Our Solar System Last minute review! Please spend the first 5 minutes silently looking over your scientists and tech terms for your Quest! After? Read and do Ch. 21. 2&3 on your chart!

The Inner Planets

Inertia Inertia is the property of matter to resist any change in motion. An object at rest will remain at rest, while an object in motion will remain in motion in a straight line at a constant speed until acted on by an outside force.

Gravity Gravity is the force of attraction between any two objects with mass. The more mass, the more gravity. The further apart the two objects are, the less gravity.

Newton’s Law of Gravity Newton realized that the moon should go in a straight line forever and ever. But the force of gravity kept pulling it towards the Earth. The moon is going fast enough that it keeps curving around the Earth. It is constantly falling towards the Earth.

Solar System There are at least eleven planets (or planet-like objects)in our solar system. Mercury is 58,000,000-km from the sun. Pluto is 5,913,000,000-km from the sun. These numbers are hard to use!

Astronomical Units We will use AU’s to measure distances in the solar system. The Earth is about 150,000,000-km (93,000,000 miles) on average from the sun. So we will call this distance 1 AU.

Planetary Distances Mercury 0.4 AU Venus 0.7 AU Earth 1.0 AU Mars 1.5 AU Jupiter 5.0 AU Saturn 10.0 AU Uranus 19.0 AU Neptune 30.0 AU Pluto 39.0 AU Light travels through space at 300,000-km/s. So it takes about 8 minutes for light from the sun to travel 1 AU and reach us. How long would it take light from the sun to reach Pluto? 39 x 8 = 312 minutes, or 5.2 hours!

Planetary Zones First Zone: Contains the rocky terrestrial planets Mercury to Mars. Asteroid belt divides the first and second zones. Second Zone: Contains the gas giants Jupiter through Neptune. Third Zone: Goes from the orbit of Neptune out to 50 AU. Includes Pluto and the “ice dwarfs” in the Kuiper Belt.

The Inner Planets Planets are rocky. Called terrestrial from the Latin word terra, which means Earth.

Mercury Roman name for the Greek messenger god. He wore winged sandals so he could fly. Since Mercury the planet is the fastest of all the planets this is appropriate.

Mercury Data Closest to the sun. Temperature ranges from 427°C in daylight to -173°C at night. Revolves slowly, in two Mercury years three Mercury days will have passed. Essentially no atmosphere. Surface similar to the moon, with craters and smooth plains. One third the size of the Earth.

Mercury Diameter: one third the size of Earth Distance: 0.4 AU Atmosphere: no atmosphere worth mentioning Features: Craters with smooth plains and most extreme temperature range in solar system Life:no life because of lack of atmosphere and extreme temperature range

Venus Named for the Roman goddess of love and beauty. Originally the Greek goddess Aphrodite.

Venus Temperature Almost same size as the Earth. Hottest surface in our solar system. The average daytime surface temperature is 464°C, compared to the Earth’s 15°C. This is hot enough to melt lead.

Venus Atmosphere Seen from Earth, Venus is completely cloud covered. Venus has an very thick atmosphere, about 96% CO2, and 4 % N2. The clouds are mainly sulfuric acid. The atmospheric pressure is 92 atmosphere’s, compared to the one atmosphere we experience on Earth. This is the pressure you would feel if you were under 915 meters of water!

Greenhouse Effect Venus is the classic example of the “runaway greenhouse effect.” Water on Earth helped tie up much of the CO2 in rocks. Life also stored CO2 in plants and shells of animals. Venus was probably too warm to have much water in the liquid state, so the water vapor added to the greenhouse effect. As the rocks got hotter, they released their CO2 into the air also. So the greenhouse effect got worse and worse.

Venus Motions Since Venus takes 7.5 Earth months to revolve around the sun and 8 months to rotate once on its axis, a day on Venus is longer than its year. Venus also rotate east to west, the only planet to do so. This retrograde rotation (backward) was probably caused by Venus being struck by a large object early in its history.

Venus Surface Since we can’t see through the clouds on Venus, we use radar to scan the surface. Venus has rocks, mountains, craters, and strange dome shape landforms not found on other planets.

Venus Explorations About 20 spacecraft have visited Venus, with more either on the way or planned. Some have even landed on the surface and sent back pictures for a short while.

The Evening Star When in the west at sunset, Venus will be the brightest object in the sky. This is because Venus has the highest albedo (0.76) of all the planets. Albedo is the percent of light reflected by an object. Our moon has an albedo of 0.07, so it reflects very little of the light that strikes it. Also called the morning star when it is in the east.

Venus Diameter: 0.9 Earth Distance: 0.7 AU Atmosphere: 96% carbon dioxide at almost 100 atmospheres. Features: hottest surface in solar system. Retrograde rotation. Life: Very doubtful, the pressure and temperatures are too high. Sulfuric acid in atmosphere does not help either.

Earth Diameter: 1 earth Distance: 1 AU Atmosphere: 78% Nitrogen, 21% Oxygen Features: water world, moderate temperature and pressures Life: teeming with life. Planet is “just right” for life as we know it.

Mars Mars is the Latin name for Ares, the Greek god of war.

Mars Atmosphere Mars has an atmosphere that is mainly carbon dioxide. It is very thin, only 0.01 atmosphere’s at the surface. Mars even has clouds, but they are thin also. The winds can create dust storms that cover much of the planet and last for months.

Mars Volcanoes Mars surface has a wide variety of landscapes. Olympus Mons is the largest volcano in our solar system. Its base would cover the state of Colorado. It is three times taller than Mt. Everest. There are many other volcanoes on Mars, but none seem to be active at this time.

Volcano Comparision Heights of Mt. Everest on the Earth, Maxwell Montes on Venus and Olympus Mons. (The horizontal scale has been drastically squashed.)

Mars Canyons Valles Marineris is an enormous canyon on the equator of Mars. It is over 4000-km long. This would reach from Los Angles to Chicago!

Mars Landscape Mars seems to have dried river and lake beds, deltas, and other features that make scientists think Mars had abundant water early in its history. If there was water it is possible that life could have existed on Mars, and still might.

Ice Caps The north and south poles of Mars are covered by ice caps composed of frozen carbon dioxide and water. They wax and wane with the seasons.

Mars Data Mars is about half the size of the Earth. A 100 pound sixth grader would weigh 39 pounds on Mars. It is very cold on Mars, with the average temperature ranging from -140° C to 20° C.

Moons Deimos Mars has two very small moons, Phobos (fear) and Diemos (terror). They are named after the horses that pulled Mars’s chariot. The larger Deimos is only 23-km in diameter. Both appear to be captured asteroids. Phobos

Mars Missions There have been many missions to Mars, starting with the Viking craft in 1976. There are currently two orbiters and two rovers collecting data on Mars. Manned missions are also currently being planned, around 2025 or so.

Mars Diameter: 0.5 Earth Distance: 1.5 AU Atmosphere: 96% carbon dioxide at 0.01 atmospheres. Features: large canyons, volcanoes. Ancient dried up lakes, streams, rivers, and seas. Life: Possibly ancient life when there was liquid water on the planet. Could still exist under the sand.