Could Arjuna 2025 PN7 Be the Lost Soviet Probe Zond‑1—or Its Rocket Stage?

Scientists Suggest Earth‑near Object Might Be Cold War Space Debris

What you’ll learn: Arjuna 2025 PN7, long classified as a faint asteroid in an Earth‑like orbit, has characteristics that match trajectory models for the Soviet Venus probe Zond‑1 (launched April 1964). Spectroscopy and follow‑up observations could confirm whether the object is manufactured hardware or a natural rock.

Arjuna 2025 PN7—named for the population of small bodies in the so‑called Arjuna belt—was first detected by the Pan‑STARRS survey in 2014 but remained essentially unnoticed until recent analyses highlighted its unusual orbit. The Arjuna population contains more than a hundred small objects that share Earth‑like, quasi‑satellite trajectories: they remain near Earth while following heliocentric orbits rather than being gravitationally captured mini‑moons.

In a study recently submitted for publication, Harvard astrophysicist Avi Loeb and colleague Adam Hibberd note that a quasi‑satellite’s orbital period is close to one year, explaining the object’s prolonged proximity to Earth despite orbiting the Sun. Using interplanetary trajectory models for 1960s‑era missions, Hibberd identified the failed Soviet Venus probe Zond‑1 as the most plausible historical candidate associated with 2025 PN7.

Why Zond‑1?

Zond‑1 was launched in April 1964 and experienced multiple problems en route to Venus, including engine burns, course corrections, communication glitches and depressurization of its orbital compartment. Hibberd’s reconstructions show that 2025 PN7 entered a quasi‑satellite configuration around the same time Zond‑1 was launched, and the modeled heliocentric longitude evolution for the probe’s intended path resembles the inferred path for 2025 PN7. The two objects also have comparable apparent brightness, making the probe hypothesis plausible.

“For every such trajectory, the spacecraft positions and velocities were compared against those of 2025 PN7, in order to ascertain whether this object could be associated with the mission in question,” Loeb and Hibberd write.

What would prove the link?

The definitive test is spectroscopy. Measuring the object’s reflected light spectrum could identify metallic or painted surfaces and other signatures of manufactured materials, distinguishing them from ordinary asteroid rock. Radar observations, high‑precision astrometry and comparison with archival launch telemetry and mission records would strengthen or weaken the Zond‑1 association.

One complication is that some reconstructions predict a different perihelion (closest approach to the Sun) than what 2025 PN7 has been observed to achieve, so the identification is not straightforward. Loeb and Hibberd emphasize caution: they are skeptical but argue the hypothesis is testable and worth follow‑up—if not the probe itself, the object could be a discarded upper stage or other jettisoned hardware from the mission.

Broader context

The proposal joins other debates over strange visitors to the inner solar system—objects such as ʻOumuamua whose nature remains uncertain—and highlights how historical space missions can leave detectable technosignatures in near‑Earth space. While the Zond‑1 link remains unproven, it provides a concrete, falsifiable hypothesis that can be resolved with targeted observations.

Next steps: obtain high‑signal spectroscopic and radar data during the object’s next favorable apparition, refine dynamical models including non‑gravitational forces (e.g., solar radiation pressure), and compare results with hardware signatures from archived Soviet engineering documents.