A new category of objects observed within our solar system has emerged in recent years, Interstellar Objects. They resembles comets or asteroids but are moving too fast to be bound to the gravitational well of the Sun. As of early 2026, only three objects have been detected. Surely many more such objects have passed undetcted through the solar system. Unlike solar system objects, the time available to study Interstellar Objects is linited by the briefness of their passages through our neighborhood.

Wikipedia entry
NASA Webpage
Encyclopaedia of Exoplanetary Systems

NOTES: tent = tentative detection; disp = disputed detection; conf = confirmed detection; nd = non-detection.


NAME (MPC DESIGNATION)
MOLECULES
DISCOVERY CITATION
1I/'Oumuamua (C/2017 U1)
Bergner & Seligman+(2023): H2O(?), H2(?)
Comet C/2017 u1 (panstarrs)
P. Bacci+. Minor Planet Electronic Circ., No. 2017-U181 (2017).
2I/Borisov (C/2019 Q4)
Fitzsimmons+(2019): CN, C2(nd)
Lin+(2020): C2
Cordiner+(2020): HCN, CO
Bodewits+(2020): CO
Xing+(2020): OH, H2O
de León+(2020): CN
Prodan+(2024): CN, NH2
Deam+(2026): NH2, CN, C2
Comet C/2019 Q4 (Borisov)
Bacci+. Minor Planet Electronic Circ., No. 2019-S62 (2019).
3I/ATLAS (C/2025 N1)
Coulson+(2026): HCN
Combi+(2026): H2O
Li+(2026): OH, CO OH, CO
Roth+(2026): CH3OH, HCN
Lisse+(2026):H2O, CO2, 13CO2(tent), CO(tent)
Kawakita+(2026): CN, C3, C2, NH2(nd)
Belyakov+(2026): H2, CO2, CH4
Biver+(2026): HCN, CH3OH, CO, H2O, CS(tent), CH3CN(tent), H2S(nd)
Shinnaka+(2026): CO2/H2O ratio
Zhao+(2026): CN, C2, C3, CH
Roth+(2026): CO, CO2, H2O, CH3OH, CH4
Salazar Manzano+(2026): H2O, HDO
Cordiner+(2026): H2O, HDO, CO2, 13CO2, CO, 13CO, HCN
Bockelée-Morvan+(2026): H2O, CO2, aliphatic hydrocarbons(?)
Santa-Ros(2026+) CN
Noonan+(2026): CO, H2S(nd), SO(nd), SO2(nd)
3I/ATLAS = C/2025 n1 (atlas)
L. Denneau+ Minor Planet Electronic Circ., No. 2025-N12.

Acronyms
ATLAS Asteroid Terrestrial-Impact Last Alert System

Maintained by DE Woon
Updated 25 August 2026