- Asteroid 2024 YR4 has been a source of consternation because it carries an uncommonly high risk of colliding into Earth.
- It’s the most hazardous space rock detected since astronomers first discovered the notorious Apophis in 2004, which was eventually dismissed as a threat when it approaches in 2029.
- NASA and the Europeans Space Agency are among the world’s space agencies developing methods of protecting Earth from inbound threats.
The infinite cosmos is a dangerous place brimming with threatening space rocks that, at any moment, could be discovered on a treacherous collision course with Earth.
Just ask the dinosaurs.
The ancient animals infamously met their demise 66 million years ago when a huge space rock known as the Chicxulub impactor is widely believed to have ended their reign. The asteroid altered the planet’s climate and paved the way for mammals to rise from the proverbial ashes.
But thankfully, humanity has come a long, long way in the past several millions of years.
Now, ever-improving technology at our disposal has equipped us here on Earth to better detect – and prepare for – inbound asteroids, remnants from the early formation of our solar system some 4.6 billion years ago.
That’s why scientists aren’t too concerned – yet – about an asteroid spotted late in 2024 that poses the single biggest impact threat to Earth in two decades.
Estimated to be about 130 to 300 feet wide, the asteroid dubbed 2024 YR4 has just above a 1% chance of crashing into Earth in 2032. The object, classified as a near-Earth asteroid because its orbit would bring it within 30 million miles of Earth, is the most hazardous space rock detected since astronomers first discovered the notorious Apophis in 2004.
In the case of Apophis, further observations eventually allowed astronomers in 2021 to rule out the possibility of an impact when the asteroid makes a close flyby to Earth in 2029 and again in 2036. Scientists expect the same outcome as YR4 continues to be monitored around the world.
Should any asteroids ever do pose a serious threat to Earth, the world’s space agencies have for years begun to build a planetary defense against dangerous space rocks.
“We aren’t just waiting for an asteroid to strike,” Richard Moissl, head of the European Space Agency’s Planetary Defence Office, said in a recent statement. “We are taking active measures to help Earth defend itself against a potential impact.”
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What is asteroid 2024 YR4 and why are scientists paying attention to it?
Asteroid 2024 YR4 has been a source of consternation because it carries an uncommonly high risk of colliding into Earth – an event that would be catastrophic, even if it wouldn’t cause a mass extinction.
The space rock was spotted late last year and reported on Dec. 27, 2024 to the Minor Planet Center, the official authority for observing and reporting new asteroids, comets and other small bodies in the solar system. The object eventually caught the attention of NASA and other astronomers when it rose on the U.S. Space Agency’s Sentry Impact Risk Table, which tracks any known asteroids with a non-zero probability of hitting Earth.
Based on projections, the asteroid has little more than a 1% chance of impacting Earth on Dec. 22, 2032. Asteroid 2024 YR4 also rates 3 of 10 on the Torino Impact Hazard Scale, a method for astronomers to categorize and rate the threat of near-Earth objects.
For those reasons, the asteroid is one astronomers and public officials are keeping their eyes on until it’s likely to be ruled out as a threat.
Remember Apophis? Asteroid once posed even bigger threat
Asteroid 2024 YR4’s rating of 3 on the Torino Scale is the second-highest an asteroid has ever reached after the notorious Apophis briefly hit a rating of 4 many when it was first discovered. The risk of Apophis impacting Earth during its 2029 flyby even rose as high as 2.7% on the Sentry Impact Risk Table.
The Torino rating and impact likelihood made Apophis one of the most threatening asteroids ever observed. But as often happens, that initial dire assessment has since changed as astronomers tracked it and learned more about the orbit of the asteroid.
A radar observation campaign in March 2021 during a distant flyby that – combined with precise orbit analysis – is what eventually allowed astronomers to determine that the asteroid poses no risk of crashing into Earth for at least a century.
Instead, Apophis, which measures a quarter of a mile long – about the size of a cruise ship – is projected to come within 20,000 miles of our planet’s surface on April 13, 2029. The approach, which is closer than telecommunications satellites, will mark the closest any large asteroid has ever come to Earth, according to the ESA.
NASA, ESA prepare to send spacecraft to study Apophis
In the coming years, both NASA and the European Space Agency, NASA’s counterpart across the pond, plan to take advantage of the rare flyby by sending uncrewed spacecraft to observe Apophis.
NASA’s OSIRIS-REx, which gathered and returned a sample of asteroid Bennu in September, has been renamed OSIRIS-APophis EXplorer (OSIRIS-APEX) and sent on a trajectory that would allow it to cross paths with the asteroid in 2029. Though it will not collect samples this time around, OSIRIS-APEX will spend 18 months mapping the asteroid’s surface and analyzing its chemical makeup when it has its rendezvous with Apophis in June that year, according to NASA.
The ESA plans to launch a spacecraft of its own called Ramses. The Ramses spacecraft, which must be ready to launch a year ahead of time, will meet Apophis before it passes by Earth and accompany it on its way out of our orbit.
During that time, the mission will observe how the surface of the asteroid changes from being in such close proximity to Earth, the agency said in July.
DART and Hera: Missions to test, study asteroid-obliterating tech
The ongoing scientific preparation is not just about observation. In September 2022, NASA demonstrated that it was possible to nudge an incoming asteroid out of harm’s way by slamming a spacecraft into it as part of its Double Asteroid Redirection Test, or DART.
Launched in November 2021, DART traveled for more than 10 months before crashing into Dimorphos at roughly 14,000 mph. Though the tiny asteroid posed no threat to Earth, NASA had set out to test a method of redirecting threatening objects hurtling toward Earth.
Now, a craft from the European Space Agency is on the way to get an up-close look at the asteroid’s remnants.
Hera launched Oct. 7 from Cape Canaveral Space Force Station in Florida on a two-year journey to Dimorphos, which is a tiny moonlet asteroid orbiting the larger 2,560-foot space rock Didymos.
The spacecraft is expected to enter the Didymos binary system’s orbit in October 2026, when it will determine just how effective NASA’s test was, according to the agency. Officials hope that by analyzing the results of NASA’s experiment, space agencies will be better positioned to repeat the maneuver.
NASA is additionally working on an asteroid-hunting telescope known as the NEO Surveyor to find near-Earth objects capable of causing significant damage. Set to launch no earlier than June 2028, the telescope is designed to discover 90% of asteroids and comets that are 460 feet in size or larger and come within 30 million miles of Earth’s orbit.
UN designates 2029 ‘international year of asteroid awareness’
Public awareness is also crucial to understanding the cosmic threat Earth could one day face. In that spirit, the ESA recently announced its support of the United Nation’s designation of 2029 as “the International Year of Asteroid Awareness and Planetary Defense.”
The designation, intentionally timed for the year of Apophis’ close approach, is meant to foster international cooperation on planetary defense strategies while educating the public on near-Earth asteroids, the ESA said.
“As our technology improves, we will detect more asteroids on trajectories that bring them safely past Earth that we would have missed in the past,” the ESA’s Moissl said. “It is critical that we continue to support public engagement in order (to) help people around the world separate the facts from the fiction.”
Eric Lagatta covers breaking and trending news for USA TODAY. Reach him at elagatta@gannett.com