New research findings reveal that aqueous processes on small planetary bodies occurred within less than 20 million years from the beginning of the solar system's formation.
After analyzing mineral samples from two meteorites, a researcher from the McDonnell Center for the Space Sciences in Arts and Sciences and two German colleagues reported that liquid water on planetary bodies was present about 30 million years earlier in the evolution of the solar system than previously had been shown.
Ernst Zinner, Ph.D., research professor in physics and in earth and planetary sciences, both in Arts and Sciences, and Magnus Endress and Adolf Bischoff of the Institute of Planetology at the University of Münster in Germany discuss this finding in the Feb. 22 issue of Nature. Zinner also is the director of the McDonnell Center's Ion Microprobe Laboratory.
In the article, titled "Early Aqueous Activity on Primitive Meteorite Parent Bodies," Zinner and his colleagues explain that scientists had speculated a time lag of nearly 50 million years between the formation of "Allende refractory inclusions," the first solids in the solar system, and the formation of carbonates from a mixture of water and minerals on small planets. This estimate was based on chemical measurements of meteorite samples with the 87Strontium/86Strontium isotope dating system, which is not accurate for determining the length of time between events separated by a few million years, Zinner explained.
To more precisely determine the sequence of early, rapidly occurring cosmic events, Zinner employed the McDonnell Center's ion microprobe. The microprobe measures isotopes in small particles in meteorite samples, allowing Zinner to use the 53Manganese (53Mn)-53Chromium (53Cr) isotope dating system.
"The 53Mn isotope has a short half-life compared to the 87Rb isotope," said Zinner. "It decays into the 53Cr isotope in 3.7 million years, so application of the short-lived 53Mn chronometer offers the opportunity to obtain age information of an even finer relative time scale."
Meteorites are fragments of solar system bodies that fell to Earth, and the class of primitive meteorites provides a record of processes that formed the solar system 4.5 billion years ago, explained Zinner. One type of meteorite, called carbonaceous chondrite, offers the best example of the chemical composition of the average solar body and, consequently, the most accurate information about the origin of the sun and planets.
One of the ongoing cosmic events recorded in the carbonaceous chondrite meteorites evaluated by Zinner and his colleagues was "aqueous alteration." This process began when the temperature rose on the parent bodies of primitive meteorites and ice crystals melted and reacted with minerals, producing the carbonates studied by Zinner and his colleagues.
Studying samples of primitive meteorites indicates when parent bodies formed and what processes shaped them. Aqueous alteration is one of the most powerful cosmic processes and still is shaping the planets.
-- Susan Killenberg
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