Washington D.C. – Earth remains vulnerable to a significant threat from space, with an estimated 15,000 "city-killer" asteroids still undetected, according to a top NASA official. These mid-sized asteroids, capable of widespread regional destruction, pose the greatest concern to planetary defense experts. Kelly Fast, NASA's acting Planetary Defense Officer, recently stated that the asteroids scientists do not know about are what keep her awake at night.
The Unseen Danger in Space
Scientists estimate roughly 25,000 near-Earth asteroids exist that are 140 meters (about 460 feet) or larger. An impact from an object of this size would not cause global extinction but could flatten a major city, ignite fires, and severely disrupt infrastructure across a wide area. However, current detection systems have only identified about 40 percent of these potentially hazardous objects. This leaves approximately 15,000 "city-killer" asteroids untracked and capable of approaching Earth without warning.[m+18]
These asteroids are particularly difficult to spot for several reasons. Many travel along paths close to Earth's orbit around the Sun, where they reflect little sunlight toward ground-based telescopes. The Sun's intense glare effectively hides them, creating a significant blind spot for observatories. Even advanced telescopes struggle to detect objects that approach from the Sun's direction, limiting the warning time available to scientists if one were headed for impact.[greekreporter+20]
Closing the Detection Gap
To address this critical detection gap, NASA plans to launch the Near-Earth Object Surveyor (NEO Surveyor) space telescope. The mission is scheduled for launch in late 2027 or 2027-2028. Unlike traditional telescopes that rely on visible light, NEO Surveyor will search for asteroids and comets by detecting their heat signatures using infrared wavelengths. This method allows the telescope to find dark asteroids and those hidden by solar glare, which are often missed by optical instruments. Researchers expect NEO Surveyor to uncover thousands of previously hidden objects. The mission aims to significantly improve identification rates and achieve the goal of cataloguing 90 percent of near-Earth asteroids larger than 140 meters within the next decade.[greekreporter+23]
Current Defense Limitations
While detection efforts are improving, Earth currently lacks an immediate defense system against a rapidly approaching "city-killer" asteroid. NASA's Double Asteroid Redirection Test (DART) mission in 2022 successfully demonstrated that it is possible to alter an asteroid's trajectory by crashing a spacecraft into it. This groundbreaking test proved the concept of kinetic impact. However, experts caution that a deflection mission like DART requires years of advance warning and a specially designed spacecraft. Nancy Chabot, who led the DART mission at Johns Hopkins University, highlighted that no dedicated deflection spacecraft is currently on standby. This means Earth is not prepared for a rapid response if a dangerous asteroid is detected with limited lead time.[m+15]
Lessons from Recent Close Calls
Recent events underscore the challenges of asteroid detection and the need for improved systems. Asteroid 2024 YR4, discovered in December 2024, briefly raised alarms with an estimated 4 percent chance of striking the Moon in 2032. Although the risk to Earth remained low, and later observations downgraded the probability, the incident highlighted how quickly risks can escalate. This event also demonstrated the narrow windows available for radar confirmation and the rapid risk assessment needs of planetary defense. The asteroid 2024 YR4 was initially only discovered a week after it passed Earth on Christmas Day 2024.[greekreporter+8]
Global Effort for Planetary Safety
NASA established the Planetary Defense Coordination Office (PDCO) in 2016 to manage the ongoing mission of finding, tracking, and understanding potentially hazardous asteroids and comets. The PDCO also coordinates with international partners through the International Asteroid Warning Network (IAWN), a global collaboration of asteroid observers and modelers. Over 40,000 near-Earth asteroids have been detected since 1990, and more than 90 percent of objects larger than 1 kilometer (0.62 miles) have been found. These larger "planet-killer" asteroids are closely monitored.[science+5]
However, the continued existence of thousands of undiscovered "city-killer" asteroids represents a significant blind spot. Experts warn that 2026 could be a critical year for planetary defense planning, emphasizing that swift action is needed to safeguard human populations from these hidden cosmic threats. Future efforts will require sustained investment in advanced telescopic monitoring, AI-assisted tracking, and strong international collaboration to enhance early detection and response capabilities.[greekreporter+8]
Washington D.C. – Earth remains vulnerable to a significant threat from space, with an estimated 15,000 "city-killer" asteroids still undetected, according to a top NASA official. These mid-sized asteroids, capable of widespread regional destruction, pose the greatest concern to planetary defense experts. Kelly Fast, NASA's acting Planetary Defense Officer, recently stated that the asteroids scientists do not know about are what keep her awake at night.
The Unseen Danger in Space
Scientists estimate roughly 25,000 near-Earth asteroids exist that are 140 meters (about 460 feet) or larger. An impact from an object of this size would not cause global extinction but could flatten a major city, ignite fires, and severely disrupt infrastructure across a wide area. However, current detection systems have only identified about 40 percent of these potentially hazardous objects. This leaves approximately 15,000 "city-killer" asteroids untracked and capable of approaching Earth without warning.[m+18]
These asteroids are particularly difficult to spot for several reasons. Many travel along paths close to Earth's orbit around the Sun, where they reflect little sunlight toward ground-based telescopes. TheSun's intense glare effectively hides them, creating a significant blind spot for observatories. Even advanced telescopes struggle to detect objects that approach from the Sun's direction, limiting the warning time available to scientists if one were headed for impact.[greekreporter+20]
Closing the Detection Gap
To address this critical detection gap, NASA plans to launch the Near-Earth Object Surveyor (NEO Surveyor) space telescope. Themission is scheduled for launch in late 2027 or 2027-2028. Unlike traditional telescopes that rely on visible light, NEO Surveyor will search for asteroids and comets by detecting their heat signatures using infrared wavelengths. This method allows the telescope to find dark asteroids and those hidden by solar glare, which are often missed by optical instruments. Researchers expect NEO Surveyor to uncover thousands of previously hidden objects. Themission aims to significantly improve identification rates and achieve the goal of cataloguing 90 percent of near-Earth asteroids larger than 140 meters within the next decade.[greekreporter+23]
Current Defense Limitations
While detection efforts are improving, Earth currently lacks an immediate defense system against a rapidly approaching "city-killer" asteroid. NASA's Double Asteroid Redirection Test (DART) mission in 2022 successfully demonstrated that it is possible to alter an asteroid's trajectory by crashing a spacecraft into it. This groundbreaking test proved the concept of kinetic impact. However, experts caution that a deflection mission like DART requires years of advance warning and a specially designed spacecraft. Nancy Chabot, who led the DART mission at Johns Hopkins University, highlighted that no dedicated deflection spacecraft is currently on standby. This means Earth is not prepared for a rapid response if a dangerous asteroid is detected with limited lead time.[m+15]
Lessons from Recent Close Calls
Recent events underscore the challenges of asteroid detection and the need for improved systems. Asteroid 2024 YR4, discovered in December 2024, briefly raised alarms with an estimated 4 percent chance of striking the Moon in 2032. Although the risk to Earth remained low, and later observations downgraded the probability, the incident highlighted how quickly risks can escalate. This event also demonstrated the narrow windows available for radar confirmation and the rapid risk assessment needs of planetary defense. Theasteroid 2024 YR4 was initially only discovered a week after it passed Earth on Christmas Day 2024.[greekreporter+8]
Global Effort for Planetary Safety
NASA established the Planetary Defense Coordination Office (PDCO) in 2016 to manage the ongoing mission of finding, tracking, and understanding potentially hazardous asteroids and comets. ThePDCO also coordinates with international partners through the International Asteroid Warning Network (IAWN), a global collaboration of asteroid observers and modelers. Over 40,000 near-Earth asteroids have been detected since 1990, and more than 90 percent of objects larger than 1 kilometer (0.62 miles) have been found. These larger "planet-killer" asteroids are closely monitored.[science+5]
However, the continued existence of thousands of undiscovered "city-killer" asteroids represents a significant blind spot. Experts warn that 2026 could be a critical year for planetary defense planning, emphasizing that swift action is needed to safeguard human populations from these hidden cosmic threats. Future efforts will require sustained investment in advanced telescopic monitoring, AI-assisted tracking, and strong international collaboration to enhance early detection and response capabilities.[greekreporter+8]
