Astronomy Exam #2 (2. Terrestrial Planets)

Cratering and Surface Ages

impacts from asteroids and comets produce craters on planetary surfaces

a surface with many preserved craters has generally experienced less recent resurfacing than a surface with few craters

heavily cratered regions are generally older than less-cratered regions, assuming comparable impact histories

a lack of preserved craters does not mean a planet was never bombarded

Geological resurfacing

geological processes can erase or cover impact craters including volcanism, tectonic activity, and erosion

if a terrestrial planet has few preserved impact craters, geological processes may have erased older crates

volcanism

lava covers older terrain and its craters

tectonic activity

crustal deformation changes the surface

erosion

surface features gradually wear down

Venus and the greenhouse effect

Venus is hotter than earth and mercury even though mercury is closer to the sun primarily due to its greenhouse effect

greenhouse gases absorb some infrared radiation emitted by a planet’s surface, making it harder for that energy to escape directly to space

Venus’s dense, carbon-dioxide rich atmosphere produces an exceptionally strong greenhouse effect