A
numerical measure of
asteroid collision hazards
similar to the
Richter scale for earthquakes. The below was taken wholesale from http://neo.jpl.nasa.gov/torino_scale.html and appears to not be copyrighted.
Events Having No Likely
Consequences
(White Zone)
Level 0 :
The
likelihood of a collision is zero, or well
below the chance that a
random object of
the same size will strike the
Earth within the
next few decades. This
designation also
applies to any small object that, in the
event of a collision, is unlikely to reach the
Earth's surface
intact.
Events Meriting Careful
Monitoring
(Green Zone)
Level 1 :
The chance of collision is extremely
unlikely, about the same as a random object
of the same size striking the Earth within
the next few
decades.
Events Meriting Concern
(Yellow Zone)
Level 2 :
A somewhat close, but not unusual
encounter. Collision is very unlikely.
Level 3 :
A close encounter, with 1
% or greater
chance of a collision capable of causing
localized
destruction.
Level 4 :
A close encounter, with 1% or greater
chance of a collision capable of causing
regional devastation.
Threatening Events
(Orange Zone)
Level 5 :
A close encounter, with a significant threat
of a collision capable of causing regional
devastation.
Level 6 :
A close encounter, with a significant threat
of a collision capable of causing a global
catastrophe.
Level 7 :
A close encounter, with an extremely
significant threat of a collision capable of
causing a global catastrophe.
Certain Collisions
(Red Zone)
Level 8 :
A collision capable of causing localized
destruction. Such events occur somewhere
on Earth between once per 50 years and
once per
1000 years.
Level 9 :
A collision capable of causing regional
devastation. Such events
occur between
once per 1000 years and once per
100,000
years.
Level 10 :
A collision capable of causing a global
climatic catastrophe. Such events occur
once per 100,000 years, or less often.