Solar System — Reading Comprehension Lesson

Reading Passage

Solar System

Our solar system consists of the sun and everything bound to it by gravity: eight planets, dozens of moons, millions of asteroids, billions of comets, and vast amounts of dust and gas. It formed about 4.6 billion years ago from a giant cloud of gas and dust called a solar nebula. As the cloud collapsed under gravity, most of the material collected at the center to form the sun, while the remaining material flattened into a rotating disk from which the planets and other bodies formed. The solar system extends far beyond the orbit of Neptune to the distant Oort Cloud, a spherical shell of comets that may reach a quarter of the way to the nearest star.

The eight planets of our solar system divide into two groups. The inner, terrestrial planets — Mercury, Venus, Earth, and Mars — are small, dense, rocky worlds with few or no moons. The outer, giant planets — Jupiter, Saturn, Uranus, and Neptune — are much larger and are composed primarily of gas and ice rather than rock. Jupiter is the largest planet, with a mass more than twice that of all the other planets combined. Saturn is famous for its spectacular ring system, which is made up of billions of pieces of ice and rock ranging in size from tiny grains to chunks as large as a house.

Between Mars and Jupiter lies the asteroid belt, a region containing millions of rocky objects ranging in size from dust grains to the dwarf planet Ceres, which is about 590 miles across. Beyond Neptune lies the Kuiper Belt, a flattened disk of icy objects including the dwarf planet Pluto. Pluto was reclassified from a planet to a dwarf planet in 2006 when astronomers defined a planet as a body that has cleared the neighborhood around its orbit — Pluto shares its orbital zone with many other Kuiper Belt objects. The New Horizons spacecraft flew past Pluto in 2015 and revealed a world of surprising geological complexity.

Gravity is the force that holds the solar system together. The sun contains 99.8 percent of all the mass in the solar system, and its gravitational pull keeps the planets in their orbits. Each planet also has its own gravitational field, which holds its moons in orbit. Our moon is unusually large compared to Earth — it is thought to have formed when a Mars-sized body collided with the early Earth, blasting debris into orbit that eventually coalesced into the Moon. The Moon’s gravity causes Earth’s ocean tides and has gradually slowed Earth’s rotation over billions of years.

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