Why are the Jovian planets so much larger than the terrestrial planets?

With the exception of Pluto, planets in our solar system are classified as either terrestrial (Earth-like) or Jovian (Jupiter-like) planets. Terrestrial planets include Mercury, Venus, Earth, and Mars. These planets are relatively small in size and in mass. A terrestrial planet has a solid rocky surface, with metals deep in its interior. In the solar system, these planets are closer to the sun and are therefore warmer than the planets located farther out in the solar system. Future space missions are being designed to search remotely for terrestrial planets around other stars. The layers of gases surrounding the surface of a planet make up what is known as an atmosphere. The atmospheres of the terrestrial planets range from thin to thick. Mercury has almost no atmosphere. A thick atmosphere made mostly of carbon dioxide covers Venus, trapping heat and raising surface temperatures. Clouds on Venus form from sulfuric acid. Earth's atmosphere is 77 percent nitrogen, 21 percent oxygen, and 1 percent argon, with variable amounts of water vapor, and trace amounts of other gases. White clouds of water vapor hide much of Earth's surface in views of Earth from space. Mars has a very thin atmosphere containing mostly carbon dioxide, with nitrogen, argon, and trace amounts of oxygen and water vapor. The atmosphere also contains thin water and carbon dioxide clouds, and is frequently affected by dust storms. Jovian planets include Jupiter, Saturn, Uranus, and Neptune. These planets have larger sizes and masses. Jovian planets do not have solid surfaces. They are sometimes called gas giants because they are large and made mostly of gases. Small amounts of rocky materials are only found deep in the cores of Jovian planets. In the solar system, Jovian planets are located farther from the sun than terrestrial planets, and are therefore cooler. Scientists have found more than 100 Jovian planets around other stars. The majority of the extrasolar Jovian planets that have been discovered so far are closer to their stars than the Jovian planets in the solar system are to the sun.