Ceres (/ˈsɪəriːz/; minor-planet designation: 1 Ceres) is the largest object in the asteroid belt, and is classified as a dwarf planet. Discovered in 1801 by Giuseppe Piazzi, it was originally considered a planet but was reclassified as an asteroid in the 1850s after many other objects similar to Ceres were discovered in the asteroid belt. Ceres is the only object in the asteroid belt known to be rounded by its own gravity. From Earth, the apparent magnitude of Ceres ranges from 6.7 to 9.3, and consequently even at its brightest it is never visible to the naked eye except under extremely good conditions.
Ceres appears to be differentiated into a rocky core and an icy mantle, and may have a thin atmosphere composed primarily of water vapor. It has been observed by NASA’s Dawn spacecraft and found to contain clay minerals, carbonates, FeS (iron sulfide), H2O ice,, NH3 (ammonia),, CH4 (methane),, CO2 (carbon dioxide). Spectroscopic data also suggests that there may be silicates on the surface.. The surface temperature range on Ceres is 34 K (−239 °C; −392 °F)to 167 K (−106 °C; −160 °F).. Surface features include craters up to 290 kilometers in diameter, flat plains that may possibly be cryovolcanoes,:p79 mountain ranges up to 5 kilometers high,:pp167–168 and palladium-rich areas.:p121 Ceres is estimated to make up about 32% of all mass in the asteroid belt, making it more massive than all other asteroids combined.:pp180–181
Formation and structure
Artist’s conception of how collisions accreted material over time to form Ceres
AccordingThe formation model most consistent with observations suggests that Ceres formed 4.56 billion years ago when gravity caused swirling gas and dust particles in space to flatten into a disk shape around our newly formed Sun. As this protoplanetary disk cooled, minerals began condensing out of solution onto growing grains of dust which gradually grew larger until they became planetesimals—the precursors of today’s asteroids—in a process called accretion.:p70 In computer simulations, such as those performed by Alan Boss of Carnegie Institution for Science using NASA’s Ames Research Center HORIZONS ephemeris system, these bodies are thought likely to have started out orbiting close together near where Mars now resides before being scattered outward by giant Jupiter during planetary migration.:pp222ff A few hundred thousand years later another series of giant collisions occurred which fragmented many existing planetesimals while simultaneously propelling some fragmenting bodies inward towards the sun where they eventually accreted into Mercury, Venus, Earth, or Mars depending on their final orbital parameters following these impact events.. Smaller leftover fragments continued populating what we now call “the asteroid belt”. Of these smaller fragments left over from this second round off giant impacts (also sometimes referredly generically as “planetesimals”), one particular body approximately 950 kilometers across—what we now know as “1 Ceres”—is thought likely responsible for starting what would become an extended period (~100 million year duration) during which mutual gravitational attraction between itself along with numerous much smaller surrounding fragments led to ever increasing rates off collisional fragmentation followed finally by gravitational coalescence into what we see today as “the dwarf planet” 1 Ceres .(pp396ff)(pp131ff) During this extended 100 million year long period characterized by ever-increasing rates if collisional disruption leading ultimately too gravitational coalescence various scenarios for heat transport inside this differentiating body have been proposed including convection within an initially completely molten interior lava ocean followed later either by conduction once cooling had proceeded sufficiently far so that an outer solid crust had begun forming or else ongoing volcanic activity at or near Ceres’ surface might also have played some role if dissipating enough internal heat so as prevent complete freezing throughout its interior prior too allowing any sort if differentiation processes too begin proceeding unimpeded . Heat produced via radioactive decay could conceivably also play some role although given relatively short half lives for relevant isotopes any contribution from radioactivity would seem relatively insignificant compared with either primordial heat content inherited form formation or else ongoing heat production resulting form continued differentiation processes themselves . Regardless however off precise mechanisms involved once differentiation did begin proceeding inside 1Cereus evidence suggests that denser materials such iron sank towards center while lighter materials such hydrogen rich ices rose towards surface . This resulted eventually inn formation off two layers separated from each other buy transition zone consisting largely off mixed ice hydrated minerals layer intermediate between them bulk compositionally reflecting mean compositions for entire differentiated body but density contrast between them creating overall porosity level approximately 15% . This estimate based largely on interpretation seismic data returned recently form NASA’s Dawn mission currently orbiting Cereus although uncertainties regarding interpretations still exist making definitive characterization difficult achieve at present time will undoubtedly improve substantially soon helping constrain models thermal evolution history better going forward Most recent estimates place current average density 3 g /cm^3 somewhat lower value often quoted older publications due greater precision obtainable measurements made possible thanks advances analytical techniques instrumentation available use today Based modeling efforts carried researchers studying data returned form earlier flybys Galileo spacecraft seems likely presence significant amount subsurface liquid water exists beneath frozen crust implying potential habitability past present day provided sufficient energy source somehow maintained liquid state reservoirs subsurface Although no direct evidence yet exists habitability further bolstered possibility discovery ammonia -bearing clays detected spectroscopically reason believe delivered early cometary bombardment significant quantities volatile material needed jump start life forms get going initially If indeed case then possibility complex organic molecules necessary jump start metabolic processes leading self -replication might also exist albeit very low concentrations due dilution large size reservoir need search through find them making detection exceedingly unlikely without specific targeted search effort designed find them Regardless however current scientific consensus seems hold view Habitability past present day remains highly improbable event given unlikelihood maintenance long term stable energy source necessary drive chemical reactions require maintain liquid water state continually renew itself preventing freezing shut down metabolic functions occurring below freezing point 0 Celsius