Aug 15th 2025
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NASA is seriously considering one of the most ambitious planetary missions ever conceived: a spacecraft that would orbit Pluto for years, searching for signs of a hidden ocean that might harbor life. The proposed mission, called Persephone, would represent a dramatic leap beyond the historic New Horizons flyby that captivated the world in 2015.
A Mission of Unprecedented Duration
During a recent episode of This Week in Space, hosts Rod Pyle and Tariq Malik discussed the extraordinary scope of the Persephone mission. As Pyle explained, this wouldn't be a quick visit like its predecessor. "Unlike its predecessor, New Horizons, however, which is a quick flyby, Persephone would go into orbit around Pluto for about three years, which means they can map the entire planet," he noted.
The mission timeline is staggering by any measure. The spacecraft would take 27 years just to reach Pluto, making it the longest planned travel time for any NASA mission. Combined with the three-year orbital mission and potential extended operations, Persephone could operate for up to 50 years total.
The Hunt for Pluto's Hidden Ocean
What makes this lengthy journey worthwhile? Scientists believe Pluto may harbor one of the solar system's most surprising secrets: a subsurface ocean. The gravitational dance between Pluto and its large moon Charon creates tidal forces that could keep liquid water from freezing solid beneath the dwarf planet's icy crust.
"One of the key targets they have is to determine if there's possibly a warm subsurface surface ocean on Pluto, as we found on so many moons in the solar system," Pyle explained during the podcast discussion. The evidence is already intriguing. Observations from New Horizons revealed a planetary bulge that could indicate liquid beneath the surface, along with surprisingly light cratering that suggests ongoing geological activity.
This geological dynamism could result from cryovolcanoes—ice volcanoes that shoot liquid up through the crust, constantly reshaping Pluto's surface. Such activity would be impossible without some form of subsurface liquid reservoir.
Building on New Horizons' Success
The New Horizons mission transformed our understanding of Pluto when it flew by the distant world in July 2015. Malik reflected on the mission's impact, recalling "being in the audience when they unveiled that first photo from the flyby, the first close-up one. And on Instagram no less."
That historic flyby provided humanity's first detailed look at Pluto's complex surface features, including vast plains, towering mountains, and evidence of active geology. But a flyby, no matter how successful, provides only a snapshot. An orbiter would allow scientists to study seasonal changes, map the entire surface in detail, and conduct long-term monitoring of any geological activity.
As Malik noted, the mission would provide crucial baseline data: "you have like you mentioned earlier, that baseline now, you know, being Pluto being explored from 2015 from the flyby, all the photos, the maps, the new areas that we have close up imagery of, then you can compare how that changes and evolves over time."
Technical Challenges and Power Requirements
The Persephone mission faces significant technical hurdles, particularly regarding power generation. The spacecraft would require five Radioisotope Thermoelectric Generators (RTGs) to operate in the frigid outer solar system, where solar panels would be useless. As Pyle pointed out, "we don't [have] that much plutonium" to power such an ambitious mission.
This power requirement highlights one of the ongoing challenges in outer solar system exploration: the need for nuclear power sources and the limited supply of plutonium-238 needed to fuel them. The mission would essentially require the entire current U.S. stockpile of space-grade plutonium.
Extended Mission Possibilities
Like many successful NASA missions, Persephone could potentially continue operating beyond its primary objectives. The spacecraft might explore Kuiper Belt Objects after completing its Pluto studies, similar to how New Horizons continued to the object Arrokoth after its primary mission.
Malik expressed enthusiasm for this possibility, suggesting the orbiter "feels like if you have a spacecraft in orbit around Pluto that is now a bit something that you could repurpose to look a little bit deeper into the outer solar system too as like a station when it's not busy doing reconnaissance work on Pluto and its five moons."
The Long Road to Approval
Despite the scientific excitement, Persephone faces the same funding challenges that plague many ambitious NASA missions. As Pyle noted, "keeping funding for anything for a decade is hard enough" - and this mission would require funding commitment for potentially five decades.
The mission represents the kind of long-term thinking that characterized the golden age of planetary exploration, when missions like Voyager were designed with extended operations in mind. Whether modern funding cycles can support such ambitious timelines remains to be seen.
The Persephone mission would cap off humanity's initial reconnaissance of the solar system, providing detailed study of the last major world beyond Neptune. If approved and successfully launched, it would stand as one of NASA's most ambitious undertakings, potentially revealing whether life-sustaining conditions exist in the most unexpected corners of our solar system.
For now, Persephone remains a compelling concept that highlights both our growing understanding of Pluto's complexity and our technological capability to mount increasingly sophisticated missions to the outer reaches of the solar system.
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