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Chondrules in the chondrite classification Grassland. A millimeter scale is shown. Chondrules in the Carbonaceous Chondrite NWA 13887. A chondrule (from Ancient Greek χόνδρος chondros, grain) is a round grain found in a chondrite. Chondrules form as molten or partially molten droplets in space before being accreted to their parent asteroids.
Their chondrules are generally in the range of 0.5 to 1 mm in diameter. Ordinary chondrites are distinguished chemically by their depletions in refractory lithophile elements, such as Ca, Al, Ti, and rare earths , relative to Si, and isotopically by their unusually high 17 O/ 16 O ratios relative to 18 O/ 16 O compared to Earth rocks.
Chondrules, metal grains, and other components likely formed in the solar nebula. These accreted together to form parent asteroids. These accreted together to form parent asteroids. Some of these bodies subsequently melted, forming metallic cores and olivine -rich mantles ; others were aqueously altered. [ 35 ]
There are many indicators why some achondrites are deemed primitive. Some contain relic chondrules (e.g. Acapulcoite, Lodranite) and some have oxygen isotope ratios that are similar to chondrites. There are similarities in trace element concentrations between primitive achondrites and chondrites.
The Sun; Sirius A with Sirius B, a white dwarf; the Crab Nebula, a remnant supernova A black hole (artist concept); Vela Pulsar , a rotating neutron star M80 , a globular cluster , and the Pleiades , an open star cluster
Aqueous alteration promotes a composition of hydrous phyllosilicates, magnetite, and olivine crystals occurring in a black matrix, and a possible lack of chondrules. It is thought they have not been heated above 50 °C (122 °F), indicating that they condensed in the cooler outer portion of the solar nebula.
Lyman alpha nebulae around quasars can have sizes between 15 kpc and 460 kpc. [1] Especially large Enormous Lyα nebula (ELAN) can have large sizes of ≳100 kpc. [2] Farina et al. 2019 table 5 has an extensive compilation of Lyman alpha nebulae around quasars. [1] For now this list contains only the largest ELANs, with sizes larger than 300 kpc.
Cometary knots, also referred as globules, are structures observed in several nearby planetary nebulae (PNe), including the Helix Nebula (NGC 7293), the Ring Nebula (NGC 6720), the Dumbbell Nebula (NGC 6853), the Eskimo Nebula (NGC 2392), and the Retina Nebula (IC 4406). [1] [2] They are believed to be a common feature of the evolution of ...