Editing Asteroid impact avoidance (section)

== Impact probability calculation pattern ==
[[Image:AsteroidImpactProb.png|thumb|Why asteroid impact probability often goes up, then down.]]
The ellipses in the diagram on the right show the predicted position of an example asteroid at closest Earth approach. At first, with only a few asteroid observations, the error ellipse is very large and includes the Earth. Further observations shrink the error ellipse, but it still includes the Earth. This raises the predicted impact probability, since the Earth now covers a larger fraction of the error region. Finally, yet more observations (often radar observations, or discovery of a previous sighting of the same asteroid on archival images) shrink the ellipse revealing that the Earth is outside the error region, and the impact probability is near zero.<ref>{{cite web|url=http://www.spaceguarduk.com/scares.htm |title=Why we have Asteroid "Scares" |publisher=Spaceguard UK |archive-url=https://web.archive.org/web/20071222114100/http://www.spaceguarduk.com/scares.htm |archive-date=December 22, 2007}}</ref>

For asteroids that are actually on track to hit Earth the predicted probability of impact continues to increase as more observations are made. This similar pattern makes it difficult to differentiate between asteroids that will only come close to Earth and those that will actually hit it. This in turn makes it difficult to decide when to raise an alarm as gaining more certainty takes time, which reduces time available to react to a predicted impact. However, raising the alarm too soon has the danger of causing a [[false alarm]] and creating a [[Boy Who Cried Wolf]] effect if the asteroid in fact misses Earth.<ref>{{cite magazine |last=Tedeschi |first=Diane |date=October 2019 |title=How Worried Should We Be About Asteroids? |url=https://www.smithsonianmag.com/air-space-magazine/how-dangerous-are-asteroids-180973155/ |access-date=October 29, 2024 |magazine=Air & Space/Smithsonian |publisher=Smithsonian Institution |location=Washington, D.C.}}</ref>