Chapter 7bGeologically Dead!

Images from http://pds.jpl.nasa.gov/planets/welcome.htm

Mercury

craterssmooth plains,

cliffs

Mercury• Orbital distance:

– 57 910 000 km (0.38 AU)– Eccentric (46 M – 70 M)

• Year:– 87.969 d

• Day:– 56.646 d– 3:2 ratio of year/day

• Temperature:– Day: 425 degrees celcius

• 797 degrees Fahrenheit

– Night: -170 degrees• -274 degrees Fahrenheit

• Diameter:– 4880 km

• Density:– 5.427 g/cm3

• Composition:– Rocky with large iron

core• Axial Tilt:

– 2.11 o

• Moons: none• Other: LINK

– Weak magnetic field– Heavily cratered

Moon

craterssmooth plains

Earth’s Moon• Orbital distance:

– 384 400 km • Month:

– 29.5 d• Day:

– 56.646 d• Temperature:

– Day: 107 degrees Celsius

– Night: -153 degrees C

• Diameter:– 3476 km

• Density:– 3.346 g/cm3

• Composition:– Rocky with iron core– Mantle, crust

asymmetrical• Axial Tilt:

– 6.6 o to orbital plane• Other: LINK

– No magnetic field– Highlands– Maria

7.2 Mercury and the Moon: Geologically Dead

• Our Goals for Learning• Was there ever geological activity on the

Moon or Mercury?

Was there ever geological activity on the Moon or

Mercury?

Moon

• Some volcanic activity 3 billion years ago must have flooded lunar craters, creating lunar maria.

• The Moon is now geologically dead.

Mercury

• Plenty of craters - including a huge ‘basin’• Smooth plains from volcanism (recent or long

ago???)

Did Mercury shrink?

Steep long cliffs formed when the core cooled, shrinking the planet by ~20 km.

Mercury is now geologically dead.

What have we learned?

• Was there ever geological activity on the Moon or Mercury?

• Both the Moon and Mercury had some volcanism and tectonics when they were young. However, because of their small sizes, their interiors long ago cooled too much for ongoing geological activity.