Hubble and Juno: Tag-Teaming Jupiter's Auroras

The Juno spacecraft is getting an up-close look at Jupiter’s powerful auroras, but it can’t see the whole picture. Scientists are using the Hubble Space Telescope to provide the wide-angle view, creating a cosmic tag-team to unlock the secrets of the gas giant’s magnetic storms.

In 2016, the NASA Juno mission arrived at Jupiter with a specific goal: to fly over the planet’s poles and understand its spectacular auroras. Juno is equipped to do something incredible – measure the energetic particles raining down into the atmosphere while simultaneously seeing the auroral light they create. This is like catching the rain and seeing the puddle form at the same exact time. However, there’s a big problem. Juno’s prime science time happens in a frantic, 6-hour window during its closest approach. For the rest of its two-week orbit, its view is limited. Scientists realized that without knowing what the *entire* aurora was doing before, during, and after this flyby, Juno’s data would be like a single puzzle piece with no box. This led to a proposal for a ‘Juno Initiative’, a plan to use the Hubble Space Telescope as Juno’s essential partner in the sky.

Read about the Hubble-Juno collaboration on NASA’s official site

It is of extreme importance that HST captures as much additional information as possible on Jupiter’s UV aurora.
— Denis Grodent, Lead Author

Imagine you’re a detective investigating a huge, city-wide blackout. The Juno spacecraft is like your agent on the ground, right at the power station, measuring the voltage spikes and seeing which specific wires are sparking. This data is incredibly detailed but tells you nothing about what’s happening in the rest of the city. The Hubble Space Telescope is like your eye in the sky, a satellite showing you a map of the entire city’s power grid. Hubble can see which neighborhoods went dark first and how the blackout spread over time. By combining Juno’s on-the-ground details with Hubble’s city-wide overview, you can finally understand the full story. Hubble provides the crucial global context, showing whether Jupiter’s auroras are having a calm day or are in the middle of a planet-wide magnetic storm while Juno makes its precise local measurements.

The HST UV instruments can greatly contribute to the success of the Juno mission by providing key complementary views.
— The Juno Initiative White Paper

Here on Earth, our beautiful auroras are primarily caused by the solar wind, a stream of particles from the Sun, interacting with our planet’s magnetic field. Jupiter’s auroras are a different beast entirely. While the solar wind plays a role, Jupiter’s light show is mainly powered by its own ridiculously fast rotation—one day on Jupiter is less than 10 hours long! This rapid spin drags its enormous magnetic field through space, scooping up particles from its volcanic moon Io and slinging them into its atmosphere. This makes Jupiter a colossal ‘aurora factory’. Studying this system with both Juno and Hubble helps us understand the fundamental physics of magnetospheres. It teaches us how these invisible magnetic bubbles around planets work, protecting them from space radiation and creating the most spectacular light shows in the solar system, providing clues to how similar processes work around distant stars and exotic cosmic objects.

This research wasn’t a discovery, but a crucial proposal to make discoveries possible. The authors argued that the panel reviewing telescope time should create a special category for ‘NASA Juno Mission Support’. This would set aside a large number of Hubble’s orbits specifically for Jupiter observations, ensuring the team-up could happen. The plan involved coordinating Hubble’s STIS and ACS instruments, which see in ultraviolet light (the main wavelength of Jupiter’s aurora), with Juno’s close flybys. For the first time, this would allow for simultaneous views of both the northern and southern auroras—with Hubble watching one pole while Juno flies over the other. This coordinated campaign is a masterclass in mission planning, turning two separate observatories into one powerful, planet-studying machine to solve the long-standing mysteries of Jupiter’s auroras.

We recommend that a category of HST time be allocated specifically for ‘NASA Juno Mission Support’ … a ‘Juno initiative’.
— Grodent et al.

Q: Why can’t Juno just look at the whole aurora?
A: When Juno is close enough to make detailed measurements, it’s too close to see the entire aurora at once. It’s like trying to take a picture of a whole football stadium while standing on the field – you can only see the seats right in front of you. Hubble provides the view from the Goodyear blimp.

Q: Are Jupiter’s auroras like the Northern Lights?
A: Yes and no. They are created by similar physics—charged particles hitting an atmosphere in a magnetic field. But Jupiter’s are permanent, thousands of times bigger than Earth itself, and hundreds of times more powerful. They also glow brightest in ultraviolet light, which is invisible to our naked eyes.

Q: What can we learn from seeing both poles at once?
A: It helps scientists test their models of Jupiter’s magnetic field. They can see if an event at the north pole, like a sudden brightening, has an immediate and matching effect at the south pole. This reveals how the two poles are connected through the deep interior of the planet.

Q: Why is Juno’s main mission only one year long?
A: Jupiter is surrounded by intense radiation belts that are deadly to spacecraft electronics. Juno’s orbit is designed to minimize its time in the harshest regions, but the cumulative damage will eventually cause the spacecraft to fail. The nominal mission was designed to get the most critical science done before that happens.