Palermo Technical Impact Hazard Scale Facts for Kids

The Palermo Technical Impact Hazard Scale is a special way astronomers measure how risky it is for a near-Earth object (like an asteroid or comet) to hit Earth. It's like a scientific score that tells us if an object is a big worry or not.

This scale uses two main things to give a score:

How likely it is for the object to hit Earth (its probability).
How much energy it would release if it did hit (its kinetic yield).

A score of 0 means the risk is about the same as the normal "background" risk from similar objects over time. If an object gets a score of +2, it means the risk is 100 times higher than this normal background risk. Scores below -2 mean there's almost no chance of impact. Scores between -2 and 0 mean scientists should keep a close eye on the object.

There's also a simpler scale called the Torino Scale. This one is used for easier explanations in news and media.

As of early 2025, no asteroid has a total Palermo Scale rating above 0. Only a few asteroids have ratings between -2 and 0. In the past, some asteroids had higher ratings, but these usually went down after more observations.

How the Palermo Scale Works
Asteroids with High Ratings
See also

How the Palermo Scale Works

The Palermo Scale is a logarithmic scale. This means that each step on the scale represents a big change in risk. For example, a score of 1 is 10 times riskier than a score of 0. A score of 2 is 100 times riskier than a score of 0.

The scale helps scientists compare the risk of different space objects. It combines the chance of impact with how powerful the impact would be. This gives a single number that shows the overall danger.

Asteroids with High Ratings

This picture shows how the chance of an asteroid hitting Earth changes. As scientists get more information, the area where the asteroid could be gets smaller. Sometimes, this smaller area might show a higher chance of impact if Earth is in the way. But usually, with more data, the chance drops to zero as we learn Earth is safe.

Over time, some asteroids have had higher Palermo Scale ratings. But as scientists gather more information, these ratings often change. More observations help us understand an asteroid's path much better.

Asteroid 2002 NT7

In 2002, an asteroid named (89959) 2002 NT₇ got a Palermo Scale rating of 0.18. This meant it was considered a higher-than-normal threat for a short time. However, after scientists made more measurements, the risk score went down. By August 2002, this asteroid was no longer seen as a risk. It was removed from the Sentry Risk Table, which lists potentially dangerous objects.

Asteroid 1950 DA

In September 2002, the asteroid (29075) 1950 DA had a Palermo rating of 0.17. This was for a possible collision far in the future, in the year 2880. By March 2022, its rating had dropped to -2.0. As of October 2024, its rating is -0.93. This shows how ratings can change as we learn more.

Asteroid Apophis

For a short time in late 2004, asteroid [[99942 Apophis{{{2}}}|99942 Apophis_{{{2}}}]] had the highest Palermo Scale value ever recorded. It reached 1.10 for a possible collision in 2029. This score meant a collision with Apophis was thought to be almost 12.6 times more likely than a random background event. The chance was estimated as 1 in 37, compared to a normal risk of 1 in 472.

However, with more observations up to 2021, scientists are now sure there is no risk from Apophis for over 100 years. This is a great example of how more data helps us understand and reduce worries about space objects.

Current Higher-Rated Asteroids

As of January 2025, three asteroids have a total Palermo Scale value above -2:

2024 YR₄ (-0.43)
(29075) 1950 DA (-0.92)
101955 Bennu (-1.40)

Several other asteroids have scores between -2 and -4, meaning they are being watched but pose a very low risk.

Palermo Technical Impact Hazard Scale facts for kids

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