[meteorite-list] Stardust Mission Results: Hot in Cold

[Ron Baalke]

http://www.sciencemag.org/cgi/content/full/312/5780/1599

Science 16 June 2006:
Vol. 312. no. 5780, p. 1599

Letters

Stardust Mission Results: Hot in Cold

The News of the Week article "Minerals point to a hot origin for icy 
comets" by R. A. Kerr (17 Mar., p. 1536) highlighted the recent 
results from the Stardust mission, which sampled dust from comet 
Wild 2. The subsequent finding that a major portion of the dust 
was crystalline and had formation temperatures in excess of 1400 K 
appears to be surprising, because comets are icy objects that 
formed some 5 to 40 Astronomical Units (AU) from the sun and were 
never exposed to such temperatures.

This "hot" in "cold" structure suggests that some solar nebula 
material was processed in the hot, innermost regions of the solar 
nebula and transported to the cooler outer regions. Supporting 
evidence for this idea is provided by observations of young 
stellar objects (YSOs), which indicate that similar crystalline 
dust is formed in the inner disk regions, within 1 or 2 AU of a 
star (1).

It was first suggested in 1990 (2) that crystalline olivine dust 
could have formed in an early solar bipolar outflow and was then 
transported to other regions of the solar nebula. These high-speed 
jets are produced from and flow perpendicular to the inner regions 
of the disks that surround young stars. They may exist for millions 
of years and typically eject about 10% of the material that accretes 
onto a star (3). A solar mass (M.) YSO will subsequently eject around 
0.1 M. of material of which 10-3 M. will probably be "rock-like." If 
only 10% of this rock-like material falls back to the nebula, then we 
have 10-4 M. of high-temperature, processed material in the solar 
nebula, an amount that is approximately equal to the total rock mass 
of the Solar System (4). This argument (5) plus other lines of 
evidence suggest that a significant portion of the dust in the solar 
nebula may have been processed by a solar jet (6, 7).

The Stardust results are consistent with this jet flow model, which 
may provide a potentially coherent and predictive framework for 
understanding the formation and transport of rocky material in the 
solar nebula.

Kurt Liffman
Centre for Fluid Dynamics
CSIRO/MIT
Post Office Box 56
Highett, VIC 3190, Australia
E-mail: Kurt.Liffman at csiro.au

References

   1. R. van Boekel et al., Nature, 432, 479 (2004).
   2. W. R. Skinner, Lunar Planet. Sci. XXI, 1166 (1990).
   3. N. Calvet, in Herbig-Haro Flows and the Birth of Low Mass Stars 
      (IAU Symp. 182), B. Reipurth, C. Bertout, Eds. (Kluwer, 
      Dordrecht, Netherlands, 1997), pp. 417-432.
   4. W. B. Hubbard, M. S. Marley, Icarus 78, 102 (1989).
   5. K. Liffman, M. Brown, Icarus 116, 275 (1995).
   6. K. Liffman, M. J. I. Brown, in Chondrules and the Protoplanetary 
      Disk, R. Hewins, R. H. Jones, E. R. D. Scott, Eds. (Cambridge 
      Univ. Press, Cambridge, 1996), pp. 285-302.
   7. F. Shu, H. Shang, T. Lee, Science 271, 1545 (1996).