Atari made it look so simple: press a few buttons to move, rotate, vanish through hyperspace, fire missiles, and boom: total asteroid destruction.
But unless asteroid-defense completely deflects or entirely reduces a massive space object to space dust, any rubble from a partially-destroyed asteroid could still threaten humanity through wind-blasts hurling humans through the air and flattening forests, shockwaves rupturing internal organs, and heat roasting entire populations to death. So, humanity really needs a way to detect killer asteroids on collision-course for Earth while we still have time to do stop them.
At least there’s an app for that, right? Sort of – there is free software NASA distributed to aid in asteroid early detection. While Japan used its Hayabusa2 deep space probe to bomb asteroid Ryugu, that mission was to collect samples for analysis, rather than learning how to “Bruce Willis” the asteroid to smithereens as in the movie Armageddon.
But since the 1980s-era US Strategic Defense Initiative, someone has been trying to make space-based lasers effective at destruction, even for zapping comets. If detection works and deflection won’t, there’s the hours-before-impact “shotgun” defense which shoots 10 X 10 arrays of 100-kg (220-lb) steel rods to rip killer asteroids – including Apophis, which will come very close to Earth in 2029 – into countless meteors which might burn to cinders in the atmosphere.
But what if we shred an asteroid into boulders that don’t hit the Earth, and instead hit the Moon?
According to Aaron Rosengren at the Department of Mechanical and Aerospace Engineering at UC San Diego, such an impact would be devastating not simply for future lunar bases, but for terrestrial civilization itself. That’s because, as he and his fellow researchers at the University of Arizona, have learned, the impact on the Moon would eject lunar chunks into space similar to near-Earth asteroid Kamo’oalewa and object 2024 PT5, and a horrifyingly large proportion of those chunks would form a co-orbital disaster field that could make Han Solo nervous to navigate.
“The problem is no longer just ‘Will something hit the ground’” on Earth, says Rosengren, “but ‘What are the long-term consequences for the Earth-Moon system we now rely upon?”.
That’s because debris from such a collision could initiate the Kessler syndrome, a chain-reaction in which the shrapnel of shredded satellites in turn shreds more satellites and on and on until low-Earth orbit is inaccessible for centuries, looking like that near-space frag-field in WALL-E. Traveling through that would be the least of our problems, given that humanity needs its satellites for GPS navigation, cellular networks, satellite telephones, search-and-rescue, weather-forecasting, escaping hurricanes, military action, and a little thing called the World Wide Web.
So now we’re back to early detection – as in really early.
“For the class of objects we worry most about from a planetary-defense standpoint [which is] hundreds of meters across,” says Rosengren, “a realistic goal is to have at least five to 10 years of warning. That sounds like a long time, but in engineering terms it’s barely enough: we would need to detect the threat, converge on a reliable impact probability, design and fund a deflection mission, build and launch a spacecraft, and then give it time to reach the asteroid and gently ‘nudge’ it so that, many orbits later, it misses Earth.”
While it’s hardly easy to detect massive space objects that could one day collide with Earth, it’s much easier than detecting small ones that could still be hyper-destructive. That’s why Rosengren, UCSD colleagues Thomas Bewley and Ben Hanson, and colleagues at the University of Arizona are investigating rare, low-probability chances for destruction, thereby offering authorities the best advice on when to launch deflection missions.
Instead of crowd-sourcing such risk-assessing calculations, their work coordinates detection from numerous observatories and telescopic arrays including in South Africa, Chile, and the Pan-STARRS telescopes in Hawaii, sending the results to the Minor Planet Center at Harvard’s Smithsonian Astrophysical Observatory. Then the Solar System Dynamics Group at NASA’s Jet Propulsion Laboratory analyzes the objects that will come closest to Earth, using infrared-scanning telescopes such as NEOWISE to estimate the size of asteroids, especially darker ones that are difficult to see in the visible spectrum.
The work is productive: now we can detect an estimated 95% of planet-killing space objects at least 1 km (0.625 miles) across. In 2022, similar detection work resulted in NASA’s Double Asteroid Redirection Test (DART) mission, which slammed the DART spacecraft into the small asteroid Dimorphos orbiting the larger asteroid Didymos, changing the orbits of both child and parent around the sun.
Unfortunately, any of the giant armada of smaller objects tens of meters wide is still large enough to annihilate Beijing, Lagos, or New York – objects such as the one that exploded over Chelyabinsk, Russia in 2013 – and those are far harder to detect. As Bewley warns, “There are many near-Earth objects which could create such collisions, and astronomers identify several more each and every year.” So, don’t sleep tight, Earthlings … instead, watch the skies.
Source: UC San Diego