Finding new objects

Near-Earth objects (NEOs) are discovered by wide-field survey telescopes that photograph large swaths of the sky repeatedly each night, then compare successive images to spot anything that moves against the fixed background of stars. The major NASA-funded surveys include the Catalina Sky Survey, Pan-STARRS, the ATLAS network (Asteroid Terrestrial-impact Last Alert System), and, since 2023, the NSF-funded Vera C. Rubin Observatory. NASA also flies the NEOWISE space telescope, which detects asteroids by their infrared heat signature rather than reflected sunlight — useful for finding dark objects that optical surveys miss.

A single detection isn't enough to confirm a new object; astronomers need several observations across multiple nights to calculate a preliminary orbit. Candidate detections are submitted to the Minor Planet Center, the international clearinghouse (operated under the IAU) that collects observations from professional and amateur astronomers worldwide and assigns provisional designations.

Refining the orbit

Once an object has enough observations, NASA's Center for Near-Earth Object Studies (CNEOS) at the Jet Propulsion Laboratory computes and continuously refines its orbit using JPL's orbit-determination software. Because gravity from the Sun, planets, and even the slight thermal push of sunlight (the Yarkovsky effect) all nudge an asteroid's path over time, orbits are recalculated as new observations come in, and uncertainty shrinks the longer an object has been tracked.

This is also how close-approach dates and miss distances — the kind of data shown live on this site via NASA's NeoWs API — get calculated: by projecting a well-constrained orbit forward and finding where it passes nearest to Earth.

Radar and spacecraft follow-up

For objects passing unusually close, ground-based planetary radar — historically at Goldstone in California and, until its 2020 collapse, the Arecibo Observatory in Puerto Rico — can bounce radio waves off an asteroid to measure its distance, speed, shape, rotation, and surface features with far more precision than optical telescopes alone. Radar has revealed some near-Earth asteroids to be binary systems, elongated "peanut" shapes, or even loosely bound rubble piles.

NASA has also sent spacecraft to study NEOs directly: OSIRIS-REx returned a physical sample from asteroid Bennu in 2023, and the DART mission deliberately collided with the moonlet Dimorphos in 2022 to test whether a spacecraft impact can measurably change an asteroid's orbit — a real-world test of planetary defense, not just tracking.

The planetary defense pipeline

All of this feeds into NASA's Planetary Defense Coordination Office, which is tasked by Congress with finding at least 90% of NEOs 140 meters or larger. CNEOS maintains a public Sentry Impact Risk table that lists every object with a nonzero, however small, calculated impact probability, and updates it automatically as new observations arrive — nearly all entries eventually drop off the list once their orbits are pinned down.