How NASA Tracks Near-Earth Asteroids

Every asteroid you see on the Orbitfall tracker exists in the catalog because a chain of telescopes, astronomers, and software noticed a faint dot moving where a fixed star should be. That chain is remarkably automated, and it runs every clear night.

Step 1 — Discovery: the survey telescopes

Most new near-Earth asteroids are found by dedicated survey telescopes. They aren't especially large, but they image wide patches of sky again and again. Software subtracts one exposure from the next; anything that moves stands out. The major surveys include:

• Catalina Sky Survey (Arizona) — one of the most prolific NEO discoverers.
• Pan-STARRS (Hawaii) — wide-field surveys with a large camera and rapid cadence.
• ATLAS (Hawaii, South Africa, Chile) — designed specifically to spot small, fast-moving objects on final approach.
• NEOWISE — a space-based infrared survey particularly good at finding dark, hard-to-see asteroids.

Step 2 — Confirmation: the Minor Planet Center

A candidate NEO is reported to the Minor Planet Center (MPC), the IAU-sanctioned clearinghouse for small-body observations. The MPC publishes the candidate on its confirmation page so observatories around the world can point their telescopes at it and add follow-up astrometry. Only after several independent observations — usually across two or more nights — is the object's orbit good enough to be considered "confirmed" and given a provisional designation.

Step 3 — Cataloguing: CNEOS and JPL

Once an orbit exists, the observations flow into the Center for Near-Earth Object Studies (CNEOS) at NASA's Jet Propulsion Laboratory. CNEOS maintains the master catalog of near-Earth objects: their orbits, physical properties, and every predicted close approach for the next several decades.

Each new observation refines the orbit fit, which shrinks the uncertainty on where the object will be in the future. That's why an asteroid discovered years ago typically has a very tightly-known trajectory, while one found last week may still have some wiggle room.

Step 4 — Impact monitoring: Sentry

Every newly catalogued object gets fed into Sentry, an automated system that continuously scans the catalog for any asteroid with a non-zero probability of impacting Earth within the next hundred years. Sentry considers not just the best-fit orbit but the entire cloud of orbits consistent with the observations, and looks for any resonant return that could line up with Earth.

When new observations come in, Sentry recomputes. In the overwhelming majority of cases, more observations remove risk: the possible impact scenarios simply don't happen at the improved orbit. Objects come off the Sentry table far more often than they go on.

Step 5 — Public data: NeoWs

NASA exposes all of this through the Near Earth Object Web Service (NeoWs), a public HTTP API. NeoWs provides close-approach data by date range, detailed lookups for individual objects, and an index of the entire NEO catalog. It's what powers the Orbitfall tracker: the rows you see are NeoWs records, reformatted and ranked by the Orbitfall Index.

Why this pipeline matters

Together, these steps mean that the world knows about the vast majority of the largest near-Earth asteroids — the ones that could cause regional or global damage if they ever hit — and their orbits are pinned down well enough to say confidently that none of them are on impact trajectories within any timeframe we can predict. The gap is at the small end, where objects are faint, numerous, and often only spotted at the last moment. Filling in that gap is what surveys like ATLAS and future missions like NASA's NEO Surveyor are designed to do.