Restaurant menus include animals that we eat without inhibition because we regard ourselves at the top of the food chain on Earth right now. The human species emerged only in the last 0.1% of Earth’s history, a few million years ago. The top of the food chain was occupied by dinosaurs during the much longer Mesozoic Era between 252 to 66 million years ago. Their top status was demolished by the Chicxulub impactor, a rock the size of Manhattan Island, which struck Earth 66 million years ago. Tough luck.
In an effort to avoid a similar fate, the U.S. Congress tasked NASA in 2005 to find 90% of all Near Earth Objects (NEOs) larger than 140 meters. Accordingly, the Pan STARRS and Rubin telescopes were constructed with the goal of addressing the Congressional task. In 2016, NASA established the Planetary Defense Coordination Office to manage the finding and tracking of NEOs. The latest strategy and action plan were summarized in a 2023 report.
NASA’s NEO Surveyor, planned for launch in late 2027, aims to discover and characterize most of the potentially hazardous asteroids and comets that arrive within 50 million kilometers of Earth. Located at the first Lagrange Point (L1) between the Sun and the Earth, its telescope, half a meter in diameter, will point towards Earth and search over five-years for NEOs larger than 140 meters that are coming from the direction of the Sun and are difficult to observe from Earth. This space telescope could also find Earth Trojans, which lead and trail our planet’s orbit and are difficult to observe from Earth or near-Earth satellites. The NEO Surveyor will use two infrared imaging channels to detect the heat emitted by NEOs and constrain their sizes, composition, shapes, rotational states, and orbits.
This is the first telescope designed by NASA for planetary defense. Interestingly, it can also be used to defend humanity against visits by extraterrestrial technological civilizations or other Unidentified Anomalous Phenomena (UAP). Detecting threats from suspicious objects is only the first step in any defense system. The follow-up question is what to do about it?
Impact mitigation methods could include destroying or fragmenting the approaching object by a nuclear detonation; triggering a rocket effect by ablating its surface with a high-power laser; painting the object’s surface to enhance the push from solar radiation pressure; or shepherding the object gravitationally away from Earth by a massive spacecraft. The required level of deflection gets smaller the larger the approaching object’s distance is from Earth.
NASA’s Double Asteroid Redirection Test (DART) aimed at testing the simplest technique for planetary defense, borrowed from players in the National Football League (NFL), namely using an impact to deflect an object from its intended trajectory. The target asteroid for the demonstration was Dimorphos, a moon of Didymos. DART collided with Dimorphos on September 26, 2022 and deflected it mainly through the recoil associated with the ejected debris. Think of Dimorphos as a football player who changed trajectory by losing his armor or helmet.
Given our modern technological infrastructure, the financial risk from killer asteroids is substantial. There are about a thousand NEOs larger than a kilometer, capable of causing global impact effects. Approximately 95% of these objects have been identified and none pose a current threat. So far, less than half of the 25,000 objects larger than 140 meters in diameter have been detected and tracked. It is estimated that there are at least 230,000 objects larger than 50 meters in size that could decimate a concentrated urban area. Less than 8% of these are known. It is alarming to recognize that less than a percent of smaller NEOs have been discovered.
In recent weeks, the asteroid 2024 YR4 was assigned a likelihood of 2.2% for colliding with Earth on December 22, 2032. This NEO is smaller than the congressional limit of 140-meters, as its estimated diameter is about 54 meters. The corresponding mass is a quarter of a million tons, which upon impact could release 7.7 megatons, equivalent to five hundred times the Hiroshima atomic bomb energy. Hence, 2024 YR 4 is capable of destroying a city. Given that 71% of Earth is covered by oceans, its potential impact is most likely to trigger a giant tsunami. The Webb Telescope is scheduled to observe 2024 YR4 in March and May 2025. The current uncertainty region for the 2032 asteroid passage is 2 million kilometers wide. Once this uncertainty is narrowed down, astronomers would be able to predict which city or ocean might be struck by it. If it happens to be a highly populated city, its real estate value will likely drop dramatically by 2032, as its residents will flock elsewhere.
Indeed, lessons were learned from the extinction of non-avian dinosaurs. The species that inherited their place at the top of the food chain, built telescopes and is preparing to protect itself from giant rocks falling from the sky. But new wars are often different than their predecessors. While we may be successful at deflecting killer asteroids, our latest technologies made humanity vulnerable to the Trojan Horse of artificial intelligence (AI). Our inability to survive self-inflicted wounds might explain why we are not detecting radio signals from extraterrestrials like us.
A more inspiring message might be delivered by the NEO Surveyor, in case it discovers a visitor from a civilization that managed to venture to interstellar space.
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.
