On June 30, 1908, Akulina, a reindeer herder in Siberia, left her tent to greet the day. It was about 7 a.m., and all she could see for miles around her was the vast forest, standing tall against the clear blue sky. A heartbeat later, that forest vanished. A preternatural screech issued from above, and the world flushed crimson. “All around, we saw a miracle, a terrible miracle,” Akulina later recalled. An estimated 80 million trees across an 800-square-mile patch of forest—larger than the city of Houston—had been felled instantaneously.
This devastation, known as the Tunguska event, resulted from the force of a 10-to-20-megaton blast. It was so tremendous that its glow lit up the dark, moonless night sky in Northern Ireland, 3,500 miles away. And it was caused by the midair explosion of a space rock just 180 feet long.
As best as anyone can tell, if any hazardously sized asteroid were to hit Earth in the relatively near future, it would most likely be 2024 YR4, a 130-to-300-foot rock that’s essentially the same size as the asteroid that exploded over Siberia. Not long after it was discovered, just two days after it zipped right past Earth, NASA and the European Space Agency’s sky watchers calculated that 2024 YR4 has a nonzero chance of hitting Earth on December 22, 2032. Right now, the asteroid is 68 million kilometers away from the planet, but it’ll come back around. The odds of an impact in December 2032 have been fluctuating, but—based on the latest telescopic observations—they stand at just over 2 percent.
These odds will likely drop close to zero when more observations come in. But the current odds are still higher than anyone would prefer. A strike in a remote part of the world wouldn’t be a problem. But if the asteroid directly hits a city, millions could die.
However apocalyptic that might sound, the fact that we can imagine 2024 YR4’s impact is by design: Space agencies—particularly NASA—have become rather good at spotting asteroids. And two revolutionary observatories coming online in the next few years will only continue to strengthen those skills, so that the planet will have an even better shot at blocking any real threats. That people are effectively taking bets on Earth’s chance of being hit is a reason to be genuinely optimistic about the future of the world: Asteroid strikes are a rare but very real type of natural disaster, and we have never been safer from them.
Right now, NASA’s Near-Earth Object Observations Program funds several observatories whose only directive is to spot and track near-Earth asteroids and comets, just in case one of them may be bound for Earth. 2024 YR4, a relatively small asteroid by space standards, was spotted by one of those groups, the Asteroid Terrestrial-impact Last Alert System, which has found almost 1,200 near-Earth asteroids to date. Another group of telescopes, the Catalina Sky Survey, in Arizona, has found 16,500 near-Earth asteroids since 1995. In total, the program’s observatories have collectively found close to 40,000.
Earth can’t defend itself against an asteroid if no one sees it coming. 2024 YR4 was spotted eight years in advance of its potential impact, which means that space agencies can decide to do something about it—whether that’s trying to ram into it with an uncrewed spacecraft, using a nuclear weapon to deflect or vaporize it, or evacuating the future impact site. The best chance to act may be in 2028, the asteroid’s next Earth flyby. That doesn’t leave a lot of time to plan an anti-asteroid defense mission, but the planet is certainly in a better position than it would be not knowing 2024 YR4 existed.
Asteroid spotters were still somewhat fortunate to have noticed it though. Near-Earth objects are found when they reflect starlight, and huge asteroids, the sort that could end civilization, are essentially giant spherical mirrors floating about in space—very easy to spot. As they get smaller and smaller, though, asteroids look like specks of light. An asteroid the size of 2024 YR4 is stealthy enough that astronomers may not have seen it until 2028, or even just prior to its possible impact in 2032.
This will soon be an uncommon problem. The U.S. has invested heavily in two next-generation observatories that will be able to spot alarming asteroids with ruthless efficiency. One of them is the Vera C. Rubin Observatory, a nearly complete facility atop a Chilean mountain, which was funded by both the U.S. National Science Foundation and the Department of Energy. Rubin has an ambitious goal: to document everything that shimmers, explodes, or zips by in the night sky. It is a multipurpose, polymathic telescope that will look for exploding stars and distant galaxies. But it will also find an abundance of asteroids. After the Italian priest and astronomer Giuseppe Piazzi first discovered an asteroid in 1801, astronomers needed two centuries to tally 1 million of them. Thanks to an extremely wide-angle lens and a colossal nest of light-collecting mirrors, Rubin will likely double this number just a few months after it starts its survey—and plenty of the asteroids it finds may be those that linger disquietingly close to Earth’s orbit.
But Rubin, for all its strengths, will still rely on reflected starlight, which can be deceptive. If an asteroid has a dusty coating, it reflects less light than one with a shiny shell. That means that a tiny, shiny asteroid looks the same as a large, dusty space rock—and astronomers cannot tell how large it is. (This is the case with 2024 YR4, hence the size range given.)
The Near-Earth Object Surveyor, funded by NASA’s Planetary Defense Coordination Office, works differently. After surviving a painful gantlet of funding cuts, the observatory is scheduled to launch into space before the decade’s end and make its way to a lonely spot far from Earth. Because of its sunshade and its very dark paint job, it will be an extremely cold object—which will allow its infrared, heat-seeking eyes to operate with unparalleled precision. And when viewed in infrared, a large asteroid glows brighter than a smaller one, with no exceptions.
NEO Surveyor will also be unimpeded by Earth’s obfuscating atmosphere and will even be able to spot small asteroids hidden by the bright, thermonuclear glare of the sun, where several near-Earth objects are thought to be hiding. As the name suggests, this observatory will be solely dedicated to looking for near-Earth objects, and within a decade of its operations, it should find at least 90 percent of near-Earth asteroids that are at least 460 feet long.
Such asteroids are called “city killers” because if one hits a city, it’s virtually guaranteed to destroy it. There are estimated to be 25,000 city-killer-size asteroids in near-Earth orbits, and just under half have been found. 2024 YR4–size asteroids are far more plentiful. There are 230,000 of them in near-Earth orbits, and only about 7 percent of them have been found. Some of them will have a greater than 2 percent chance of hitting us, but humanity has never been less reliant on luck to dodge this kind of space-borne catastrophe.
Achieving the next level of certainty, though, requires both Rubin and NEO Surveyor to go forward as planned. Planetary defense is an international-security issue, and NASA’s partners, particularly the European Space Agency and the Japan Aerospace Exploration Agency, are developing their own asteroid-studying space missions and expanding their Earth-based telescopic coverage. The U.S., though, is clearly leading the way. Anti-asteroid research efforts are celebrated by the American public, and have garnered support in Congress from both Democrats and Republicans for decades.
Still, the second Trump administration has not yet outlined its space priorities, and deep funding cuts are expected for a variety of scientific programs. NASA declined to comment on the future of planetary-defense programs; a spokesperson noted in an email that they are “looking forward to hearing more about the Trump Administration’s plans for the agency.” And planetary defense could remain a priority: Elon Musk, who has so far been central to Trump’s drive to shrink the federal government, has well-documented interests in space and existential risk (albeit with more of a focus on getting humans to Mars than defending Earth). But if the cuts at the level experts fear go through, “we would face severe program disruptions at NASA, even for widely supported activities like planetary defense,” Casey Dreier, the chief of space policy at The Planetary Society, told me.
The odds of this impact happening are arguably higher than 2024 YR4’s chances of hitting Earth, but Patrick Michel, the principal investigator of Europe’s asteroid-chasing Hera mission, told me that, “at least for now, NASA keeps very active in planetary defense. And I don’t have any indication that it would change.” Even so, he notes, developing more redundancy in technology that can spot, examine, or deflect asteroids would keep Earth safer in the long run. 2024 YR4 will probably turn out to be harmless. But if it is heading Earth’s way—or the next asteroid is—the world will look to America to prevent a potentially catastrophic impact.
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