How many near-Earth asteroids are there, and how many are worth a closer look?

Astronomers know of more than 42,000 near-Earth asteroids. That number sounds like a crowded shortlist for prospecting. It is not. Once you filter by size, by how hard each one is to reach, and by how much we actually know about what it is made of, the list of asteroids worth a closer look shrinks to a few hundred, and most of those still have no measured composition.

This article walks through that funnel using public data from NASA's Center for Near Earth Object Studies (CNEOS), the JPL Small-Body Database, and published spectroscopic surveys. Every figure links to its source.

How many near-Earth asteroids are known?

A near-Earth object is an asteroid or comet whose orbit brings it within 1.3 astronomical units of the Sun at its closest point (CNEOS, NEO groups). As of 19 October 2026, the CNEOS discovery statistics list 42,834 known near-Earth asteroids, plus 125 near-Earth comets.

The count has grown fast. On 1 January 2000 the same CNEOS table listed 884 known near-Earth asteroids (CNEOS data file). Most of the growth comes from small objects found by dedicated sky surveys.

CNEOS groups these asteroids by orbit (group definitions; counts):

Orbit group	What it means	Known (19 Oct 2026)
Apollo	Crosses Earth's orbit from outside	24,398
Amor	Approaches Earth's orbit from outside without crossing it	14,885
Aten	Crosses Earth's orbit from inside	3,511
Atira	Orbits entirely inside Earth's orbit	40

How many are large?

Size matters for prospecting because a larger body holds more material and is easier to find again, track, and study. CNEOS reports 11,689 known near-Earth asteroids roughly 140 meters or larger and 885 roughly 1 kilometer or larger (CNEOS). CNEOS states that more than 90% of near-Earth objects larger than 1 kilometer have already been found, and that NASA's program now focuses on finding 90% of those larger than 140 meters (CNEOS statistics introduction).

Those sizes are estimates. Most asteroids are only points of light, so CNEOS infers diameter from brightness (absolute magnitude, H) and an assumed reflectivity of 14%. Under that assumption a 1 kilometer asteroid has H = 17.75 (CNEOS). Real reflectivity varies a lot. Dark carbon-rich classes average about 6% and brighter stony classes about 20% (CNEOS, citing Pravec et al. 2012). The same brightness can therefore mean quite different sizes.

How many can be reached cheaply?

Distance in space is measured in velocity change, or delta-v: how much a spacecraft must change its speed to get somewhere. Lower delta-v means less propellant and a smaller, cheaper spacecraft.

JPL's Lance Benner maintains a list of estimated rendezvous delta-v for every known near-Earth asteroid, starting from low Earth orbit. For comparison, the list gives 6.0 km/s to rendezvous with the Moon and 6.3 km/s for Mars (Benner, JPL delta-v list). Filtering the version updated 19 October 2026, which covers 42,799 asteroids, gives:

• 10,457 asteroids (about 24%) with an estimated rendezvous delta-v below the Moon's 6.0 km/s.
• 2,693 below 5.0 km/s.

These are first-order estimates using the Shoemaker and Helin method, not mission designs (Benner).

NASA's NHATS study takes a stricter view: full round trips with real launch dates. Under its default limits (total delta-v up to 12 km/s, up to 450 days, at least 8 days at the asteroid, launch between 2020 and 2045), 7,151 near-Earth asteroids have at least one viable trajectory. Under the tighter "standard" limits used on the CNEOS page (6 km/s, 360 days, H of 26 or brighter, reasonably well-known orbit), that drops to 122 (NHATS API; parameter definitions). NHATS was built for human missions, so robotic prospecting could use looser limits, but the drop shows how quickly accessibility narrows the field.

Big and easy to reach: the overlap is small

Combine size and accessibility. Using CNEOS's 14% reflectivity assumption, an asteroid five magnitudes fainter than H = 17.75 is ten times smaller, so H = 22 corresponds to roughly 140 meters (CNEOS). Filtering Benner's list (JPL):

• 539 asteroids have both an estimated rendezvous delta-v below 6.0 km/s and H of 22 or brighter (roughly 140 meters or larger).
• Only 8 combine that delta-v with H of 17.75 or brighter (roughly 1 kilometer or larger).

So out of more than 42,000 known objects, the set that is both reasonably large and cheaper to reach than the Moon numbers in the hundreds.

What are they made of? Mostly unknown

Composition is where the funnel tightens most. Asteroids are sorted into spectral classes by how they reflect light. Broadly, C-type asteroids are dark and carbon-rich, S-type asteroids are stony, and X-type asteroids include some that may be metallic. A class is a hint about composition, not an assay.

The JPL Small-Body Database lists a Bus or Tholen spectral class for only 327 of 42,794 near-Earth asteroids, under 1% (JPL SBDB Query API). Of those 327, classes beginning with S account for 183, X for 48, and C for 21. A measured diameter appears for 1,246 (JPL SBDB Query API). CNEOS itself notes that "the taxonomic class of most NEAs is unknown" (CNEOS).

Research surveys go further than the database fields. The MIT-Hawaii Near-Earth Object Spectroscopic Survey (MITHNEOS) published spectra for more than 1,000 near-Earth objects (Binzel et al. 2019). Even so, characterized objects remain a small slice of the known population, and the most accessible asteroids are often small and faint, which makes them harder to observe.

The funnel, in one view

Filter	Count	Source
Known near-Earth asteroids	42,834	CNEOS
Roughly 140 m or larger	11,689	CNEOS
Rendezvous delta-v below the Moon (6.0 km/s)	10,457	Benner, JPL
Both of the above (H of 22 or brighter)	539	Benner, JPL
Spectral class listed in SBDB (any size or orbit)	327	JPL SBDB

The last row is not a subset of the row above it. It covers every near-Earth asteroid with a catalogued class, regardless of size or orbit. Its size is the point: the population that is large and accessible is already bigger than the entire set with a catalogued spectral class.

What this means for prospecting

Discovery is no longer the main bottleneck for resource work. Characterization is. A ranked target list needs three things for each candidate: a reliable size, a realistic trajectory cost, and evidence about composition. Public catalogs supply the first two for many objects, with caveats. The third is missing for almost all of them.

That gap is why a survey-first approach makes sense. Before anyone designs extraction hardware, the job is to gather enough spectral, thermal, and physical data to rank targets honestly, then test the best candidates with small samples.

Near Earth AI is an early-stage research and development company working on that first step at the concept level. We are researching how target ranking could work with public catalogs like the ones cited here, and developing concepts for survey-first prospecting. We have not found, surveyed, or ranked any asteroid. Every figure in this article comes from NASA and JPL public data.

Sources

1. NASA JPL Center for Near Earth Object Studies, Discovery Statistics: Cumulative Totals, accessed 21 October 2026 (data through 19 October 2026).
2. NASA JPL CNEOS, cumulative totals data file (numbers.json), accessed 21 October 2026.
3. NASA JPL CNEOS, NEO Basics: NEO Groups, accessed 21 October 2026.
4. NASA JPL CNEOS, Discovery Statistics: Introduction, accessed 21 October 2026.
5. L. A. M. Benner, JPL, Near-Earth Asteroid Delta-V for Spacecraft Rendezvous, updated 19 October 2026. Counts are simple filters of the published table.
6. NASA JPL, NHATS Data API and API documentation, queried 21 October 2026.
7. NASA JPL, Small-Body Database Query API, queried 21 October 2026 for all near-Earth asteroids (fields: spectral class, diameter). Counts are simple tallies of the returned records.
8. R. P. Binzel et al., Compositional distributions and evolutionary processes for the near-Earth object population: Results from the MIT-Hawaii Near-Earth Object Spectroscopic Survey (MITHNEOS), Icarus 324 (2019).