Intro to Our Solar System

Our Solar System Most of the planets in our solar system can be seen without a telescope. Uranus and Neptune are the only two too far to see. The largest planet is about 10 times larger than Earth across.

Our Solar System

Distances Astronomers use astronomical units, or AUs, to measure distance in space. 1 AU = distance from Sun to Earth; about 150 million km. The first four (inner) planets are relatively close to one another; the outer planets are much more spaced out.

Orbits More than 99% of the Mass in our Solar System is the Sun. This results in a strong gravitational pull on everything else. Each planet (and other objects) orbits the Sun in an elliptical, or oval, shape.

Orbits All planets orbit in the same direction, and most other objects do, also. Scientists think this is a clue – the solar system formed from a huge cloud of gases and dust; most mass = Sun, the rest clumped together to form planets. Not all of them were large enough to planets; resulting in asteroids, comets, and moons.

The Inner Planets

Inner Planets Mercury, Venus, Earth, and Mars Called terrestrial planets Rocky crust, dense mantles and cores

Processes and Surface Features They all have layers; the heaviest materials sank to the center in their collisions and the lightest rose to become crust. Four main processes shaped the crust: Tectonics Volcanism Weathering and erosion Impact cratering

Tectonics Earth’s crust has tectonic plates that are moved by convection in the mantle. As the plates move, different features (mountains, valleys) are formed. The other planets do not have plates, but still are able to move with the mantle. Tectonics: process of change in the crust due to motion of material in the mantle.

Volcanism Occurs when molten rock moves from the interior to the surface. Volcanoes are on Earth, Venus, and Mars. When the inside of a planet cools enough, no more molten rock reaches the surface.

Weathering and Erosion Water and wind are important factors on Earth. Planets without wind still have weathering due to heating and cooling of the surface.

Impact Cratering When small objects hit a larger object and leave a resulting indentation. Harder to find on Earth Easily found on other planets due to less weathering/erosion.

Atmospheres Mainly formed from volcanic gases. Venus, Earth, and Mars have enough gravity to hold in gases like CO 2, but lighter gases escaped. Earth is mostly nitrogen. Can make a planet warmer due to loss of energy

Mercury Believed to shrink from original size, creating cliffs. Large areas of cooled lava. Several impact craters, suggesting the surface has not changed much. Longest cycle of day and night – 3 months of daylight, 3 months of darkness. Can get 800+ F during day, and -170 F during night.

Mercury

Venus Slightly smaller than Earth. 8 months to turn once; retrograde rotation (opposite way than orbit) creates 2 months of daylight and 2 months of darkness. Very dense, mostly CO2. Temp = about 470 F. Sulfuric acid in atmosphere form thick clouds.

Mars About half the size of Earth Two moons – Deimos and Phobos Red because of iron/rust Large valley – Valles Marineris Large areas of cooled lava; several volcanoes Winds up to 300 mph; sand dunes. Several craters

Mars Mostly CO2 in atmosphere, but very low air pressure. Temps vary from about 60 F in day to -130 F at night. Polar caps, mostly made of dry ice. No liquid water on surface, but there is frozen water in ground.

The Outer Planets

Outer Planets Jupiter, Saturn, Uranus, and Neptune – gas giants : mostly made of H, He, and other gases. The atmosphere is very thick, almost like a liquid in some places. They are all believed to have a large, solid core.

Jupiter Largest planet 5.2 AU from Sun 1 year = 12 Earth years Fast rotation = fast wind and storms White clouds made of ammonia; lower clouds are brown/red and made of chemicals Storms form between winds; the largest is the Great Red Spot (100+ years old).

Saturn Gas particles spread out more, forming layers of clouds. Rings: wide, flat zone of small particles that orbit a planet. Bright rings made out of water ice chunks, with moons mixed in. Axis is tilted at 27 degrees; rings appear to change b/c of this. 1 year = almost 30 Earth years.

Uranus and Neptune Mostly methane, ammonia, and water. Uranus = blue/green; Neptune = dark blue – colors are from methane.

Uranus 1 year = 84 Earth years Rings and moons around equator Seems to spin on its side Scientists think the unusual rotation was caused from a collision.

Neptune Sometimes looks white due to methane clouds Severe storms, such as the Great Dark Spot, can be seen in darker shades of blue. This storm moved toward the equator, where it is thought that the winds broke up the storm.

Other Objects

Pluto Was once a planet. Discovered in 1930 No spacecraft has been close to it. Has a moon, Charon – they orbit each other; sometimes called a “double planet”. More oval-shaped orbit 1 year = 248 Earth years

Asteroids Small, solid, rocky bodies that orbit close to Sun. Most have irregular shapes Most between Mars and Jupiter – The Asteroid Belt Craters, broken rock, and dust cover them; most have no atmosphere and no layers, so surfaces don’t change. Can hit Earth – 65 mya, a 6 mi asteroid hit Earth and sent dust into the air, most likely changing the temps of Earth and killing off any living organisms.

Comets Have oval orbits Have a coma (cloud of material) and a tail (gets longer closer to the Sun). Small, icy rock is hard to see without the parts above. The tail always points away from the Sun. Halley’s Comet – orbits approx. every 75 years; expected to return in 2061.

Meteors & Meteorites Meteors: Brief streaks of light caused by hot particles/air in the upper atmosphere. Usually can see a few/hour in the night sky. Usually very quick, only a few seconds. Meteorites: space object that reaches Earth’s surface Usually smooth on the outside from melting; inside can still be icy.