Two leading space scientists propose redefining the outer boundary of the solar system out to 3.8 light-years, relying on measurements of the Milky Way’s gravitational field and dark matter, Space reported. Jim Green, former NASA chief scientist and past director of the space agency’s Planetary Science Division, and Ed Belbruno, a professor of mathematics at Yeshiva University and a senior research associate at Princeton University, outline the theory in the August 2026 issue of the magazine ROOM – the Space Journal of Asgardia.
The updated frontier places the solar system’s edge at roughly 241,000 astronomical units from the sun. Rather than a sharp physical wall, the researchers argue that the border is shaped by a complex interplay of forces, energies, and trajectories on a scale comparable to the separation between neighboring stars.
Gravitational Portals at Lagrange Points
The theory suggests that gravitationally stable Solar Lagrange points L1 and L2 act as a funnel or portal for interstellar visitors. Objects such as the comet 3I/ATLAS, which passed through the solar system in 2025, could use these regions to enter and potentially become trapped by the sun’s gravity.
“Discovering the solar-galactic center L1 location is important since slow moving objects that enter this region can be captured by our sun and become part of our solar system,” Green told Space. “Who knows if there may be a large captured rogue planet on its way into the solar system right now.”
Green is currently discussing potential observations with the New Horizons spacecraft team. The probe explored Pluto in 2015 and now operates in the outer heliosphere, where accumulated dust could help verify calculations regarding galactic dark matter.
Belbruno’s work builds upon weak stability boundary theory, which he first applied in 1987 to plot low-fuel lunar trajectories using ballistic capture. “Now, its application is substantially extended to ballistic capture into our solar system from interstellar space and in estimating the size of our solar system,” Belbruno told Space.
Searching for Advanced Technosignatures
The published article also raises questions about potential distant alien civilizations. The authors suggest that touring the galaxy via interstellar travel requires mastering gravity, utilizing portals created at Lagrange locations for navigation.
“Interstellar travel requires a mastery of gravity, which an advanced extraterrestrial civilization might use to tour the galaxy, using portals created at Lagrange points for leverage,” Green and Belbruno write. “Remaining at these locations, they could observe the life within a stellar system with essentially no energy expenditure, so perhaps we should be looking for large space stations at stellar L1 and L2 locations as a techno-signature of advanced intelligent life?”
Questions About Solar System Boundaries
How far does the newly proposed solar system boundary extend?
The revised frontier extends to nearly 3.8 light-years from the sun, or approximately 241,000 astronomical units, matching the scale of distances between neighboring stars.
What mechanisms could capture interstellar objects?
The theory points to gravitationally stable Solar Lagrange points L1 and L2 as potential portals that funnel slow-moving interstellar visitors into the solar system via ballistic capture.
Where was the new theory published?
Jim Green and Ed Belbruno published their findings in the August 2026 issue of ROOM – the Space Journal of Asgardia, drawing from a keynote lecture delivered at the Niels Bohr Institute in August 2025.
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