Wayward asteroids pose a serious threat to life on Earth, and we may not have long to react should we discover one on a collision course. NASA is now investigating a proposal for a defense system that could break apart a hazardous space rock just days or even hours before a potential Earth strike.
The dinosaurs wouldn’t have seen that world-ending rock coming, some 65 million years ago. Fortunately, we now have the tools to scan the skies for any asteroids with apocalyptic aspirations – NASA’s Near-Earth Object Observations (NEOO) Program has identified almost 28,000 objects whose orbits bring them close to our planet.
But spotting them is only half the battle: if we were to find a big space rock headed our way, we need tools to defend ourselves. Thankfully, NASA is already working on that too, with the DART mission currently en route to the asteroid Didymos B, which it will crash into with the goal of shifting the rock’s orbit by a fraction of a percent. While Didymos poses no threat to Earth, it’s a useful test run for the technique, which could be enacted for any serious threats that might emerge from the depths of space.
The problem is, this deflection method of self-defense relies on a long lead time – we’d need to know about this threat months or even years in advance. Considering how often asteroids are discovered just weeks, days or hours before they whizz past Earth, all the DARTs in the world might not help if we suddenly realize doomsday is penciled in for next Tuesday.
A new defense method known as Pi – Terminal Defense for Humanity could be put into action far more quickly. The project was proposed by Philip Lubin, an engineer at the University of California Santa Barbara, and has now been selected for Phase One of the NASA Innovative Advanced Concepts (NIAC) Program.
Rather than deflecting a dangerous rock, Pi is designed to destroy. An array of small rods would be fired at the asteroid like a shotgun blast, causing it to break apart into much smaller chunks that would burn up harmlessly in Earth’s atmosphere. Depending on the size of the rock, these penetrating rods could be delivered in arrays of 10 x 10, each with a mass of 100 kg (220 lb), or arrays of 50 x 50 with 40 kg (88 lb) each. Several waves of missiles could be launched at one object, or they could be boosted with chemical explosives or nuclear weapons.
To reach the target quickly, Lubin proposes that the Pi system could be locked and loaded and deployed in orbit or on the Moon. The latter would make a perfect outpost, Lubin says – the Moon has no atmosphere and much lower gravity, meaning it could be set up with long-range optical or near-infrared detection systems and launch within minutes if a threat was identified.
By Lubin’s calculations, a 50-m (164-ft) asteroid could be intercepted with only five hours before Earth impact. An object of this size could devastate a city with a yield of around 10 megatons, around the scale of the 1908 Tunguska explosion.
An asteroid with a diameter of 100 m (328 ft), which would produce a 100-megaton blast, could be intercepted within one day. Even Apophis, the overhyped “doomsday” asteroid that will sail past Earth in 2029, would be no match – just 10 days’ notice would be enough to intercept its 370-m (1,214-ft) diameter.
Smaller rocks, like the 20-m (66-ft) one that exploded over Chelyabinsk in 2013, could be intercepted with as little as 15 minutes before impact. That could prevent the damage to buildings and injuries to people seen with that event.
We’d need a bit more warning for larger rocks, but the Pi system still provides a much faster turnaround than the alternatives. An asteroid that’s 1 km (0.6 miles) wide could be intercepted with 60 days’ notice, preventing devastation that would be on a continental scale.
Of course, the Pi system is still very much in the concept phase, but with NASA taking an official interest in the project its development is underway, and it could eventually become an important part of our planetary defense system.
More details about the Pi Terminal Planetary Defense system can be read in the technical paper, published on ArXiv (PDF).
Source: NASA
