The Detectability Limit of Organic Molecules Within Mars South Polar Laboratory Analogs

Abstract

Our neighboring planet, Mars, has increasingly been the target of scientific exploration and of particular interest are its geological history, current environmental conditions, and perhaps most importantly, its potential as a host for extraterrestrial life (Fairén et al., 2010). The polar caps of Mars have more recently emerged as an area of scientific interest due to their abundance of water ice and their dynamic nature, especially with the discovery of a possible stable body of liquid water beneath the Martian South Pole (Orosei et al., 2018). The Martian North and South Pole have permanent ice caps that expand throughout their respective winters, and maintain residual caps in the summer. The North Polar Cap is composed almost entirely of water ice, while the longer, colder winter in the higher altitude southern hemisphere means that the central part Abstract A series of laboratory experiments was carried out in order to generate a diagnostic spectrum for polycyclic aromatic hydrocarbons (PAHs) of astrobiological interest in the context of the Martian South Polar Residual Cap (SPRC), to establish PAH spectral features more easily detectable in CO 2 ice (mixed with small amounts of H 2 O ice) than the previously reported absorption feature at 3.29 µm in order to constrain their detectability limit. There is currently no existing literature on PAH detection within SPRC features, making this work novel and impactful given the recent discovery of a possible subglacial lake beneath the Martian South Pole. Although they have been detected in Martian meteorites, PAHs have not been detected yet on Mars, possibly due to the deleterious effects of ultraviolet radiation on the surface of the planet. SPRC features may provide protection to fragile molecules, and this work seeks to provide laboratory data to improve interpretation of orbital remote sensing spectroscopic imaging data. We also ascertain the effect of CO 2 ice sublimation on organic spectra, as well as provide PAH reference spectra in mixtures relevant to Mars. A detectability limit of ∼0.04% has been recorded for observing PAHs in CO 2 ice using laboratory instrument parameters emulating those of the Compact Reconnaissance Imaging Spectrometer for Mars, with new spectral slope features revealed between 0.7 and 1.1 µm, and absorption features at 1.14 and most sensitively, at 1.685 µm. Mars regolith analog mixed with a concentration of 1.5% PAHs resulted in no discernible organic spectral features. These detectability limits measured in the laboratory are discussed and extrapolated to the effective conditions on the Mars South Polar Cap in terms of dust and water ice abundance and CO 2 ice grain size for both the main perennial cap and the H 2 O ice-dust sublimation lag deposit.Plain Language Summary Carbon molecule chains, or organics, are considered important in the search for life, as all life that we know of on Earth is made from carbon. A particular type of organic, PAHs, that are really common on Earth and throughout space, have never been found on Mars ...

Toward Detecting Polycyclic Aromatic Hydrocarbons on Planetary Objects with ORIGIN

“…Despite these discoveries, PAHs have not yet been directly detected on the surface of Mars, and it is suggested that the ultraviolet radiation from the Sun destroys them in a time frame of 4-9.6 sols (solar day as measured on Mars) without shielding (Dartnell et al 2012). The PAHs could be shielded in the south polar residual cap region by the present ice (Campbell et al 2021) or found in the subsurface soil. Although PAHs are thought to be destroyed over a short time frame on the surface of Mars due to the UV radiation, a number of PAHs could survive under Venus-like conditions, as they form stable solutions in concentrated sulfuric acid, among them perylene (Bains et al 2021).…”

Nine Martian Years of polar caps observations by SPICAM-IR

“…SPICAM-IR nadir data were already successfully used for long-term atmospheric studies, such as water vapor and the O 2 emission mapping (Trokhimovskiy et al, 2015;Guslyakova et al, 2016), but have never been used for analysis of the surface reflectance. IR observations at high spectral resolution may also be useful for detecting impurities in ice, such as PAHs (Campbell et al, 2021).…”