Seen below, Apollo 16 astronaut John Young easily jumped half a meter off the surface to demonstrate the moon's lower gravity. On Earth, Young and his space suit, with a combined mass of 180 kg, weighed about 1600 Newtons (390 lbs). On the moon, Young and his suit weighed only about 270 Newtons (65 lbs). Don't believe he's off the surface? Find his shadow on the ground!

Due to its larger target area and stronger gravity, scientists estimate that Earth should be struck by twice as many asteroids per square kilometer as the moon. The evidence for this bombardment on the moon is obvious, but evidence of these collisions on Earth is very scarce.

Compare the landscape in this photograph to the landscape where you live. Notice the many small craters pictured here, some as small as a few centimeters in diameter. What do you think might happen to the object that created one of these small craters if it were headed toward Earth?