Australasian Science: Australia's authority on science since 1938

New Theory Explains Meteorite Mystery

By Stephen Luntz

Tiny components of meteorites have long posed a puzzle for astronomers, but researchers at the Australian National University believe they have an explanation that sheds light on our solar system’s birth.

Chondrules are spherical and just 1 mm in diameter, but can represent as much as 80% of the mass of a meteorite. They carry clear indications of having been formed at more than 1000°C, but are found next to other materials that have never been exposed to temperatures of a few hundred degrees.

“Most of the solar system is cold, so it’s been unclear for decades what caused the chondrules to experience such extreme heat,” says Dr Raquel Salmeron of the Research School of Astronomy and Astrophysics. “We believe that chondrules formed in jets of material ejected from flattened disks called protostellar disks, which encircle young stars.”

These jets travel at enormous speeds, and Salmeron suggests that the kinetic energy of the gases is transferred to particles travelling within the stream at different rates, causing them to heat up.

According to Salmeron, larger particles never get ejected with the gas jets, and temperatures in subsonic parts of the gas are much lower than for particles exposed to supersonic gas speeds. This creates the previously puzzling sharp transition between the temperatures at which chondrules formed and those experienced by other meteorite components.

While some chondrules would have been incorporated into the planets as they formed, billions of years of secondary processing have removed the traces so they are now only observed in meteorites.