Changes in blast zone albedo patterns around new martian impact craters

• Published in: Icarus (New York, N.Y. 1962) N.Y. 1962), 2016-03, Vol.267, p.86-105
• Main Authors: Daubar, I.J., Dundas, C.M., Byrne, S., Geissler, P., Bart, G.D., McEwen, A.S., Russell, P.S., Chojnacki, M., Golombek, M.P.
• Format: Article
• Language: English
• Subjects: Aeolian processes; Albedo; Cratering; Craters; Dust; Fading; Halos; Impact processes; Mars; Mars (planet); Mars craters; Mars, surface
• ISSN: 0019-1035; 1090-2643
• DOI: 10.1016/j.icarus.2015.11.032

•Survey of changes in blast zone (BZ) albedo patterns around new martian impacts.•Some BZs change quickly, but half show no changes over several Mars years.•More changes are seen at higher latitudes, lower elevations, and smaller craters.•Median of estimated minimum fading lifetimes for BZs is ∼8Marsyears.•Daubar et al. (2013) PF is not low due to fading, but may contribute to shallow SFD. “Blast zones” (BZs) around new martian craters comprise various albedo features caused by the initial impact, including diffuse halos, extended linear and arcuate rays, secondary craters, ejecta patterns, and dust avalanches. We examined these features for changes in repeat images separated by up to four Mars years. Here we present the first comprehensive survey of the qualitative and quantitative changes observed in impact blast zones over time. Such changes are most likely due to airfall of high-albedo dust restoring darkened areas to their original albedo, the albedo of adjacent non-impacted surfaces. Although some sites show drastic changes over short timescales, nearly half of the sites show no obvious changes over several Mars years. Albedo changes are more likely to occur at higher-latitude sites, lower-elevation sites, and at sites with smaller central craters. No correlation was seen between amount of change and Dust Cover Index, relative halo size, or historical regional albedo changes. Quantitative albedo measurements of the diffuse dark halos relative to their surroundings yielded estimates of fading lifetimes for these features. The average lifetime among sites with measurable fading is ∼15Marsyears; the median is ∼8Marsyears for a linear brightening. However, at approximately half of sites with three or more repeat images, a nonlinear function with rapid initial fading followed by a slow increase in albedo provides a better fit to the fading behavior; this would predict even longer lifetimes. The predicted lifetimes of BZs are comparable to those of slope streaks, and considered representative of fading by global atmospheric dust deposition; they last significantly longer than dust devil or rover tracks, albedo features that are erased by different processes. These relatively long lifetimes indicate that the measurement of the current impact rate by Daubar et al. (Daubar, I.J. et al. [2013]. Icarus 225, 506–516. http://dx.doi.org/10.1016/j.icarus.2013.04.009) does not suffer significantly from overall under-sampling due to blast zones fading before new impa