FLYBY FREQUENCY

How Often Do Asteroids
Pass Earth?

More than 2,000 asteroid close approaches are recorded each year in the CNEOS database. The number keeps rising as survey telescopes improve. Here is what those statistics actually mean, and what counts as close.

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The actual numbers

NASA's Centre for Near Earth Object Studies (CNEOS) maintains a close-approach catalogue that records every predicted pass within 0.05 AU of Earth (roughly 7.5 million kilometres). The current rate exceeds 2,000 entries per year. In the early 2000s, the same database recorded a few hundred per year. The asteroids did not multiply: the telescopes improved.

The raw count is not a measure of danger. The vast majority of recorded approaches are by objects under 25 metres in diameter, most of which would burn up entirely if they entered the atmosphere. Distance matters too: most recorded passes occur at several million kilometres, which is "close" only by astronomical standards.

Context matters: A close approach in astronomical terms is not close in everyday terms. Most objects counted in the CNEOS database pass at millions of kilometres. The Moon is 384,400 kilometres away, and that is considered extremely close for asteroid flybys.

Approach frequency by distance

Distance Band	Approximate Frequency	Typical Object Size	Notes
Within 1 lunar distance (384,400 km)	A few per year of detectable objects	Sub-10 m	Most in this range are undiscovered until after the pass; atmosphere would destroy impactors
1-10 lunar distances (~384,000-3,844,000 km)	Tens to low hundreds per year	3-100 m	Detection rates improving with better survey coverage; many still undiscovered
10-30 lunar distances (~3.8-11.5 million km)	Several hundred per year	10 m to 1 km+	Most known NEAs detected; large objects well-catalogued in this range
Within 0.05 AU (~7.5 million km, full CNEOS catalogue)	2,000+ per year	All sizes	Standard reporting threshold; count dominated by small objects

Why the count keeps rising

Three survey systems have dramatically increased detection rates over the past two decades. The Catalina Sky Survey (CSS) operates from Arizona and has been running since 1998. Pan-STARRS (Panoramic Survey Telescope and Rapid Response System) in Hawaii began systematic asteroid surveys around 2010. ATLAS (Asteroid Terrestrial-impact Last Alert System), also based in Hawaii with additional stations, was designed specifically for short-warning detection of impactors and has been operational since 2017.

The forthcoming Vera C. Rubin Observatory in Chile, with its ten-year Legacy Survey of Space and Time (LSST), is expected to roughly double the known near-Earth asteroid catalogue within a few years of first light. The recorded flyby count will increase substantially again once LSST data begins flowing.

The closest recorded passes

The very closest confirmed asteroid passes have been by extremely small objects. 2020 VT4 passed at approximately 370 kilometres above Earth's surface in November 2020, well below the orbital altitude of the International Space Station. It was roughly 5 metres across and was discovered after the flyby had already occurred.

2023 BU holds the record as the closest pre-detected pass. Astronomers spotted it five days before its closest approach on 26 January 2023, when it passed at about 3,600 kilometres above the surface. At 4-8 metres across, it would have produced a fireball if it had hit the atmosphere, not a crater.

These extreme close passes share a pattern: the objects involved are very small, very faint, and often discovered only after the event. The largest object to pass at a close distance in recent history was 2019 OK, estimated at 57 to 130 metres, which passed at roughly 73,000 kilometres in July 2019. It was discovered only about 24 hours before closest approach.

Size and the atmosphere as filter

Objects under approximately 25 metres do not reach Earth's surface intact. The atmosphere dissipates their kinetic energy as heat and light, producing a fireball or bolide. The Chelyabinsk event in 2013 involved an object estimated at 17-20 metres: it exploded at roughly 30 kilometres altitude, releasing energy equivalent to about 400-500 kilotonnes of TNT. The blast shattered windows across a wide area and injured over 1,400 people, but the object itself largely disintegrated.

Objects in the 25-140 metre range can produce local to regional damage. Above 140 metres, the Planetary Defence community classifies objects as "potentially hazardous", because surface impact would cause major regional destruction. Most close-approach objects in the CNEOS catalogue are well below this threshold.

Next Asteroid Close Approach

Upcoming passes tracked live from the CNEOS database.

What Is a Close Approach?

How close approach distance is defined and measured.

Closest Approaches Ever Recorded

The top-ten nearest confirmed asteroid passes in history.

CNEOS Explained

How NASA's Centre for Near Earth Object Studies works.

Potentially Hazardous Asteroids

What the PHA classification means and how it is assigned.

Lunar Distance Explained

What "lunar distance" means as a unit of measurement.

Common questions

How many asteroids pass Earth per year?

The CNEOS close-approach database records over 2,000 asteroid passes within 0.05 AU of Earth per year. This number has grown substantially over the past two decades, not because more asteroids are appearing, but because survey telescopes have improved dramatically. Many of the objects in that count are very small, some just a few metres across, and most pass at distances of millions of kilometres.

How often does a large asteroid pass close to Earth?

Objects larger than 140 metres, the threshold for "potentially hazardous asteroid" classification, pass within 0.05 AU of Earth several dozen times per year. Passes within 10 lunar distances (about 3.8 million kilometres) by objects of this size are less frequent, perhaps once every few years on average. Kilometre-scale objects pass at very close range extremely rarely: the 2017 flyby of Florence (4.9 km) at 7 lunar distances was notable as the largest asteroid to pass that close in recorded history.

Has an asteroid ever passed closer than the Moon?

Yes, many times. Small objects pass inside the Moon's orbital distance regularly. In 2020 alone, 2020 VT4 passed at approximately 370 kilometres above Earth's surface (well below the International Space Station's orbit) and 2020 QG passed at around 2,950 kilometres. These objects were very small, roughly 3 to 6 metres across, and would have burnt up in the atmosphere if they had been on an impact trajectory.

What is the most frequent type of asteroid flyby?

The most frequent close passes are by very small objects, under 10 metres, which are extremely numerous and faint. Most pass undetected until after the event, if they are detected at all. Objects in the 10-50 metre range are detected more often as survey telescopes improve. Large objects (over 1 kilometre) pass at close range very rarely and are tracked years or decades in advance.

Will any known asteroid hit Earth?

No currently known asteroid has a confirmed impact trajectory. The highest-probability entry on the current Sentry risk table is Bennu, with a cumulative impact probability of roughly 1 in 1,750 through 2300. All other known objects carry lower probabilities. The key word is "known": survey completeness for large objects (over 1 km) is above 95%, but for smaller objects completeness drops sharply. An undiscovered object could theoretically hit with little warning.