Near-Earth Object
138971 (2001 CB21
NASA ID: 20138971
138971 (2001 CB21 will pass Earth on 29 September 2026 at a distance of 21.06 lunar distances (LD) - about 8,096,702 km - travelling at 36,822 km/h. Its estimated diameter is between 521 and 1,164 metres, roughly the size of Ben Nevis (1,345 m tall). NASA classifies it as a potentially hazardous asteroid (PHA) - a designation based on size and orbital proximity, not on any predicted impact.
Close Approach Date
29 September 2026
In 97 days
Miss Distance
21.06 LD
8,096,702 km
21 times the Moon's distance from Earth
Velocity
36,822 km/h
1.3 times the orbital speed of the International Space Station
Est. Diameter
521–1,164 m
Absolute Magnitude
H = 18.54
The brightness measure astronomers use to estimate size
Hazard Classification
Potentially Hazardous
A watch-list label based on size and orbit, not a predicted impact
The real orbit in 3D
The actual path of 138971 (2001 CB21 around the Sun, computed from JPL orbital elements. Drag to rotate, scroll to zoom, and use the time controls to run the orbit forwards or back.
Every recorded pass
Each dot is one close approach of 138971 (2001 CB21 to Earth between 1901 and 2088, from JPL's records. Lower means closer: a dot under the dashed line passed nearer than the Moon. The orange dot is the approach on this page.
Size Comparison
Reading the Numbers
- A lunar distance (LD) is the average gap between Earth and the Moon, about 384,400 km. It is the standard yardstick for close approaches. Read more →
- Diameter estimates come from brightness. A dark surface reflects less light than a bright one, so the true size can sit anywhere in the quoted range. Read more →
- Potentially hazardous is a watch-list label based on size and orbital proximity. It does not mean an impact is expected. Read more →
