Planetary defense, the effort to protect Earth from potentially hazardous asteroids and comets, is a critical endeavor that deserves increased attention and funding from NASA and space agencies around the world. While the chances of a catastrophic impact in our lifetimes are low, the consequences would be devastating on a global scale. By investing in the search for near-Earth objects, developing deflection technologies, and fostering international collaboration, we can significantly reduce the existential risk to human civilization and all life on our planet.
The Impact Threat
Earth’s history is marked by evidence of past collisions with asteroids and comets. The craters scattered across our planet’s surface serve as stark reminders of these ancient impacts. While major impacts are rare on human timescales, they have the potential to cause unprecedented destruction.
An asteroid just 140 meters wide striking Earth would release energy equivalent to over 100 megatons of TNT, enough to level a large city. The explosion would trigger firestorms, powerful shock waves, and seismic activity. If the object struck in the ocean, it could generate devastating tsunamis affecting coastlines thousands of kilometers away.
Even more concerning is the prospect of a larger kilometer-sized asteroid impact. Such an event, which occurs on average every few hundred thousand years, would have global consequences. The impact would inject vast amounts of dust and ash into the atmosphere, blocking sunlight and disrupting photosynthesis. This could lead to widespread crop failures, famine, and the collapse of ecosystems. Human civilization as we know it might struggle to endure.
The State of Planetary Defense
Recognizing the impact threat, NASA and other space agencies have taken important steps to improve our planetary defense capabilities in recent decades. NASA established the Planetary Defense Coordination Office in 2016 to manage the agency’s efforts to find, track, and characterize near-Earth objects. Other space agencies around the world have also contributed to this effort through the International Asteroid Warning Network.
Ground-based telescopes have discovered tens of thousands of near-Earth asteroids, but many more remain undetected, especially smaller objects that are faint and difficult to spot. NASA estimates that while we have found over 95% of near-Earth asteroids larger than 1 kilometer, only about 40% of those larger than 140 meters have been discovered. With our current capabilities, a small asteroid on a collision course might only be detected days or weeks before impact, too late for any effective response.
To address this shortcoming, space-based infrared telescopes offer a promising solution. By operating above Earth’s atmosphere and observing in thermal infrared wavelengths, these telescopes could discover many more asteroids much faster than ground-based surveys. NASA’s upcoming NEO Surveyor mission aims to accelerate the search for hazardous asteroids using this approach.
In addition to improving detection, NASA has also made strides in demonstrating asteroid deflection technology. The Double Asteroid Redirection Test (DART) mission successfully impacted the small asteroid Dimorphos in 2022, slightly altering its orbit. This first test of the kinetic impact technique is a major milestone, but further development and testing of deflection technologies is needed.
The Current State of Near-Earth Objects
As of May 2023, over 31,000 near-Earth asteroids have been discovered. Of these, 10,336 are larger than 140 meters in diameter and 891 are larger than 1 kilometer. While no known asteroid currently poses a significant impact risk, ongoing searches continue to find new objects on a regular basis.
The most concerning near-Earth asteroids are classified as potentially hazardous asteroids (PHAs). These are objects larger than about 140 meters that can come within 7.5 million kilometers of Earth’s orbit. As of May 2023, there are 2,352 known PHAs. While none of these are predicted to impact Earth in the next century, even a small change to their orbits from gravitational perturbations or other effects could put them on a collision course in the more distant future.
Comets can also pose an impact risk, although they are much rarer than asteroids. Comets are icy objects that originate in the outer solar system and develop comas and tails as they approach the Sun. There are currently 117 known near-Earth comets. While most comets are discovered long before they enter the inner solar system, some called long-period comets can appear with little warning, leaving minimal time to respond to a potential impact.
Detecting and tracking near-Earth objects is an ongoing challenge that requires persistent effort. Ground-based telescopes like Pan-STARRS, the Catalina Sky Survey, and ATLAS continuously scan the skies, while space-based assets like NEOWISE provide complementary infrared observations. Upcoming missions like NEO Surveyor will greatly enhance our detection capabilities.
When a new near-Earth object is discovered, follow-up observations are critical to determine its orbit and assess whether it poses any risk of impact. This often requires coordination between professional and amateur astronomers around the world. If an object is found to pose a threat, further observations to characterize its size and composition would inform the choice of deflection strategy.
The Case for Increased Investment
Despite the progress made so far, planetary defense remains severely underfunded compared to the scope of the challenge. In 2022, NASA spent just $234 million on planetary defense, a mere 0.7% of the agency’s total budget. Other space agencies have similarly modest planetary defense budgets. This level of funding is insufficient to adequately address such a complex problem with potentially existential stakes.
A 2010 National Research Council report recommended that NASA’s annual budget for finding hazardous near-Earth objects be increased to $250-300 million per year over a decade. Adjusted for inflation, that would be over $350 million today. However, NASA’s funding has consistently fallen short of that recommendation. The limited budget has slowed progress on key efforts like the NEO Surveyor mission, which could discover over 80% of potentially hazardous asteroids larger than 140 meters within a decade of launch.
Increased investment would accelerate the search for near-Earth objects, provide better characterization of their properties, and allow for more robust development and testing of deflection technologies. With more funding, multiple space-based telescopes could be deployed to find asteroids faster. Additional missions could demonstrate various deflection techniques like gravity tractors, ion beam deflection, and nuclear explosives.
Crucially, larger budgets would also bolster international collaboration on planetary defense. By pooling resources and expertise, space agencies could achieve far more than they can individually. A well-funded international effort could establish a comprehensive monitoring system to provide early warning of potential impacts and coordinate deflection missions if needed.
Preparing for the Worst
Even with a robust planetary defense program, the possibility remains that an asteroid on a collision course might be detected with insufficient time for deflection. In that dire scenario, having a well-prepared response could still save countless lives. Space agencies should work with governments around the world to develop detailed impact response plans.
These plans should include strategies for evacuating populations from affected areas, providing emergency aid and supplies, and mitigating the global effects of a large impact. Regular exercises and simulations can help identify gaps in preparedness and improve coordination between space agencies, emergency management organizations, and policymakers.
Investing in basic research on the environmental effects of impacts can also inform response planning. Better models of impact physics, atmospheric effects, and tsunami propagation would help predict the consequences of different impact scenarios more accurately. This knowledge could guide decisions on evacuation zones, aid distribution, and other response measures.
Conclusion
The threat of an asteroid or comet impacting Earth is one of the few natural disasters that humanity can potentially prevent, but only if we choose to act. By increasing investment in planetary defense, we can protect our planet and safeguard the future of human civilization.
NASA and other space agencies have laid the foundation for an effective planetary defense program, but current funding levels are inadequate for the magnitude of the challenge. A sustained commitment of resources is needed to accelerate the search for hazardous objects, develop robust deflection capabilities, and prepare for the worst-case scenario.
Failing to adequately address the impact threat would be a tragic missed opportunity. The cost of a comprehensive planetary defense program pales in comparison to the potential loss of life and devastation that a major impact would cause. By working together and dedicating the necessary resources, we can significantly reduce this existential risk.
In the vast expanse of the universe, Earth is a rare oasis of life and human civilization. It is our responsibility to be good stewards of our planet and to use our knowledge and technology to protect it. Investing in planetary defense is not just a matter of science and exploration; it is an ethical imperative. We owe it to ourselves and to future generations to do everything in our power to preserve our world. The time to act is now, before it is too late.
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