How NASA Tracks Near-Earth Objects: From DART to Planetary Defense

Updated on August 25, 2025 | By Jameswebb Discovery Editorial Team 

Inside NASA’s Planetary Defense: How Near-Earth Objects Are Tracked and Deflected

Introduction: Why Near-Earth Objects Matter

Every year, Earth passes through a dynamic cosmic environment filled with asteroids, comets, and other small celestial bodies collectively known as Near-Earth Objects (NEOs). While most of these remain at a safe distance, some venture close enough to raise questions of planetary safety. Humanity has long been fascinated and wary of space rocks—fossil evidence even suggests that asteroid impacts shaped the trajectory of life on Earth, including the extinction of the dinosaurs 66 million years ago.

In the 21st century, with advanced telescopes and spacecraft missions, we are no longer passive observers. NASA has developed a planetary defense strategy, combining detection, tracking, modeling, and even impact prevention missions like DART (Double Asteroid Redirection Test). This approach is designed not only to predict potential threats but also to give humanity the tools to protect the planet.

This article explores how NASA tracks NEOs, the methods used to calculate impact risks, and the technologies shaping our planetary defense systems. By the end, you will see why planetary defense is one of the most ambitious and critical undertakings in space science.

What Are Near-Earth Objects?

NEOs are asteroids and comets whose orbits bring them within 1.3 astronomical units (AU) of the Sun, meaning they can approach Earth’s neighborhood. They are categorized into two main groups:

• Near-Earth Asteroids (NEAs): Rocky bodies left over from the early solar system.

• Near-Earth Comets (NECs): Icy bodies that release gas and dust, creating tails when they approach the Sun.

Astronomers further classify NEAs into subcategories like Atira, Amor, Apollo, and Aten, depending on their orbits relative to Earth. Some remain entirely outside Earth’s orbit, while others cross our path, raising the possibility of a collision.

Why Tracking Them Is Essential

An asteroid only a few hundred meters wide can cause devastating regional destruction, while one several kilometers across could have global consequences. Even smaller objects, such as the 20-meter Chelyabinsk meteor in 2013, can cause injuries and damage when they explode in the atmosphere. NASA’s job is to detect such objects early enough to plan mitigation strategies.

How NASA Detects Near-Earth Objects

Ground-Based Observations

The search for NEOs begins with Earth-based telescopes. These observatories continuously scan the sky to detect moving points of light against the background stars. NASA partners with observatories worldwide, creating a planetary defense network.

Key facilities include:

• Pan-STARRS (Hawaii): One of the most prolific asteroid-hunting telescopes.

• Catalina Sky Survey (Arizona): Responsible for many NEO discoveries.

• ATLAS (Asteroid Terrestrial-impact Last Alert System): A rapid survey system that can detect smaller asteroids hours before they approach Earth.

Space-Based Observations

Ground-based telescopes have limitations, especially in detecting asteroids approaching from the Sun’s direction. To overcome this, NASA is developing NEO Surveyor, a space telescope that will use infrared sensors to detect dark, heat-emitting asteroids invisible to optical telescopes.

Follow-Up Tracking

Once an NEO is discovered, astronomers perform follow-up observations to refine its orbit. This involves measuring brightness, position, and velocity. These data points allow scientists to predict future trajectories with increasing accuracy.

How Orbits and Impact Risks Are Calculated

The Mathematics of Prediction - When an asteroid is discovered, its orbit is calculated using Newtonian physics and refined with observations over time. NASA uses systems like JPL’s Sentry Impact Monitoring to simulate orbital paths for the next 100 years or more.

Factors considered include:

• Gravitational influences: Pull from planets, especially Jupiter.

• Non-gravitational forces: The Yarkovsky effect, where uneven heating can subtly alter an asteroid’s trajectory.

• Close approaches: Small deviations during near passes can dramatically affect long-term orbits.

Risk Scales - NASA communicates asteroid threat levels using scales:

• Torino Scale (0–10): Rates the impact threat from “no hazard” to “certain global catastrophe.”

• Palermo Technical Impact Hazard Scale: A more technical, logarithmic scale comparing the impact probability to background risk.

Most detected asteroids score 0 on the Torino Scale, meaning no immediate threat.

NASA’s Planetary Defense Coordination Office (PDCO)

Establishing Planetary Defense - In 2016, NASA created the Planetary Defense Coordination Office to consolidate all asteroid detection and mitigation efforts. The PDCO works with international agencies, including ESA and other space organizations, to ensure a global planetary defense strategy.

PDCO’s Responsibilities - Detecting, tracking, and characterizing NEOs.

• Developing deflection and disruption technologies.

• Coordinating emergency response planning with FEMA and other agencies.

• Informing the public about genuine risks versus misinformation.

The Double Asteroid Redirection Test (DART)

• The First Planetary Defense Mission - On September 26, 2022, NASA successfully carried out the DART mission, the first real-world test of asteroid deflection. The target was Dimorphos, a small moonlet orbiting the larger asteroid Didymos. DART deliberately crashed into Dimorphos at 22,530 km/h (14,000 mph). The impact shortened Dimorphos’ orbital period by 32 minutes—far exceeding the 10-minute minimum mission success threshold.

• Why DART Matters - DART proved that humanity could alter the trajectory of a celestial body, validating kinetic impact as a planetary defense strategy. While Dimorphos was not a threat, the experiment showed that with sufficient lead time, Earth could redirect dangerous asteroids.

The Future of Planetary Defense Missions

Hera Mission (ESA) - Europe’s Hera mission will follow up on DART by visiting the Didymos-Dimorphos system in 2026 to measure the crater, debris, and physical properties in detail. Together, DART and Hera form the first planetary defense experiment partnership.

NEO Surveyor - Planned for launch in 2027, NEO Surveyor will be a dedicated infrared telescope designed to discover 90% of hazardous asteroids larger than 140 meters. This mission will dramatically improve detection rates.

Other Technologies in Development 

• Gravity tractors: Using spacecraft gravitational pull to subtly change asteroid paths.

• Nuclear options: As a last resort, nuclear devices could disrupt or deflect dangerous asteroids.

• Laser ablation and solar sails: Concepts for slowly nudging asteroids with energy or momentum over decades.

Global Collaboration in Planetary Defense

• International Asteroid Warning Network (IAWN) - Formed in 2013, the IAWN connects observatories, space agencies, and research institutions worldwide. Its mission is to share data and coordinate warnings about potential impact threats.

• Space Mission Partnerships - Planetary defense requires global coordination, since asteroid impacts are not confined to national borders. NASA, ESA, JAXA, and other space agencies are actively working together to test new technologies and share orbital data.

Case Studies of Asteroid Encounters

• Chelyabinsk (2013) - A 20-meter asteroid exploded over Russia, injuring over 1,000 people due to shockwaves and shattered glass. This event demonstrated that even small objects can pose serious risks.

• Tunguska (1908) - A larger object flattened 2,000 square kilometers of forest in Siberia. If such an event occurred over a populated area today, the devastation would be enormous.

• Apophis (2029) - Once feared to pose a collision risk, asteroid 99942 Apophis will safely pass within 31,000 kilometers of Earth in 2029—closer than many satellites. NASA will use the flyby to study its structure and refine planetary defense models.

The Role of Artificial Intelligence and Big Data

• AI in Tracking and Prediction - As the number of known NEOs grows into the tens of thousands, AI and machine learning are playing a critical role in analyzing orbital data and detecting subtle anomalies.

• Citizen Science Contributions - Projects like NASA’s Asteroid Data Hunter encourage citizen scientists to analyze sky survey data, broadening the search for NEOs. This crowdsourced approach expands detection capacity and engages the public.

Dispelling Myths About Asteroid Impacts

• Misconceptions and Misinformation - Social media often exaggerates or misrepresents asteroid threats. Viral headlines about “planet-killer asteroids” cause unnecessary panic. NASA’s PDCO works to separate facts from fear, ensuring the public receives accurate updates.

• The Reality of Risk - While thousands of NEOs exist, none currently pose a threat of imminent impact. NASA continuously updates its risk tables, and the most dangerous asteroids have been ruled out for centuries to come.

Preparing for the Future

• Emergency Planning - Planetary defense isn’t only about deflecting asteroids. If one were detected too late, governments would need evacuation, impact modeling, and disaster relief strategies. NASA collaborates with FEMA and global agencies to prepare for such scenarios.

• Long-Term Vision - NASA’s ultimate goal is a layered planetary defense system, combining early detection, space-based surveillance, kinetic deflection, and international readiness. This strategy could safeguard Earth for generations to come.

Conclusion: Humanity’s Role as Planetary Guardians

For the first time in history, humanity possesses the knowledge and technology to defend Earth from cosmic threats. NASA’s planetary defense program, from telescopes scanning the skies to spacecraft like DART, represents a proactive stance in securing our planet’s future.

While the likelihood of a catastrophic asteroid impact is extremely low in the near future, the consequences of inaction could be unthinkable. By tracking, modeling, and preparing mitigation strategies, NASA and its global partners are ensuring that we are not passive victims of the cosmos—but active guardians of Earth.

The story of planetary defense is not just about technology—it is about foresight, collaboration, and the recognition that protecting our world is a responsibility we all share.