Killer asteroids - Can we avert the apocalypse? | DW Documentary

Key Concepts

Asteroids, NEOs (Near-Earth Objects), Comets, Planetary Defense, Kinetic Impactor, Gravity Tractor, Yarovsky Effect, DART Mission, Hera Mission, Asteroid Deflection, Impact Events, Solar System Formation, Mass Extinction, Space Telescopes (Pan-STARRS, NEOWISE, NEO Surveyor), Binary Asteroid (Didymos & Dimorphos).

Asteroid Threat and Historical Impacts

• Asteroids pose a significant threat to Earth, capable of causing mass extinctions, as evidenced by the dinosaur extinction event 66 million years ago. This event was caused by an asteroid >10km in size impacting the Gulf of Mexico at >10 km/s, releasing energy billions of times greater than the Hiroshima bomb.
• The impact caused immediate devastation within a 100km radius, followed by longer-term effects like ejecta blocking sunlight, disrupting photosynthesis, and collapsing the food chain, leading to 75% species extinction.
• Meteorites regularly strike Earth, and even smaller asteroids can cause significant damage. The Chelyabinsk event in 2013, involving a ~20m asteroid, injured thousands and served as a wake-up call.
• The Tunguska event in 1908, caused by a similar-sized asteroid exploding in the atmosphere, flattened thousands of square kilometers of forest.
• Lunar crater analysis helps estimate asteroid populations and impact probabilities. A 100m asteroid impacts Earth on average every 6,000 years, releasing 50 megatons of energy.

Origins of Asteroids and NEOs

• The solar system formed from a solar nebula 4.5 billion years ago. The cloud collapsed, forming the sun and a disc of gas and dust.
• The outer part of the disc formed gas giants (Jupiter, Saturn, Uranus, Neptune) and comets (frozen gases, water, and loose rock).
• Asteroids are rocky remnants from the solar system's formation, primarily located in the main asteroid belt between Mars and Jupiter.
• Collisions within the main belt can eject asteroids, altering their trajectories and potentially making them NEOs.
• NEOs are asteroids and comets with orbits near Earth's, posing a collision risk.

International Planetary Defense Efforts

• Comet Shoemaker-Levy 9's impact on Jupiter in 1994 spurred international concern and planetary defense efforts.
• A three-phase action plan was developed: inventory NEOs, study their composition, and develop deflection methods.
• In 1998, the US Congress tasked NASA with identifying all NEOs >1km in diameter.
• The Pan-STARRS telescope in Hawaii and the Catalina Sky Survey Project in Arizona have significantly increased asteroid discoveries.
• The NEOWISE space telescope has identified 377 asteroids, including 63 potentially dangerous to Earth.
• NASA plans to launch the NEO Surveyor Space Telescope in 2027 to identify the remaining 60% of NEOs >140m within 10 years.

Asteroid Sample Return Missions

• JAXA's Hayabusa mission (2003) collected samples from asteroid Itokawa, revealing it was a "rubble pile."
• Hayabusa 2 (launched 2014) collected samples from asteroid Ryugu using a projectile to loosen dust.
• These missions provide crucial data on asteroid properties for developing deflection methods and understanding the solar system's origins.

Asteroid Deflection Methods

• Nuclear Explosion: While depicted in movies like Armageddon, this method is considered risky due to uncontrolled fragmentation and potential contamination.
• Yarkovsky Effect: A subtle force caused by sunlight heating and radiating from a rotating asteroid, slowly altering its trajectory. Effective only for small asteroids (<1km). Reflective paint could potentially enhance this effect, but it's not a primary method.
• Gravity Tractor: A spacecraft uses its gravitational pull to gently tug an asteroid off course. Requires a massive spacecraft and long lead times (decades). A 20-ton spacecraft could shift an asteroid by 200m in a year, starting 20 years before impact.
• Kinetic Impactor: A spacecraft collides with an asteroid at high speed to alter its trajectory. Considered the most mature and validated technique.

DART Mission: A Kinetic Impactor Success

• NASA's DART (Double Asteroid Redirection Test) mission successfully demonstrated the kinetic impactor technique.
• Launched in November 2021, DART targeted Dimorphos, a 160m moonlet orbiting the larger asteroid Didymos (780m).
• The DART probe, equipped with the DRACO camera and autonomous navigation software, impacted Dimorphos at 6 km/s on September 26, 2022.
• The impact successfully altered Dimorphos's orbit, proving the feasibility of asteroid deflection.

Hera Mission: Follow-up and Analysis

• ESA's Hera mission, launched in October 2024, will arrive at Didymos in late 2026 to study the aftermath of the DART impact.
• Hera will map Dimorphos's surface, study its mass, and deploy nano-satellites to analyze its internal structure.
• Hera will assess the effectiveness of the DART impact and provide data for future deflection missions.

Apophis Flyby

• On April 13, 2029, the 370m asteroid Apophis will pass close to Earth, within the orbits of our satellites.
• Scientists plan to observe Apophis closely to gain further insights into asteroids.

Conclusion

Asteroid impacts pose a real threat to Earth, but international efforts are underway to identify, study, and develop methods to deflect potentially hazardous objects. The DART mission's success demonstrates the viability of the kinetic impactor technique, while the Hera mission will provide further data to refine our understanding and capabilities. Continued research and investment in planetary defense are crucial for protecting future generations.