Leftovers
Trillions of comets occupy two outer regions of the solar system
Jupiter's mass prevented the asteroid belt from coalescing into a planet
After all the planets and moons formed, there was still some leftover material.
Icy planetesimals were hurled far from the Sun by encounters with the giant outer planets. Most of these icy leftovers inhabit a vast shell, called the Oort Cloud, that surrounds the present-day solar system. A passing star or interstellar cloud occasionally jostles one of the icy bodies out of its orbit. Most are ejected from the solar system, but some fall toward the Sun and become comets, with long, glowing tails. The other leftovers inhabit the Kuiper Belt, a broad region closer to the Sun than the Oort Cloud, but still beyond the orbit of Neptune.
Some rocky leftovers remained near the Sun. Many of them inhabit the asteroid belt, a zone between the orbits of Mars and Jupiter. The asteroids never formed a planet because the gravity of nearby Jupiter kept pulling them apart. Today, millions of asteroids -- some of them as big as moons -- probably inhabit the asteroid belt, with many more scattered throughout the solar system.
The solar system has probably changed little since the planets and moons formed. The Sun churns steadily along, converting hydrogen to helium in its core. The planets evolved somewhat as they radiated away the heat left over from their birth, or as ring systems came and went.
On to Life »
|
Contact StarDate | About StarDate | Friends of McDonald | Sign up for Sky Tips
