Can We Mitigate Asteroid Impact Now?
The primary goal of the Deep Impact mission was not about asteroid mitigation, although the mission made significant and historical contribution to the asteroid mitigation method.
The comet, Temple One, was a great target for the Deep Impact mission, to learn the origin of our Solar System by learning the composition of the comet. However, it was too large for verification of asteroid mitigation method:
1. The change in comet's velocity was too small to measure.
The impactor weighed 370 kg and impacted Tempel One at the speed ten times faster than the speed of a rifle bullet. The energy of the impact was 39 GJ, equivalent to 9.3 tons of TNT. Still, the comet was about 6 km in diameter, and the change in its velocity was too small for us to measure.
2. The target was too big
As mentioned in the Threat section, our next credible threat will be an asteroid or comet with 100-250 m in diameter. With the frontal projection area of 37 square kilometers, the Temple One was about 5,000 times larger target, compared to a spherical 100 meter asteroid.
3. The Deep Impact did not hit the center of gravity of Temple One
It was not intended, and it did not. However, in order to transfer the kinetic energy of impactor to change in the velocity of target asteroid, it is crucial for an impactor spacecraft to hit the center of gravity.
Mission to verify the Kinetic Impactor method is currently in progress by NASA.