Origin and evolution::Ceres (dwarf planet)


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Origin and evolution Ceres is probably a surviving protoplanet (planetary embryo), which formed 4.57 billion years ago in the asteroid belt.<ref name = "McCord2005-jgrp" /> Although the majority of inner Solar System protoplanets (including all lunar- to Mars-sized bodies) either merged with other protoplanets to form terrestrial planets or were ejected from the Solar System by Jupiter,<ref name="Petit2001">{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref> Ceres is thought to have survived relatively intact.<ref name = "McCord2005-jgrp" /> An alternative theory proposes that Ceres formed in the Kuiper belt and later migrated to the asteroid belt.<ref>Approximately a 10% chance of the asteroid belt acquiring a Ceres-mass KBO. William B. McKinnon, 2008, "On The Possibility Of Large KBOs Being Injected Into The Outer Asteroid Belt". American Astronomical Society, DPS meeting No. 40, #38.03 Archived at WebCite</ref> Another possible protoplanet, Vesta, is less than half the size of Ceres; it suffered a major impact after solidifying, losing ~1% of its mass.<ref name="Thomas1997">{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref>

The geological evolution of Ceres was dependent on the heat sources available during and after its formation: friction from planetesimal accretion, and decay of various radionuclides (possibly including short-lived isotopes such as the cosmogenic nuclide aluminium-26). These are thought to have been sufficient to allow Ceres to differentiate into a rocky core and icy mantle soon after its formation.<ref name="Li2006" /><ref name = "McCord2005-jgrp" /> This process may have caused resurfacing by water volcanism and tectonics, erasing older geological features.<ref name = "McCord2005-jgrp" /> Due to its small size, Ceres would have cooled early in its existence, causing all geological resurfacing processes to cease.<ref name = "McCord2005-jgrp" /><ref name="Castillo-Rogez2007">{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref> Any ice on the surface would have gradually sublimated, leaving behind various hydrated minerals like clay minerals and carbonates.<ref name="Rivkin2006" />

Today, Ceres appears to be a geologically inactive body, with a surface sculpted only by impacts.<ref name="Li2006" /> The presence of significant amounts of water ice in its composition<ref name="Thomas2005" /> raises the possibility that Ceres has or had a layer of liquid water in its interior.<ref name = "McCord2005-jgrp" /><ref name="Castillo-Rogez2007" /> This hypothetical layer is often called an ocean.<ref name="Rivkin2006" /> If such a layer of liquid water exists, it is hypothesized to be located between the rocky core and ice mantle like that of the theorized ocean on Europa.<ref name = "McCord2005-jgrp" /> The existence of an ocean is more likely if solutes (i.e. salts), ammonia, sulfuric acid or other antifreeze compounds are dissolved in the water.<ref name = "McCord2005-jgrp" />

Ceres (dwarf planet) sections
Intro  History  Physical characteristics  Orbit  Origin and evolution  Potential habitability  Observation  Exploration  Maps  Gallery  See also  Notes  References  External links  

Origin and evolution
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