As of November 11, 2026, NASA's Jet Propulsion Laboratory (JPL) lists 43,025 near-Earth asteroids in its Small-Body Database. The list keeps growing as surveys find more. NASA's planetary defense overview states that there is no known asteroid larger than 140 m (460 feet) with a significant chance of hitting Earth in the next 100 years.
A near-Earth asteroid is an asteroid whose orbit brings it into Earth's neighborhood. It does not mean one that is about to arrive. This article explains the exact definition, the four orbit groups, how many are known, how surveys find and follow them, and what the label "potentially hazardous" does and does not say.
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What counts as near-Earth
NASA's Center for Near-Earth Object Studies (CNEOS) defines a near-Earth object (NEO) as an asteroid or comet whose perihelion, the closest point to the Sun, is less than 1.3 astronomical units (AU). One AU is the average Earth-Sun distance, about 149.6 million km (93 million miles), so 1.3 AU is about 194 million km (121 million miles). A near-Earth comet must also have an orbital period under 200 years. NASA's planetary defense overview puts the same idea another way: NEOs come within 48 million km (30 million miles) of Earth's orbit.
Most asteroids stay in the main belt, described in the guide to the asteroid belt. Near-Earth asteroids are the ones whose paths have been bent into the inner Solar System. For the wider picture of the asteroid family, start with what asteroids are.
The four orbit groups
CNEOS splits near-Earth asteroids into four groups using three numbers from the orbit: the semi-major axis (a, half the long width of the orbit), the perihelion (q) and the aphelion (Q, the farthest point from the Sun). The cutoffs of 0.983 and 1.017 AU are Earth's own closest and farthest distances from the Sun. The ideas behind these numbers are explained in the guide to reading an orbit.
| Group | Orbit rule | Description and examples |
|---|---|---|
| Atira | a below 1.0 AU and Q below 0.983 AU | Orbit entirely inside Earth's orbit |
| Aten | a below 1.0 AU and Q above 0.983 AU | Earth-crossing; Apophis, as of November 2026 |
| Apollo | a above 1.0 AU and q below 1.017 AU | Earth-crossing; Bennu, Itokawa, Didymos |
| Amor | a above 1.0 AU and q between 1.017 and 1.3 AU | Approaches from outside Earth's orbit; Eros |
Aten and Apollo asteroids cross Earth's orbital path. Amor asteroids approach from outside it and come no closer to the Sun than 1.017 AU. Atira asteroids stay entirely inside Earth's orbit. Groups can change: Apophis will be reclassified from Aten to Apollo after its April 2029 flyby, when Earth's gravity widens its orbit, as the guide to the Apophis flyby explains.
How many are known
JPL's database lists 43,025 near-Earth asteroids as of November 11, 2026. NASA's Planetary Defense Coordination Office publishes a monthly snapshot with size breakdowns. The most recent snapshot on NASA's page is dated December 3, 2025, and gives these figures:
- 39,123 near-Earth asteroids of all sizes discovered.
- 11,343 larger than 140 m discovered, with an estimated 14,000 still to be found.
- 873 larger than 1 km (0.6 mile) discovered, with an estimated 50 still to be found.
The two sources are not measuring the same day. JPL's database count is from November 2026 and NASA's snapshot is from December 2025, so the gap of about 3,900 objects reflects almost a year of new discoveries as well as any difference in method. Those figures show a pattern that holds for all surveys. The biggest objects are the easiest to see, so most of them are already known. Smaller ones are fainter, so more are missing. The count by size is an estimate of the unfound population, not a certain number.
How surveys find and follow them
NASA's NEO Observations Program funds observatories around the world to search for undiscovered NEOs and to refine their orbits. Its discovery surveys include the Catalina Sky Survey at the University of Arizona, and ATLAS and Pan-STARRS at the University of Hawaii. A more complete tour of these instruments is in the article on the telescopes that find small bodies. A new object follows a path like this:
- A survey telescope records an object that moves against the background of fixed points.
- Its positions go to the Minor Planet Center, which NASA lists as the entity that collects NEO measurements and calculates orbits.
- Other observatories add follow-up observations. NASA also uses the Goldstone Solar System Radar to follow up discoveries and measure physical properties.
- CNEOS's Sentry system continuously scans the catalog for possible impacts over the next 100 years and publishes results as they appear.
- Orbits are refined as more data arrive, and an object leaves the risk table once no potential impact remains.
The next big step is NEO Surveyor, a NASA space telescope that uses infrared light to find dark objects that reflect little sunlight but glow as they warm. NASA's page, updated November 3, 2026, lists its launch as no earlier than September 2027.
What "potentially hazardous" means
CNEOS defines a potentially hazardous asteroid (PHA) as a near-Earth asteroid with a Minimum Orbit Intersection Distance (MOID) from Earth of 0.05 AU or less, and an absolute magnitude (H) of 22.0 or less. MOID is how close the two orbits come to touching, here about 7.5 million km (4.6 million miles). H is a brightness-based size measure, and a value of 22 corresponds roughly to 140 m, depending on how reflective the surface is. JPL's database lists 2,551 PHAs as of November 11, 2026.
The rule says nothing about when a body will pass, only about the shape of its orbit and its size. Apophis carries the PHA flag in JPL's database, yet NASA says there is no risk of it hitting Earth for at least 100 years. The article on planetary defense and the DART test shows what agencies do about the rare case that does need action.
Common mistakes and myths
Myth: "near-Earth" means "about to hit Earth." The label is an orbit class, not an arrival notice. It says where the orbit goes, not when anything will pass.
Myth: "potentially hazardous" is a forecast. It is a size-and-distance filter. NASA says in its planetary defense overview that notifications are for objects with a 1 percent or greater chance of impact in the next 50 years.
Myth: all near-Earth asteroids are known. NASA's December 2025 snapshot estimates about 14,000 asteroids larger than 140 m are still undiscovered.
Myth: near-Earth asteroids are rare oddities. Tens of thousands are cataloged, and sample missions from NASA and JAXA have targeted several of them. The story of OSIRIS-REx at Bennu is one example.
Frequently asked questions
How many near-Earth asteroids are known?
JPL's Small-Body Database lists 43,025 as of November 11, 2026. NASA's snapshot from December 3, 2025, gave 39,123. The number rises every month.
Is any known asteroid going to hit Earth?
NASA's planetary defense overview says there is no known asteroid larger than 140 m with a significant chance of hitting Earth in the next 100 years. Agencies update this as new observations arrive, so check NASA's pages for the current status.
What is Sentry?
Sentry is a CNEOS monitoring system. It scans the latest asteroid catalog for possible impacts over the next 100 years and publishes any that are found.
What is the difference between an NEO and an NEA?
An NEO is a near-Earth object, either an asteroid or a comet. An NEA is a near-Earth asteroid, so NEAs are one kind of NEO.
Sources
- NEO Groups. Center for Near-Earth Object Studies, NASA/JPL. https://cneos.jpl.nasa.gov/about/neo_groups.html
- Planetary Defense by the Numbers: near-Earth asteroid snapshot, December 3, 2025. NASA Science. https://science.nasa.gov/science-research/planetary-science/planetary-defense/near-earth-asteroids/
- Planetary Defense Overview. NASA Science. https://science.nasa.gov/planetary-defense-overview/
- NEO Observations Program. NASA Science. https://science.nasa.gov/planetary-defense-neoo/
- Sentry: Earth Impact Monitoring. Center for Near-Earth Object Studies, NASA/JPL. https://cneos.jpl.nasa.gov/sentry/
- NEO Surveyor. NASA Science, page updated November 3, 2026. https://science.nasa.gov/mission/neo-surveyor/
- Small-Body Database API (counts queried November 11, 2026; records for Apophis, Bennu, Eros, Itokawa, Didymos). NASA/JPL. https://ssd-api.jpl.nasa.gov/sbdb_query.api?fields=full_name&sb-kind=a&sb-group=neo&limit=1