Asteroid Day marks a decade of planetary defense progress, but scientists say we need more eyes on the sky
"People will be hurt and killed" if we're not vigilant, scientists warn.
Tuesday marks the 10th anniversary of International Asteroid Day.
In the decade since the United Nations established the observance, scientists say Earth is better prepared to defend itself from the dangerous impact of one of the celestial bodies, which can range in size from a few feet across to a few hundred miles.
However, experts also warn that more needs to be done to protect us, including adding more eyes fixed on space.
"There's an 100% chance that if we don't do something, a dangerous asteroid will hit and people will be hurt and killed," Bruce Betts, chief scientist and LightSail program manager for The Planetary Society, told ABC News. "And it may be tomorrow and it may be 100 years from now."
The U.N. created Asteroid Day in 2016, commemorating the anniversary of the 1908 Tunguska event, when an asteroid exploded over Siberia, flattening trees and causing destruction as far out as 22 miles from the explosion's epicenter in what stands as the largest impact event in modern history.
The Tunguska asteroid's estimated size was about 130 feet in diameter, according to NASA. Today, scientists are scanning the sky in search of asteroids far larger.
"I think one of the biggest risks for us in planetary defense is that we don't know where all of these objects are," said Katie Kumamoto, head of the planetary defense group at Lawrence Livermore National Laboratory. "And we're doing a lot of work to find them."
What's an asteroid and how do we find them?
As of April 2025, astronomers have identified nearly 40,000 near-Earth objects, or NEOs – that is, asteroids and comets whose orbits bring them close to Earth – according to a report from NASA's Office of the Inspector General.
NASA has classified a fraction of those NEOs as "potentially hazardous asteroids," a category that includes space rocks that come dangerously close to Earth's orbit and are large enough to cause significant regional or global damage were they to hit the planet.
While not every space rock is guaranteed to pose a real threat, scientists say looking for them is the first step.
"It's more important to find them, because you can't do anything about it if you don't know it's there," Betts said.
For years, astronomers and space agencies struggled to locate and track asteroids. But with the development of programs like NASA's Near-Earth Object Observations Program in the late 1990s, planetary defense has evolved from simply tracking space rocks to modeling their paths, and even testing whether one could be pushed off course. NASA's Double Asteroid Redirection Test (DART) program was the first mission to demonstrate that redirecting an asteroid is actually possible.
"We just haven't gone to that many asteroids in human history," said Kumamoto, who worked on NASA's DART mission. "The number of asteroids we've actually touched, you can count on your fingers."
In September 2022, an autonomous spacecraft was intentionally sent to collide with the asteroid Dimorphos, as it circled its moon Didymos, nearly seven million miles away from Earth.
A post-mission analysis by NASA revealed that DART's successful impact of Dimorphos changed Didymos' shape and altered its orbital path around the sun, as well as that of a neighboring asteroid.
Despite the scientific community's progress in planetary defense, it's still not enough, according to experts who say we don't have enough telescopes dedicated to spotting and tracking all of the potentially dangerous space rocks.
"The key reason that we haven't met that, we as humanity, and we as NASA, is that we haven't had the telescopes with sufficient sensitivity to detect all of these asteroids, particularly when they're far from Earth," Betts said.
Asteroids are notoriously difficult to spot from Earth against the endless darkness of space.
"We're looking for something that's not going to reflect a lot of light – it's not going to generate its own light, because it's just a rock," Kumamoto said.
To assist NASA in finding more potentially hazardous asteroids, the agency is preparing to launch the Near-Earth Object Surveyor, a space telescope designed to detect asteroids and comets that could pose a threat to Earth. Using sensitive infrared detectors, the Surveyor can detect the heat asteroids and comets absorb from the sun, making them easier to identify.
Launching as early as fall 2027, the Surveyor spacecraft is being tasked with finding at least "two-thirds of potentially hazardous asteroids" during its five-year mission, NASA said.
Kumamoto was also involved in the response when asteroid 2024 YR4 briefly emerged as the most significant impact threat in modern history. The asteroid was assessed at having a 3.1% chance of hitting Earth before additional observations ruled it out.
"Zero is where we want to be," Kumamoto said.
Once NEO Surveyor starts to spot more asteroids, "we're going to have more and more cases like this where we maybe cross that 1% probability threshold," she added. One percent is the threshold at which scientists start paying closer attention to the risk.
The next big thing
One of the most tangible examples of the celestial threats facing Earth is an asteroid named Apophis. Roughly 1,500 feet across and larger than the Empire State Building is tall, according to NASA, it's on track to pass within about 20,000 miles of Earth in April 2029.
Hundreds of miles closer to us than the moon, the massive asteroid will be visible to the naked eye.
"Although Apophis was identified as one of the most hazardous asteroids that could impact Earth, astronomers have since ruled out an impact for the next 100 years," NASA's Office of Inspector General wrote in a June 2025 report. "It has the potential destructive power to take out a metropolitan area."
In addition to Apophis being a rare occurrence and remarkably large, Betts says its proximity makes it an almost unprecedented opportunity for scientific study.
"It's a once in a thousand years type thing where you have an object that big, it's three football fields wide, flying that close to earth," Betts said. "You go partly because you don't know what we will see."
However, NASA likely won't have a spacecraft there for the main event. The agency's fiscal year 2026 and 2027 budget requests proposed terminating the Apophis flyby mission. The spacecraft that was being repurposed, OSIRIS-APEX, will now arrive only after the closest approach has already passed, according to the space agency's website.
The NASA OIG report called it a missed opportunity, noting that restoring the mission "could be a goodwill branding benchmark for NASA and the Agency's planetary defense efforts."
The European Space Agency's Ramses mission is still on track to be there during the massive asteroid's closest approach to Earth.
"Asteroids sit at this interesting cornerstone," Kumamoto said. "There's all this science about what they tell us about the early solar system, but also this applied science of, these rocks are just flying around through space and someday there will be one we have to deal with if we don't want to go the way of the dinosaurs."
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