The detection of the interstellar comet 3I/ATLAS in July produced quite the stir in the scientific community. This comet is the third interstellar object (ISO) to pass through the Solar System, the previous two being 1I/’Oumuamua and 2I/Borisov, which arrived in 2017 and 2019, respectively. Like its predecessors, the arrival of 3I/ATLAS highlighted just how common these objects are and inspired mission concepts for studying them up close. The latest comes from the Southwest Research Institute (SwRI), where a team has developed a mission study for a spacecraft that could perform a flyby with 3I/ATLAS.
Asteroids and comets are essentially material left over from the formation of the Solar System roughly 4.6 billion years ago. The study of ISOs could therefore tell us a lot about what conditions are like in other star systems without having to send missions to explore them. Using the recent discovery of 3I/ATLAS as a basis, the SwRI determined that this latest ISO could have been intercepted and observed by their proposed spacecraft. Relying on previous ISO detections, their internally funded SwRI study also lays out the design, scientific objectives, payload, and key requirements for such a mission.
The study was led by Dr. Alan Stern, a planetary scientist and the SwRI Associate Vice President. Stern is well-known for being the Principal Investigator of the New Horizons mission, which made the first flyby in history with Pluto in July 2015. He and his SwRI colleagues previously conducted a concept study for an Interstellar Object Explorer (IOE), detailed in a paper released in February 2024. With the detection of 3I/ATLAS a little over a year and a half later, he and his colleagues are once again exploring how future missions might intercept and study ISOs. Their latest proposal, said Stern, is for an Interstellar Comet Explorer (ICE):
These new kinds of objects offer humankind the first feasible opportunity to explore bodies formed in other star systems closely. An ISC flyby could give unprecedented insights into these objects’ composition, structure, and properties, and it would significantly expand our understanding of solid body formation processes in other star systems.
Comet 3I/ATLAS as observed soon after its discovery. Credit: NASA/ESA/UCLA/MPS
One of the main constraints of their study was that the spacecraft would not be able to orbit a future ISO owing to the hyperbolic trajectories and velocities involved. However, their analysis showed that a flyby reconnaissance mission was feasible, affordable, and would provide immense scientific returns. To determine trajectory options for the mission, the team relied on SwRI-developed software that simulates a population of ISCs, then calculates the minimum energy trajectory from Earth to intercept each simulated comet.
According to SwRI orbital mechanics expert, Dr. Mark Tapley, the simulations showed that a low-energy rendezvous was possible. They also indicated that the ICE would require less launch velocity and in-flight trajectory changes than many robotic missions currently exploring the Solar System. “The very encouraging thing about the appearance of 3I/ATLAS is that it further strengthens the case that our study for an ISC mission made,” he said. “We demonstrated that it doesn’t take anything harder than the technologies and launch performance like missions that NASA has already flown to encounter these interstellar comets.”
Needless to say, the scientific returns of such a mission would be immense. Detailed data on the ISC’s composition would provide a wealth of information about its formation and evolution, providing insight into its system of origin and the interstellar medium. As the ISC nears the Sun, it will form a large tail as water and other frozen volatiles sublimate, triggering outgassing and the formation of a coma. The spacecraft could examine this coma using spectrometers to learn what lies beneath the ISC’s icy surface. Said SwRI’s Matthew Freeman, the study’s project manager:
The trajectory of 3I/ATLAS is within the interceptable range of the mission we designed, and the scientific observations made during such a flyby would be groundbreaking. The proposed mission would be a high-speed, head-on flyby that would collect a large amount of valuable data and could also serve as a model for future missions to other ISCs.
Studies have shown that about seven ISOs pass through the inner Solar System annually, though some models place that number higher. These same studies showed that as many as 10,000 ISOs pass inside Neptune’s orbit annually, some of which are captured by the Solar System’s gravity and stay here. As new facilities like the Vera Rubin Observatory conduct surveys that reveal tens of thousands of objects, astronomers expect to find many more ISOs.
Further Reading: SwRI