Earth Science

The Solar System

Other Celestial Bodies

Study Tip
New guidelines in 2000 defined Pluto as a dwarf planet. Instead of nine planets, our Solar System now only has eight.

Exoplanets

  • Exoplanets are planets orbiting stars other than our Sun. They are found in solar systems other than our own.
  • Scientists can use methods to identify exoplanets, and confirmed examples are increasing rapidly.
Study Tip
New guidelines in 2000 defined Pluto as a dwarf planet. Instead of nine planets, our Solar System now only has eight.
  • Detecting slight periodic motion of a planet can indicate that it may be an exoplanet pulled by a star out of our solar system.
  • Detecting the change in brightness of a star can indicate that there might be an exoplanet passing in front of it.

Asteroids

  • Asteroids are small, irregular-shaped rocks that orbit the Sun, and often look like points of light. Their collisions with Earth have caused mass extinctions in history.
  • The asteroid belt is a region between Mars and Jupiter where many asteroids are found. Scientists believe they were supposed to form a single planet, but were pulled apart by Jupiter’s gravity.
  • Near-Earth asteroids cross Earth’s orbit path, and scientists are always on the lookout for large ones that may cause problems.
  • Scientists are fascinated by asteroids, looking to discover the origins of our universe, and possibly to mine some rare minerals.
Asteroids

Comets

  • Comets are small, icy objects that orbit the Sun. Their collisions with Earth have brought water and other substances. Ice evaporates during their flight, and reflects light from the sun, creating a colorful tail.
  • Comets only appear when they are close to the Sun. The time between one appearance of a comet and the next is called the comet’s period.
  • Short-period comets, with periods of about 200 years or less, come from a region beyond the orbit of Neptune called the Kuiper belt.
  • Comets with periods as long as thousands or even millions of years come from a very distant region of the solar system called the Oort cloud.
Comets

Earth Science

Meteors

  • Meteors are small pieces of matter burning up as they enter Earth’s atmosphere from space. People often call them “shooting stars.”
  • Meteoroids are meteors before they reach Earth’s atmosphere.
  • When Earth passes through a cluster of meteoroids, it is called a meteor shower.
  • Meteorites are leftover meteors that don’t burn up completely, and manage to strike Earth. They provide important scientific information.
Meteors

Dwarf Planet

  • A planet needs to orbit a star, be big enough that its own gravity shapes it as a sphere, be small enough that it isn’t a star itself, and have cleared its orbit of smaller objects.
  • A dwarf planet needs to orbit a star, have enough mass to be a sphere, not have cleared its orbit of smaller objects, and not be a moon.
  • Pluto is a dwarf planet. It was considered a planet before, because early scientists mistakenly thought its moon was a part of its size. It has an odd, tilted orbit, and fails to clear other bodies out of its orbit.
  • Ceres is the closest dwarf planet to the Sun, and is the largest object in the asteroid belt. It is large enough to shape itself as a sphere, but doesn’t clear its orbit.
  • Other dwarf planets include Makemake, Eris and Haumea. Scientists are still discovering and adding more to the list.
Dwarf Planet
Concept Check
  • What are exoplanets?
  • What are asteroids? How can you differentiate them from comets and meteors?
  • What is a dwarf planet? Name a dwarf planet in our Solar System.