Asteroid 138971 (2001 CB21)
Closest pass on 2026-Sep-29 07:18 TDB (Julian Date: 2461312.804162384)
Key Facts
- On 2026-Sep-29 07:18, asteroid 138971 (2001 CB21) passed Earth at a nominal distance of 8,100,000 km (21.1 lunar distances).
- At closest approach, the object was traveling at 10.2 km/s relative to Earth.
- The object has an estimated size of 696 m, which is about 2 Eiffel Towers.
- The miss distance was just over 21 times the distance to the Moon.
- Hazard classification: 140 to 1,000 meters. Causes widespread continental destruction, severe climatic cooling from injected dust, and potentially lethal ocean tsunamis if hitting water; Congress designated 140 meters as the threshold for mandatory congressional NEO tracking.
Visual Scale Comparison
| Target | 696 m |
|---|---|
| Smaller | Empire State Building: 443 m |
| Larger | Burj Khalifa: 828 m |
Object size compared to known reference benchmarks.
Miss Distance Orbital Dial
Concentric orbital rings showing Earth, Moon orbit, and asteroid trajectory.
Astrometric & Orbital Parameters
| Designation | 138971 |
|---|---|
| Full Object Name | 138971 (2001 CB21) |
| Nominal Miss Distance | 8,100,000 km (21.1 lunar distances / 0.0541231097588424 au) |
| 3-Sigma Minimum Distance | 8,096,683.265 km (21.063 LD) |
| Relative Velocity (v_rel) | 10.228326989398 km/s (about 11 rifle bullets) |
| Velocity at Infinity (v_inf) | 10.2235127550236 km/s |
| Time Uncertainty (3-sigma) | < 00:01 |
| Absolute Magnitude (H) | 18.54 mag |
| Orbit Solution ID | 377 (NASA JPL Small-Body Database) |
| Inside Moon Orbit | No |
| Inside Geostationary Ring | No |
Cite this page
Permanent URL: https://whatnearlyhitus.com/approaches/2026-Sep-29/138971-2001-cb21/ | Machine-readable twin: index.json
APA:
What Nearly Hit Us Project. (2026). Asteroid 138971 (2001 CB21) Close Approach on 2026-Sep-29 07:18. What Nearly Hit Us. Retrieved from https://whatnearlyhitus.com/approaches/2026-Sep-29/138971-2001-cb21/MLA:
"Asteroid 138971 (2001 CB21) Close Approach on 2026-Sep-29 07:18." What Nearly Hit Us, What Nearly Hit Us Project, 2026-09-24, https://whatnearlyhitus.com/approaches/2026-Sep-29/138971-2001-cb21/.BibTeX:
@misc{approach_138971_202629,
title = {Asteroid 138971 (2001 CB21) Close Approach on 2026-Sep-29 07:18},
author = {{What Nearly Hit Us Project}},
year = {2026},
url = {https://whatnearlyhitus.com/approaches/2026-Sep-29/138971-2001-cb21/},
note = {Primary upstream source: NASA/JPL CNEOS CAD API}
}