Structure
Terrestrial planets all have approximately the same type of structure: a central metallic core, mostly iron, with a surrounding silicate mantle. The Moon is similar, but has a much smaller iron core. Terrestrial planets can have canyons, craters, mountains, and volcanoes. Terrestrial planets possess secondary atmospheres, generated through internal volcanism or comet impacts, in contrast to the gas giants, whose atmospheres are primary, captured directly from the original solar nebula.
Read more about this topic: Terrestrial Planet
Famous quotes containing the word structure:
“Agnosticism is a perfectly respectable and tenable philosophical position; it is not dogmatic and makes no pronouncements about the ultimate truths of the universe. It remains open to evidence and persuasion; lacking faith, it nevertheless does not deride faith. Atheism, on the other hand, is as unyielding and dogmatic about religious belief as true believers are about heathens. It tries to use reason to demolish a structure that is not built upon reason.”
—Sydney J. Harris (1917–1986)
“What is the structure of government that will best guard against the precipitate counsels and factious combinations for unjust purposes, without a sacrifice of the fundamental principle of republicanism?”
—James Madison (1751–1836)
“I really do inhabit a system in which words are capable of shaking the entire structure of government, where words can prove mightier than ten military divisions.”
—Václav Havel (b. 1936)