<div><span style="font-size: 1rem;">NASA's DART mission to test deflecting an asteroid using "kinetic impact" with a spaceship is just one way to defend planet Earth from an approaching object -- and for now, the only method possible with current technology.</span><br></div><div><br></div><div>The operation is like playing billiards in space, using Newton's laws of motion to guide us.</div><div><br></div><div>If an asteroid threat to Earth were real, a mission might need to be launched a year or two in advance to take on a small asteroid, or decades ahead of projected impact for larger objects hundreds of kilometers in diameter that could prove catastrophic to the planet.</div><div><br></div><div>Or, a larger object might require hits with multiple spacecraft.</div><div><br></div><div>"This demonstration will start to add tools to our toolbox of methods that could be used in the future," said Lindley Johnson, NASA's planetary defense office, in a recent briefing.</div><div><br></div><div>Other proposed ideas have included a futuristic-sounding "gravity tractor," or a mission to blow up the hypothetical object with a nuclear weapon -- the method preferred by Hollywood.</div><div><br></div><div>- Gravity tractor -</div><div>Should an approaching object be detected early -- years or decades before it would hit Earth -- a spaceship could be sent to fly alongside it for long enough to divert its path via using the ship's gravitational pull, creating a so-called gravity tractor.</div><div><br></div><div>This method "has the virtue that the method of moving the asteroid is totally well understood -- it's gravity and we know how gravity works," Tom Statler, a DART program scientist at NASA said at a briefing last November when DART launched.</div><div><br></div><div>The mass of the spacecraft however would be a limiting factor -- and gravity tractors would be less effective for asteroids more than 500 meters in diameter, which are the very ones that pose the greatest threat.</div><div><br></div><div>In a 2017 paper, NASA engineers proposed a way to overcome this snag: by having the spacecraft scoop material from the asteroid to enhance its own mass, and thus, gravity.</div><div><br></div><div>But none of these concepts have been tried, and would need decades to build, launch and test.</div><div><br></div><div>- Nuclear detonation -</div><div>Another option: launching nuclear explosives to redirect or destroy an asteroid.</div><div><br></div><div>"This may be the only strategy that would be effective for the largest and most dangerous 'planet-killer' asteroids (more than one kilometer in diameter)," a NASA article on the subject says, adding such a strike might be useful as a "last resort" in case the other methods fail.</div><div><br></div><div>But these weapons are geopolitically controversial and technically banned from use in outer space.</div><div><br></div><div>Lori Glaze, NASA's planetary science division director said in a 2021 briefing that the agency believed the best way to deploy the weapons would be at a distance from an asteroid, in order to impart force on the object without blowing it into smaller pieces that could then multiply the threat to Earth.</div><div><br></div><div>A 2018 paper published in the "Journal of Experimental and Theoretical Physics" by Russian scientists looked at the direct detonation scenario.</div><div><br></div><div>E. Yu. Aristova and colleagues built miniature asteroid models and blasted them with lasers. Their experiments showed that blowing up a 200-meter asteroid would require a bomb 200 times as powerful as the one that exploded over Hiroshima in 1945.</div><div><br></div><div>They also said it would be most effective to drill into the asteroid, bury the bomb, then blow it up -- just like in the movie Armageddon. - AFP&nbsp;</div><div><br></div><div>bnbd24/fas</div>