High above Jupiter’s roiling clouds, three giant blades stretch out from a cylindrical, six-sided body. Some 66 feet (20 meters) wide, the Juno spacecraft is a dynamic engineering marvel, spinning to keep itself stable as it makes sweeping elliptical (oval-shaped) orbits around Jupiter. At their widest point, these carry Juno far from the giant planet and its moons, keeping it mostly clear of heavy radiation regions. But on closer passes, every 53 days, Juno cuts within 3,100 miles (5,000 kilometers) of Jupiter’s cloud tops. That’s when its formidable array of science instruments kicks in:
Microwave radiometer (MWR)
How it works: This instrument’s six antennas can see through Jupiter’s clouds — a talent the spacecraft’s namesake, Roman goddess Juno, is said to have possessed. It measures microwaves coming from deep within the planet’s atmosphere, penetrating to a depth of around 340 miles (550 kilometers).
How we use it: The microwave readings reveal what Jupiter’s atmosphere is made of, including ammonia, water (and thus oxygen, which is made of hydrogen and oxygen), as well as its temperature at multiple depths.
Gravity science experiment
How it works: Using a high-gain antenna and a radio transponder onboard, Juno pings NASA’s Deep Space Network in Goldstone, California, as it orbits Jupiter.
How we use it: Goldstone keeps track of subtle changes in the radio signals from Juno; these reveal shifts in Juno’s position caused by variations in Jupiter’s gravitational field. Mapping the bumps and troughs in this field can reveal important details of Jupiter’s interior structure.
Magnetometer experiment (MAG)
How it works: At the end of one of Juno’s three immense windmill-like arms — actually, its solar arrays — is a 13-foot (4-meter) boom carrying two instrument packages: sensors that measure Jupiter’s magnetic field.
How we use it: The sensors are building a 3D map of the magnetic field; the shape of this field tells scientists about the electrical “dynamo” at Jupiter’s heart — a highly charged mass of hydrogen so spectacularly compressed by the intense pressure that its core becomes metallic.
Jovian auroral distributions experiment (JADE)
How it works: As if clouds in rainbow colors, centuries-long cyclones and eerie flashes of lightning weren’t enough, Jupiter also has its own version of our planet’s northern lights — the auroras. To learn more about them, JADE has three sensors that measure electrons — negatively charged particles — and one that measures ions, or particles with either negative or positive electrical charge.
How we use it: In combination with other instruments onboard, these sensors can identify the particles that create the spectacular auroras, as well as revealing other processes involved. These sensors also help out with the mapping of Jupiter’s magnetic field, or magnetosphere.
Jupiter energetic-particle detector instrument (JEDI)
How it works: Jupiter is bombarded by high-energy particles, some that crash into its magnetic field and help create auroras in the giant planet’s northern and southern hemispheres. JEDI’s three sensors measure these.
How we use it: Together with other instruments like JADE, JEDI provides insight into the auroras and Jupiter’s intense magnetic field. JEDI helps determine the amount of energy the particles carry, their type and the direction in which they’re zipping around. JEDI also examines the processes by which the magnetic field interacts with the particles to dump energy into the planet’s atmosphere.
Jovian infrared auroral mapper (JIRAM)
How it works: JIRAM’s camera captures pictures in infrared light, on the red end of the light spectrum. An instrument called a spectrometer can split that light into a rainbow spectrum, which can be read like a bar-code to reveal which gases are present in Jupiter’s atmosphere.
How we use it: JIRAM peers beneath Jupiter’s cloud tops to measure concentrations of important gases, including water and ammonia, in its atmosphere. The instrument is also helping to map Jupiter’s auroras, and produces dazzling images of the planet's dynamic, glowing atmosphere at infrared wavelengths.
Ultraviolet imaging spectrograph (UVS)
How it works: This instrument will pitch in on measurement of Jupiter’s auroras as well, but in ultraviolet light.
How we use it: With JADE and JEDI, UVS helps further pin down the particles that smash into Jupiter’s atmosphere and how they create auroras; this will reveal further details of Jupiter’s magnetosphere.
How it works: Two Waves sensors will track radio waves as they pass through Jupiter’s magnetic field, as well as waves of plasma, a type of matter that is made entirely of charged particles.
How we use it: Keeping watch on these waves will help scientists puzzle out the way Jupiter’s atmosphere and magnetosphere interact. And, yes, this instrument too will study the auroras.
How it works: JunoCam takes pictures of Jupiter in color, and in the visible part of the light spectrum. Because Juno is spinning, it must take pictures in narrow strips that are later stitched together.
How we use it: JunoCam is responsible for the breath-taking, closeup images of Jupiter that Juno has been sending back since arriving in orbit. And what's more, most of those gorgeous images are processed by members of the public, rather than professional scientists. But while the camera was included for public engagement, it’s proving useful to scientists as well.