How to Read a Sentry Risk Table Without Panic

When NASA or ESA detects a newly discovered near-Earth asteroid with an orbit that intersects Earth path, its data is automatically published to automated impact monitoring systems like JPL Sentry and ESA NEODyS. The tables contain numbers that look alarming without context. Here is how planetary scientists interpret them:

1. Cumulative Impact Probability (IP): This is the summed statistical probability that an asteroid will impact Earth across all its predicted close approaches over the next century. Most table entries show numbers like 1.2e-5, which means 0.000012, or a 1 in 83,000 chance. The denominator tells the real story: there is a 99.9988 percent chance the asteroid misses Earth entirely.

1. Torino Scale (0 to 10): Designed for public communication, the Torino Scale combines collision probability with kinetic energy.
2. - Level 0 (White): Zero hazard. The likelihood of a collision is zero or effectively zero.
3. - Level 1 (Green): Normal discovery. An asteroid pass that requires routine tracking, virtually certain to be downgraded to 0 as more data arrives.
4. - Levels 2 to 4 (Yellow): Merits attention by astronomers.
5. - Levels 5 to 7 (Orange): Threatening encounters requiring government contingency planning.
6. - Levels 8 to 10 (Red): Certain collision capable of localized devastation, regional destruction, or global climatic catastrophe.
7. Currently, zero known objects are ranked above Level 0.

1. Palermo Technical Scale (PS): Designed for specialists, Palermo scale values are logarithmic comparisons between the probability of an impact and the background hazard posed by random space debris of the same size over the intervening years.
2. - Values below -2.0 mean the event poses less than 1 percent of the background risk.
3. - Values between -2.0 and 0.0 indicate events that warrant careful monitoring.
4. - Positive values (above 0.0) indicate an encounter where the risk exceeds the background impact hazard.

Almost every newly discovered asteroid that appears on Sentry enters with an orbital arc of only a few days. As telescopes continue tracking the object over weeks and months, the orbital ellipse shrinks by orders of magnitude, and in virtually every case, Earth falls completely outside the uncertainty ellipse, causing the probability to collapse to zero.