For a brief window, Asteroid 2024 YR4 looked like a planetary hazard in the making. At up to 90 meters (295 feet) in diameter, it was described as a potential “city killer.” On its estimated trajectory, it could’ve collided with Earth as soon as 2032. According to the Torino Impact Hazard Scale, used to characterize such threats, it ranked a Level 3 out of 10 — a highly unusual designation, suggesting a “close encounter” was plausible.
Panic is no longer in order: The National Aeronautics and Space Administration has just reduced the odds of impact to 0.0017%, down from a high of 3.1%. But the uncomfortably uncertain path of this asteroid — discovered only in late December — offered a timely reminder of how vulnerable humanity remains to hidden perils whirling through space, and how much still needs to be done to protect the planet.
More than 38,000 asteroids are known to be in Earth’s vicinity, including 973 “planet killers” of more than half a mile in diameter. Most pose no risk. But NASA estimates that only about 43% of nearby asteroids exceeding 140 meters (460 feet) have so far been found. A direct impact from one could cause mass casualties and untold damage; many more rocks the size of YR4 remain undetected.
To NASA’s credit, defenses have significantly improved in recent years. The agency has created a monitoring system, called Sentry, to scan for and publish data on nearby asteroids; established the Planetary Defense Coordination Office; and plans to launch a new infrared telescope in 2027 to hunt for threats. Most spectacularly, in 2022, its Double Asteroid Redirection Test smashed a spacecraft into a 560-foot rock called Dimorphos, some 7 million miles away, knocking it off course and confirming NASA’s ability to deflect an inbound threat.
As for YR4, defensive measures were quickly set in motion. Because its chance of impact exceeded 1%, its detection triggered a global alert among space agencies. A team of astronomers was dispatched to use the James Webb Space Telescope to study the asteroid in more detail. Two UN-sponsored groups — the International Asteroid Warning Network and the Space Mission Planning Advisory Group — helped coordinate an international response. Thankfully, new observations have determined that the worst will be avoided.
Even so, the world’s planetary-defense planning still needs work.
As a start, NASA needs to make faster progress on Congress’ 2005 mandate to find 90% of larger nearby asteroids. The new space telescope, called NEO Surveyor, will help. But the agency’s budget is under constant strain from an unnecessary and impractical mission to return astronauts to the moon on a government-built rocket, which has cost $100 billion and counting. A rededication to practical science like asteroid detection is overdue. (It is also, not incidentally, the public’s top priority for NASA.)
Relatedly, Congress should fund more missions to test interception capabilities in space, on the DART model. Smashing stuff into approaching asteroids — “kinetic impact,” as the nerds say — is only one method among many and may not be appropriate for every threat. Other options, including gravity tractors, ion beams and nuclear devices, may provide better defenses and should be the subject of serious study.
Global coordination, finally, is a work in progress. An interagency exercise last year concluded that there was “limited readiness” for an impending strike and that the decision-making process “remains unclear.” Congress should specify what role executive-branch agencies should play in such a scenario, and the US should continue to conduct planetary-defense exercises with other spacefaring nations and the United Nations Office for Outer Space Affairs.
Although YR4 no longer poses a threat, it’s increasingly clear that Earth inhabits a dangerous neighborhood. Keeping out of harm’s way will require ambition, vigilance and no small amount of human ingenuity.
— Bloomberg Opinion via TNS
