Illustration of a proto solar system in formation. Image Credit for center and lower images: S Kenyon and K Wood (CfA) and B Whitney and M Wolff (Space Science Institute). Credit for upper image: G Schneider (Steward Observatory, University of Arizona) and collaborators.
In collaboration with researchers from Harvard University, NASA and Lancaster University, the UH team co-authored the paper "Large Scale Thermal Events in the Solar Nebula: Evidence from Fe, Ni Metal Grains in Primitive Meteorites," which appeared in Science May 5.
By analyzing iron and nickel metal grains from the ancient meteorite, which was recovered on the Antarctic ice-sheet by a U.S. meteorite search expedition in 1991, the UH team will help scientists gain a better understanding of the solar system's beginnings. Keil says it is extremely rare to find such primitive materials intact.
"They're (the primitive meteorites) the most pristine, the most unadulterated materials in the solar system," he says.
Scientists have constructed a general view of how the sun formed, but they remain unsure of the details of how planets formed in the solar nebula, the gas disk in which the system's first solids accreted into larger bodies.
Meibom says there are very few traces of material that can be dated back to the earliest times in our solar system's history, and these traces can only be found in meteorites.
"Meteorites are fragments of small bodies, called asteroids, which formed in the solar system at the same time the major planets formed," Meibom says.
"As part of an asteroid, some meteorites have preserved their minerals and chemical composition relatively unchanged since their formation. The study of meteorites therefore provides a unique opportunity to look back 4.56 million years and study the physical and chemical conditions prevailing in the solar nebula."
By studying the metals in the meteorite, researchers concluded that they were formed within the solar nebula by a process known as gas-solid condensation, where atoms clump together into solid metal particles.
The team was able to constrain how fast the grains grew, the composition, temperature and pressure of the solar nebula gas and how fast the region of the nebula in which they formed cooled by radiating its heat away to interstellar space.
The team concluded that the metal grains must have condensed from the nebula gas in a matter of weeks while the nebula gas was cooling as a rate of 1 degree Fahrenheit per hour.
"This is a phenomenally fast cooling rate for a system as large as the solar nebula," Meibom says. "It means that the gas in the disk must have been moving very fast and must have been transporting the growing iron and nickel metal grains millions of miles, from the hot interior to the colder surface regions of the disk on a time scale comparable to the time it took to grow them, that is, in a matter of weeks.
"So the picture that these metal grains are drawing of the earliest time in the solar nebula is that of a highly dynamic, turbulent and rapidly evolving disk."
Keil says the research not only gives scientists a better idea of how the solar system formed, it indicates a partnership in two different fields of science.
"The great significance of this paper is the crossover from cosmochemistry, the study of extraterrestrial materials, into astrophysical theories," Keil says. "With the actual data our (UH) researchers collected, astrophysicists will be able to create direct theoretical models of how the solar system formed."
UH Manoa Hawai'i Institute of Geophysics and Planetology director Klaus Keil recently received a $343,000 grant from NASA for his study "Origin of Meteorite Parent Bodies and the Moon."
Martian Meteorites Reveal Clues To Atmospheric Processes
by Kim McDonald
San Diego - March 1, 2000 - Detailed measurements of sulfur isotopes in five Martian meteorites have enabled researchers at the University of California, San Diego to determine that the abundant sulfur on the surface of Mars is due largely to chemical reactions in the Red Planet's atmosphere that are similar to those that occur in Earth's atmosphere.