Sublimation of Mars's southern seasonal CO₂ ice cap and the formation of spiders

Abstract

[1] In this paper we define and describe morphological features that have colloquially been termed ''spiders'' and map their distribution in the south polar region of Mars. We show that these features go through a distinct seasonal evolution, exhibiting dark plumes and associated fan-shaped deposits during the local defrosting of the seasonal cap. We have documented the seasonal evolution of the cryptic region and have found that spiders only occur within this terrain. These observations are consistent with a geyser-like model for spider formation. Association with the transparent (cryptic) portion of the seasonal cap is consistent with basal sublimation and the resulting venting of CO 2 gas. Also consistent with such venting is the observation of dark fan-shaped deposits apparently emanating from spider centers. Spiders are additionally confined to the polar layered deposits presumably due to the poorly consolidated and easily eroded nature of their upper surface.

HiRISE observations of gas sublimation-driven activity in Mars’ southern polar regions: II. Surficial deposits and their origins

“…These structures form the ''classic" case as described by Piqueux et al (2003). The reflectance of the dark deposits is typically 20-40% of the surroundings early in the spring season.…”

“…Kieffer (2007) provided a detailed model of the complete process including estimates for the height of the inferred gas jets. Piqueux et al (2003) linked venting to surface structures by suggesting that ''araneiform" (spider-like) structures in the southern polar region had been produced by this process. This is the second of three papers which describe the surface morphology and sublimation-driven activity in specific areas of the martian south polar region as observed by the High Resolution Imaging Science Experiment (HiRISE) onboard NASA's Mars Reconnaissance Orbiter (MRO) spacecraft.…”

“…However, as described in Hansen et al (this issue), the Mars Orbiting Camera (MOC; Malin et al, 1998) showed the presence of fan-like dark patches on the surface of the subliming southern polar caps. Kieffer (2000) suggested that the unique properties of CO 2 ice are responsible for this phenomenon which probably results from a type of solid-state greenhouse effect (Matson and Brown, 1989;Piqueux et al, 2003;Kaufmann et al, 2006;Kaufmann, 2007;Kieffer, 2007;Piqueux and Christensen, 2008) involving CO 2 slab ice. By being translucent at optical wavelengths, but relatively opaque at infra-red wavelengths, a thin CO 2 ice sheet (the result of condensation in winter onto a dusty or rocky substrate) can result in solar energy being deposited at the boundary between the ice sheet and the substrate without a ready means of escape.…”

Introduction to the 4th Mars Polar Science and Exploration Conference special issue: Five top questions in Mars polar science

“…The seasonal CO 2 cycle, including formation of the seasonal caps, has been extensively studied (recent references include, e.g., James and Cantor, 2001;Kieffer and Titus, 2001;Smith et al, 2001;Piquex et al, 2003;Douté et al, 2006). Each year, seasonal insolation variations result in about 25% of the martian atmosphere alternatively condensing and sublimating from the poles.…”

Identifying Surface Changes on HRSC Images of the Mars South Polar Residual Cap (Sprc)

“…Although mostly unchanged, icy, CO2 dominant SPRC has dynamic phenomena related to seasonal changes on the planet. A few investigations have been performed on these changes, such as studies on layers of solid CO2 and water ice (Plaut et al, 2007), the so-called Swiss Cheese Terrain (Titus et al, 2004) analysed in HiRISE images and Mars Orbiter Camera, and spider-like channels (Piqueux et al, 2003) on the ice surface in HiRISE images. As there are yet more changes likely to be discovered in SPRC, detecting changes in the surface is necessary before doing the next step, analysing and identifying what surface processes are responsible for these changes.…”