Interstellar objects are exceptional visitors: fragments of other planetary systems that fleetingly pass through our own and offer a unique opportunity to study material formed beyond the Sun. The discovery of 3I/ATLAS opened up precisely that possibility. Like others of its kind, it functions as a true cosmic “time capsule”: the object expels carbon dioxide and water vapor that could have formed billions of years ago. The problem is that it “arrived too late.” By the time astronomers managed to detect it in July 2024, the interstellar visitor was already inside Jupiter’s orbit and traveling at more than 60 kilometers per second. In October, it reached its closest approach to the Sun and has since been rapidly receding into deep space, leaving very little time to plan a direct mission from Earth. The challenge of reaching an interstellar comet: Even so, some scientists believe the opportunity is not entirely lost. And they propose a bold idea: it would still be technically possible to send a probe to observe it up close. It would be a risky bet, capable of testing the limits of space engineering, but one that, they say, could be worthwhile. According to a study led by Adam Hibberd of the Initiative for Interstellar Studies, along with Marshall Eubanks (Space Initiatives Inc.) and Andreas Hein (University of Luxembourg), there is still a theoretical window to intercept the object. The paper—available as a preprint on arXiv and submitted for publication in the Journal of the British Interplanetary Society—proposes launching a mission in 2035 that could reach 3I/ATLAS around 2085, according to Space.com. By then, the specialized publication adds, the comet would be more than 732 astronomical units from the Sun—that is, 732 times the distance between the Earth and our star—more than four times the distance Voyager 1 has traveled in almost 48 years. The 2035 date is not arbitrary:That year, the most favorable alignment between Earth, Jupiter, the Sun, and 3I/ATLAS would occur, minimizing propulsion requirements and total flight time.

Oberth Maneuver: The Key to a Record-Breaking Mission

The proposal is based on the so-called Oberth effect, formulated in 1929 by the Austro-Hungarian scientist Hermann Oberth. The principle is simple: the faster a spacecraft moves when it fires its engines, the greater the boost it gains. The trick is to use the Sun's gravity as a kind of catapult: the spacecraft would approach the star and accelerate at the closest point in its trajectory—perihelion—when its speed is at its maximum.

“Virtually all launches use the Oberth effect,” Eubanks explained to Space.com. “However, I can’t find any record of a direct maneuver like the one we’re proposing, with a major rocket burn at the closest point during a flyby,” he added. For comparison, Space.com points out that Voyager 1—the most distant human-made object—is currently about 170 astronomical units from the Sun after nearly half a century of travel; the 3I/ATLAS interception could occur at more than 700 AU from our star. Furthermore, the flight time would depend on the delta-V—the change in velocity—achieved during the solar maneuver. At 8.36 km/s, the interception would occur after about 50 years; if 10.36 km/s were reached, it could happen in 30 years. It wouldn't be an impossible leap: NASA's Dawn probe reached 11 km/s.

If it worked, the result would be a spacecraft reaching the highest speed ever achieved by a human-made object, "by a good margin," according to Eubanks.

Extreme technical challenges: solar heat and a complex trajectory

But getting so close to the Sun comes at a price. As the scientists explain in their study, the spacecraft would have to pass through perihelion at just 3.2 solar radii from the Sun's center and fire its engines at that critical point, enduring extreme temperatures.

For reference, the Parker Solar Probe has withstood temperatures between 1370 and 1400 °C on its heat shield during its approaches to the Sun, although it didn't get as close as the proposed mission would. To withstand similar conditions, the researchers suggest using a carbon composite heat shield with additional layers of aerogel.

The proposed trajectory is also counterintuitive. Instead of heading directly for the object, the spacecraft would first fly toward Jupiter for about a year. There, it would use the gas giant's gravity to slow down and redirect its trajectory toward the Sun; without that step, the spacecraft—which is already moving at Earth's orbital speed of about 30 km/s—would simply continue orbiting on a wide path.

Following this gravitational braking would come the solar approach and the Oberth maneuver. Unlike the Parker Solar Probe—which used multiple Venus flybys to adjust its trajectory—the mission to 3I/ATLAS would have little margin for maneuvers of this type due to the object's high speed.

The researchers in their study propose launching the mission with a SpaceX Starship Block 3 refueled in low Earth orbit. The interceptor would have a mass close to 500 kilograms, comparable to that of New Horizons, and would use two or three solid rocket boosters for perihelion propulsion.

Alternatives and the future of interstellar exploration

Beyond the mission's feasibility, a key question arises: Is it worth pursuing 3I/ATLAS for decades?

The doubt is reasonable, especially since the Vera C. Rubin Observatory, which has already begun operations in Chile, could detect around one interstellar comet per year, a big jump compared to the three identified so far. “We’ll have to wait and see what happens,” Eubanks told Space.com. “Perhaps after, say, ten interstellar objects have been found, 3I will seem commonplace and no longer worth organizing an expedition to pursue it.”

On the other hand, due to the enormous speeds involved, the mission would only allow a brief flyby, considerably limiting the scientific return of such an ambitious undertaking.

Therefore, some researchers consider developing other mission architectures more promising: probes already positioned in space, ready to intercept interstellar visitors near perihelion without the need for such risky Oberth solar maneuvers.

In fact, as reported by Universe Today, the European Space Agency (ESA) plans to launch its Comet Interceptor mission in late 2028. The spacecraft will “park” at the L2 Lagrange point, where it will wait until a suitable target appears. This approach could allow for a much more practical study of future interstellar visitors.

Even so, Oberth's solar maneuvers shouldn't be ruled out. They could prove useful for exploring trans-Neptunian objects, or even for reaching the hypothetical Planet Nine, which is estimated to be located between 290 and 800 astronomical units from the Sun.

“I'm pretty sure that, when we develop the capability to reach these interstellar objects, there will be a strong desire to directly explore at least some of them,” Eubanks concluded.

For now, 3I/ATLAS continues its journey away from the solar system into interstellar space, carrying with it clues about distant planetary systems. Perhaps no one will ever reach it. Or perhaps, many decades from now,a small ground probe manages to intercept it to try to decipher them.