A "potentially hazardous" asteroid about twice the size of the Empire State Building will skim past Earth on Thursday, April 28, 2022, at over 23,000 miles per hour—but the risk to us Earthlings down below is pretty much non-existent.
The asteroid, designated 418135 (2008 AG33), is believed to be about 1,150 to 2,560 feet (350 to 780 meters) in diameter and is careening through space at about 23,300 miles per hour (37,400 kilometers an hour). According to Live Science, at its closest approach to Earth, its speed will be about 30 times faster than the speed of sound, and it will cross Earth's orbit within 2 million miles (3.2 million kilometers).
For context, that is about eight times the distance between the Earth and the Moon (a "lunar distance", or LD, which is about 238,855 miles, or 384,400 kilometers), which sounds like a massive distance to us, but in terms of the solar system, this is pretty much nothing. The James Webb Space Telescope, for example, is only about 1 million miles (1.5 million kilometers) away at Earth's second LaGrange point, and it took about a month to get there.
That said, the James Webb Space Telescope was only cruising at about 720 miles an hour, which is about 3.2% of the velocity of 418135 (2008 AG33), so the asteroid is covering about the length of Webb's entire month-long journey in about a day. Needless to say, an impact at that speed would be devastating, which is why NASA has a fairly liberal view of what it considers "potentially hazardous."
What does it mean for an asteroid to be 'potentially hazardous'?
Given the potential devastation from an impact with a Near-Earth Object (NEO), even objects like asteroids that represent a very low risk to Earth are carefully monitored by NASA's Center for Near Earth Object Studies (CNEOS), the monitoring arm of NASA's Planetary Defense Coordination Office (PDCO).
"The PDCO is responsible for providing timely and accurate information to the government, the media, and the public on close approaches to Earth by potentially hazardous objects (PHOs) and any potential for impact," NASA says.
"If any PHO is found to pose a significant chance of impacting Earth (greater than 1 percent over the next 50 years), the PDCO will provide notification messages for NASA to send to the Executive Office of the President, the U.S. Congress, and other government departments and agencies."
NASA considers any NEO coming within 30 million miles of Earth's orbit as a potential hazard, but it is most concerned about those objects that cross Earth's orbit within one LD, which is close enough to potentially hit the planet.
"Currently, an asteroid impact is the only natural disaster we might be able to prevent," NASA says. "There are a few methods that NASA is studying to deflect an asteroid on a course to impact Earth."
One of the most important will be NASA's Double-Asteroid Redirect Test (DART) mission, which will send a spacecraft on a collision course with the asteroid system Didymos later this year.
"DART’s target is a binary asteroid system where one football-stadium-sized asteroid (Didymos B) is orbiting a half-mile-wide asteroid (Didymos A)," NASA said. "NASA’s goal is to send the car-sized DART spacecraft slamming into Didymos B at 25,000 kilometers per hour (16,000 miles per hour) to determine by how much the impact can shift the orbit of Didymos B around Didymos A."
While it might seem like NASA is trying to blow up the asteroid, that isn't necessary to be an effective planetary defense.
"After all," NASA explains, "we’d only need to nudge an asteroid’s orbit enough to make it either seven minutes early or seven minutes late in its intersection with Earth’s orbit. It takes seven minutes for the Earth to travel the distance of its diameter, so if an asteroid arrives seven minutes early or late—it’ll miss us completely."