☄️ Asteroids & Cosmic Threats

Background: why this matters

Asteroid impacts are the best-documented cause of a past mass extinction. About 66 million years ago an object roughly 10 km across struck what is now Mexico's Yucatán Peninsula, forming the Chicxulub crater. The impact is widely accepted as the trigger of the extinction that ended the age of dinosaurs. Smaller impacts are far more frequent. In 1908 an airburst over Tunguska in Siberia flattened about 2,000 km² of forest. In 2013 a meteor about 20 m across exploded over Chelyabinsk, Russia, and injured around 1,500 people, mostly from broken glass.

Unlike most risks on this site, this one is well understood and largely solvable. NASA and its partners have found the great majority of the near-Earth asteroids 1 km or larger, the size that could cause global devastation, and none is on a collision course. The remaining risk is mostly from smaller objects, 140 m and up, large enough to destroy a region. The U.S. Congress set a goal of finding 90% of them, and new tools such as the Vera C. Rubin Observatory and NASA's planned NEO Surveyor space telescope aim to close the gap.

Humanity has also tested a defence. In September 2022 NASA's DART mission deliberately crashed into Dimorphos, a small moon of the asteroid Didymos, and shortened its orbit by about 32 minutes. It was the first demonstration that a spacecraft can change an asteroid's path. In early 2025 the newly found asteroid 2024 YR4 briefly reached Torino level 3, with an impact probability of a few percent for 2032, before further observations ruled out an Earth impact.

This factor uses NASA/JPL's Sentry system, which continuously computes impact probabilities for every known asteroid over the next century or more. It uses two scales. The Torino Scale (0–10) is for public communication: 0 means no hazard, and anything at 1 or above is usually downgraded to 0 as more observations come in. The Palermo Scale compares an object's risk with the background chance of a similar impact. Values below −2 are of no likely consequence, and above 0 would be genuinely concerning. We also check JPL's close-approach data for large objects passing inside the Moon's orbit.

What experts watch: newly discovered objects with non-zero Torino ratings, follow-up observations that refine their orbits, survey completeness for 140 m objects, and funding for planetary defence missions.