By Kurtis Archer | 2025-09-29

Since NASA's Juno probe concluded its primary mission in 2021, its extended mission has continued to explore our solar system's largest planet and send back data for scientific study. But not for much longer.

The Juno probe's work will finally come to an end after September, with the spacecraft slated to descend into Jupiter’s atmosphere in its final moments.

Leaving Earth in 2011 for the 1.7 billion mile journey to Jupiter, the Juno mission began traveling around the gas giant in a polar orbit in 2016.

Though radiation was expected to corrode its instruments and electronics long ago, the fully functional spacecraft explored Jupiter well beyond expectations.

Jupiter's history as the first planet to form after the sun exploded into being fueled the mission, the project’s principal investigator Scott Bolton said in April.

"Everything about Jupiter is extreme," he said. "The planet is home to gigantic polar cyclones bigger than Australia, fierce jet streams, the most volcanic body in our solar system, the most powerful aurora, and the harshest radiation belts."

Colorful storms around the planet's poles bounce around and run into each other but do not dissipate, a phenomenon scientists are still trying to understand.

Rewriting textbooks

Juno's findings have forced virtually every textbook about Jupiter to be rewritten, Juno project scientist Steve Levin told Scientific American in August.

The probe's array of instruments measure different kinds of radiation within the planet. Measurements are even made of how Juno itself is affected by small changes in its gravity, giving scientists a view of the planet's inner workings.

As it conducts its studies, Juno slows down and speeds up due to Jupiter’s uneven mass and the differing strengths of gravitational pulls.

These changes in speed cause subtle shifts in the radio transmission wavelengths Juno is constantly sending back to Earth, which scientists can use to determine the inner structure of the planet.

By measuring the radiation and gravitational pull of Jupiter’s most famous storm, a rusty oval larger than Earth dubbed the Great Red Spot, Juno discovered the storm goes down into the atmosphere for over 300 miles.

The probe has helped scientists better understand storms in Jupiter’s atmosphere and how lightning could happen at high altitudes, and has deepened their knowledge of the planet’s asymmetrical magnetic field.

Reshaping understanding

Juno’s findings have led scientists to believe that deep within the mass of metallic hydrogen there is an innermost core, and likely not a solid one.

The core is "blending gradually into the surrounding layers" with the hydrogen and core material seemingly mingling, according to JPL researcher and Juno gravity experiment lead Ryan Park.

While Jupiter was forming it absorbed rocky and icy pieces of matter -- some as large as planets.

Juno discovered Jupiter has three to four times as many heavy elements as the sun. But these heavy elements are in the upper atmosphere and not at the core, contrary to the expectation that gravity would pull heavier materials down.

Scientists are baffled, as this doesn’t fit with any model for how planets form.

One theory is that a giant meteor might have crashed into a solid core, breaking it up and mixing it with the ocean of metallic hydrogen. But the physics of the planet’s workings are simply not yet understood.

Juno also provided new information about the Jovian moons Io, Europa, Ganymede, Callisto and Almathea, Big Think reported September 3.

The probe discovered the most powerful volcanic activity in the entire solar system while observing Io, and measured Europa to have the smoothest solid surface in the solar system.

Though a funding extension that would have enabled Juno to operate until 2028 has not been approved, two new missions are headed to Jupiter, with both scheduled to arrive in the early 2030s.

These are NASA's Europa Clipper and the European Space Agency's Jupiter Icy Moons Explorer (JUICE) missions.