Editing Palermo scale (section)

{{Short description|Logarithmic scale in astronomy}}
{{Use dmy dates|date=May 2019}}

The '''Palermo scale''' or '''Palermo technical impact hazard scale'''  is a [[logarithmic scale]] used by [[astronomer]]s to rate the potential hazard of impact of a [[near-Earth object]] (NEO). It combines two types of [[data]]&mdash;[[probability]] of impact and estimated [[kinetic energy|kinetic]] yield&mdash;into a single "hazard" value. A rating of 0 means the hazard is equivalent to the '''background hazard''' (defined as the average risk posed by objects of the same size or larger over the years until the date of the potential impact).<ref name="palermo"/> A rating of +2 would indicate the hazard is 100 times as great as a random background event. Scale values less than −2 reflect events for which there are no likely consequences, while Palermo scale values between −2 and 0 indicate situations that merit careful monitoring. A similar but less complex scale is the [[Torino scale]], which is used for simpler descriptions in the non-scientific media.

{{As of|2025|4|10}}, no asteroid has a cumulative rating for impacts above 0, and only two asteroids have ratings between −2 and 0. Historically, three asteroids had ratings above 0 and half a dozen more above −1, but most were downrated since.