BLOOMINGTON, Ind. — The process that formed the giant planet Jupiter may
also have spawned some of the tiniest and oldest members of our solar
system — millimeter-sized spheres called chondrules, the major part of
the most primitive meteorites. As witnesses to the early history of the
solar system, chondrules may provide important clues to how the planets

A report of this research result, by theorists Alan P. Boss of the
Carnegie Institution of Washington and Richard H. Durisen of Indiana
University in Bloomington, will be published in the March 10 issue of
Astrophysical Journal Letters.

Chondrules are glassy particles that experienced flash-melting and rapid
cooling. They are found in meteorites but not in terrestrial rocks, and
they are among the first solids that formed in the cloud of gas and dust
called the solar nebula that swirled around the young sun and eventually
gave rise to the solar system.

“One of the great puzzles of solar system origin has been that the bulk of
primitive meteorites, which come from the asteroid belt, consists of
chondrules,” Durisen said. “The texture of chondrules shows that they were
flash-melted and rapidly cooled. Most of the solid material in the inner
nebula apparently experienced these mysterious energetic melting events.”

“Understanding what formed the chondrules has been one of biggest problems in
the field for over a century,” Boss said. “Scientists realized several
years ago
that a shock wave was probably responsible for generating the heat that
these meteoritic components. But no one could explain convincingly how the
front was generated in the solar nebula some 4.6 billion years ago. These
calculations show how a shock front could have formed as a result of
spiral arms
roiling the solar nebula at Jupiter’s orbit. The shock front extended into
inner solar nebula, where the compressed gas and radiation heated dust
as they struck the shock front at 20,000 miles per hour, thereby creating

Independent simulations by Boss and by Durisen’s research group show that
waves in a gravitationally unstable disk of gas and dust at or beyond
distance from the sun (five times the Earth-sun distance) could have produced
shock waves at half that distance in the inner solar system — especially
in the
asteroid belt — that were capable of melting dust clumps to form chondrules.

“A striking consequence of these waves is revealed in our simulations at
University,” Durisen said. “A considerable amount of gas and dust is kicked
upward by the shock-heating. We see gigantic curling and breaking waves
arc over
the surface of the solar nebula, like waves crashing on a beach. These
waves are
huge, comparable in size to a substantial fraction of the distance from
Earth to
the sun.”

IU graduate student Aaron C. Boley, who works with Durisen on
chondrule-producing spiral waves, said, “The crashing waves produce strong
shocks, mix chondrules and their precursors around the nebula like shells
in the
surf, and produce turbulence that may have assisted in compacting newly
chondrules into larger solid bodies.”

An animation of a crashing wave of gas in the solar nebula is available at (“Shock waves”). A
illustration is available at

“This calculation has probably removed the last obstacle to acceptance of how
chondrules were melted,” said theorist Steven J. Desch of Arizona State
University, who showed several years ago that shock waves could do the job.
“Meteoriticists have recognized that the ways chondrules are melted by shocks
are consistent with everything we know about chondrules. But without a proven
source of shocks, they have remained mostly unconvinced about how chondrules
were melted. The work of Boss and Durisen demonstrates that our early solar
nebula experienced the right types of shocks, at the right times, and at the
right places in the nebula to melt chondrules. I think for many
this closes the deal. With nebular shocks identified as the culprit, we can
finally begin to understand what the chondrules are telling us about the
earliest stages of our solar system’s evolution.”

Although Durisen’s group and Boss have some disagreements about exactly
how gas
giant planets form, they agree that, in order to make Jupiter, the solar
had to have been at least marginally gravitationally unstable, so that it
have developed spiral arms at an early stage and resembled a spiral galaxy.
Chondrules would have formed at the very earliest times and would have
to form for a few million years, until the solar nebula disappeared.
Late-forming chondrules in meteorites are thus the last souvenirs of the
that formed our planetary system.

Boss’s research is supported in part by the NASA Planetary Geology and
Geophysics Program and the NASA Origins of Solar Systems Program. The
calculations were performed on the Carnegie Alpha Cluster, the purchase of
was supported in part by the National Science Foundation’s Major Research
Instrumentation Program, and on Indiana University’s IBM SP supercomputer
cluster. Durisen’s research also was supported in part by the NASA Origins
of Solar Systems Program.