IDE database - Impactor Classification

Impactor Classification

A final paper describing impactor classification procedures and results in detail is under preparation at the time of archive closure and is to be submitted to the Journal of Spacecraft and Rockets for publication.

The data in the archive can be used to classify impactor residues into three general categories:

  1. manmade debris
  2. micrometeoroid
  3. indeterminate
Category (1) can be further divided into subcategories including paint particles, aluminum oxide particles (not detectable on the MOS and Al substrates in this study) and other. In practice, high concentrations of Ti and sometimes Cu was used to identify manmade debris (paint).

Category (2) can be divided into subcategories of different types of Interplanetary Dust Particles (IDP's) to the extent that knowledge of the relative abundances of 12C, 24Mg, 40 Ca, and 56Fe allow. Mass fractionation effects must be considered when assigning these subcategories.

Most impact sites examined in this study were on Al/Si based MOS substrates, therefore Al and Si were not quantifiable. Because of the limitations and contamination issues (Refs 1-3), the final SIMS analytical data is limited. There are little or no data for Mn, Cr, and S. There is relatively complete data with high confidence for 23Na, 24Mg, 39K, 40Ca, 48Ti, and 56Fe. Ca was a contaminant at the 100 ppm level in the substrate, so only very high signals (relative to the blank levels) can be interpreted. The mass 48 signal in the SIMS images includes contributions from both 48Ti and 48Ca. The signal can easily be corrected for interference from 48Ca (natural abundance = 0.185%) before quantifying the data using relative sensitivity factors (RSF). This correction is already applied to the abundance data files in this archive.

Two kinds of analytical "blanks" on MOS substrates have useful information:

The levels of ion species present in these features was, in general, extremely low. These values were used to determine when a signal was great enough to warrant further quantitative reduction.

Two sets of RSF's were used for quantitative reduction in this study. These values are listed here for use by interested parties. The first set was developed by investigators at Washington University McDonnell Center for the Space Sciences using a Cameca 3f with an oxygen beam similar to the instrument used in this study. These values are based on average ion yields for the listed species from several Lunar analogue glasses (LAG). These RSF's were intended for application to meteorite residues deposited in molten or vapor condensate form on pure Ge and Ta substrates. In these forms, the "nearest neighbor" of the resident atoms in the residue would be other atoms in the residue , i.e. very similar to the LAG. The second set of RSF's is for species implanted in Si at concentrations <1% (Ref. 4) and was used for residues on the MOS substrates where the impactor materials frequently were intermixed with the Si and SiO2 substrate materials. Both sets of values were used in practice in order to define the limits of the observed compositions.

Always remember that the ion images are for RAW PIXEL INTENSITY files. The IDE data file editor, developed during the archival process, can be used to define an area of the image to be quantified. The boxes on each image in this file were the ones we selected for further reduction after careful consideration. You may select other areas, but we caution you against contamination spots around, and sometimes (rarely) within impact feature sites. These spots may be of interest to some investigators. There are also debris sprays around some sites, particularly on Al samples.

References

  1. "Ion microprobe elemental analysis of impact features on Interplanetary Dust Experiment sensor surfaces." C.G. Simon, J.L. Hunter, D.P. Griffis, and J.J. Wortman, LDEF-69 Months in Space: First Post Retrieval Symposium, NASA CP 3134, pp.529-548 (1991).
  2. "Contaminant interferences with SIMS analyses of microparticle impactor residues on LDEF surfaces." C.G. Simon, J.L. Hunter, D.P. Griffis, V. Misra, D.A. Ricks, and J.J. Wortman, Adv. Space Res., Vol. 13, No 8, pp. (8)115-(8)118, (1993).
  3. "Elemental analyses of hypervelocity microparticle impact sites on Interplanetary Dust Experiment sensor surfaces." C.G. Simon, J.L. Hunter, D.P. Griffis, V. Misra, D.A. Ricks, J.J. Wortman, and D.E. Brownlee, LDEF-69 Months in Space: Second Post Retrieval Symposium, NASA CP 3194, pp. 677-692 (1993).
  4. R.G.Wilson, F.A. Stevie, and C.W. Magee, Secondary Ion Mass Spectrometry - A Practical Handbook for Depth Profiling and Bulk Impurity Analysis, J. Wiley & Sons, p. E-17 (1989).
    Charles G. Simon and Klaus G. Paul, 7-8-1994