Fourteen thousand unseen
Astronomers have now charted more than 40,000 asteroids that cross Earth’s neighbourhood. The biggest, planet-wrecking ones are nearly all accounted for. The ones big enough to erase a city mostly are not.
Small rocks hit often. Big ones, rarely.
How often an asteroid of each size strikes Earth, on average. Each step up in size is a far rarer — and far worse — day.
Long-run averages, not forecasts. Interval for 140 m varies by study (~5,000–20,000 yrs). *10 km is an order-of-magnitude figure. Sources: NASA NEO Program; Catalina Sky Survey.
Forty-five years of finding
Known near-Earth asteroids went from 51 in 1980 to more than 40,000 in 2025. The ≥140 m line climbs too — but is still less than halfway to its estimated finish line.
Cumulative discoveries. Grey: all sizes. Vermilion: ≥140 m. Dashed: NASA’s estimated total ≥140 m population (model estimate). Source: NASA JPL CNEOS via Our World in Data.
The giants are found. The city-killers aren’t.
Share of each size class discovered, against the goals set for the search.
Solid: found. Dashed outline: goals. 45% and ~37% are computed from NASA/CNEOS counts and estimated populations (see notes).
Dark rocks, a blinding Sun, and a sky that’s mostly unwatched
Many asteroids are as dark as charcoal, and some approach from the daytime sky where optical telescopes can’t look. Two new instruments aim to close the gap.
new asteroids — including 7 near-Earth — in roughly 10 hours of first-look imaging. For scale, all telescopes combined find about 20,000 asteroids of every kind in a year.
of ≥140 m near-Earth objects targeted within five years by this ~$1.4B infrared telescope, which sees asteroids by their heat rather than reflected sunlight.
What it costs to be surprised — and what it takes to push back
Three numbers from the last thirteen years of planetary defence.
A ~19 m rock nobody saw coming — it arrived from the Sun’s direction and burst with ~400–500 kt of energy, shattering windows across the city.
A rock roughly 40–90 m across. Further tracking cut the odds to ~0.004% within a week.
About 5× the ~7 minutes expected from the spacecraft’s push alone — debris blasted off the asteroid did most of the work.
An asteroid impact is the one natural disaster we can, in principle, prevent entirely — DART proved a spacecraft can nudge one. But you can only deflect a rock you have found, years in advance.
- Look before you panic. Early impact odds often rise, then collapse as observations pile up — 2024 YR4 went from 3.1% to ~0.004% in days. Check NASA’s Sentry table, not headlines.
- Back the infrared eye. NEO Surveyor (~$1.4B) is built to spot dark asteroids that reflect little sunlight but glow in heat. Its launch date depends on sustained funding.
- Lend your eyes. Catalina Sky Survey’s “Daily Minor Planet” project on Zooniverse lets volunteers vet candidate detections from real survey images.
- Watch Rubin’s sky. Vera Rubin Observatory found 2,104 new asteroids — 7 near-Earth — in about 10 hours of first-look imaging. Expect the catalogue to surge.
Sources & notes
- NASA Planetary Defense / JPL CNEOS — near-Earth asteroid counts as of Dec 2025: 11,343 ≥140 m found, ~14,000 estimated still unfound; ~95% of ≥1 km found
- NASA JPL CNEOS discovery statistics, via Our World in Data (2025) — cumulative discoveries by size, 1980–2025
- Thomas et al., Nature (2023) — DART: Dimorphos period change −33.0 ± 1.0 min; ~7 min expected without ejecta boost
- NASA / IAWN notifications, Feb 2025 — 2024 YR4 peak impact probability 3.1% (18 Feb 2025), later ~0.004%
- Popova et al., Science (2013); NASA — Chelyabinsk: ~19 m, ~400–500 kt, ~1,500 injured
- NASA NEO Program (Johnson, 2013); Catalina Sky Survey FAQ; Natl. Academies (2019) — average impact intervals by size
- NASA JPL, NEO Surveyor (2025) — launch NET Sept 2027; ≥2/3 of ≥140 m NEOs in 5 years; ~$1.4B reported cost
- George E. Brown Jr. NEO Survey Act (2005) — goal: find 90% of ≥140 m NEOs by 2020
- NSF–DOE Vera C. Rubin Observatory (June 2025) — 2,104 new asteroids, 7 NEAs, in ~10 hours of First Look imaging
Counts differ slightly by snapshot date: the trend chart (CNEOS via OWID) shows 11,501 ≥140 m for 2025; NASA’s Dec 2025 summary gives 11,343. Computed: 45% = 11,343 ÷ (11,343 + ~14,000); ~37% by 2020 = 9,399 found (CNEOS via OWID) ÷ ~25,000 estimated. Population totals are model estimates. Impact intervals are long-run averages, not forecasts; estimates for 140 m vary (~5,000–20,000 yrs). *10 km interval is an order-of-magnitude figure.