Asteroids have been a source of fascination and fear for centuries, with the potential to cause catastrophic damage to our planet. While the chances of a large asteroid hitting Earth are slim, the consequences could be devastating. In recent years, scientists and policymakers have increasingly focused on the importance of planetary defense – the effort to detect, track, and potentially deflect asteroids that pose a threat to Earth.
Despite the growing awareness of the asteroid threat, many aspects of planetary defense remain little known to the public. From the surprising number of near-Earth objects to the innovative technologies being developed to protect our planet, there is much to learn about this critical field of study. In this article, we explore 10 surprising facts about planetary defense that shed light on the complex and evolving effort to keep Earth safe from asteroid impacts.
1. Millions of Near-Earth Objects Exist
While many people are aware of the asteroid belt between Mars and Jupiter, it may come as a surprise that millions of asteroids and comets orbit much closer to Earth. These near-Earth objects (NEOs) have orbits that bring them within 30 million miles of Earth’s path around the Sun. Over 25,000 NEOs have been discovered so far, and astronomers estimate there could be over 25 million larger than 30 meters across. Fortunately, the vast majority will never come close to impacting our planet.
2. Small Asteroids Strike Earth Frequently
Every day, roughly 100 tons of sand-sized particles and small rocks rain down on Earth from space. Occasionally, an asteroid the size of a car will enter the atmosphere, producing a bright fireball before burning up. About once per year, an asteroid the size of a small house impacts Earth, but most go unnoticed as they explode over the oceans or uninhabited areas. The last significant asteroid impact occurred in 2013 when a 20-meter object exploded over Chelyabinsk, Russia, shattering windows with its shockwave.
3. Asteroid Impacts Have Shaped Earth’s History
While the idea of a major asteroid strike seems like science fiction, these impacts have played a major role in shaping Earth’s history. The most famous is the Chicxulub impact 66 million years ago, which caused the extinction of the dinosaurs and 75% of life on Earth. Other major impacts, like the one that formed the Vredefort crater in South Africa over 2 billion years ago, have punctuated the history of our planet. Even today, over 190 impact craters are visible on Earth’s surface.
4. NASA Tracks Potentially Hazardous Asteroids
To monitor the skies for potentially dangerous asteroids, NASA established the Center for Near-Earth Object Studies (CNEOS) in 1998. Astronomers at CNEOS use a network of telescopes to track the orbits of known NEOs and look for new ones. When a new NEO is found, they project its orbit decades into the future to check if it could potentially impact Earth. As of 2023, no known asteroids over 140 meters in size have a significant chance of hitting Earth in the next century.
5. Asteroid Deflection Was Successfully Tested
In 2022, NASA’s Double Asteroid Redirection Test (DART) mission successfully changed the orbit of a small asteroid by crashing a spacecraft into it. The target was Dimorphos, a 160-meter moon orbiting the larger asteroid Didymos. By precisely impacting Dimorphos at over 14,000 mph, DART shortened its orbital period by 33 minutes, surpassing the minimum mission goal of 73 seconds. This proved the viability of the kinetic impact technique for deflecting a potentially hazardous asteroid.
6. Nuclear Explosives Are Considered a Last Resort
For short-warning or very large threats, delivering a nuclear explosive device is considered the most viable option. Detonating a nuclear device above an asteroid’s surface would vaporize part of it, generating an impulse to alter its trajectory. However, this approach faces major political and legal hurdles due to international treaties prohibiting nuclear weapons in space. It would only be considered if no other options were feasible and the asteroid posed a clear danger to Earth.
7. Asteroid Mining Could Aid Planetary Defense
Several companies are developing spacecraft to extract valuable resources like water, metals, and rare-earth elements from asteroids. In addition to the economic benefits, asteroid mining could also assist planetary defense efforts. Extracting mass from an asteroid would slightly alter its trajectory over time. Water extracted from asteroids could also be used to make rocket propellant, which would be useful for fueling asteroid deflection missions.
8. Amateur Astronomers Play a Key Role
Amateur astronomers with backyard telescopes play an important part in planetary defense by helping discover and track near-Earth asteroids. The Catalina Sky Survey in Arizona, which is responsible for finding the majority of new NEOs, relies on a dedicated team of amateur observers. The International Astronomical Search Collaboration also enables citizen scientists around the world to make asteroid discoveries using professional telescope data.
9. Asteroid Impacts Pose Global Risks
The damage from an asteroid impact depends on its size, composition, speed, and angle of entry. An asteroid just 140 meters across could destroy a city and affect an area hundreds of kilometers wide. Asteroids over 300 meters across could cause regional devastation and trigger global climate effects like a “nuclear winter.” Larger impacts, like Chicxulub, can eject enough dust into the atmosphere to alter the climate for years, decimating agriculture and leading to mass extinctions.
10. Planetary Defense Requires International Cooperation
Because an asteroid impact could have global consequences, planetary defense is an inherently international endeavor. In 2014, the United Nations established the International Asteroid Warning Network (IAWN) to facilitate collaboration between the many scientific organizations involved in detecting and tracking NEOs. The UN also formed the Space Mission Planning Advisory Group (SMPAG) to coordinate multinational asteroid deflection missions. Effective planetary defense will require ongoing international cooperation to address this rare but potentially catastrophic natural threat.
Summary
As our understanding of the asteroid threat continues to grow, so too does the importance of investing in planetary defense. From improving our ability to detect and track NEOs to developing new technologies for asteroid deflection, there is much work to be done to protect Earth from the risk of an asteroid impact. By raising awareness of this critical issue and supporting the efforts of scientists and policymakers around the world, we can help ensure a safer future for our planet and all who call it home.
