Planetary Defense

As interesting as asteroids are, they also pose a threat. On February 15, 2013, a bolide (a meteor that explodes in the atmosphere) near Chelyabinsk, Russia created an airburst whose shockwave struck six cities across Russia. The impact may have been caused by an asteroid just 21 yds. (20 m.) in diameter. Prevalent dashboard cameras in Russia have offered many images of the meteor hurling across the sky, and visual evidence of the damage that would accompany an asteroid impact.

Bolides such as the Chelyabinsk event are continually colliding with Earth; however, most of these objects are very small and pose no threat to human activity or property. The Chelyabinsk event reminded us that while the chance of a major asteroid impact is low, the potential consequences to life and property could be very severe.

The Chelyabinsk Event

As interesting as asteroids are, they also pose a threat. On February 15, 2013, a bolide (a meteor that explodes in the atmosphere), entered Earth's atmosphere near Chelyabinsk, Russia and created an airburst whose shockwave struck six cities across Russia. The impact may have been caused by an asteroid just 21 yds. (20 m.) in diameter. Prevalent dashboard cameras in Russia have offered many images of the meteor hurling across the sky, and visual evidence of the damage that would accompany an asteroid impact.

Planetary Defense

Despite the worldwide attention of the Chelyabinsk event, these bodies are continually colliding with Earth; however, the vast majority of these objects are very small and pose no threat to human activity. Although the chance of a major asteroid impact is low, the potential consequences to our society could be very severe.

This map of data gathered from 1994-2013 shows where small asteroids impacted Earth's atmosphere and disintegrated to create very bright meteors, technically called “bolides” and commonly referred to as “fireballs”. Sizes of orange dots (daytime impacts) and blue dots (nighttime impacts) are proportional to the optical radiated energy of impacts measured in billions of Joules (GJ) of energy, and show the location of impacts from objects about 1 meter (3 feet) to almost 20 meters (60 feet) in size. Credit: NASA

Small asteroids – sizes of only about a meter – hit Earth's atmosphere and disintegrate with surprising frequency – around every other week.

Impact craters are visual evidence of the meteor strike. The 1908 Tunguska impact in Siberia, the largest impact in recorded history, is thought to have been triggered by an incoming object of 65-207 yards (60-190 meters) in diameter.

What can we do?

Researchers in the U.S. and Europe have been considering the use of space missions for asteroid risk assessment for almost two decades. We have several technologies available to mitigate such a threat, but none have been tested in realistic conditions. Moreover, the design of an efficient mitigation strategy relies on our understanding of the physical properties of threatening objects and their responses to mitigation techniques, which is still extremely poor.

Most of the techniques that have been proposed to avoid an Earth impact event are linked to altering the trajectory of an asteroid on a collision course with Earth. Among these proposals, the one that is currently being considered as more mature, because it is based on existing and affordable spacecraft technology, is the kinetic impactor, which changes the orbit of an asteroid by a direct hit of a spacecraft at a very high relative speed.

In the joint NASA/ESA AIDA mission, the kinetic impactor is the DART spacecraft. DART's counterpart, the Asteroid Impact Mission (AIM), will provide the assessment capabilities required to study the concept and effects of impactor, as well as study the make-up of the double asteroid system Didymos.

Adapted from ESA's Asteroid Impact Mission “Planetary Defence”

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