| A | B |
|---|
| accretion | Process where particles collide and stick together in a solar nebula. Gravity is NOT involved. |
| planetesimal | First stage in forming a planet by process of accretion. |
| protoplanet | Step in planet formation where planetesimal is large enough to begin having gravitational accretion. |
| inner planet | Formed in hotter, inner solar nebula by silicate minerals and metals. |
| outer planet | Formed in colder, outer solar nebula by ices and gases. |
| differentiation | Process in planet formation where the homogeneous interior begins to separate out into layers of different compositions/densities. |
| terrestrial planets | Small, rocky, dense planets in the inner solar nebula (Mercury, Venus, Earth, Mars) |
| Jovian planets | Large, gassy, low density planets in the outer region of a solar nebula (Jupiter, Saturn, Neptune, Uranus) |
| Asteroid | Large, solid particle in space. |
| Asteroid Belt | Large field of asteroids situated between Mars & Jupiter. |
| Kuiper Belt | Large field of ice, rock material, and comets located out beyond the gas giants. |
| planet | Protoplanet with large enough gravitational field to "sweep" its orbital path of loose gases. |
| dwarf planet | A protoplanet, such as Pluto, that has high enough gravity to pull itself into a spherical shape but not to sweep its neighborhood. |
| Oort Cloud | Spherical shell around the entire solar system and containing comets with orbits outside the plane of the planets. |
| meteoroid | Small, solid particle in space. Most grain-sized. |
| meteor | A meteoroid that enters a planet's atmosphere. |
| meteorite | Any portion of a meteoroid that reaches a planet's surface. |
| Fission Theory | Early theory that the moon formed because the sun pulled a piece of the rapidly rotating Earth. |
| Capture Theory | Early theory that the moon was a small, wandering planet captured by Earth's gravity. |
| Coaccretion | Early theory that the moon had formed along side the earth in the same manner as earth. |
| Giant Impact Theory | Moon formed from ejected debris caused by impact of Mars-sized planetesimal with Earth. |
| regolith | Layer of soil-like debris on the moon. |
| highlands | Oldest, light-colored surface of the moon, including mountain ranges. |
| maria basins | Smooth, darker portions of the moon surface that resemble seas. |
| rayed craters | Thin layer of recent impact debris that covers the moon's surface. |
| comet | Small objects of frozen gases, dust, and traces of organic material orbiting in space. |
