At a glance
- Width
- 221 to 494 m
- about 1,788 bananas
- Speed
- 38.18 km/s
- 137,450 km/h · 85,407 mph
- Misses us by
- 188.2 lunar
- 72,375,948 km · 44,972,315 miles
- First spotted by us
- 13th November 2026
- 1 page view
How far is "close"?
Same gap, ranked against places you have heard of, on a log scale because the Sun is awkwardly far away.
How big is it, really?
NASA only estimates the width, so we show the biggest guess. Log scale again. Everest is just there to make everything else look reasonable.
How fast is it going?
Speed relative to Earth at closest approach. The International Space Station is the fastest thing most of us will ever stand under. This lot would lap it.
If it hit (it will not)
Rough impact energy at the biggest size estimate, assuming solid rock, in tonnes, kilotons and megatons of TNT, which is how everyone who has to do this maths measures it. Treat it as a ballpark. The point stands: no impact is scheduled.
Where it actually lives
A top-down view of the orbit, to scale, with Earth's and Mars's orbits for company. The tilt of the orbit is ignored, so treat the shape as right and the exact position as roughly right. The Sun is the orange dot in the middle.
- Orbit class
- APOApollo: crosses Earth's orbit, but spends most of its time further out than us. The most common troublemaker type.
- Year length
- 1.87 Earth years (685 days)One lap of the Sun. Your commute is shorter, and so is your patience.
- Eccentricity
- 0.714How squashed the orbit is. 0 is a perfect circle, 1 is "leaving". Very stretched. This rock commutes the long way round.
- Tilt
- 11.7°The angle of its orbit against the flat plane the planets share. Slightly tipsy.
- Closest to the Sun
- 0.43 AU65 million km. One AU is the distance from Earth to the Sun.
- Furthest from the Sun
- 2.61 AU390 million km. Out past Mars.
- Closest orbit-to-orbit gap
- 0.173 AUIf you only compare the two orbits, not where the planets are, they come within 67 lunar distances. The rock is rarely there at the same time as us, which is the entire reason we are still here.
- Observations used
- 54NASA has measured this one 54 times. It has been stalked thoroughly.
- Watched for
- 4.0 years2015-01-24 to 2019-02-05. Not long, so the orbit is still being refined and the rock is still a bit of a stranger.
- Orbit uncertainty
- 0 out of 90 means we know exactly where it is going. 9 means a shrug. Lower is better.
Is it actually hazardous?
This one fails at least one test, so it is not on the list. It is comfortably, boringly harmless.
Not on NASA's Sentry impact-risk watch list. No further action, no thoughts, head empty.
Its history with us
Every known pass this rock makes, 1900 to 2200. Dim dots are the past, green dots are still to come, the big orange ring is this one. The dashed line is the Moon's distance, so anything below it is closer than the Moon. Almost nothing is.
| Date | Miss distance | Speed |
|---|---|---|
| 6th November 2071 | 124.5 LD · 47,885,020 km | 32.3 km/s |
| 29th August 2073 | 189.6 LD · 72,931,236 km | 19.9 km/s |
| 20th March 2077 | 104.0 LD · 40,013,489 km | 18.6 km/s |
| 3rd November 2086 | 103.9 LD · 39,958,999 km | 30.3 km/s |
| 16th March 2092 | 89.6 LD · 34,454,180 km | 20.5 km/s |
| 2nd November 2101 | 89.6 LD · 34,465,929 km | 28.8 km/s |
| 15th March 2107 | 81.4 LD · 31,294,189 km | 22.0 km/s |
| 30th October 2116 | 78.7 LD · 30,273,444 km | 27.4 km/s |
| 13th March 2122 | 77.4 LD · 29,758,001 km | 23.4 km/s |
| 29th October 2131 | 69.8 LD · 26,854,207 km | 25.8 km/s |
By the numbers
- Estimated mass
- 17.0 million tonnes to 189.8 million tonnesVolume of a sphere at NASA's smallest and largest width estimates, times 3,000 kg per cubic metre (typical rock). Real shapes are lumpier, so treat it as a ballpark.
- Swimming pools of rock
- 9,587 Olympic poolsSphere volume at the middle width estimate, divided by 2,500 cubic metres per Olympic pool.
- Impact energy, if it hit
- 2,957 megatons to 33,060 megatonsHalf mass times speed squared, at the small and large width estimates, converted to TNT (1 kiloton is 4.184 trillion joules). A rock this far away is not going to do this.
- Speed against escape velocity
- 3.4 timesIts speed relative to Earth, divided by the 11.186 km/s needed to leave Earth's gravity. It is travelling a lot faster than we can throw things.
- Speed against Earth in orbit
- 1.28 timesDivided by Earth's own orbital speed of 29.78 km/s around the Sun.
- Time to cross the UK
- 25.4 secondsLand's End to John o' Groats is about 970 km in a straight line. Divided by its speed.
- Time to fly the miss distance
- 21.9 daysThe miss distance divided by its speed. This is how long it needs to cover a gap of that size, which is a measure of how near or far the pass is.
- Light takes to cross the gap
- 241.4 secondsMiss distance divided by the speed of light.
- Width from brightness alone
- 221 to 494 mAstronomers estimate size from how bright an asteroid is (H 20.4) and how reflective it is. A shiny rock (albedo 0.25) is smaller than a dark one (0.05) for the same brightness. NASA's own estimate above uses the same idea.
- Laps of the Sun since first spotted
- 2.21,473 days of observation divided by its 685-day year.
- Known close approaches, 1900 to 2200
- 490 inside the Moon's orbit and 0 within ten lunar distances.
- Closest pass in that period
- 65.86 lunar distancesOn 25th October 2176.
- Next visit after this one
- 8th October 2028At 139.6 lunar distances. Closer than this time.
- Average gap between visits
- 6.0 yearsThe span of the record divided by the number of gaps between approaches.
- Rank by size
- 8 of 42Among every asteroid this site has tracked, biggest first.
- Rank by closeness
- 41 of 42Among every asteroid this site has tracked, using each one's most recent pass, closest first.
- Rank by speed
- 1 of 42Among every asteroid this site has tracked, fastest first.
How reliable are these?
Width, speed, miss distance and orbit come straight from NASA. Mass, energy, volume and the rankings are our own arithmetic on top, and the assumptions are written beside each one. NASA publishes a range for width because nobody has seen most of these rocks up close, so wherever we show one number it uses the biggest estimate and says so.
Will asteroid 2017 BK123 hit Earth? Questions answered
Will asteroid 2017 BK123 hit Earth?
No. 2017 BK123 passes Earth on 14th November 2026 at 188.2 lunar distances (72,375,948 km), which is 188.2 times the distance to the Moon. It is not on NASA's potentially hazardous list. It is not on NASA's Sentry impact-risk watch list.
How big is asteroid 2017 BK123?
NASA estimates it is between 221 m and 494 m wide, which at the top end is about 4.7 football pitches long. Nobody has seen it up close, so the width is an estimate from its brightness.
How fast is asteroid 2017 BK123 travelling?
38.2 km/s relative to Earth at closest approach, about 137,450 km/h (85,407 mph). That is 5.0 times the speed of the International Space Station.
Is 2017 BK123 a potentially hazardous asteroid?
No. NASA gives the label to asteroids whose orbit comes within 0.05 astronomical units of Earth's (about 7.5 million km) and which are bigger than roughly 140 m. 2017 BK123 has an absolute magnitude of 20.4 and its orbit comes within 0.173 AU of Earth's.
When is asteroid 2017 BK123's next close approach?
After this pass, the next one in NASA's record is on 14th November 2026, at 188.2 lunar distances.
Unhelpful facts
- 48.38% of the way to the Sun. Nobody is cancelling summer.
- A jet would have to circle Earth 1,806 times to cover the gap. Baggage still lost.
- Absolute magnitude of 20.4. Lower means brighter, so the biggest numbers belong to the smallest rocks. Astronomers did that on purpose.
- About 1,412 wheels of Gouda across. A brave scientist would call that a dairy event.
- Light crosses the gap in 241.42 seconds. That is not enough time to say "what was that".
- It passes in 1 day, which is 7 dog days. Your dog is already nervous, mostly about the post.
- That is 2,846 times the speed limit on a 30 zone. Nobody has fined it yet.
- If it did hit, that would release roughly 33,060 megatons of TNT, assuming solid rock. It will not, so enjoy the number.
- Line up 82 elephants to match its width. The elephants would like to be consulted first.
- If this one did hit Earth, your next meeting would be cancelled. Look on the bright side.
- Roughly 760 car tyres wide. Check the tread before you worry about the rock.
- A snail would need 175,669 years to cover the gap. The snail would take the day off.