Planets Ch. 21 Notes

Astronomical Unit The average distance between the Earth and the sun; approximately 150 million kilometers AU Most useful unit for measuring distances within the solar system

Planets VS. Dwarf Planets Must be round Orbit the sun Have cleared out the region of the solar system along its orbit Object that orbits the sun Has enough gravity to be spherical Has not cleared the area of its orbit 5 known: Pluto, Eris, Ceres, Makemake, and Haumea List the planets in order of increasing distance from the sun (Science Starter) Where is the largest gap between planets? Mars and Jupiter

Inner Planets Mercury, Venus, Earth and Mars Small Dense Rocky surfaces Called “Terrestrial Planets” Mercury is the only inner planet without an atmosphere

Inner Planets Which planet is the largest? Which planet has the most moons? Which planet is most similar to Earth in size?

Smallest terrestrial planet Closest to the sun Mercury Smallest terrestrial planet Closest to the sun Temps. Range from 430 Celsius to -170 Degrees Celsius Surface: flat plains Atmosphere: None Because Mercury’s mass is small, its gravity is weak. Gas particles can easily escape into space. Temps. Range from 430 to -170 C because during the day it’s facing the sun and at night is not

Venus Earth’s twin Retrograde: spins clockwise Atmosphere: think and it is always cloudy, mostly made up of carbon dioxide Hottest planet, covered in rock Greenhouse effect: the trapping of heat near a planet’s surface by certain gases in the planet’s atmosphere Earth’s twin because of size and mass Clouds are made of sulfuric acid You would not be able to breathe on Venus because of the CO2 CO2 traps heat 1970 first probe on Venus: Venera 7 lasted only a few mins. before it blew up from high temp/pressure In 1990, The Magellan probe was able to map out all of Venus’ surface using radar instruments

Earth The only planet in the solar system where you could live easily. Earth has liquid water and a suitable temperature range and atmosphere for living. Like Venus, Earth experiences a greenhouse effect. Without the atmosphere, Earth would be much cooler.

Mars “Red planet” Has ice (two polar caps) Atmosphere: 95% Carbon Dioxide Temperatures on the surface range from -140C to 20 C Volcanoes Mars has 2 very small moons (Phobos and Deimos) Known as red planet because of the breakdown of iron-rich rocks, leaving rusty dust behind Mars is too cold for liquid water now and had liquid water in the past You can walk on Mars however you need your own oxygen supply Mars use to be much warmer due to a thicker atmosphere We have been to Mars with Rovers called Spirit and Opportunity Phownix mission took samples of soil

Jupiter, Saturn, Uranus, and Neptune Gas Giants Many moons The outer planets Jupiter, Saturn, Uranus, and Neptune Gas Giants Many moons Surrounded by a set of rings These planets do not have a solid surface Rings: a thin disk of small particles of ice and rock

Jupiter Largest and most massive planet Atmosphere: thick atmosphere made up of hydrogen and helium Great Red Spot Moons: at least 63 Galileo Galilei found Jupiter’s largest moon in 1610

Saturn 2nd largest planet Atmosphere: thick, made up of hydrogen and helium Has the most spectacular rings of any planet made of ice and rock Moons: at least 61 moons Has the lowest density of any planet. If you could build a bathtub big enough, Saturn would float!

Uranus Blue-green in color due to methane in its atmosphere Surrounded by dark, thin, flat rings Moons: at least 27 Rotates from top to bottom Astronomers think that billions of years ago, an object hit Uranus and knocked it on its side

Neptune Similar in size and color to Uranus Cold, blue planet Atmosphere: contains no clouds Moons: at least 13 (largest: Triton) Blue comes from methane in atmosphere Neptune’s interior is hot due to energy left over from it’s formation.