The Palermo Technical Impact Hazard Scale is a

logarithmic scale A logarithmic scale (or log scale) is a way of displaying numerical data over a very wide range of values in a compact way—typically the largest numbers in the data are hundreds or even thousands of times larger than the smallest numbers. Such a ...

used by

astronomer An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as stars, planets, moons, comets and galaxies – in either ...

s to rate the potential hazard of impact of a

near-Earth object A near-Earth object (NEO) is any small Solar System body whose orbit brings it into proximity with Earth. By convention, a Solar System body is a NEO if its closest approach to the Sun (Apsis, perihelion) is less than 1.3 astronomical unit ...

(NEO). It combines two types of

data In the pursuit of knowledge, data (; ) is a collection of discrete values that convey information, describing quantity, quality, fact, statistics, other basic units of meaning, or simply sequences of symbols that may be further interpret ...

—

probability Probability is the branch of mathematics concerning numerical descriptions of how likely an event is to occur, or how likely it is that a proposition is true. The probability of an event is a number between 0 and 1, where, roughly speaking, ...

of impact and estimated

kinetic Kinetic (Ancient Greek: κίνησις “kinesis”, movement or to move) may refer to: * Kinetic theory, describing a gas as particles in random motion * Kinetic energy, the energy of an object that it possesses due to its motion Art and ent ...

yield—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). 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 December 2022, one asteroid has a cumulative Palermo Scale value above −2:

101955 Bennu 101955 Bennu (provisional designation ) is a carbonaceous asteroid in the Apollo group discovered by the LINEAR Project on 11 September 1999. It is a potentially hazardous object that is listed on the Sentry Risk Table and has the highest cumul ...

(−1.41). Five have cumulative Palermo Scale values between −2 and −3:

(29075) 1950 DA , provisional designation ', is a risk–listed asteroid, classified as a near-Earth object and potentially hazardous asteroid of the Apollo group, approximately in diameter. It once had the highest known probability of impacting Earth. In 200 ...

(−2.05), 1979 XB (−2.72), (−2.79), (−2.83), and (−2.98). There are 21 that have a cumulative Palermo Scale value between −3 and −4, three of which were discovered in 2022: (−3.20), (−3.56), and (−3.94).

Scale

The scale compares the likelihood of the detected potential impact with the average risk posed by objects of the same size or larger over the years until the date of the potential impact. This average risk from random impacts is known as the background risk. The Palermo Scale value, ''P'', is defined by the equation: :

P \equiv \log_ \frac

where :*''p_i'' is the impact probability :*''T'' is the time interval over which ''p_i'' is considered :*''f_B'' is the background impact frequency The background impact frequency is defined for this purpose as: :

f_B = \frac E^ \text^\;

where the energy threshold E is measured in

megatons TNT equivalent is a convention for expressing energy, typically used to describe the energy released in an explosion. The is a unit of energy defined by that convention to be , which is the approximate energy released in the detonation of a ...

, and yr is the unit of T divided by one year.

Positive rating

In 2002 the near-Earth object reached a positive rating on the scale of 0.18, indicating a higher-than-background threat. The value was subsequently lowered after more measurements were taken. is no longer considered to pose any risk and was removed from the

Sentry Risk Table Sentry is a highly automated impact prediction system operated by the JPL Center for NEO Studies (CNEOS) since 2002. It continually monitors the most up-to-date asteroid catalog for possibilities of future impact with Earth over the next 100+ y ...

on 1 August 2002. In September 2002, the highest Palermo rating was that of asteroid

, with a value of 0.17 for a possible collision in the year 2880. By March 2022, the rating had been reduced to −2.0. For a brief period in late December 2004, with an

observation arc In observational astronomy, the observation arc (or arc length) of a Solar System body is the time period between its earliest and latest observations, used for tracing the body's path. It is usually given in days or years. The term is mostly use ...

of 190 days, asteroid (then known only by its

provisional designation Provisional designation in astronomy is the naming convention applied to astronomical objects immediately following their discovery. The provisional designation is usually superseded by a permanent designation once a reliable orbit has been calc ...

) held the record for the highest Palermo scale value, with a value of 1.10 for a possible collision in the year 2029. The 1.10 value indicated that a collision with this object was considered to be almost 12.6Math: 10^1.10 = 12.589 times as likely as a random background event: 1 in 37 instead of 1 in 472. With further observation through 2021 there is no risk from Apophis for the next 100+ years.

References

External links

Palermo Technical Impact Hazard Scale
at the Sentry monitoring system by CNEOS at JPL from

NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeedin ...

{{Portal bar, Astronomy, Stars, Spaceflight, Outer space, Solar System, Science Alert measurement systems Hazard scales Planetary defense Logarithmic scales of measurement

Scale

Positive rating

See also

References

Further reading

External links