Asteroid Tracker

About near-Earth object tracking

How we classify asteroids, what the numbers mean, and where the data comes from.

What counts as a hazardous asteroid?

NASA flags an asteroid as potentially hazardous (a PHA) when its orbit brings it within 0.05 AU (about 19.5 LD) of Earth and it's at least ~140 m across. A PHA flag doesn't mean impact — it means the object is big enough and close enough to warrant monitoring.

What does LD mean?

LD = lunar distance, the average distance from Earth to the Moon (~384,400 km). Miss distances are often expressed in LD because the Moon is the nearest reference most people intuitively understand — 1 LD is very close, 20 LD is comfortably far.

How often is this data updated?

The tracker auto-refreshes every 60 seconds from NASA's NeoWs API. The underlying orbital solutions are updated by JPL as new observations come in, typically several times a day for actively watched objects.

How is the risk class computed?

Each object is classified from two signals — miss distance (in LD) and estimated diameter. Significant means a large object passing unusually close; notable is anything inside 10 LD; watch is a close-but-comfortable flyby; everything else is no risk.