Congress recognized this threat, and in the 1998 Spaceguard Survey, it tasked NASA to find and track 90% of the estimated total of near-Earth objects 0.6 miles (1 kilometer) across or bigger within 10 years. NASA surpassed the 90% goal in 2011.

In 2005, Congress passed another bill requiring NASA to expand its search and track at least 90% of all near-Earth objects 460 feet (140 meters) or larger by the end of 2020. That year has come and gone and, mostly because of a lack of financial resources, only 40% of those objects have been mapped.

As of Sept. 18, 2022, astronomers have located 29,724 near-Earth asteroids, of which 10,189 are 460 feet (140 meters) or larger in diameter and 855 are at least 0.6 miles (1 kilometer) across. About 30 new objects are added each week.

A new mission funded by Congress in 2018 is scheduled in 2026 to launch an infrared space-based telescope – NEO Surveyor – dedicated to searching for potentially dangerous asteroids.

We can prevent a disaster only if we know it is coming, and asteroids have sneaked up on Earth before.

A so-called “city-killer” asteroid the size of a football field passed less than 45,000 miles (72,420 kilometers) from Earth in 2019. An asteroid the size of a 747 jet came close in 2021, as did an asteroid 0.6 miles (1 kilometer) wide in 2012. Each of these was discovered only about a day before it passed Earth.

Research suggests that Earth’s rotation creates a blind spot, hiding some asteroids from detection or making them appear stationary. This may be a problem, as some surprise asteroids do not miss us. In 2008, astronomers spotted a small asteroid only 19 hours before it crashed into rural Sudan.

The recent discovery of an asteroid 1.2 miles (2 kilometers) in diameter suggests that there are still big objects lurking.

To protect the planet from cosmic dangers, early detection is key. At the 2021 Planetary Defense Conference, scientists recommended a minimum of five to 10 years’ preparation time to mount a successful defense against hazardous asteroids.

If astronomers find a dangerous object, there are four ways to mitigate a disaster. The first involves regional first-aid and evacuation measures. A second approach would involve sending a spacecraft to fly near a small- or medium-sized asteroid; the gravity of the craft would slowly change the object’s orbit. To change a bigger asteroid’s path, we can either crash something into it at high speed or detonate a nuclear warhead nearby.

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