In an hour-long interview with the brilliant NewsNation reporter, Natasha Zouves, I expressed concern a few days ago that the city killer asteroid 2024 YR4 was reported to have a 3.1% chance of impacting Earth and releasing the energy of 500 Hiroshima atomic bombs. The asteroid was first spotted in December and January.
Tonight, in a follow-up interview I explained that thanks to new data on the asteroid’s position and velocity gathered in recent days, the probability of the asteroid colliding with Earth has now dropped to less than one part in 20,000.
The impact risk from 2024 YR4 is expected to keep sinking closer to zero, as astronomers use time on the Webb telescope in the coming months to further constrain the asteroid’s trajectory and size.
The asteroid’s diameter is about 55 meters. The corresponding mass of 220,000 tons and impact speed of 17.3 kilometers per second could have wiped out a large urban region upon impact on Earth, with devastating economic implications. An asteroid this large would have probably triggered a DART-like mission, during which a spacecraft would have been sent towards it in order to knock it away from an impact on Earth.
A dozen years ago, on February 15, 2013, a meteor exploded into a giant fireball at an altitude of about 30 kilometers above the city of Chelyabinsk in Russia. The explosion generated a bright flash of light accompanied by a strong blast wave and many small meteoritic fragments. It was the largest asteroid to crash to Earth since 1908, when a 50-meter object arrived at 27 kilometers per second and released 3–30 megatons of TNT energy over Tunguska in Siberia. The Chelyabinsk meteor was 18 meters in diameter, corresponding to a mass of 12,500 tons. It arrived at a speed of 19 kilometers per second, and released an energy equivalent of 500 kilotons of TNT or about 30 Hiroshima atomic bombs.
An asteroid the size of a person hits the Earth every year and releases the Hiroshima bomb energy in the upper atmosphere. We know about only 8% of the hundreds of thousands of near-Earth objects with a diameter exceeding 50 meters.
The risk is real. About 66 million years ago, the 10-kilometer Chicxulub impactor wiped out the non-avian dinosaurs from the surface of Earth. This represents a look back time of just 1.4% of the history of Earth. Bigger impactors, with more severe consequences, collided with Earth over the past 4.6 billion years. The food chain hierarchy must have been scrambled about a hundred times as a result of Chicxulub-scale impacts on Earth. This does not bode well for the future of humanity, unless we protect Earth or migrate to other locations in the Solar system and beyond.
Extraterrestrial civilizations may have gone extinct if did not protect themselves from similar existential risks on their exoplanets. Most of my first conversation with Natasha focused on them.
NASA’s Near-Earth Object Surveyor, scheduled for launch in September 2027, will scan the Solar System from the first Lagrange point (L1) between the Earth and the Sun, searching for objects larger than 140 meters in diameter, including those coming from the direction of the Sun that would be missed otherwise from Earth owing to their day-side approach. The European Space Agency’s NEOMIR mission, planned for launch in around 2030, will look for smaller, faster-moving asteroids.
The Vera C. Rubin observatory in Chile, expected to start operations this year, will use a 3.2 gigapixel camera to identify many more dangerous objects near Earth. The Rubin alarm system will probably go off in the coming years. If the potential for future geopolitical catastrophes do not keep you up at night, the Rubin warnings might do.
ABOUT THE AUTHOR
Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024.
