| A | B |
|---|
| nebula | cloud of dust and gases in space |
| Asteroid | Large, irregular shaped rocks that orbit the sun |
| Comet | Masses of ice and embedded rock debris which orbit the Sun. |
| planetesimal | they clumped together to form planets by accetion |
| terrestrial (inner) planets | Mercury, Venus, Earth, Mars |
| Jovian (outer) planets | Jupiter, Saturn, Uranus, Neptune |
| Terrestrial planets characteristics | small, dense, thin atmosphere, longer day |
| Meteoroid | Rock fragments in space that can be very small or very large. |
| Moons | Solid objects which orbit planets |
| Maria | Ancient lava flowa on the Moon |
| Craters | Caused by meteorite impacts |
| Rotate | To spin on an imaginary axis. Earth rotates once on its axis every 24 hours. this is why we have day and night, sunrises and sunsets. |
| Solar System's age | 4.6 billion years old |
| Objects used to date solar system | Earth rocks meteorites, Moon rocks |
| Weathering & erosion | recycles Earth rocks & erases craters |
| Astronomical unit (AU) | Used to measure distances in the Solar system |
| Jupiter's great spot | rotating stormy |
| Olympus Mons | Solar system's largest volcano (Mars) |
| Most abundant gases in Solar system | hydrogen and helium |
| Why Moon rocks date older | No weathering or erosion on Moon |
| Power's the Sun | Nuclear fusion |
| Hottest and brightest planet | Venus |
| Mercury | planet with craters and largest temperature extremes |
| Jupiter | Largest planet |
| Planets with ring systems | all Jovian planets |
| High mass and low temperature | thick atmospheres |
| Uranus | rotates sideways (axis parallel to plane of orbit) |
| comet's tail | always points away from the Sun |
| Kuiper belt & Oort cloud | places where comet's form |
| Meteorites | Small rocks from space that impact Earth |
| Asteroid belt | Located between Mars & Jupiter |
