Impact was imminent. Occasional gasps arose as the asteroid took shape and a jagged, rocky surface filled the view.Then the images abruptly stopped.
The mission control room at Johns Hopkins university Applied Physics Lab in Laurel, Md., erupted in cheers. “We have impact!” said the lead engineer,who gave a two-handed high five to a nearby colleague. Others waved their hands in the air in victory and slapped each other on the back.
This had been a test, and humanity had passed it, taking one crucial step closer to protecting Earth from an asteroid impact. The test was the culmination of NASA’s Double asteroid Redirection Test (DART) mission, for wich I was the coordination lead. on 26 September 2022, the DART spacecraft had successfully crashed into Dimorphos, a roughly 150-meter-diameter asteroid that was 11 million kilometers from Earth. The collision nudged the asteroid and modified its trajectory.
in 2022, NASA’s Double Asteroid Redirection Test slammed a golf-cart-size spacecraft, DART, into the near-Earth asteroid Dimorphos (1). DART-which first deployed a small observer craft, LICIACube, to observe the collision (2)-bumped Dimorphos’s trajectory (3) enough to alter its future course (4).GyGinfographics; Source: NASA
The celebrations in the control room were the culmination of years of effort to prove that the momentum from a golf-cart-size spacecraft can alter an asteroid’s future path. And DART’s collision with asteroid Dimorphos kicked off a new era in space explorationin which technologies for planetary defense are now taking shape.
If one day an asteroid like Dimorphos is discovered to be headed toward Earth, an interceptor craft like DART could collide with the asteroid years in advance to avert disaster. Here’s how that might work.
Step 1: Find and track Near-Earth Asteroids
The first step in averting an asteroid impact with Earth is just to know what near-earth objects (NEOs) are out there.
The University of Hawaii’s Asteroid Terrestrial-impact Last Alert System (ATLAS) station, in Chile plays a critical role in these observations of NEOs, which are asteroids orbiting near Earth’s orbit. In late December, it detected a previously unknown NEO during a routine sweep of the skies. The asteroid was given the name 2024 YR4, following the standard astronomical convention for new objects. “2024 Y” represents the 24th-half-month of the year 2024-that is, 16 to 31 December. The “R4” encodes the sequence of discovery-in this case, that it was the 117th object found during the year’s final couple of weeks.
chris Philpot
This european Space Agency mission will rendezvous with the Didymos-Dimorphos asteroid system and study the aftereffects of NASA’s DART impact close up.
Launch:
2024
Rendezvous:
2026
Until that point in the year, more than 3,000 NEOs had already been discovered. Nothing about 2024 yr4 initially stood out as concerning.It was a seemingly run-of-the-mill asteroid. However, further observations soon suggested it wasn’t ordinary at all.
Throughout the first weeks of 2025, the probability of a 2024 YR4 collision with Earth kept growing. on 29 January, astronomers calculated its odds of eventual impact to be 1.3 percent. And in crossing the 1 percent threshold, 2024 YR4 triggered an alert from the International Asteroid Warning Network to the United Nations’ Office for Outer Space Affairs about the potential impact. Such alerts are posted publicly on the IAWN’s website.The 29 January notice assessed the regions of the planet at highest risk from 2024 YR4 (also known as its risk corridor), and also the expected damage if the asteroid did crash into Earth.
on average, an object of 2024 YR4’s size-estimated at 60 meters across-slams into our planet onc every thousand years.Its considered a “city-killer” asteroid-not big enough to trigger a mass extinction, like the estimated 10-km one that likely killed the dinosaursbut still big enough to be deadly up to roughly 50 km from the impact location. Fortunately, by 24 February, further observations by telescopes across the globe had refined the asteroid’s trajectory enough to rule out near-term Earth impact.
Yet when it comes to asteroids and Earth, there won’t always be such an uncomplicated, happy ending.Another asteroid that size or even larger will eventually be on a collision course with the planet [see chart below].
Among near-Earth object (NEO) asteroids, the most devastating and least widely catalogued categories today are the 50-meter and 140-meter classes-also known as the “city killers.”
The world’s space agencies track an estimated 95 percent of NEOs greater than 1 km in diameter. The International Asteroid Warning Network and a related Space Mission Planning Advisory Group (SMPAG) are global coordinating bodies that monitor these efforts.And thankfully, none of the giant NEOs tracked by the above pose an impact risk to Earth for at least the next hundred years.(Meanwhile,comet impacts with Earth are even rarer than those of asteroids.)
But you can only track the NEOs that are known. and plenty of city-killer asteroids remain lurking and undiscovered, perhaps still posing a real risk to life on the planet. In the 50-meter range, a meager 7 percent of NEOs have been found.That’s not for lack of trying. It’s just more difficult to find small asteroids because smaller asteroids appear dimmer than larger ones.
New hardware is clearly needed. Sometime soon, the Vera C. Rubin Observatoryin chile,is expected to see first light. The observatory will survey the entire visible sky every few nights, through a 3,200-megapixel camera on an 8.4-meter telescope. no Earth-based telescope in the history of the NEO hunt can match its capabilities. Adding to our NEO search will be NASA’s NEO surveyoran infrared space telescope scheduled to launch as soon as 2027. Together, the two new facilities are expected to discover thousands of new-to-us near-Earth asteroids. For objects 140 meters and larger, the two telescopes will locate an anticipated 90 pe
