- Asteroids and comets could hit the Earth, leading to a calamity.
- We can monitor and respond to threats, with many ongoing programs.
- Much more readiness is needed to stop a disaster.
A morose mammoth, a lispy sloth, and a sleek sabre-toothed tiger trudge across the weary landscape with their motley mammalian crew. While an obsessive squirrel desperately collects and protects acorns with bone-breaking antics, the group’s mission is to gather magnetic crystals to form a ball with which they block a volcano’s vent.
The volcano’s pressure builds until its eruption launches the crystals into space, diverting an incoming apocalyptic asteroid. The animals heroically saved Planet Earth and simultaneously solved their personal and personality difficulties.
Thus plays out the plot of the 2016 movie Ice Age: Collision Course, introducing many children to the idea of space objects striking our planet. For the kids, it might also be an entry into the abiding debate of what wiped out the dinosaurs: a meteorite, volcanic activity, a combination, or (as theorized in Gary Larson’s The Far Side comic) smoking.
If a space object, such as a comet or asteroid (often termed “a near-Earth object” or NEO), menaces humanity, should we give up and accept our doom? Absolutely not. We have the technology to search for and detect potential threats. Many monitoring programs involving space agencies around the world already exist. We are also fortunate that trade-offs support early action, so we must be ready when a threat is identified.
The threat of space objects
In general, more massive objects lead to more destructive potential. Since most expected space objects are composed of somewhat similar materials, a higher mass typically (but not always) indicates a larger size. As another general rule, with nuances, the larger or more massive an object, the easier it should be to detect, if we are looking.
Meanwhile, the faster a space object moves, the more powerful its punch, yet the higher the chance we have of spotting it. If we are continually watching, then we should catch most objects in time to respond, showing why we should invest in prevention through a complete system to monitor and be ready for dangerous space objects.
Without this system, objects skipping through the atmosphere or burning up before reaching the surface (called meteors) produce pressure and heatwaves, blasting infrastructure and people. Objects slamming into the ground are labeled meteorites and can easily rip through infrastructure and vehicles. Anecdotes throughout history describe people being injured or killed when bonked by a meteorite. Few have been confirmed, compared to clear examples of meteor casualties.
In the Tunguska region of Siberia, a massive explosion shattered the morning of June 30, 1908, snapping trees in a huge radius and tossing a man from his chair dozens of kilometres away. An impact crater was never found, leading to the assumption that some form of space object had detonated and disintegrated before reaching the surface. Uncorroborated local folklore attests that some people disappeared, perhaps incinerated.
Then, also in Russia, on February 15, 2013, a meteor streaked through the dawn of the Chelyabinsk region. Captured on video by security cameras, phones, and dashcams, the shockwave set off car alarms and smashed panes of glass. Over 1,200 people were injured. No one reported being hit by fragments, although chunks were found around the area.
Several millennia ago, a space object formed the Kaali craters around the island of Saaremaa, Estonia. The dates of human habitation of the area and of the meteorite are debated, so the possible impacts on people are unclear. If people were living there at the time, casualties would have been likely.
Much larger space objects are implicated in mass extinctions long ago. Crater remnants with diameters that are dozens of kilometres across are scattered across our planet from past eons. Others have disappeared under the relentless tectonics through which continents are born and die. These impacts fill the world with dust, blocking sunlight, plummeting temperatures, and battering ecosystems for years. Today, food supplies would be devastated, leading to mass starvation.
A meteorite’s water landing would generate tsunamis smashing shorelines and razing settlements far inland. A hit in the vastness of an ocean might give a maximum of hours to evacuate millions. An impact near an inhabited coast might leave witnesses seconds before succumbing to the pressure wave or the tower of water.
What can be done to prevent impact?
Instead of suffering massive losses, requiring countries to reconstruct, stopping a strike is easier and cheaper. Magnetic crystals dumped into a volcano will not do the job. The movies Armageddon and Deep Impact, both released in 1998, advocate for nuclear bombs and heroic self-sacrifice.
Reality is not always as dramatic. A typical plan is deflecting an object so that it misses the Earth. When an object is far away, the difference between a planetary catastrophe and a near miss is equivalent to a hair’s breadth, so early detection alongside preparation for immediate response are paramount.
To deflect, science fiction writers have posited placing a huge tank of water on the object’s surface and piercing a small hole in the tank. The water vents into the vacuum of space inducing an equal and opposite reaction which is a rocket-like push, moving the space object. Other stories describe a spacecraft prodding the object, attaching an engine to it, or painting it black on one side to absorb sunlight and the differential heating shifts the object’s path.
All these proposals are tremendously expensive in terms of energy and money, yet they remain far preferable to an impact’s monstrous costs. Would they work? We do not really know without trying them, and the references provide many more suggestions for deflecting or destroying an object. Multiple ideas should be pursued in tandem in case one fails.
We could avert disaster from standard space objects if we choose to. Then there is another challenge of non-standard space objects bringing a planet-wrecking surprise.
Bobrowsky, P.T. and H. Rickman (editors). 2007. Comet/Asteroid Impacts and Human Society: An Interdisciplinary Approach. Springer: Berlin and Heidelberg, Germany.
Janzwood, S. 2021. R&D priority-setting for global catastrophic risks: The case of the NASA planetary defense mission. Research Policy, vol. 50, no. 6, article 104225.
Sánchez-Lozano, J.M., M. Fernández-Martínez, A.A. Saucedo-Fernández, and J.M. Trigo-Rodriguez. 2020. Evaluation of NEA deflection techniques. A fuzzy Multi-Criteria Decision Making analysis for planetary defense. Acta Astronautica, vol. 176, pp. 383-397.
Schmidt, N. (editor). 2019. Planetary defense: global collaboration for defending Earth from asteroids and comets. Switzerland: Springer.