The Inner Planets Lesson 4

Objectives Students will be able to describe the characteristics that the inner planets have in common. Students will be able to identify the main characteristics that distinguish each of the inner planets.

What Do the Inner Planets Have in Common? The inner planets are small and dense and have rocky surfaces. Often called terrestrial planets which means “Earth” All have relatively high densities. Rich in rocky and metallic materials, including iron and silicon. Each has a solid surface. All have atmospheres except Mercury.

Data Planet Mercury Venus Earth Mars Diameter (km) 4,879 12,104 12,756 6,794 Period of rotation (Earth days) 58.9 244 1.0 1.01 Average distance from sun 0.39 0.72 1.52 Period of revolution (Earth days) 88 224.7 365.2 687 Number of moons 1 2

How Do They Differ? Size Composition Distance from the sun

Mercury Temperature range 430°C to below -170°C Smallest terrestrial planet Not much larger than Earth’s moon Interior made up of dense metal iron 430C = 806F -170C = -274F Closest to the sun Craters formed early in the history of the solar system Due to no water and little atmosphere, craters have not worn away over time

Surface- flat plains and craters; no water and not much atmosphere Atmosphere- small in mass= weak gravity, gas particles easily escape into space, small amounts of sodium and other gases have been detected around Mercury Exploring Mercury- most information comes from space probes Mariner 10 flew by Mercury 3 times in 1974 and 1975 Mercury Messenger passed Mercury several times and began orbiting in 2011

Venus Similar in size and mass to Earth, called “Earth’s twin” Density and internal structure similar to Earth Thick atmosphere Unusual pattern of rotation Hottest surface of any planet

Atmosphere- so thick that it is always cloudy; at the surface you would be quickly crushed by the weight of its atmosphere; pressure is 90 times greater than the pressure of Earth’s atmosphere; you couldn’t breathe on Venus because its atmosphere is mostly carbon dioxide Rotation- takes about 7.5 Earth months to revolve around the sun and 8 months to rotate once on its axis; rotates from east to west; maybe because a large object struck Venus billions of years ago causing it to change direction or Venus’s thick atmosphere could have somehow altered its rotation Clouds made up mostly of droplets of sulfuric acid Day is longer than its year Rotation opposite of most planets and moons

Magellan probe landed in 1990 Venus Express Hot Planet- receives more solar energy than Earth because its closer to the sun; much of the radiation is reflected by Venus’s atmosphere; some radiation reaches the surface and is later given off as heat; carbon dioxide in atmosphere traps heat so well that it has the hottest surface; average surface temperature is 460°C Greenhouse effect- trapping of heat by the atmosphere Exploring Venus- Venera 7 landed in 1970 Magellan probe landed in 1990 Venus Express 460C = 860F Venera 7- first probe to land on Venus, survived a few minutes because of high temp and pressure Magellan carried radar instruments which works through clouds so it was able to map nearly the entire surface; confirmed Venus is covered with rock and surface has more than 10,000 volcanoes; lava flows formed plains Venus express has helped scientists understand how Venus’s clouds form and change

Earth Only planet in the solar system where you could live easily Has liquid water Suitable temperature range Atmosphere for living things to survive Water Planet- about 70% of Earth’s surface is covered with water

Temperature- if Earth were a little closer to the sun, it would be so hot that liquid water would evaporate; if it were a little farther away and colder, water would always be solid ice Atmosphere- has enough gravity to hold on to most gases that make up Earth’s atmosphere; only planet with an atmosphere that is rich in oxygen; like Venus, Earth experiences a greenhouse effect; traps less heat than Venus’s atmosphere; without the atmosphere, Earth would be much colder Temperature- called having “Goldilocks” conditions, not too hot and not too cold Oxygen makes up about 20 % of Earth’s atmosphere, rest is nitrogen and small amounts of argon, carbon dioxide and water vapor

Mars Called the “red planet” Reddish color is due to the breakdown of iron-rich rocks, leaving a rusty dust behind Too cold for liquid water Does have water ice now and liquid water in the past

Atmosphere- more than 95% carbon dioxide; has few clouds but very thin compared to clouds on Earth; temperatures range from -140°C to 20°C Water and Ice- atmosphere is so thin that any liquid water would quickly turn into a gas; water is located in the planet’s two polar ice caps made entirely of frozen water located under the surface Volcanoes- some regions have giant volcanoes that are rarely active anymore; Olympus Mons is the largest volcano in the solar system Could walk around on Mars but you would have to wear an airtight suit and carry your own oxygen 140C = -220F 20C = 68F

Mars’s Moons- has two very small moons that are covered with craters 1. Phobos- larger about 22km across 2. Deimos- even smaller 13km across Exploring Mars- recent missions have focused on finding signs of water and possible life on Mars Spirit and Opportunity- found traces of salts and minerals that form in the presence of water Phoenix mission- took samples of soil and found frozen water near the north polar cap Mars Express spacecraft- detected methane gas in Mars’s atmosphere