by V. E. Hamilton, P. R. Christensen, H. Y. McSween, Jr., and J. L. Bandfield

This is only a summary of the discussion found in the above article. Please refer to the article for additional information.

In examining our deconvolution results, we found a large number of pixels with detectable concentrations of the Nakhla end member, but these pixels did not demonstrate any obvious spatial coherence. A plot of when these spectra were acquired (in terms of TES orbit number, or OCK) versus latitude show that these pixels primarily are restricted to data collected subsequent to OCK 7000, and are correlated with sub-solar latitude. (Figure 1)

This pattern is similar to a pattern of noise in the TES data previously identified by the TES team (Figure 2), and briefly mentioned by Bandfield [2002], suggesting that our identifications of Nakhla-like material are spurious. The pattern in the TES data is due to microphonic noise induced by vibration of the aging MGS spacecraft. The manifestation of this noise in the the TES spectral data is random in time, but affects all six TES detectors simultaneously, confirming an instrumental/spacecraft source. There are three spurious features that are introduced into the spectral data as a result of this noise; the most important of these (for this study) is a feature at ~1000 cm^-1. Whether the feature is a positive (emission maximum) or a negative (emission minimum) feature is random - averages of dozens or more spectra average out the spurious features. The Nakhla spectrum was used in the best fits to these spectra because it is dominated by the features of clinopyroxene, one of which is a strong emission maximum near ~1000 cm^-1 . It is important to note that clinopyroxene is not necessarily the only mineral that could be erroneously identified in the post-OCK 7000 data; any mineral with a strong emission minimum or maximum at these wave numbers could be identified incorrectly (e.g., sulfate), unless averages of numerous spectra are used, and/or results are verified by manual inspection. Note that this discussion pertains to data acquired in the TES 10 cm^-1 mode; the noise has a stronger effect on data collected at 5 cm^-1 sampling. Note also that non-spectral data (e.g., thermal and visible bolometers) are not affected by this noise, nor are spectral data at wavelengths >20 microns affected.

The other two spurious features that are introduced into the TES data are correlated with the motion of the high gain antenna (HGA) and the solar panels. (In fact, a minor contribution from solar panel motion is observed in Figure 2 as the "streamer" of slightly higher values between 30 - 90 deg. N latitude between OCKs 5000 - 8500.) Data that were acquired during periods of HGA and solar panel motion are avoided easily by utilizing the appropriate quality fields included in the TES database.