What if the impact changes the orbit of the comet so that it collides with the Earth?
A collision between a 6 km comet and the Earth would be very bad. Fortunately, Tempel 1 (the comet of Deep Impact) is absolutely safe: its current orbit never, ever approaches the Earth. The nearest approach was in May, and the comet was still at more than 100 million km. At the time of the impact, it will be at 130 million km. While the 370kg impactor will move very fast (38 000 km/h), and cause a big explosion, this is negligible compared to the mass and energy of the comet. The effect of the impactor on the comet’s orbit will be less than that of a fly hitting a plane. The orbit will not be changed, so there is still no risk of impact between Comet Tempel 1 and the Earth. Note for those who really like to worry: there are many, many unknown comets and asteroids around – these are the ones one should worry about. What will happen to the comet: We don’t know for sure, that’s why the experiment is interesting. The most likely scenario is that the impactor will create a crater about the
