Rutgers Geologists Re-Create Solar Nebula History In The Lab

"We created a mixture matching the dust out in the solar system, containing familiar elements such as iron, magnesium, silicon, sulfur, sodium, calcium and oxygen," said Cohen. "We wanted to find out how solar dust was melted and formed into chondrules, the small spherical droplets often found in meteorites. Our experiments in the lab, re-creating the physical and chemical processes responsible for chondrule formation, have enabled us to deduce more of what actually took place when the solar system was young, expanding our understanding and our knowledge."

Chondrules were created in the solar nebula, the gaseous cloud that gave rise to our solar system, during an event of intense heat early in the history of the solar system. While the exact timing of this event is uncertain, Cohen notes that these chondrules coalesced, forming asteroids about 4.5 billion years ago, which went on to contribute to meteoroids.

The authors explain that chondrules have a variety of chemical compositions. Some are rich in magnesium while others have a significant presence of iron; both types vary in silica content. However, most chondrules are similar in texture and character, appearing as a porphyry -- large crystals in a distinctly finer grain or glassy matrix.

To achieve this uniform appearance, each chemically different chondrule would have had to have been exposed to a different "just-right" temperature – a highly unlikely scenario. Suspect origins for the heating, such as solar flares or impact-induced shock waves, would all have produced about the same temperature.

Seeking a more logical explanation of the mechanisms that came into play, the investigators held temperature constant and varied the duration of the heat exposure. Using a vacuum furnace to replicate the conditions of chondrule formation (1,580 degrees centigrade in a low pressure/low oxygen environment), the samples of the simulated solar dust were subjected for different lengths of time (from one to 18 hours).

The resulting products or residues displayed the range of compositions parallel to what is found in nature while they all showed the characteristic porphyry-like appearance of chondrules. "We were able to observe minerals dissolving, elements evaporating and crystals forming, providing more precise information on the processes taking place," said Cohen.

The paper in Nature is titled "Evaporation in the Young Solar Nebula as the Origin of ‘Just-Right' Melting of Chondrules," by Cohen, Rutgers geology Professor Roger H. Hewins and Yang Yu, a former postdoctoral geology fellow at Rutgers. Journalists can view the paper prior to publication at http://press.nature.com/.

NOTE TO REPORTERS: Bosmat Cohen, department of geology at Rutgers, can be reached for interviews at (732) 445-2044 or 445-1013, or via e-mail at bosmat@eden.rutgers.edu.