Chapter 7b Geologically Dead! Images from

Mercury craters smooth plains, cliffs

Mercury Orbital distance: – km (0.38 AU) –Eccentric (46 M – 70 M) Year: – d Day: – 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/cm 3 Composition: –Rocky with large iron core Axial Tilt: –2.11 o Moons: none Other: LINKLINK –Weak magnetic field –Heavily cratered

Moon craters smooth plains

Earth’s Moon Orbital distance: – km Month: –29.5 d Day: – d Temperature: –Day: 107 degrees Celsius –Night: -153 degrees C Diameter: –3476 km Density: –3.346 g/cm 3 Composition: –Rocky with iron core –Mantle, crust asymmetrical Axial Tilt: –6.6 o to orbital plane Other: LINKLINK –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?

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.