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Searching for the Solar System’s Chemical Recipe Print
Wednesday, 20 February 2013 00:00

The ratio of isotopes in elements like oxygen, sulfur, and nitrogen were once thought to be much the same everywhere, determined only by their different masses. Then isotope ratios in meteorites, interplanetary dust and gas, and the sun itself were found to differ from those on Earth. Planetary researchers like UC San Diego’s Mark Thiemens and his colleagues, working with Musa Ahmed of the Chemical Sciences Division, are now using the Chemical Dynamics Beamline at the Advanced Light Source to study these “mass-independent” effects and their origins in the chemical processes of the early solar system.

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The protosun evolved in a hot nebula of infalling gas and dust that formed an accretion disk (green) of surrounding matter. Visible and ultraviolet light poured from the sun, irradiating abundant clouds of carbon monoxide, hydrogen sulfide, and other chemicals. Temperatures near the sun were hot enough to melt silicates and other minerals, forming the chondrules found in early meteoroids (dashed black circles). Beyond the “snowline” (dashed white curves), water, methane, and other compounds condensed to ice. Numerous chemical reactions contributed to the isotopic ratios seen in relics of the early solar system today.