A mission NASA might kill is still returning fascinating science from Jupiter

Background

NASA’s Juno spacecraft has been quietly transforming our picture of the Solar System’s biggest planet since it slipped into Jupiter orbit in 2016. Designed to probe the gas giant’s interior, atmosphere, magnetosphere, and origins, Juno carries a suite of instruments unusual for a Jovian orbiter: a microwave radiometer to sense deep atmospheric structure, a magnetometer to map the planet’s enormous magnetic field, plasma and radio instruments to listen to charged-particle activity, an infrared mapper to study heat and auroras, and a visible-light camera that—although conceived for public engagement—has proven scientifically useful for tracking cloud systems and storms.

Juno’s original prime mission has already been completed. Because the spacecraft and instruments remained healthy, NASA extended the mission to take advantage of a rare opportunity: flybys of the Galilean moons and high-value passes through different parts of Jupiter’s radiation environment that were never in the original plan. Since 2021, Juno has executed close passes by Ganymede and Europa and, more recently, a remarkable series of encounters with Io, the most volcanically active world in the Solar System.

Extended missions are where NASA often gets the best science per dollar. The expensive parts—launch, cruise, and initial checkout—are long behind, and operations are comparatively inexpensive. These extensions are typically vetted through a “Senior Review” process where panels rank scientific payoff against cost and risk. Yet that doesn’t immunize them against budget stress. On tight years, NASA has to choose between continuing a fleet of productive veterans and starting the next generation of missions.

That tension is acute now. NASA’s Science Mission Directorate, and especially the Planetary Science Division, has been squeezed by flat budgets, inflation, and large-ticket commitments such as Mars Sample Return. Leadership has been blunt in public briefings: if the budget remains constrained, even high-performing extended missions may be wound down. Juno is one of the names that keeps surfacing in those conversations.

What happened

In recent budget updates, NASA officials warned that the agency might not be able to sustain all operating missions at current levels. Among the candidates for early termination is Juno—despite the fact that it is still returning new and surprising results from the Jovian system. The message is essentially triage: start what the Decadal Survey says is next, keep flying the most critical assets, and prepare for the hard truth that “we can’t fund everything we’ve been doing.”

The timing is awkward because Juno remains in a sweet spot scientifically:

• Io up close: During recent close and near-close passes, Juno’s instruments have captured time-variable thermal hotspots across Io’s surface, revealing lava lakes fringed by thin crusts, reshaped caldera floors, and possible towering eruption plumes detected indirectly through their heat signatures and effects on the surrounding plasma environment. Io’s volcanic activity also pumps material into a donut-shaped cloud (the Io torus) that threads Jupiter’s magnetosphere; Juno has been mapping how that plasma feeds the planet’s spectacular auroras.

• Auroras in context: Juno’s polar orbit repeatedly dives over Jupiter’s auroral ovals, sampling the charged particles and radio emissions that drive curtains of light far larger than anything on Earth. By coordinating with Earth-based telescopes and space observatories, Juno has helped disentangle the roles of the solar wind, Jupiter’s fast rotation, and moon-derived plasma in powering the lights. The result is a more unified picture of how giant-planet magnetospheres work—knowledge we’ll carry to exoplanets bathed in even harsher fields.

• Deep weather and “mushballs”: The microwave radiometer has revealed that Jovian weather is not just skin-deep. Bands and zones extend hundreds of kilometers down, and localized storm systems appear to ferry ammonia and water deep into the atmosphere, where they may form slushy hail—so-called ammonia “mushballs.” These processes help explain puzzling depletions of ammonia at cloud tops and offer a laboratory for understanding gas-giant meteorology in general.

• Interior structure: Gravity and magnetic-field measurements suggest Jupiter’s core is not a compact, rocky nugget but a diffuse, heavy-element-rich region spread over a substantial fraction of the planet’s radius. That “dilute core” reshapes theories of giant planet formation—perhaps hinting that early collisions or long-term mixing blurred what began as a sharp boundary.

• Rings and environment: Juno’s instruments have probed the faint ring system and its interaction with the planet’s magnetic and plasma environment, adding pieces to the puzzle of how micrometeoroid impacts on small moons feed dusty rings and how “ring rain” may drizzle into the upper atmosphere.

These are not stale rehashes of early findings. They are ongoing, incremental advances that rely on repeated passes through changing conditions: different longitudes and latitudes, different solar-wind states, and different phases of Io’s restless eruptions. Terminating Juno now would end a unique time series—one that spans a larger fraction of the solar cycle and a broader range of Jovian “weather” than any mission before it.

Why target a productive mission? Because the line that pays to fly extended missions is finite. If big programs slip or inflation erodes buying power, managers start trading: continue an older mission for another year, or preserve funds to ramp up new starts mandated by the planetary decadal plan. Even a relatively lean operations budget—tens of millions per year for a mission like Juno—becomes a tempting pot when the books don’t balance.

Key takeaways

• Juno is still scientifically vibrant. From Io’s lava lakes to deep atmospheric dynamics and auroral physics, the spacecraft keeps delivering firsts and filling gaps in our understanding of giant planets.

• Extended missions offer exceptional value. The cost to keep Juno operating is a small fraction of its original price tag, yet its recent data may prove as influential as anything from its prime mission.

• Budget pressure is real. NASA’s planetary program is juggling marquee commitments alongside operations of many veteran missions. Without relief from Congress or internal rebalancing, some extended missions will end earlier than scientists would prefer.

• Timing matters. Juno’s current orbital geometry and recent close interactions with Io create a high-payoff window that won’t recur soon. Ending the mission now would forfeit comparative, multi-pass coverage of phenomena that change on weeks-to-years timescales.

• The next Jovian missions won’t fully replace Juno. Europa Clipper (arrival early 2030s) will revolutionize our view of Europa, and ESA’s JUICE will ultimately orbit Ganymede. Neither will occupy a long-lived, polar orbit around Jupiter itself, nor will they frequently sample the auroral regions and inner magnetosphere in the same way Juno has.

What to watch next

• The budget calendar. The President’s budget request is only the opening bid. House and Senate appropriators will set the real numbers in the months ahead. In recent years, Congress has sometimes restored funding for extended missions after the science community and the public made their case. Watch the appropriations subcommittees that oversee NASA for language about “extended mission operations.”

• NASA’s internal reviews. The agency’s Senior Review process scores extended missions on science per dollar. If NASA is forced to prioritize, this process will guide decisions. Expect a staged plan: reduced operations tempo first, then a formal closeout timeline if cuts deepen.

• Juno’s radiation clock. The longer a spacecraft loiters in Jupiter’s harsh environment, the more it accumulates damage. So far, Juno has weathered the storm impressively thanks to shielding and careful navigation, but risk ratchets up with time. If a graceful end-of-mission is coming, engineers will want to plan it before failures cascade.

• Science milestones still ahead. If funding holds even briefly, Juno could complete additional targeted passes that round out its Io campaign, sample different auroral longitudes, and fill in remaining gaps in deep-atmosphere microwave coverage. Coordinated campaigns with ground-based observatories during solar maximum could be especially rich.

• Handshakes with the next generation. As Europa Clipper and JUICE approach Jupiter in the next decade, there is value in a continuous thread of context measurements—how the magnetosphere breathes, how Io’s output waxes and wanes, what “weather regimes” dominate. If Juno can bridge even part of that gap, it reduces risk and sharpens planning for the newcomers.

FAQ

• Why consider ending Juno if it’s still productive?

  • Because NASA’s planetary program is working within a flat-to-declining real budget while shouldering major commitments. Extended missions are often the least painful place to cut in the short term, even when they’re delivering strong science.

• How much does it cost to keep Juno going?

  • NASA doesn’t publish a single fixed number, but extended deep-space missions typically run in the ballpark of tens of millions of dollars per year for operations, data processing, and science analysis. That’s a fraction of development costs but still significant when budgets are tight.

• Will Europa Clipper or JUICE replace what Juno does?

  • Not directly. Clipper will fly dozens of close passes by Europa to study its habitability. JUICE will focus on Ganymede and the outer system. Juno’s polar sampling of Jupiter’s auroras, inner magnetosphere, and deep atmosphere is unique and complementary.

• What happens to Juno if funding ends?

  • NASA would execute an end-of-mission plan that safely disposes of the spacecraft—typically a controlled descent into Jupiter to minimize any long-term risk of contaminating the Galilean moons, consistent with planetary protection guidelines.

• Is JunoCam just for pretty pictures?

  • It began as a public-engagement camera, but the mission team and the wider community have extracted serious science from its images: tracking cloud morphology, wind shears, and storm evolution, especially at high latitudes difficult to study from Earth.

• Can public support make a difference?

  • The science community often engages Congress during appropriations season to explain the value of extended missions. Public interest can help by keeping attention on the scientific return and the relatively low cost of continued operations.

Why it matters

The choice facing NASA is not simply about one spacecraft but about how we steward a diverse, aging, and still remarkably capable fleet. Juno illustrates the upside of patience: let a well-built explorer linger in a dynamic system, and it will keep catching nature in the act. Cut it too soon, and we lose a living record of change at a world that anchors our understanding of giant planets—from the storms that churn its atmosphere to the volcanoes that electrify its skies.

Source & original reading: https://arstechnica.com/space/2026/03/a-mission-nasa-might-kill-is-still-returning-fascinating-science-from-jupiter/