The Terrestrial Planets

1. The Terrestrial Planets Chapter 4 Section 3 ISN p. 47

3. The Terrestrial Planets • The terrestrial planets are the inner four planets of Mercury, Venus, Earth, and Mars that are close to the size of Earth and have solid, rocky surfaces. • My Very Excellent Mother Just Served Us Nachos OR My VERY EXCELLENT MUSTACHE JUST SAW UGLY NINJAS • The gas giant planets are the outer planets of Jupiter, Saturn, Uranus, and Neptune which are much larger, more gaseous, and lack solid surfaces. • Pluto, the ninth planet from the Sun, has a solid surface, but it does not fit into either category.

5. Mercury • Mercury is the closest planet to the Sun and has no moons. • Mercury is about 1/3 the size of Earth and has a smaller mass and radius. • Mercury has a slow spin of 1407.6 hours; in 2 of Mercury’s yrs., 3 of Mercury’s days have passed.

6. Mercury’s Atmosphere • Mercury has essentially no atmosphere, and what little does exist is composed primarily of oxygen and sodium. • The daytime surface temperature on Mercury is 700 K (427ºC), while temperatures at night fall to 100 K (–173ºC). • So what do you think the surface is like?

7. Mercury’s Surface • Most of what we know about Mercury is based on radio observations and images from a United States space probe mission, called Mariner 10. • Mercury’s surface is covered with craters and plains. The plains of Mercury’s surface are smooth and relatively crater free. • Mercury has a planet wide system of cliffs, called scarps, that may have developed as Mercury’s crust shrank and fractured early in the planet’s geological history.

8. Mercury’s Interior • The high density of Mercury suggests that it has an extensive nickel-iron core, filling about 42% of Mercury’s volume. • The detectable magnetic field suggests that Mercury has a molten zone in its interior. • Mercury’s small size, high density, and probable molten interior zone resemble what Earth might be like if its crust and mantle were removed.

11. Venus • Venus, the 2nd planet from the Sun, has no moons. • Venus’s high albedo and its proximity to Earth make it the brightest planet in Earth’s nighttime sky. • The surface of Venus is very hot, and it rotates slowly clockwise with one day equaling 243 Earth days. • Venus has been explored by radar and spacecraft.

12. Venus’s Atmosphere • Venus is the hottest planet in the solar system with an average surface temperature of about 737 K (464°C). • The atmospheric pressure on Venus is equivalent to 92 Earth atmospheres. • An efficient greenhouse effect is achieved with an atmosphere that is primarily carbon dioxide and nitrogen with clouds of sulfuric acid.

13. Venus’s Surface • The 1989 Magellan missions of the U.S. used radar reflection measurements to map the surface of Venus in detail. • The surface has been smoothed by volcanic lava flows, and it has only a few impact craters. • The most recent global episode of volcanic activity took place about 500 million years ago. • There is little evidence of current tectonic activity on Venus, and there is no well-defined system of crustal plates. Why do you think that it appears to be blue in some photographs?

14. Venus’s Interior • The size and density of Venus are similar to Earth, so the internal structure is most likely similar. • It is theorized that Venus has a liquid metal core that extends halfway to the surface. • There is no measurable magnetic field despite this liquid core, which is probably due to Venus’s slow rotation rate.

15. Earth • Earth, the 3rd planet from the Sun, has many unique properties. • Its distance from the Sun and its nearly circular orbit allow liquid water to exist on its surface in all 3 states: solid, liquid, and gas. • Liquid water is required for life. • Earth’s moderately dense atmosphere (78 percent nitrogen and 21 percent oxygen) and a mild greenhouse effect support conditions suitable for life.

16. Earth’s Wobble • Earth’s axis is tilted and has a wobble. • Precession is the wobble in Earth’s rotational axis. • It takes Earth’s rotational axis about 26 000 years to go through one cycle of precession. • The sideways pull that causes precession comes from the Moon’s gravitational force on Earth, as well as to a lesser extent, the Sun’s gravitational force.

19. Mars • Mars is the 4th planet from the Sun and the outermost of the terrestrial planets. • Mars is smaller and less dense than Earth and has two irregularly-shaped moons, Phobos and Deimos. • Mars has been explored by telescopes on Earth and with probes beginning in the 1960s that have flown by, orbited, or landed.

20. Mars’ Atmosphere • The composition of Mars’s atmosphere is similar to Venus’s atmosphere, but with much lower density and pressure. • The thin atmosphere creates a constant wind on Mars. • Martian dust storms may last for weeks at a time.

21. Mars’ Surface • The southern hemisphere of Mars is a heavily cratered, highland region, while the northern hemisphere is dominated by plains that are sparsely cratered. • Four gigantic shield volcanoes including Olympus Mons, the largest mountain in the solar system. • An enormous canyon, Valles Marineris lies on the Martian equator. • The Martian surface contains erosional features that suggest that liquid water once existed on the surface of Mars. • Mars has polar ice caps of frozen carbon dioxide covering both poles that grow and shrink with the seasons on Mars. • Water ice lies beneath the carbon dioxide ice in the northern cap.

22. Mars’ Interior • Astronomers are unsure about the internal structure of Mars. • It is thought to have a core of iron and nickel, and possibly sulfur which is covered by a mantle. • Because Mars has no magnetic field, the core is probably solid. • There is no evidence of current tectonic activity or tectonic plates on the surface of the crust.