1. Chapter 9: Cratered Worlds -The Moon and Mercury

2. Earth’s interior is revealed by seismology, the study of earthquakes
Earth’s interior is revealed by seismology, the study of earthquakes. Layers are revealed:
A layered object:
Inner core
Outer core
Mantle
Crust
Hydrosphere
Atmosphere
Magnetosphere

4. Earth’s Moon: the interior is not as well understood
Missing:
Hydrosphere
Atmosphere
Magnetosphere

5. Full Moon, Near Side

6. Two Faces of the Moon Near Side Far Side Maria Impact Basin Cratered
Highlands
Near Side
Far Side

7. Lunar Tides are due to the gravity of the Moon

8. Solar and Lunar effects on Tides depend on the relative orientations of the Earth, Moon, and Sun (see OpenStax - section 4.6)

9. The tidal bulge is actually offset somewhat from being directly underneath the Moon. This produces a torque, a kind of twisting force on the Earth.
The tides cause the Earth to slow down and the
Moon’s orbit to increase in radius (4 cm per century).
Also, the Moon’s rotation is synchronous with its orbit.

10. The Moon’s formation is believed to be due to a collision of a massive (Mars-sized) object with the early Earth. Computer simulation show that this could leave a moon-sized satellite in the correct orbit.

11. Data for the Terrestrial Planets

12. Terrestrial Planets’ Spin Axis and Rotation Rate

13. Terrestrial Planets’ Spin
Mercury’s sidereal rotation is tidally locked to 2/3 of an orbit.
Venus rotates very slowly backwards compared to the other
Planets, so that it is rotating clockwise (others are CCW).
Mercury and Venus both have almost no axial tilt, Earth and
Mars both have similar axial tilts and rotation rates.

14. See following slides for details.
Mercury’s Rotation is tidally locked to the orbital revolution period (the Mercury-year). The solar day on Mercury is 176 days long, which is two Mercury-years!
See following slides for details.

15. During the Mercury-year the planet rotates 1
During the Mercury-year the planet rotates 1.5 times with respect to the stars, but only half of a solar day. For an observer at the location of the arrow, noon to sunset would take 44 Earth-days. After 88 Earth-days the observer would experience midnight (next slide).

16. During the Mercury-year the planet rotates 1
During the Mercury-year the planet rotates 1.5 times with respect to the stars, but only half of a solar day. For the observer, midnight to sunrise would take another 44 Earth-days. Then after another 44 Earth-days the observer would experience noon (day 176, next slide).

17. So it takes two Mercury-years for the planet to rotate through a solar day. This solar day lasts 176 Earth-days. Mercury orbits the sun in 88 Earth-days.

18. This tidal locking is different from that of the
Mercury’s Rotation is tidally locked to the orbital revolution period. The solar day on Mercury is 176 days long, which is two Mercury-years!
This tidal locking is different from that of the
Moon revolving around Earth because Mercury’s
orbit is elliptical and not nearly circular like the Moon’s.

19. Atmospheres and Temperatures
Mercury has no atmosphere, just like our moon. Because there is no atmosphere to trap heat, the night side of Mercury gets very cold (100 K or -280oF). The day side of Mercury gets up to 700 K (or 800oF).
The atmosphere of Venus is made up of carbon dioxide, with
clouds of sulfuric acid. The atmosphere is some 90 times
denser than Earth’s. The Greenhouse effect causes the surface temperature of Venus to be close to 730K (or 860oF) day or night.
Mars has a very thin atmosphere (less than 1% of Earth’s) of mainly carbon dioxide. The surface temperature is approximately 50 K (50oC) lower than Earth’s.

20. Mercury Maps and images
USGS has a website with planet maps
These can provide tennis ball projects for kids
Newer results have resulted from the MESSENGER spacecraft.
Launched in August 2004, the Mercury Surface, Space Environment, Geochemistry and Ranging spacecraft, known as MESSENGER, entered into orbit around Mercury in The following photos are from this spacecraft.

27. Terrestrial Planet Magnetic Fields
Mercury has a very weak magnetic field, partly due to its slow
rotation, even though it may have liquid iron in the core.
Venus has no measurable magnetic field, probably due to its
very slow rotation rate.
Mars has a magnetic field weaker than Mercury, meaning
that its core is either not liquid or not metallic.