EARTH’S MOON
T e next example of an Earth look-alike is a little closer to home. I’m talking about the moon. As a child, I spent hours looking up at it and wondering why it had so many dents. Scientists once thought those dents were
volcanoes. Now, thanks to data collected by astronauts, telescopes, and orbiters, we know better. Each dent shows where a space object slammed into the moon. T e impact shatters rocks. Some melt. In seconds, a crater forms. Like the moon, Earth has taken big hits.
One occurred 215 million years ago when an asteroid or comet slammed into Earth. T e impact blasted a crater 100 km wide. It’s so big that astronauts can easily spot it from space. From the size of the crater, we believe that whatever hit Earth was about 5 km wide. T is crater in Canada is unusual. Most
space rocks don’t reach the ground. Instead, they burn up as they streak through Earth’s atmosphere. Craters that do form don’t last long. Wind and rain pound them, wearing and washing their rock away. Dirt fills them, and plants cover them. Tectonic plates shiſt . Over millions of years, all this action erases craters.
Smash Hits T e moon has no atmosphere. It doesn’t have wind or plants. It doesn’t have tectonic plates. So lots of space rocks hit it and the marks stay almost forever. Some scientists estimate that as many as a half billion craters cover the moon. T e biggest moon crater formed 4 billion
years ago. T at’s when an asteroid slammed into the south pole of the moon. It dug deep into the moon’s crust. We’ve measured the crater using data
collected by an orbiter circling the moon. It’s 2,500 km wide and 8 km deep. Imagine the size of the asteroid that blasted out a hole that big!
14 NATIONAL GEOGRAPHIC EXTREME EXPLORER
A space rock slammed into Earth millions of years ago, forming a crater 100 km wide.
This crater’s impact pattern is so clear that it can tell us what older craters once looked like.
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24