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Near-Earth objects (NEOs) are asteroids and comets that have orbits bringing them close to Earth’s vicinity. These objects vary in size, composition, and trajectory, with some posing a potential risk of collision. Scientists classify NEOs based on their proximity to Earth and their potential hazard level. Those that come within 0.05 astronomical units (approximately 7.5 million kilometers) and have a diameter of at least 140 meters are designated as potentially hazardous objects (PHOs). Though large impacts are rare, the potential consequences of such an event make ongoing observation and research a necessity.
Observations of NEOs rely on ground-based and space-based telescopes equipped with advanced imaging and tracking technology. Surveys such as NASA’s Near-Earth Object Observations (NEOO) program and international efforts like the European Space Agency’s NEO Coordination Centre contribute to a growing database of detected objects. By monitoring trajectories and calculating future positions, scientists assess the probability of impact and determine whether an object requires further observation.
Historical events demonstrate the potential consequences of NEO impacts. The Tunguska event in 1908 flattened over 2,000 square kilometers of forest in Siberia, likely caused by the atmospheric explosion of a small asteroid. More recently, in 2013, a meteor approximately 20 meters in diameter entered Earth’s atmosphere over Chelyabinsk, Russia, causing a shockwave that damaged buildings and injured over a thousand people. While neither of these events resulted in fatalities from direct impact, they highlight the destructive force that even relatively small objects can exert.
Asteroids and comets threaten Earth in different ways. Stony and metallic asteroids, depending on their size, can survive atmospheric entry and create craters upon impact. Comets, which often have highly elliptical orbits, can approach at higher velocities, increasing the energy released if a collision occurs. Larger impacts could trigger regional or even global consequences, such as wildfires, climate disruption, and tsunamis. The geological record contains evidence of past impacts, including the Chicxulub crater, linked to the mass extinction that ended the reign of the dinosaurs around 66 million years ago.
While many NEOs follow predictable paths, gravitational influences from planets, subtle forces like the Yarkovsky effect, and collisions with other objects can slightly alter their trajectories over time. These factors make continuous monitoring necessary. Advances in detection technology and international collaboration contribute to improving predictions and reducing uncertainties in impact risk assessments.
Efforts to reduce the risk of a catastrophic impact employ a variety of strategies based on an object’s size, composition, and projected path. These methods generally fall into two categories: deflection and disruption. Deflection techniques seek to alter an object’s trajectory so that it no longer poses a threat, while disruption involves breaking the object into smaller fragments, ideally ensuring that no significant pieces reach Earth’s surface.
One of the most studied deflection methods involves kinetic impactors. This approach requires sending a high-speed spacecraft to collide with the object, transferring momentum and slightly adjusting its orbit. NASA’s Double Asteroid Redirection Test (DART) mission demonstrated this technique in 2022 when it successfully altered the orbit of the asteroid moonlet Dimorphos. While this test did not involve a hazardous asteroid, it provided valuable data on how kinetic impactors could be used in a real threat scenario.
Another proposed technique involves using a gravity tractor. In this method, a spacecraft would fly alongside the hazardous object for an extended period, using its own gravitational influence to gradually shift the asteroid’s trajectory. This approach allows for a controlled and predictable change in movement but requires significant time to be effective, making it most suitable for objects detected well in advance of a potential impact.
More aggressive measures, such as nuclear devices, have been studied for both deflection and disruption. Detonating a nuclear explosion near an asteroid could vaporize part of its surface, creating a reaction force that alters its trajectory. Alternatively, a direct nuclear impact could fragment the object. However, this approach presents challenges, including international treaties on space-based nuclear explosions and the potential risk of creating multiple hazardous fragments instead of eliminating the threat entirely.
Non-nuclear energy-focused methods include using solar reflectors or lasers to gradually heat an asteroid’s surface, generating small thrusts as material is ejected. While this concept remains largely theoretical, it could provide a low-impact way to shift an asteroid’s path over time.
In cases where an impact cannot be avoided, emergency response strategies emphasize evacuation plans, impact location predictions, and civil defense measures. These include coordinating with international space agencies, governments, and disaster management teams to prepare for potential scenarios. If a significant impact were predicted, early warning systems could allow populations in the affected region to be relocated, reducing casualties.
International collaboration plays a major role in planetary defense. Organizations such as the United Nations Office for Outer Space Affairs (UNOOSA) and its Space Mission Planning Advisory Group (SMPAG) facilitate coordination among space agencies. The International Asteroid Warning Network (IAWN) also helps share observations and data on potentially hazardous objects, enabling a faster and more informed response.
Advancements in observational technology and mission planning continue to improve planetary defense capabilities. With ongoing improvements in detection systems and response strategies, scientists and policymakers are working toward minimizing the risks posed by near-Earth objects through coordinated efforts and technological innovation.
10 Best Selling Books About Asteroids
Asteroid Hunters by Carrie Nugent
This concise nonfiction book explains how scientists and survey programs find and track near-Earth asteroids, using real detection methods, data pipelines, and follow-up observations. It also describes why asteroid discovery supports planetary defense decision-making and long-term monitoring of potential impact risks.
How to Kill an Asteroid: The Real Science of Planetary Defense by Robin George Andrews
This nonfiction narrative describes how modern planetary defense works, including detection, orbit prediction, and deflection concepts that are used to reduce asteroid impact risk. It connects these methods to mission planning, engineering constraints, and the practical realities of responding to a hazardous near-Earth object.
Fire in the Sky: Cosmic Collisions, Killer Asteroids, and the Race to Defend Earth by Gordon L. Dillow
This nonfiction account outlines the history of major impact events and the scientific evidence that supports modern impact-hazard estimates. It also explains how asteroid surveys, risk modeling, and response planning shape current planetary defense policy and technology choices.
Catching Stardust: Comets, Asteroids and the Birth of the Solar System by Natalie Starkey
This nonfiction book explains what meteorites and asteroid samples reveal about early solar system chemistry, planetary formation, and the origins of water and organics. It links laboratory techniques and space missions to the broader field of asteroid science for general readers.
Asteroids by Clifford J. Cunningham
This nonfiction overview summarizes how asteroids were discovered, how their orbits are measured, and how asteroid populations are classified and studied over time. It also explains how cultural interest in asteroids has tracked alongside advances in observation, missions, and impact-risk awareness.
Cosmic Impact: Understanding the Threat to Earth from Asteroids and Comets by Andrew May
This nonfiction book explains the physical processes behind impacts, including entry dynamics, blast effects, and the role of size and speed in determining damage outcomes. It also presents how scientists estimate frequencies and build impact-hazard scenarios for near-Earth objects.
Mining the Sky: Untold Riches from the Asteroids, Comets, and Planets by John S. Lewis
This nonfiction work describes the resource potential of asteroids, including metals and volatiles, and explains how in-space materials could support industrial activity beyond Earth. It also connects asteroid mining concepts to mission logistics, propulsion tradeoffs, and the economics of operating far from terrestrial supply chains.
Rain of Iron and Ice: The Very Real Threat of Comet and Asteroid Bombardment by John S. Lewis
This nonfiction book explains the geological and historical evidence for large impacts and bombardment episodes, including what crater records indicate about long-term risk. It also describes how impact science informs public risk perception and the practical case for asteroid detection and mitigation planning.
The Asteroid Threat: Defending Our Planet from Deadly Near-Earth Objects by William E. Burrows
This nonfiction book focuses on near-Earth objects, explaining how discovery shortfalls, tracking uncertainty, and communication gaps can affect real-world preparedness. It also describes the institutional and technical steps that can reduce impact risk, from survey coverage to response coordination and deflection readiness.
Bennu 3-D: Anatomy of an Asteroid by Dante S. Lauretta
This nonfiction atlas-style book presents asteroid Bennu through mission imagery and structured mapping, tying surface features to the science goals of sample-return exploration. It is coauthored by a team connected to the OSIRIS-REx effort and is designed to make asteroid geology and mission results accessible to nontechnical readers.
Today’s 10 Most Popular Science Fiction Books
[amazon bestseller=”science fiction books” items=”10″]
