Apophis: a close call, not a collision

An asteroid can become more interesting as it becomes less dangerous. Apophis is a useful example: the date remains on the calendar, while the reason to watch it has changed.

The observation changed the story

Apophis was discovered in 2004. Early orbit estimates raised concern about a possible future impact. A short observation arc leaves room for multiple trajectories; collecting more measurements helps narrow that room. NASA’s 2021 analysis used radar observations to improve the orbit and ruled out an impact for at least a century.

The 2029 passage brings the asteroid about 32,000 kilometres above Earth’s surface, closer than geostationary satellites. That distance is a close approach in astronomical terms. It is not the distance to an impact, and being closer than one class of satellites does not imply a collision with them.

Why the date stays here

The ledger includes real events alongside predictions so that readers can compare their evidence. For Apophis, the event is a close approach. Its orbit is measured and modelled; the “end of the world” interpretation is not the current scientific conclusion. The entry therefore gets a scheduled-event label and a day-level date.

The earlier design attached a precise time without an adequately checked source. This version keeps the well-supported day and does not manufacture a second-by-second impact clock. A future timing refinement would be a change to the event record, with its source retained.

What would change our assessment?

New measurements and an updated orbit solution would be relevant evidence. A dramatic headline, a recycled early probability or an image of a different asteroid would not. That is a practical rule for reading asteroid news: identify the object, the encounter date, the observation date and the version of the risk calculation.

Risk assessment is allowed to improve. Removing an object from a risk list after better measurements is the process doing useful work. It is not a missed prophecy, nor proof that every asteroid can safely be ignored.

A better next question

Instead of asking whether this close approach “counts as doomsday”, ask what can be learned from it. Observing a nearby asteroid can improve knowledge of its motion and physical properties. The companion DART story asks a separate question: whether humans can deliberately change an asteroid’s motion. Measurement and intervention belong on different lines of the ledger.