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 througthrough our neighborhood.

Wikipedia entry
NASA Webpage

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+(YEAR): CN, NH2
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
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 12 April 2026