In the new story of the solar system, the future is a bit dicey, and it all began in chaos. The dust speck had been plucked from the tail of a comet more than 200 million miles away.
Now, under an electron microscope in a basement lab at the University of Washington, its image grew larger, until it filled the computer screen like an alien landscape. Zooming in on a dark patch that looked like a jagged cliff, Dave Joswiak upped the magnification to 900,000. Art by Dana Berry/ National Geographic Sources: Stephen Mojzsis, University of Colorado/NASA
Above: Lunar Science Institute, William Bottke, Southwest Research Institute
About 3.8 to 4 billion years ago Earth suffered what scientists call the Late Heavy Bombardment: a mysterious rain of astroids and comets that pummeled most of its surface. The moon was heavily cratered then too.
Art by Dana Berry/National Geographic Sources: Harold Levison and Dan Durda, Southwest Research Institute (SWRI)
The Late Heavy Bombardment of Earth may have resulted from a dramatic disturbance of planetary orbits. That led Neptune (foreground) and Uranus to disrupt a belt of comets, and Jupiter the asteroid belt. According to the Nice model (named for the French town where it was conceived), Jupiter, Saturn, Uranus, and Neptune had been born close together in a solar nebula, a disk-shaped cloud littered with rocky and icy debris. As the four giants’ strong gravity sucked in or slung away such debris, their own orbits slowly shifted-until they hit a tipping point.
The images are from the July issue of National Geographic magazine.
source National Geographic