Far beyond the familiar planets, a spacecraft called New Horizons continues its solitary passage toward the edge of the Sun's domain — carrying instruments that no other human-made object can replicate at such distances. A gap of just two million dollars a year now threatens to silence those instruments before they can witness the most consequential boundaries of our solar neighborhood. In the long history of exploration, few moments have been lost simply because the cost of listening was deemed too high; scientists are now asking whether this will become one of them.
NASA Budget Cuts Threaten New Horizons' Heliospheric Science Mission
Only New Horizons can measure what comes next
Mark
So New Horizons is about to lose its ability to study the solar wind. How much of the mission does that actually represent?
Mimi
It's not the whole mission—planetary science continues. But heliospheric science has been running in parallel since launch, with equal priority. It's the continuous measurement of solar wind conditions across the entire solar system that's at stake.
Luke
Equal priority in theory, but the funding tells a different story. Planetary science gets $10 million a year. Heliophysics got $2 million until it stopped. That's not equal.
Mark
Why did the heliophysics funding stop?
Mimi
Budget cuts. The source doesn't specify where the cuts came from or why heliophysics was hit, just that the money stopped in 2024.
Luke
Right. We don't know if it was a deliberate choice to defund heliophysics or if it was a broader squeeze. That matters for understanding whether this is fixable.
Mark
What makes this moment critical?
Mimi
New Horizons is about to reach the termination shock in a couple of years, then the heliopause in about a decade. Those are the boundaries where the solar wind ends and interstellar space begins. No other spacecraft can measure those events.
Luke
The Voyagers measured them, but that was in the 1980s and 90s. New Horizons has newer instruments. But we should be clear: the science value is real, but it's also being advocated for by people with a stake in the mission.
Mark
Is there any chance the funding comes back?
Mimi
Scientists are circulating a petition. James Green, who ran planetary science at NASA, is pushing for it. He says NASA responds to community pressure.
Luke
That's true historically. But we don't know if this particular request will succeed, or how long the decision will take. October is coming fast.
Il Polso
- New Horizons' heliospheric instruments — SWAP and PEPSSI — face a hard shutdown in October 2026 after NASA's Heliophysics division stopped their $2M annual funding in 2024, leaving data piling up untransmitted on the spacecraft's recorders.
- The timing could not be worse: the probe is years away from crossing the termination shock and roughly a decade from the heliopause, the very boundaries that define where our Sun ends and interstellar space begins — crossings no other active mission can observe.
- Unlike the aging Voyager probes, New Horizons carries far more sophisticated sensors capable of painting a continuous, high-resolution portrait of solar wind from Earth's orbit all the way to the edge of the heliosphere — a dataset that would vanish with the instruments.
- The spacecraft itself remains funded at roughly $10M per year through Planetary Science, meaning the probe survives but its heliospheric eyes go blind — a bureaucratic boundary as stark as the physical one it is approaching.
- Heliophysicist James Green, backed by hundreds of scientists and a public petition on Change.org, is pressing NASA Administrator Isaacman to restore the funding, framing it as a small price for irreplaceable data from a spacecraft still capable of operating into the 2050s.
Far beyond the familiar planets, a spacecraft called New Horizons continues its solitary passage toward the edge of the Sun's domain — carrying instruments that no other human-made object can replicate at such distances. A gap of just two million dollars a year now threatens to silence those instruments before they can witness the most consequential boundaries of our solar neighborhood. In the long history of exploration, few moments have been lost simply because the cost of listening was deemed too high; scientists are now asking whether this will become one of them.
New Horizons has been traveling since its launch, studying Jupiter, Pluto, and the distant icy object Arrokoth before receiving two mission extensions that kept it scientifically productive. Now, as it pushes deeper into the outer solar system, a funding gap threatens to shut down the very instruments that make its current position so valuable.
The spacecraft carries two heliospheric sensors — SWAP and PEPSSI — more advanced than anything the Voyager probes carried. Together they have built a nearly unbroken record of solar wind conditions stretching from Earth to New Horizons' current location. Mission principal investigator Alan Stern calls this data stream irreplaceable: within a few years the probe will cross the termination shock, and within a decade the heliopause — the threshold of interstellar space. Only New Horizons can measure these transitions now, and only these two instruments can do it.
The financial reality is blunt. The $2 million per year that once covered heliospheric operations stopped in fiscal year 2024. The broader mission still receives about $10 million annually from NASA's Planetary Science division, but that money keeps the spacecraft alive and supports planetary work — not the heliospheric instruments. Without dedicated funding, the team cannot staff mission control year-round or process the backlog of data sitting on the spacecraft's recorders. Each year the gap widens.
Planetary scientist Fran Bagenal acknowledges that NASA's Heliophysics division is already stretched, supporting instruments closer to Earth that monitor space weather. But she argues New Horizons offers something those missions cannot: a continuous trace of the solar wind across the full span of the solar system. The data also carries implications beyond our own star — understanding how our heliosphere behaves at its boundaries helps scientists model the magnetic environments of distant stars and assess how those environments might affect the habitability of orbiting planets.
James Green, who led NASA's Planetary Science division for twelve years and served as the agency's chief scientist, is now circulating a petition on Change.org, already signed by several hundred scientists, asking NASA Administrator Isaacman to restore the $2 million annually. His argument is straightforward: the spacecraft will remain functional into the 2050s, the data it can gather is uniquely American, and the cost of letting that capability go dark is far greater than the cost of keeping it alive.
New Horizons woke from hibernation recently and began transmitting data again, continuing its long journey through the Kuiper Belt. The spacecraft has been working since its launch, studying Jupiter in 2007, Pluto in 2015, and the icy object Arrokoth in early 2019. Two mission extensions—one in 2016 and another in 2023—kept the probe active and productive. But now, budget cuts at NASA threaten to silence a crucial part of its work as early as October 2026.
The spacecraft carries two instruments designed to study the heliosphere, the vast bubble of solar wind and magnetic field that the Sun extends throughout the solar system. PEPSSI and SWAP are more advanced than anything the Voyager probes carried decades ago, and they have been collecting an almost continuous record of solar wind conditions from Earth all the way out to New Horizons' current position. According to mission principal investigator Alan Stern, this data stream is irreplaceable. In the next couple of years, New Horizons will pass through the heliosphere's termination shock—the boundary where the solar wind begins to slow. Within a decade, it will cross the heliopause, entering interstellar space. These are moments only New Horizons can measure now, and only these two instruments can do it.
The problem is money. Heliophysics funding for New Horizons has been $2 million per year, covering the cost of operating the instruments and transmitting their data back to Earth. That funding stopped in fiscal year 2024. The overall mission still receives support—about $10 million annually from NASA's Planetary Science division—but that money goes to keeping the spacecraft alive and managing its planetary science work. With no dedicated heliophysics budget, the team cannot afford to staff mission control year-round or process the heliospheric data. They have been forced to put the spacecraft into hibernation to save money, and data from PEPSSI and SWAP has been piling up on the spacecraft's recorders, waiting to be transmitted. Each year, more backlog accumulates. Each year, the team has asked for heliophysics funding to resume. Each year, it has not come.
Stern laid out the situation plainly: beginning in October, New Horizons will have to stop collecting heliospheric data entirely. The instruments will go silent unless someone finds $2 million per year to restart them. This is not a dispute between NASA divisions or a matter of competing priorities. It is simply that the budget cannot cover the operational costs anymore. Fran Bagenal, a planetary scientist on the New Horizons team, understands the broader squeeze. The Heliophysics division at NASA is stretched thin, funding instruments around Earth and at the L1 point that measure solar wind and space weather. But she argues the case for New Horizons is compelling. The spacecraft's newer instruments offer something unique: a continuous trace of the solar wind from the inner solar system all the way to the outer reaches, a measurement no other mission can provide.
What makes this loss particularly acute is timing. New Horizons is approaching the most scientifically valuable part of its journey. The termination shock and heliopause—the boundaries between the solar wind and interstellar space—have been measured by Voyager 1 and 2, but those measurements are decades old and limited. New Horizons' instruments are more sophisticated and could reveal these regions in far greater detail. Beyond that, the data has implications for understanding other stars. Every star has a magnetic field and likely planets around it. As stars move through interstellar clouds, they experience the same physics as our Sun. By understanding how our heliosphere works, scientists can better understand how the magnetic fields of distant stars—their astrospheres—affect the habitability of planets orbiting them.
James Green, a heliophysicist who spent twelve years leading NASA's Planetary Science division and two years as the agency's chief scientist, has become an advocate for restoring the funding. He notes that NASA does respond when the scientific community makes a clear case. He is circulating a public petition, already signed by several hundred scientists, urging NASA Administrator Isaacman to find the $2 million annually needed to keep PEPSSI and SWAP operational. The petition is open to public signatures on Change.org. Green's message is direct: this is a small investment for data that only the United States can gather, from a spacecraft that will remain functional through the 2050s. The choice facing NASA is whether to let that capability go dark.
Citazioni salienti
There is an almost continuous trace of data across the solar system from Earth outward from these instruments since launch. This data from SWAP and PEPSSI are the only chance we or anyone else will have to measure those events and then to study interstellar space after Voyager.— Alan Stern, New Horizons Principal Investigator
It seems absurd that we're focusing on trying to keep the money flowing to keep these instruments working when it's so obvious that we can keep getting heliophysics data at relatively small cost. This really ought to be dealt with by people at NASA to step in and say, we're NASA and only the United States can do this heliospheric science at the frontier of our solar system.— Fran Bagenal, New Horizons planetary scientist
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