Interstellar Objects: Physical, Chemical, and Dynamical Characterization

The discovery of 1I/'Oumuamua in 2017 revealed that our Solar System is visited by objects formed around other stars, opening an entirely new class of small bodies to study. With 2I/Borisov confirming that interstellar comets exist and follow cometary activity patterns familiar from Solar System comets, and the more recent detection of 3I/ATLAS, it is now clear that these objects are not rare curiosities, but a population that samples planetary formation processes far beyond our own system. Each interstellar object carries a physical record of the environment in which it formed, making them precious time-capsules to study stellar systems other than ours, and possibly unveiling material samples older than the 4.6 Gyr age of the Solar System.

Characterizing these objects is a race against time: interstellar visitors are typically discovered only weeks to months before or after perihelion, on hyperbolic trajectories that guarantee a single, brief passage through the Solar System. This has driven rapid advances in survey-based discovery and alerting (e.g., Pan-STARRS, ATLAS, and the now operational Vera Rubin Observatory), rapid orbit determination and non-gravitational force modeling, and coordinated follow-up campaigns spanning ground-based photometry and spectroscopy, space-based assets such as JWST and HST, and interplanetary spacecraft repurposed for opportunistic observation. These efforts have already returned surprising results, from 'Oumuamua's unexpected non-gravitational acceleration to Borisov's near-pristine cometary composition to the ongoing characterization of 3I/ATLAS, and they raise as many questions as they answer about the diversity of extrasolar planetesimal populations, the efficiency of interstellar ejection, and the interpretation of activity and non-gravitational effects in objects that cannot be revisited.

This Research Topic aims to bring together contributions addressing the discovery, characterization, and interpretation of interstellar objects and their implications for planetary system formation.
We welcome manuscripts on remote sensing techniques applied to interstellar and Solar System small bodies, including reflectance spectral characterization, theoretical and laboratory spectral modeling, machine learning techniques and comparative analyses with known Solar System populations. Contributions addressing surface properties of interstellar objects and the composition, dust properties, and size distribution of cometary comae are particularly encouraged.

Topics of interest include, but are not limited to:

• Physical and chemical characterization: composition, activity, rotation state, morphology of 1I/'Oumuamua, 2I/Borisov, 3I/ATLAS
• Spectroscopic observations across optical, near-infrared, and radio wavelengths for compositional and coma characterization
• Laboratory astrophysics and analog measurements (ices, silicates, organics) supporting the interpretation of observational data
• Dust properties, including grain size distribution, morphology, and dynamics of interstellar object comae and tails
• Isotopic diagnostics (e.g., D/H, ¹²C/¹³C, ¹⁴N/¹⁵N) as tracers of formation environment and interstellar heritage
• Machine-learning and data-driven approaches for the discovery, classification, and rapid characterization of interstellar objects in survey data streams
• Dynamical modeling of interstellar object populations, including encounter frequency and orbital geometry statistics
• Statistical and population-level inference on the size, composition, and origin of the galactic interstellar object reservoirs
• Survey strategies, detection efficiency, and follow-up coordination for time-critical interstellar targets, including predictions for LSST-era discovery rates
• Mission concepts and opportunities for in situ characterization of future interstellar visitors (e.g., Comet Interceptor-class rapid-response missions)
• Detection and characterization of interstellar or hyperbolic meteoroids
• Impact cratering modeling from super-fast impactors
• Comparative studies between interstellar objects and Solar System comets, active asteroids, and trans-Neptunian objects
• Evidence for exotic isotope compositions from ultra-carbonaceous IDPs/meteorites/xenoliths.

By bringing together dynamicists, observers, spectroscopists, astrochemists and mission planners, this collection seeks to consolidate what interstellar objects have taught us so far and to prepare the community for the discoveries expected as survey capabilities improve. We particularly encourage submissions building on recent 3I/ATLAS characterization efforts and on lessons learned from coordinated, time-critical response to interstellar discoveries.




Conflict of Interest Statement

Thomas Marshall Eubanks is Chief Scientist at Space Initiatives Inc. All other Topic Editors declare no competing interests.

Article types and fees

This Research Topic accepts the following article types, unless otherwise specified in the Research Topic description:

• Brief Research Report
• Curriculum, Instruction, and Pedagogy
• Data Report
• Editorial
• FAIR² Data
• General Commentary
• Hypothesis and Theory
• Methods
• Mini Review
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Article types

This Research Topic accepts the following article types, unless otherwise specified in the Research Topic description:

• Brief Research Report
• Curriculum, Instruction, and Pedagogy
• Data Report
• Editorial
• FAIR² Data
• General Commentary
• Hypothesis and Theory
• Methods
• Mini Review
• Opinion
• Original Research
• Perspective
• Review
• Study Protocol
• Technology and Code

Keywords: Interstellar objects, 3I/ATLAS, 1I/'Oumuamua in 2017, 2I/Borisov, Planetary system formation, Survey astronomy, Physical characterization, Interstellar medium, Mission concepts

Important note: All contributions to this Research Topic must be within the scope of the section and journal to which they are submitted, as defined in their mission statements. Frontiers reserves the right to guide an out-of-scope manuscript to a more suitable section or journal at any stage of peer review.