The 25 Most Dangerous Things Around Earth Right Now

Scientists have classified a number of near-Earth objects as potentially hazardous asteroids, or PHAs, because of their size and orbits that periodically bring them close — in space terms — to Earth. Didymos, which is about half a mile in size, is a PHA that travels around the sun every two years, often coming close to Earth. In 2003, it came within 4.45 million miles of Earth. In 2123, it will come within 3.33 millions miles, and in 2144, within 2.91 million miles.

Didymos B is the relatively tiny (about 558 feet across) moon of Didymos A, which is about 2,560 feet across. NASA, working with the ESA, will use Didymos to begin testing a system designed to deflect near-Earth objects from a collision course with Earth. The double asteroid redirection test, or DART, will target Didymos in a launch scheduled for next year, with impact the following year. If the test is successful, it will very slightly alter the orbit of Didymos B around Didymos A.

At 4 miles in diameter, JM8 is the largest of all PHAs. Though it has come as close as a few million miles from Earth in the last century, when it next approaches Earth in 2075 it will be at a distance of 23.8 million miles. In 2137, it will close in again at 7.1 million miles. For comparison, Venus is just 25 million miles away.

As part of its Sentry monitoring system, NASA lists asteroids that pose some risk, however small, of hitting the Earth in the next 100 years. Asteroids are listed in order of their rating on the Palermo Technical Impact Hazard Scale, which measures both the probability of an asteroid’s collision with Earth and the amount of energy that would be released on impact.

For the last several years, the PHA known as 1950 DA has been given the highest Palermo rating because of its large size, about two-thirds of a mile in diameter, and the devastating impact it would have on the biosphere and climate were it to strike Earth. Still, the chance of such an encounter on the next closet visit in 2880 is 1 in 8,300.

The asteroid known as Bennu is second only to 29075 (1950 DA) on the Palermo Scale. About one-third of a mile in diameter, it has been described by a NASA scientist as a pile of rubble because of its low density. Its chance of colliding with Earth in its next near visit is 1 in 2,700.