Is the Orbitfall Index a probability of impact?

No. It's a ranking of how notable a close approach is. It doesn't estimate probability of impact and shouldn't be read as risk, danger, or a threat level. For real impact-monitoring output, see NASA CNEOS Sentry.

What data does it use?

Miss distance (in lunar distances), average estimated diameter, relative velocity in km/s, and whether NASA has flagged the object as potentially hazardous. All values come from NASA's NeoWs API.

Why these four inputs?

They're the four things that most obviously make a close approach worth reading about: how close, how big, how fast, and whether it's on NASA's watch list.

How the Orbitfall Index Works

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A 0–100 score that ranks how notable an asteroid close approach is. It is not an impact prediction.

The Orbitfall Index is a single 0–100 number attached to every close approach in the tracker. Its only job is to answer one question: how notable is this pass, compared to the others?

It is not a probability of impact, a threat level, or a danger score. For genuine impact-monitoring output, the authoritative source is NASA CNEOS's Sentry system. Orbitfall is a ranking on top of NASA's public NeoWs data.

What goes into the score

The index is the sum of four components, each capped independently:

Proximity — up to 40 points. Based on the miss distance in lunar distances. A pass at 0 LD would score the full 40; a pass at 20 LD or beyond scores 0. Between the two, the score scales linearly.
Size — up to 25 points. Based on the average estimated diameter, on a logarithmic scale. A ~1 m rock scores near 0; a body approaching 1 km across scores the full 25.
Velocity — up to 20 points. Based on relative velocity in km/s. A pass at 40 km/s or faster scores the full 20; slower passes scale down linearly.
Hazard flag — 15 points, flat. Added whenever NASA has classified the object as potentially hazardous.

The tiers

0–24 — Quiet Pass. A routine, distant, or small approach.
25–49 — Notable Pass. Worth a look; a combination of size, distance, or speed that stands out.
50–74 — Close Watch. An unusually close, large, or fast pass — the kind planetary-defense astronomers keep an eye on.
75–100 — Main Event. The rare pass where multiple factors stack: close, large, fast, and on the PHA list.

What it deliberately isn't

The Orbitfall Index doesn't attempt to estimate impact probability, because the objects in NASA's public feed already have well-determined orbits — they are, by definition, passes that miss. Modelling collision odds from those figures would be misleading.

The disclaimer "This score ranks how notable the asteroid approach is. It is not an impact prediction." appears next to every score in the tracker for exactly that reason.

Where the numbers come from

All inputs — miss distance, diameter estimate, velocity, and hazard flag — come directly from NASA's NeoWs API for the date range you're viewing. Orbitfall doesn't override, re-estimate, or interpolate any of those values. How NASA tracks near-Earth asteroids walks through where each data point originates.

Frequently asked questions

Is the Orbitfall Index a probability of impact?: No. It's a ranking of how notable a close approach is. It doesn't estimate probability of impact and shouldn't be read as risk, danger, or a threat level. For real impact-monitoring output, see NASA CNEOS Sentry.
What data does it use?: Miss distance (in lunar distances), average estimated diameter, relative velocity in km/s, and whether NASA has flagged the object as potentially hazardous. All values come from NASA's NeoWs API.
Why these four inputs?: They're the four things that most obviously make a close approach worth reading about: how close, how big, how fast, and whether it's on NASA's watch list.