Astronomy Chapter 9

Do either Venus or Mars have composite volcanoes? Why or why not?

Mars and Venus only have shield volcanoes. Geological processes are vertical on these planets, and plate tectonics and significant horizontal crust motion do not occur.

Why are Phobos and Deimos nonspherical? Why is Earth's Moon much more spherical?

Phobos and Deimos are small captured asteroids, too small for gravity to pull them into spherical shapes. Comparatively, Earth's Moon is massive; its gravity is strong enough to shape a sphere.

Describe evidence of crustal movement (horizontal or vertical) on Venus. Select all that apply.

Rare folded mountain ranges, coronea, fault and deep chasms

If Venus once had significant amounts of water, where did that water come from? Where did it go?

Water vapor was outgassed from the planet's interior during differentiation. Then it was destroyed by ultraviolet radiation from the Sun, and hydrogen leaked away into space.

How are a weather radar map and an image of a highland on Venus related?

Weather radar reveals information that cannot be obtained using visible wavelengths. An image of a highland on Venus is also made by radar because its surface is hidden by thick clouds.

If Venus and Earth outgassed a similar amount of CO2 early in their histories, why are their surface temperatures so different today?

Venus was closer to the Sun, water tended to be in the atmosphere rather than in oceans, and CO2 couldn't be dissolved. Therefore, the runaway greenhouse effect made the surface of Venus much hotter.

Name four properties of Venus that are different from those of Earth today.

Very slow, retrograde rotation; no magnetic field; very dense and hot atmosphere of mostly ; no surface water

Name four properties of Mars that are different from those of Earth today.

No magnetic field; lower density; thin atmosphere of mostly CO2 ; no plate tectonics.

Does Venus's surface experience meteorite impacts today? How do you know?

Not many. Since the atmosphere of Venus is very thick, most meteorites cannot reach the surface of Venus.

Why doesn't Mars have folded mountain ranges like the ones on Earth?

Because Mars does not have plate tectonics.

How are today's atmospheres of Venus and Mars similar? How are they different?

Both atmospheres consist of primarily CO2 and protect the surface from micrometeorite impacts. The atmosphere of Venus is very thick, and Mars's atmosphere is very thin.

Propose an explanation for the nearly pure CO2 atmospheres of Venus and Mars. Why is Earth's atmosphere different?

CO2 was released into the atmospheres when the planets differentiated and later due to volcanism, and did not escape. On Earth, a large amount of liquid water absorbed much of the CO2.

Name four properties of Venus that are similar to those of Earth today.

Equatorial radius; mass; average density; location within the Solar System.

Name four properties of Mars that are similar to those of Earth today.

Differentiated body; location in the Solar System; has weather and seasons; surface temperatures can be Earthlike.

Why doesn't Earth have large volcanoes like those on Mars?

Earth's crust is not thick enough to support such large mountains, moreover, its plates move.

Where is the oxygen on Mars today? How do you know?

It is locked within chemical compounds as oxides in the soils, as is evident by the reddish color of Mars's surface.

Why isn't the crust of Venus broken into mobile plates as Earth's crust is? How do you know?

Low-density, dryness, and pliability of Venus's crust probably prevented it from breaking into rigid plates. On Venus there are no chains of composite volcanoes that form at plate boundaries.

Why isn't the crust of Mars broken into mobile plates as Earth's crust is?

The crust of Mars is very thick (since it can sustain large shield volcanoes), too thick to have broken into moving plates.