Asteroid's Chance of Smacking Earth Drops Dramatically. Here's What to Know

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Whew. Earth has dodged an asteroid scare. Asteroid 2024 YR4 was looming large in humanity's vision. At one point, it was calculated to have a roughly 3.1% chance of impacting Earth on Dec. 22, 2032. That was enough to trigger some concern, but astronomers cautioned that more data was needed to fully understand the asteroid's trajectory and size.

The new data is in.

"NASA has significantly lowered the risk of near-Earth asteroid 2024 YR4 as an impact threat to Earth for the foreseeable future," the space agency said in an update on Feb. 24. The European Space Agency said the asteroid "no longer poses significant impact risk."

Asteroid 2024 YR4 will come close to Earth in late 2032, but we won't have to make any doomsday preparations. It's expected to pass safely by.

The asteroid was first reported by the Minor Planet Center on Dec. 27. The MPC, part of the International Astronomical Union, maintains an official catalog of near-Earth objects like asteroids and comets. It reports, names and numbers new discoveries. Multiple observatories spotted the asteroid.

With only early data to go on, ESA placed 2024 YR4 at the top of its asteroid risk list. Similarly, the space rock also took the top spot on NASA's Sentry risk list. The Sentry list contains all known near-Earth asteroids with a nonzero probability of striking Earth. Those designations were fortunately temporary.

Rating asteroids and their impact hazards

No Hazard (White Zone) 0 The likelihood of a collision is zero, or is so low as to be effectively zero. Also applies to small objects such as meteors and bodies that burn up in the atmosphere as well as infrequent meteorite falls that rarely cause damage. Normal (Green Zone) 1 A routine discovery in which a pass near the Earth is predicted that poses no unusual level of danger. Current calculations show the chance of collision is extremely unlikely with no cause for public attention or public concern. New telescopic observations very likely will lead to re-assignment to Level 0. Meriting Attention by Astronomers (Yellow Zone) 2 A discovery, which may become routine with expanded searches, of an object making a somewhat close but not highly unusual pass near the Earth. While meriting attention by astronomers, there is no cause for public attention or public concern as an actual collision is very unlikely. New telescopic observations very likely will lead to re-assignment to Level 0. 3 A close encounter, meriting attention by astronomers. Current calculations give a 1% or greater chance of collision capable of localized destruction. Most likely, new telescopic observations will lead to re-assignment to Level 0. Attention by public and by public officials is merited if the encounter is less than a decade away. 4 A close encounter, meriting attention by astronomers. Current calculations give a 1% or greater chance of collision capable of regional devastation. Most likely, new telescopic observations will lead to re-assignment to Level 0. Attention by public and by public officials is merited if the encounter is less than a decade away. Threatening (Orange Zone) 5 A close encounter posing a serious, but still uncertain threat of regional devastation. Critical attention by astronomers is needed to determine conclusively whether or not a collision will occur. If the encounter is less than a decade away, governmental contingency planning may be warranted. 6 A close encounter by a large object posing a serious but still uncertain threat of a global catastrophe. Critical attention by astronomers is needed to determine conclusively whether or not a collision will occur. If the encounter is less than three decades away, governmental contingency planning may be warranted. 7 A very close encounter by a large object, which if occurring over the next century, poses an unprecedented but still uncertain threat of a global catastrophe. For such a threat, international contingency planning is warranted, especially to determine urgently and conclusively whether or not a collision will occur. Certain Collisions (Red Zone) 8 A collision is certain, capable of causing localized destruction for an impact over land or possibly a tsunami if close offshore. Such events occur on average between once per 50 years and once per several 1000 years. 9 A collision is certain, capable of causing unprecedented regional devastation for a land impact or the threat of a major tsunami for an ocean impact. Such events occur on average between once per 10,000 years and once per 100,000 years. 10 A collision is certain, capable of causing global climatic catastrophe that may threaten the future of civilization as we know it, whether impacting land or ocean. Such events occur on average once per 100,000 years, or less often.

The asteroid had been rated a 3 out of 10 on the Torino Impact Hazard Scale, a tool used for categorizing potential impacts. That meant 2024 YR4 merited attention from astronomers, the public and public officials, since a possible strike was less than a decade away.

"An object that reaches this level is not uncommon; there have been several objects in the past that have reached this same rating and eventually dropped off as more data have come in," NASA said in a statement on Jan. 29. That proved to be the case with 2024 YR4.

The highest level on the Torino Scale is a 10, which indicates a certain collision capable of catastrophic damage on a global level. Asteroid 2024 YR4 is now at a Level 0 on the scale.

The asteroid's numbers yo-yoed over time. It started at a roughly 1% impact probability, then NASA revised that to 2.3% on Feb. 7. Later, it hit 3.1%.

"The key takeaway is the increase is expected at this stage and is not a cause for concern," Planetary Society spokesperson Danielle Gunn told CNET over email in reference to the asteroid reaching 3.1%.

Now, the Sentry entry for 2024 YR4 shows a 0.0017% chance of striking Earth. New telescopic observations helped to dial in the udpated probability.

"Note that often, counterintuitively, the odds of impact go up before they drop to zero," said Planetary Society Chief Scientist Bruce Betts in a statement in January. Betts noted the increase is usually temporary.

The data gathering and probability calculation process worked like it was supposed to.

"The rise and fall of the asteroid's impact probability has followed an expected and understood pattern," ESA said in a statement on Feb. 25.

Size estimates of asteroid 2024 YR4

The NASA-funded Asteroid Terrestrial-impact Last Alert System in Chile captured imagery of asteroid 2024 YR4.

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The asteroid is estimated to be 130 and 300 feet wide. For scale, the Statue of Liberty (pedestal included) is about 300 feet tall. That's worrisome for an asteroid, but it's not a "planet killer."

"An asteroid this size impacts Earth on average every few thousand years and could cause severe damage to a local region," the ESA said in a statement. That's why the asteroid was referred to as a "city killer" in some headlines.

The James Webb Space Telescope is scheduled to set its sights on the asteroid in March to get a better idea of the space rock's size. NASA didn't immediately respond to a request for comment on what Webb could tell us about 2024 YR4.

What's next for asteroid 2024 YR4

Illustration of two gray asteroids with NASA's boxy solar-powered DART spacecraft nearby.

The asteroid is currently on the move away from Earth. Space agencies and organizations coordinated efforts to track the asteroid and better understand its trajectory and size.

NASA and other space agencies have been working on planetary defense options in the case of a dangerous asteroid. NASA's Double Asteroid Redirection Test mission successfully redirected an asteroid moonlet by smashing a spacecraft into it in 2022. The ESA suggested a spacecraft-based response could be explored if 2024 YR4 turned out to be a serious threat.

While Earth is in the clear, the asteroid currently has a 1.7% probability of hitting the moon. That number could change as observations continue to come in.

NASA has a page dedicated to 2024 YR4 so the public can stay updated on the latest information about the asteroid before it visits in 2032.

For now, a collective sigh of relief is in order.

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