Reference

The largest
near-Earth asteroids

NASA's Near-Earth Object catalogue contains more than 38,000 entries. Here are the largest - from city-scale boulders to objects that dwarf the highest mountains - with their orbital class, hazard status, and any spacecraft visits.

Asteroid size comparison →

Ranked by diameter

Diameter estimates are approximate. Data from NASA Small-Body Database.

#	Name	Diameter	Class	PHA	Notes
1	1036 Ganymed Largest known	~37.7 km	Amor	No	Largest known NEA. Never comes within 0.05 AU of Earth.
2	433 Eros	~34.4 km	Amor	No	First NEA visited by a spacecraft (NEAR Shoemaker, 2001).
3	3552 Don Quixote	~19 km	Apollo	No	Likely an extinct comet nucleus with a faint coma detected.
4	1627 Ivar	~8.3 km	Amor	No	S-type asteroid. Radar observations confirmed elongated shape.
5	4954 Eric	~8.0 km	Amor	No	Named after astronomer Eric Elst. Low-inclination orbit.
6	3908 Nyx	~7.8 km	Apollo	No	Named for Greek goddess of night. Crosses Earth orbit.
7	2061 Anza	~6.4 km	Amor	No	Named after Spanish explorer Juan Bautista de Anza.
8	4179 Toutatis	~4.5 km	Apollo	No	Complex tumbling rotation. Multiple radar imaging campaigns.
9	1580 Betulia	~5.0 km	Amor	No	C-type asteroid. Well-studied via radar and photometry.
10	162173 Ryugu	~900 m	Apollo	No	Sample returned to Earth by JAXA Hayabusa2 mission (2020).
11	25143 Itokawa	~535 m	Apollo	No	First asteroid from which samples were retrieved (Hayabusa, 2010).
12	101955 Bennu	~490 m	Apollo	Yes	Sample returned by NASA OSIRIS-REx (2023). Low but non-zero long-term impact probability.
13	99942 Apophis	~370 m	Apollo	Yes	April 2029 flyby at ~38,000 km from Earth centre. No impact risk.
14	65803 Didymos	~780 m	Apollo	Yes	Binary system. Target of ESA Hera mission (2024). Moonlet Dimorphos was deflected by DART in 2022.

Why the largest NEOs are not the most watched

The largest near-Earth asteroids - Ganymed, Eros, Don Quixote - are not the objects that generate planetary defence concern. Their orbits are well-characterised and their paths do not intersect Earth's on any timescale of practical interest.

The objects that attract the most monitoring are medium-sized PHAs (potentially hazardous asteroids) whose orbital solutions still carry some uncertainty. Bennu, Apophis, and a handful of others in the 200 metre to 1 kilometre range sit at the intersection of "large enough to cause serious damage" and "orbit close enough to Earth to warrant sustained attention."

The routine close-approach events shown in the approaches table on this tracker are dominated by small, recently discovered objects - typically under 100 metres - not the large named asteroids on this list. The large ones have predictable, well-separated orbits.

Asteroid size comparison

How asteroid sizes compare to everyday landmarks.

Near-Earth objects explained

NEO classifications - Amor, Apollo, Aten, Atira.

Famous close approaches

Notable historical flybys and the science behind them.

Apophis - the 2029 flyby

Details on the most closely watched upcoming encounter.

Common questions

What is the largest known near-Earth asteroid?

1036 Ganymed is the largest known near-Earth asteroid at approximately 37.7 km in diameter. It is an Amor-class asteroid, meaning its orbit approaches but does not currently cross Earth's orbit. Despite its size, it never comes within 0.05 AU of Earth and poses no impact risk.

Are any of the largest near-Earth asteroids dangerous?

The largest near-Earth asteroids - Ganymed, Eros, Don Quixote - orbit in the Amor class and their paths do not currently cross Earth's. Even for those that do cross Earth's orbit (Apollo class), the geometry of each encounter determines whether a close approach occurs. None of the objects on this list have a meaningful impact probability in the next century.

Why do the largest NEOs rarely produce close approaches?

Large NEOs tend to have well-studied orbits that are known not to intersect Earth's path on any near-term encounter. Also, the largest objects - Ganymed, Eros - are Amor-class asteroids whose perihelia do not bring them inside Earth's orbit. The close approaches that appear in NASA's NeoWs feed are mostly from smaller, recently discovered objects, not from the well-catalogued large ones.

How do scientists measure the size of an asteroid?

Several methods are used in combination. Apparent brightness plus assumed reflectivity (albedo) gives a rough estimate. Thermal infrared observations - which measure heat radiated by the surface - give more reliable results independent of surface colour. Radar from facilities like Goldstone in California can resolve shape and size for objects that pass close enough. Spacecraft visits provide the most precise measurements via direct imaging.

Could a large NEO become dangerous in the future?

Orbits evolve over time under gravitational influences from the Sun and planets. A large NEO whose orbit currently does not intersect Earth's could gradually shift into a crossing orbit over millions of years. On human timescales - centuries to millennia - the known large NEOs are not expected to develop meaningful impact probabilities. Planetary scientists monitor orbital evolution models for all known large objects.

Sean Barraclough

Creator of closeapproach.space

The largest
near-Earth asteroids

Ranked by diameter

Why the largest NEOs are not the most watched

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Common questions

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