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Revised Periodic Table Slanted Toward Astronomers

October 15, 2003
Washington University In St. Louis
The periodic table isn't what it used to be, thanks to innovations by a planetary chemist at Washington University in St. Louis.

The periodic table isn't what it used to be, thanks to innovations by a planetary chemist at Washington University in St. Louis.

Katharina Lodders, Ph.D., Washington University research associate professor in Earth and Planetary Sciences in Arts & Sciences, has evalutated data from numerous studies including her own and arranged the data into a periodic table slanted toward astronomers and cosmochemists. It's the Cosmochemical Periodic Table of the Elements in the Solar System. Instead of atomic number, atomic weights, and melting- and boiling points, for example, Lodders provides elemental abundances and condensation temperatures. And it's color-coded to indicate host phases of the elements - the phase where the element condenses into metal, sulfide, or silicate rock.

It's an outright work of art, definitely not your father's periodic table.

"For the first time, there is a periodic table providing self-consistent data for abundances and condensation temperatures," she said. "The idea was to combine everything for easy comparison and quick reference." It's one-stop shopping for astronomers and cosmochemists, a sort of Sam's Club for researchers of the cosmos.

The table will be very valuable for researchers modeling planets and planetary satellites, meteorites and asteroids, and other stars and solar systems. And it also is beneficial because the abundances of elements presented in the table reflect the latest developments in astronomy. One of the most recent influential findings is that the heavier elements - everything heavier than helium - in the sun's outer layer, its photosphere, settle towards its interior. Because the sun contains more than 99 percent of the entire mass of the solar system, the composition of the sun tells astronomers much of what they need to know of the whole solar system. But if the heavy elements settled from the photosphere, researchers can no longer use the photospheric abundances observed today as representative of solar system abundances about 4.5 billion years ago when the planets formed.

Lodders takes that into account. In her table for the abundances and the condensation temperatures she calculated for the new abundance set. In part, she used results from models of the sun's evolution to assemble the abundance data together with recent redeterminations of several important elemental abundances, including the key biogenic elements carbon, oxygen, and nitrogen.

"It turns out that these abundances are only roughly half of that previously thought," she said. "This is important because if the abundances of carbon and oxygen, a major fraction of the heavy elements in the sun and solar system, have been revised downward, then there will be changes introduced in the amount of condensates that can form and in the amount of oxygen tied up into rocky condensates and ices.

"If I use the old abundances, about 15 percent of the total oxygen goes into rock, but now it's about 23 percent oxygen that can go into rocky condensates. This means less oxygen is available to form ices, which is an important consequence for modeling all of the chemistry of the outer solar system - giant planets, their satellites and other icy bodies such as comets."

Lodders' table made its debut in July 31, 2003 at the Meteoritical Society Meeting in Munster, Germany. All of the data appear in table and text in "Solar System Abundances and Condensation Temperatures of the Elements," published July 10, 2003, in The Astrophysical Journal.

"This table reflects the work of many astronomers and cosmochemists going back to the '60s and '70s, and abundance determinations and condensation modeling are continuing," said Lodders. "But the abundance tables and the related condensation temperatures needed desperate updating because of all the new developments. It was time to put it all together."

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