Near-Earth Objects (NEOs)
by Floro Mercene
The International Academy of Astronautics (IAA) holds a bi-annual Planetary Defense Conference. This brings together world experts to discuss the threat to Earth posed by asteroids and comets and actions that might be taken to deflect a threatening object. Its 5th conference was held in May 2017 in Tokyo. Aspects discussed included remote-sensing technologies, the carrying out of mission campaigns and actions that might be taken to deflect a threatening object.
As of 2017, the number of discovered Near-Earth asteroids totaled more than 17,000. Experts estimate that an impact of an object the size of the one that exploded over Chelyabinsk, Russia, in 2013 – approximately 17 meters in size – takes place once or twice a century. Impacts of larger objects are expected to be far less frequent. However, given the current incompleteness of the NEO catalogue, an unpredicted impact – such as the Chelyabinsk event – could occur at any time. The key to preventing an impact is to find any potential threat as early as possible. With a couple of decades of warning, which would be possible for 100-meter-sized asteroids with a more capable detection network, several options are technically feasible for preventing an asteroid impact.
Given several years warning time, existing technology could be used to deflect the threatening object away from Earth. The key point in this mitigation process is to find the threatening object years ahead of time. Deflecting an asteroid that is on an impact course with Earth requires changing the velocity of the object by less than an inch per second years in advance of the predicted impact. The two most promising techniques that NASA is investigating are the kinetic impactor (hitting an asteroid with an object to slightly slow it down) and the gravity tractor (gravitationally tugging on an asteroid by station-keeping a large mass near it).