New clues to the early Solar System from ancient meteorites

July 22, 2012

Washington, D.C. -- In order to understand Earth's earliest history--its formation from Solar System material into the present-day layering of metal core and mantle, and crust--scientists look to meteorites. New research from a team including Carnegie's Doug Rumble and Liping Qin focuses on one particularly old type of meteorite called diogenites. These samples were examined using an array of techniques, including precise analysis of certain elements for important clues to some of the Solar System's earliest chemical processing. Their work is published online July 22 by Nature Geoscience.

At some point after terrestrial planets or large bodies accreted from surrounding Solar System material, they differentiate into a metallic core, asilicate mantle, and a crust. This involved a great deal of heating. The sources of this heat are the decay of short-lived radioisotopes, the energy conversion that occurs when dense metals are physically separated from lighter silicate, and the impact of large objects. Studies indicate that the Earth's and Moon's mantles may have formed more than 4.4 billion years ago, and Mars's more than 4.5 billion years ago.

Theoretically, when a planet or large body differentiates enough to form a core, certain elements including osmium, iridium, ruthenium, platinum, palladium, and rhenium--known as highly siderophile elements--are segregated into the core. But studies show that mantles of the Earth, Moon and Mars contain more of these elements than they should. Scientists have several theories about why this is the case and the research team--which included lead author James Day of Scripps Institution of Oceanography and Richard Walker of the University of Maryland--set out to explore these theories by looking at diogenite meteorites.

Diogenites are a kind of meteorite that may have come from the asteroid Vesta, or a similar body. They represent some of the Solar System's oldest existing examples of heat-related chemical processing. What's more, Vesta or their other parent bodies were large enough to have undergone a similar degree of differentiation to Earth, thus forming a kind of scale model of a terrestrial planet.

The team examined seven diogenites from Antarctica and two that landed in the African desert. They were able to confirm that these samples came from no fewer than two parent bodies and that the crystallization of their minerals occurred about 4.6 billion years ago, only 2 million years after condensation of the oldest solids in the Solar System.

Examination of the samples determined that the highly siderophile elements present in the diogenite meteorites were present during formation of the rocks, which could only occur if late addition or 'accretion' of these elements after core formation had taken place. This timing of late accretion is earlier than previously thought, and much earlier than similar processes are thought to have occurred on Earth, Mars, or the Moon.

Remarkably, these results demonstrate that accretion, core formation, primary differentiation, and late accretion were all accomplished in just over 2 to 3 million years on some parent bodies. In the case of Earth, there followed crust formation, the development of an atmosphere, and plate tectonics, among other geologic processes, so the evidence for this early period is no longer preserved.

"This new understanding of diogenites gives us a better picture of the earliest days of our Solar System and will help us understand the Earth's birth and infancy," Rumble said. "Clearly we can now see that early events in planetary formation set the stage very quickly for protracted subsequent histories."
-end-
This work was supported by NASA.

The Carnegie Institution for Science (carnegiescience.edu) is a private, nonprofit organization headquartered in Washington, D.C., with six research departments throughout the U.S. Since its founding in 1902, the Carnegie Institution has been a pioneering force in basic scientific research. Carnegie scientists are leaders in plant biology, developmental biology, astronomy, materials science, global ecology, and Earth and planetary science.

Carnegie Institution for Science

Related Solar System Articles from Brightsurf:

Ultraviolet shines light on origins of the solar system
In the search to discover the origins of our solar system, an international team of researchers, including planetary scientist and cosmochemist James Lyons of Arizona State University, has compared the composition of the sun to the composition of the most ancient materials that formed in our solar system: refractory inclusions in unmetamorphosed meteorites.

Second alignment plane of solar system discovered
A study of comet motions indicates that the Solar System has a second alignment plane.

Pressure runs high at edge of solar system
Out at the boundary of our solar system, pressure runs high.

What a dying star's ashes tell us about the birth of our solar system
A UA-led team of researchers discovered a dust grain forged in a stellar explosion before our solar system was born.

What scientists found after sifting through dust in the solar system
Two recent studies report discoveries of dust rings in the inner solar system: a dust ring at Mercury's orbit, and a group of never-before-detected asteroids co-orbiting with Venus, supplying the dust in Venus' orbit.

Discovered: The most-distant solar system object ever observed
A team of astronomers has discovered the most-distant body ever observed in our solar system.

Discovery of the first body in the Solar System with an extrasolar origin
Asteroid 2015 BZ509 is the very first object in the Solar System shown to have an extrasolar origin.

First interstellar immigrant discovered in the solar system
A new study has discovered the first known permanent immigrant to our solar system.

A star disturbed the comets of the solar system in prehistory
About 70,000 years ago, when the human species was already on Earth, a small reddish star approached our solar system and gravitationally disturbed comets and asteroids.

Scientists detect comets outside our solar system
Scientists from MIT and other institutions, working closely with amateur astronomers, have spotted the dusty tails of six exocomets -- comets outside our solar system -- orbiting a faint star 800 light years from Earth.

Read More: Solar System News and Solar System Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.