5. Colliding Worlds

Breaking a date with doomsday

Finding the hidden threat

Fig. .. 

While we know that asteroids and comets have collided with the Earth in the past, and that they will inevitably hit our planet in the future, we do not yet know if any them are now headed for a deathly collision with our solitary outpost of life. Astronomers are therefore taking a census of everything out there that is big enough and close enough to threaten us (Fig. 14.17). Once all of these near-Earth objects are located, and their current trajectories known, astronomers can use computers and refined observations to determine their precise future paths and establish whether and when any of them will strike the Earth.

Doing something about the threat

Sooner or later we will discover an asteroid or comet headed toward collision with the Earth. But unlike most natural disasters, the impact can be forestalled once the killer object has been fingered and we can see it coming. Evasive action will depend on the lead-time available and the expected physical nature of the object, including whether the object is a binary system.

And what do we do if we find a large asteroid or comet headed our way? The Earth cannot be moved out of the way, but we could launch an intercept mission to redirect the objectís course. If the impact is many years away and the threatening object relatively far away from us, all you have to do is give it a little nudge. By the time the asteroid or comet reaches the Earthís vicinity, that small change in trajectory will make a big difference, enabling it to bypass the planet.

If the warning time is only a matter of months or less, the sole recourse might be to send a high-powered rocket armed with a bomb powerful enough to redirect the object or blow it up. Such a possibility has sparked the interest of bomb designers and some members of the military. A conventional nuclear weapon might be used to deflect or destroy a small, solid, rocky asteroid, but a much larger explosion could be needed to divert or pulverize a loosely bound object, like some large asteroids and most comets.

Fig. .. 

(Fig. 14.18. Summary Diagram)

(page 4 of 4)

Copyright 2010, Professor Kenneth R. Lang, Tufts University