The Palermo Technical Impact Hazard Scale is a logarithmic scale used by astronomers to rate the potential hazard of impact of a near-earth object (NEO). It combines two types of data—probability of impact, and estimated kinetic yield—into a single "hazard" value. A rating of 0 means the hazard is as likely as 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 more likely than 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.
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:
- pi is the impact probability
- T is the time interval over which pi is considered
- fB is the background impact frequency
The background impact frequency is defined for this purpose as:
where the energy threshold E is measured in megatons, yr is the unit of T divided by one year.
The near-Earth object (89959) 2002 NT7 was the first near-Earth object detected by NASA's latest NEO program to be given a positive rating on the scale of 0.06, indicating a higher-than-background threat. The value was subsequently lowered after more measurements were taken and 2002 NT7 is no longer considered to pose any risk, and was removed from the Sentry Risk Table on 1 August 2002.
For a brief period in late December 2004, asteroid (99942) Apophis (then known only by its provisional designation 2004 MN4) held the record for Palermo scale values, 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 12.6 times more likely than a random background event: 1 in 37 instead of 1 in 472. With further observations, the possibility of a 2029 impact was eliminated, but as of August 2011 a maximum Palermo rating of −3.08 applies, due to a possible event in 2036.
Since September 2002, the highest Palermo rating maintained has been that of asteroid (29075) 1950 DA, with a value of 0.17 for a possible collision in the year 2880. 1950 DA is the only known asteroid whose hazard could be above the background level.
Famous quotes containing the words scale, hazard, technical and/or impact:
“That age will be rich indeed when those relics which we call Classics, and the still older and more than classic but even less known Scriptures of the nations, shall have still further accumulated, when the Vaticans shall be filled with Vedas and Zendavestas and Bibles, with Homers and Dantes and Shakespeares, and all the centuries to come shall have successively deposited their trophies in the forum of the world. By such a pile we may hope to scale heaven at last.”
—Henry David Thoreau (18171862)
“Who chooseth me must give and hazard all he hath.
Must givefor what? for lead, hazard for lead?
This casket threatens. Men that hazard all
Do it in hope of fair advantages;
A golden mind stoops not to shows of dross.”
—William Shakespeare (15641616)
“Woman is the future of man. That means that the world which was once formed in mans image will now be transformed to the image of woman. The more technical and mechanical, cold and metallic it becomes, the more it will need the kind of warmth that only the woman can give it. If we want to save the world, we must adapt to the woman, let ourselves be led by the woman, let ourselves be penetrated by the Ewigweiblich, the eternally feminine!”
—Milan Kundera (b. 1929)
“Too many existing classrooms for young children have this overriding goal: To get the children ready for first grade. This goal is unworthy. It is hurtful. This goal has had the most distorting impact on five-year-olds. It causes kindergartens to be merely the handmaidens of first grade.... Kindergarten teachers cannot look at their own children and plan for their present needs as five-year-olds.”
—James L. Hymes, Jr. (20th century)