Suppose a spacecraft already in Jupiter orbit could be reused to pursue an interstellar visitor? That is the question behind a daring plan to send NASA’s Juno spacecraft on a course for 3I/ATLAS, the third known interstellar object to visit our Solar System, with one of the most economical deep-space maneuvers in orbital physics the Jupiter Oberth Maneuver.
3I/ATLAS, which was found on July 1, 2025 by the Asteroid Terrestrial-impact Last Alert System in Chile, has a hyperbolic path that will have it approach within 53.6 million kilometers of Jupiter on March 16, 2026. It is traveling at about 210,000 kilometers per hour, the record for the quickest inbound speed of a Solar System visitor. This speed, together with its estimated size observations by Hubble Space Telescope limit its nucleus to under 2.8 kilometers in diameter renders it an extremely elusive target for detailed investigation.
The proposal, brainstormed by Harvard astrophysicist Abraham Loeb with Adam Hibberd and Adam Crowl of the Initiative for Interstellar Studies, relies on leveraging Jupiter’s gigantic gravity well. During an Oberth Maneuver, a space vessel fires its engines at periapsis, when it is moving fastest in its orbit, thereby achieving greatest energy acquired from a specific change in velocity (∆V). For Juno, the best chain of events would be a ∆V burn on Sept. 9, 2025 eight days ahead of its originally scheduled deorbit into Jupiter’s atmosphere to decrease its altitude, then a follow-up burn at point of closest approach to Jupiter. This two-step maneuver can provide the 2.675 km/s change in velocity required to set Juno on an intercept course with 3I/ATLAS.
Determining such a trajectory needed sophisticated mission design software. Hibberd’s Optimum Interplanetary Trajectory Software (OITS) was used to solve the Lambert problem for Juno and 3I/ATLAS positions and velocities, iterating to determine the minimum ∆V solution. Further modeling using NASA’s SPICE toolkit and the NOMAD nonlinear solver combined motions of Jupiter, Juno, and the comet, further refining intercept geometry. The payoff: a viable flyby mission that bypasses the infeasibility of sending a new spacecraft on short notice a hurdle made greater by the comet’s late discovery and high speed.
If it goes forward, Juno’s entire complement of instruments would be available. Its near-infrared spectrometer would be able to map surface chemistry; the magnetometer and radio/plasma wave sensors would be able to sense any natural magnetic field or plasma surround; the microwave radiometer would be able to sound under the surface; and its UV and visible-light imagers would be able to obtain high-resolution images of the coma and nucleus. Such in situ measurements would dwarf anything Earth-based or even space telescopes could do for an object of this size and speed.
The scientific gamble is considerable. Observing an interstellar object close up provides a direct sample of material from outside the Solar System, possibly showing the chemistry, mineralogy, and structural properties of small bodies created elsewhere around another star. Loeb and coauthors have also flirted gingerly with the more out-of-the-box hypothesis that 3I/ATLAS might be an artificial probe. “Our paper is contingent on a remarkable but testable hypothesis that 3I/ATLAS is a functioning technological artifact, to which I and my two co-authors do not necessarily ascribe,” Loeb said. This hypothesis deserves scientific analysis because its consequences could be dire for humanity—and it’s also an intriguing idea to explore.
Although recent Hubble images displaying a dust plume and coma morphology typical of natural comets might undermine the artificial-object argument, the encounter would still yield unprecedented knowledge about the dynamics and composition of an interstellar body. The comet’s calculated birthplace in the Milky Way thick disk, and its age of 3 to 11 billion years, add to the mystery, providing a time capsule from a stellar population infrequently sampled.
The Juno intercept mission proposal also makes a larger point in mission design: current spacecraft, when opportunistically repurposed, can catch passing opportunities to investigate transient events. As the next Vera C. Rubin Observatory starts to detect interstellar objects at much higher rates, such tactics potentially supplemented by rapid-response engines such as directed-energy-driven lightsails may allow humanity to observe these visitors from other worlds before they fade back into the void.
