unclip their Lego legs just in time.

They’ve snuck on board a Lego hyperdrive—it clips perfectly to the fluxgate magnetometer. A solar panel reroutes power to the core of a carbonite Lego propellor. It spins and the hyperdrive ignites and they’re off, soaring upwards through the swirls these crewmembers in their new spacecraft, as the satellite Juno disappears into Jupiter, and they turn to wave goodbye. But they sail on. Travelling northward, sailing fast along the lick of a metallic hydrogen sea. They zigzag between the red lightning of a red storm and further and further they go. Way up to the northern lights, and there in pale Jupiter evening these blue-green beams blot through their Lego windshield to shine colours on aluminium faces, glowing in the dark under spells of strobic shadow through the flightroom portholes. Their ship glides through the colour. Onwards and into space. The Lego people look to the rings of Saturn. But still they fly further, catching the solar winds, past lonely Pluto and beyond. They leave our solar system and still they sail. The heat from the hyperdrive keeps them warm. The Lego people pass nebulas and blackholes, they reach distant galaxies, they pass planets of other humans and planets of Lego people. They travel lightyears and still they go on, reaching out into the mystic darkness as like the arm of a dreamer from her bed, reaching beyond space and further than distance can know, these Lego explorers all the way from Earth.

You can learn plenty more about Juno, the craft, the mission and the equipment on NASA’s official page.

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