Deflecting Asteroids Away From Earth

230 ft. diameter 33 ft. The Earth is in the middle of a cosmic target gallery: We know of nearly 400,000 objects in the inner solar system. Just two months ago – on Nov. 6, 2009 – an asteroid 22 feet in diameter passed 8,700 miles above Earth, the cosmic equivalent of a bullet buzzing close to the skin. Diameter: diameter more than 0.6 miles Frequency of impact: Twice every million years Once per year Once every thousand years Moon Mercury Usually explode in atmosphere, but fragments reach the surface Example of consequences: Cretaceous extinction Tunguska event SUN Verius Mars • Earth Red dots are objects that cross Earth's orbit, (Positions as of Jan. 5, 2009) Asteroid 2009 VA was discovered only 15 hours before its close approach. Earth 2009 VA trajectory Orbiter Some methods of deflecting an impact Impactor ASTEROID ORBIT AFTER DEFLECTION ASTEROID TRACTOR Every object exerts a gravitational pull, including a single spacecraft. Merely by hovering above the asteroid, it could pull the rock off course. The KINETIC IMPACTOR ASTEROID Any projectile that collides with an asteroid would alter its momentum. The European Space Agency is preparing a 2011 mission called Don Quixote that will position an orbiter around an asteroid, launch an impactor against it, and measure the changes in trajectory. COLLISION ORBIT approach could even be tried with the Dawn spacecraft, scheduled to finish its tasks in the asteroid belt by 2015. However, such a strategy would be very slow, requiring years or even decades to alter the path of the asteroid., Photons Probe orbit Solar sail Gravitational pull SOLAR SAIL A solar sail would use the small but constant pressure of sunlight over a large area to steadily move the asteroid. Difficulties include the size – the sail would need a surface of 5,000 square kilometers - and the fact that it would be attached to a spinning rock. Mass driver Nuclear explosion NUCLEAR EXPLOSIONS Earth As immortalized in the movie "Armageddon," we could plant a bomb on an asteroid and blow it out of the sky like so much interplanetary skeet. But there's a catch: The explosion could divide the rock into smaller pieces (as any player of Atari's Asteroids knows). The pieces could still hit Earth, and would be more difficult to detect. It's a last-minute, last-ditch option. MASS DRIVER A mining device would drill material from the rock and eject it at high speed, essentially using the asteroid's own innards as propellant to give it a slow steady push, while also decreasing its mass. Mercury Mars SUN Painted surface MULTIPLE EXPLOSIONS A better use of nuclear weapons might be to detonate a series of smaller nuclear devices alongside the asteroid, far enough away as not to fracture the object. In space, the nuclear blasts would transmit relatively little force, but several of them could create a form of propulsion, enough to steer the rock away. LOTS OF PAINT The Yarkovski effect, named for the Russian engineer who discovered it a century ago, suggests that the Sun warms an asteroid more on the "day" side than on the "night" side. The warmer side emits more thermal radiation, gently nudging the object. Painting some areas of an asteroid would change this pattern, altering its path. Venus SOURCES: NASA Near Object Program, Armagh Observatory