UH Manoa Scientists' Research Featured in Science

University of Hawaiʻi at Mānoa
Shawn Nakamoto, 956-9095
Director of Public Relations
Kristen Cabral, 956-5039
Public Information Officer
Posted: Feb 25, 2002

HONOLULU — Results from the analysis of minerals in meteorites by University of Hawaiʻi at Mānoa scientists from the Hawaiʻi Institute of Geophysics and Planetology (HIGP) have provided clues for understanding processes in the early solar system. These meteorites originated about 4.5 billion years ago in a swirling disk of dust and gas that became the solar system.

Drs. Alexander Krot and Edward Scott of HIGP collaborated with Dr. Kevin McKeegan of the University of California, Los Angeles, Dr. Laurie Leshin of Arizona State University, and Dr. Glenn MacPherson of the U.S. National Museum of Natural History, on a paper describing these findings that was featured in a recent issue of the journal Science.

Researchers analyzed components of the chondritic meteorites (chondrites) Efremovka, which landed in Russia in 1962, and Vigarano that landed in Italy in 1910. Chondrites are fragments of asteroids that formed between Mars and Jupiter and preserved records of physical and chemical processes that occurred during the earliest stages of the formation of the solar system. They are comprised of three major components: calcium-aluminum-rich inclusions (CAIs), which are particles that contain abundant oxides of calcium and aluminum; chondrules, particles that are much more abundant and composed largely of oxides of iron, magnesium and silicon; and a fine-grained matrix, which is richer in volatile elements.

CAIs and chondrules formed at high temperatures by evaporation of dust and condensation of vapor, and, in many cases by subsequent multiple heating and melting events. However, mineralogical and bulk chemical differences between CAIs and chondrules suggest that CAIs formed from materials that were processed at higher nebular temperatures than chondrules, and the matrix escaped any significant high-temperature processing. Meteorite researchers would like to know how these diverse particles formed and were brought together.

A major puzzle for understanding the origin of chondrules and CAIs is that they have remarkable oxygen-isotopic compositions. There are three stable varieties of oxygen atoms called isotopes that have the same chemical properties but different relative masses of 16, 17, and 18. Most CAIs have 16O-rich compositions, while chondrules have relatively 16O-poor isotopic compositions.

Using an ion microprobe, Krot and colleagues analyzed the oxygen-isotopic compositions of minerals in the CAIs from Efremovka and Vigarano. They found that minerals that condensed at high temperatures were rich in 16O. This shows that an 16O-rich gaseous reservoir must have existed in the region where CAIs formed. This finding challenges a generally accepted conclusion amongst scientists that CAIs formed by heating of 16O-rich, interstellar dust grains that then exchanged oxygen atoms with an 16O-poor gas made from interstellar ices. It supports a relatively new idea amongst some scientists that chondrules and CAIs formed close to the Sun and were subsequently transported to the cold outer region of the solar system where they accreted into chondritic asteroids.

These are significant findings for scientists who believe in this new theory. UH researchers plan on continuing studies to provide further evidence to support their theories.

HIGP Contacts:

Dr. Alexander Krot, Associate Researcher, (808) 956-3900, sasha@higp.hawaii.edu

Dr. Edward Scott, Planetary Scientist, (808) 956-3955, escott@higp.hawaii.edu