On the relation of the lunar recession and the length-of-the-day

We review the problem of the consistency between the observed values of the lunar recession from Lunar Laser Ranging (LLR) and of the increase of the length-of-the-day (LOD). From observations of lunar occultations completed by recent IERS data, we derive a variation rate of the LOD equal to 1.09 ms/cy from 1680 to 2020, which compares well with McCarthy and Babcock (Phys. Earth Planet. Inter. 44: 281, 1986) and Sidorenkov (Astron. Astrophys. Trans. 24: 425, 2005). This rate is lower than the mean rate of 1.78 ms/cy derived by Stephenson et al. (Proc. R. Soc. A 472: 20160404, 2016) on the basis of eclipses in the Antiquity and Middle Age. The difference in the two observed rates starts at the epoch of a major change in the data accuracy with telescopic observations. The observed lunar recession appears too large when compared to the tidal slowing down of the Earth determined from eclipses in the Antiquity and Middle Age and even much more when determined from lunar occultations and IERS data from 1680 to 2020. With a proper account of the tidal effects and of the detailed studies on the atmospheric effects, the melting from icefields, the changes of the sea level, the glacial isostatic adjustment, and the core-mantle coupling, we conclude that the long-standing problem of the presence or absence of a local cosmological expansion is still an open question.

Less Known Results on the Solar System

For a two half millennium evolution of knowledge from the Democrit’s natural, rational atomized material conception to the Newtonian, Maxwellian, Einsteinian mathematized physics, the research in the most cases has followed a deductive route from observable facts/reality according to the Mach’s rigorous positivism principle. During the last century both experimental and computational technology progress has accumulated a solid factual datum support on the better knowledge of our actual world, so that the research is beginning on inductive route of the hidden/dark detailed processes as a whole. This revolutionary stage of physics, based on a holistic integral approach, is concerned with the relativity-gravity evolution in a quantifiable space-time universe created after the morphogenetic light explosion (or the 4D-BIG BANG). The paper presented herein contains some less known aspects on the work of solar system as a whole, along with the specific activity of the Earth-planet as a part integrated into the solar complex.

Mesospheric water ice clouds in Mars Year 34-35 as identified in ExoMars UVIS occultation opacities

<p><strong>Introduction:</strong>  Suspended atmospheric aerosols are key components of the martian atmosphere, and their vertical distribution has long been a subject of investigation with orbital observations and modelling. The aerosols found in Mars' atmosphere are mineral dust, water ice, and CO<sub>2</sub> ice, and each have distinct spatiotemporal distributions and radiative effects.</p> <p>Of particular interest for this study is the vertical distribution of atmospheric aerosols. In recent years, dust has been observed to have a more complex vertical distribution structure than previously thought, with the detection of detached dust layers [1] and large plume-like structures during Global Dust Storms (GDS) [2].</p> <p>Water ice distribution is tied to the seasonal behaviour of its associated cloud formations, with seasonally recurring features including the aphelion cloud belt (ACB) [3] and polar hood clouds [4] at tropospheric altitudes, as well as higher altitude mesospheric (>40 km) clouds during Mars’ perihelion season [5] as well as during GDS [6,7].</p> <p>Mars’ low atmospheric temperatures also enable the formation of CO<sub>2</sub> ice clouds, which have been detected at mesospheric altitudes over the tropics/subtropics and generally during the colder aphelion season [5,8]. These are thought to be more ephemeral than their water ice counterparts, with lifetimes as low as minutes [9]. More persistent and optically thicker CO2 ice clouds have been detected at tropospheric altitudes in the polar night [10].</p> <p> The Ultraviolet and Visible (UVIS) Spectrometer [11], part of the Nadir and Occultation for MArs Discovery (NOMAD) spectrometer suite aboard the ExoMars Trace Gas Orbiter (TGO) [12], has now observed the martian atmospheric limb via solar occultations for over 1.5 martian years. This period covers the 2018/Mars Year (MY) 34 GDS and regional dust storm, as well as the entirety of the more typical MY 35. As such, UVIS solar occultation data provides a great opportunity to examine Mars’ vertical aerosol structure.</p> <p><strong>Results: </strong>We present a new UVIS occultation opacity profile dataset, openly available for use by the community. We also discuss particular features of interest in the dataset, and interpret these features by reference to previous published work and by comparison with the MGCM. In particular,<strong> </strong>we focus on notable mesospheric water ice cloud phenomena observed in both MY 34 and MY 35. We describe the spatiotemporal distribution of these features, and the link between specific water ice features and strong atmospheric dust activity from global and regional storms. The MGCM temperature and aerosol opacity fields provide valuable points of comparison with the UVIS dataset, for the purposes of both explanation and validation of the MGCM’s existing parametrizations. The UVIS dataset offers opportunities for further research into the vertical aerosol structure of the martian atmosphere, and improvement of how this is represented in numerical models.</p> <p><strong>References:</strong> [1] Heavens, N. G. et al (2011) <em>JGR (Planets), 116(E4), </em>E04003. [2] Heavens, N. G. et al (2019) <em>GRL, 124</em>(11), 2863-2892. [3] Smith M. D. (2008) <em>Annu. Rev. Earth Planet Sci, 26, </em>191-219. [4] Wang, H. & Ingersoll, A. P. (2002) <em>JGR (Planets), 107(E10), </em>8-1-8-16. [5] Clancy, R. T. et al (2019) <em>Icarus, 328, </em>246-273. [6] Liuzzi G. et al (2020) <em>JGR (Planets), 125</em>(4). [7] Stcherbinine, A. et al (2020) <em>JGR (Planets), 125</em>(3). [8] Aoki, S. et al (2018) <em>Icarus, 302, </em>175-190. [9] Listowski, C. et al (2014) <em>Icarus, 237, </em>239-261. [10] Hayne, P. O. et al (2012) <em>JGR (Planets), 117</em>(E8). [11] Patel, M. R. et al (2017) <em>Appl. Opt., 56</em>(10), 2771-2782. [12] Vandaele, A. C. et al (2015) <em>Planet. Space Sci., 119</em>, 233-249.</p>

Preservation of organic compounds and constraints on diagenetic processes by reactive iron phases on Mars

<p>Over 20% of organic carbon in sediments on Earth are bound to reactive Fe mineral phases [1]. These reactive Fe phases are generally Fe (oxyhydr)oxides, often associated with clay minerals. It is important to note that they occur as nanoparticulate and X-ray amorphous phases that are challenging to identify. On Earth, proxy methods such as chemical sequential extractions are often used but they can produce misleading results when used for mineral identification [2,3]. We develop and use Mössbauer spectroscopy applications to identify these phase [2-4] and compare these to Raman spectroscopy because the Mars 2020 Perseverance rover and the ExoMars 2022 Rosalind Franklin rover use Raman spectrometers for mineralogical identification.</p> <p>Reactive Fe phases are abundant on Mars. It is important to note that they are not the well-crystalline expression of Fe (oxyhydr)oxides such as hematite and goethite that have been observed from orbit and with a variety of rover-based instruments. Instead, reactive Fe phases are represented by as yet unidentified Fe phases: Aqueously altered rocks and soils in Gusev crater and at Meridiani Planum (including the Burns formation) contain large amounts of nanophase iron oxides (npOx and Fe3D3) [5]; and 20-60 wt% of minerals in fluvio-lacustrine deposits in Gale crater are X-ray amorphous and this amorphous phase is rich in iron [6]. Mineralogical interpretation of CRISM data of Rosalind Franklin's landing site at Oxia Planum also suggest the presence of these phase. These reactive Fe phases can be any combination of a number of minerals including ferrihydrite, lepidocrocite, akaganèite, hissingerite, schwertmannite, and superparamagnetic (i.e. nanoparticulate) hematite and goethite [5].</p> <p>The preservation of organic compounds by reactive Fe species is effective over hundreds of thousands of years in Earth sediments [1]. In return, organic compounds slow down the transformation of reactive Fe species such as ferrihydrite into the more crystalline and thermodynamically stable Fe (oxyhydr)oxides hematite or goethite during diagenetic processes. With temperature and pressure rising further during diagenesis, however, organic compounds are oxidized and destroyed through the reduction of Fe (resulting in the diagenetic formation of the Fe carbonate siderite, for example), and the non-reduced Fe species are transformed into thermodynamically stable minerals. Thus, the presence of reactive Fe species in Martian sediments/sedimentary rocks indicates only little diagenetic overprinting and therefore a high preservation potential of organic compounds. Such samples will be of high priority for analysis with MOMA. However, the presence of Fe species during pyrolysis can reduce the detectability of certain organic compounds. This effect depends on the specific Fe species present and is mitigated in the presence of clay minerals [7,8].</p> <p>We will present Mössbauer and Raman spectrocopy investigations of reactive Fe phases in various sedimenatry settings and compare these results into the context of rover landing sites on Mars.</p> <p>References:</p> <p>[1] Lalonde et al (2012) <em>Nature</em> 483, 198-200. [2] Schröder et al (2016) <em>Hyperfine Interact </em>237, 85<em>.</em> [3] Hebpburn et al (2020) <em>Chem Geol</em> 543, 119584. [4] Klingelhöfer et al (2003) <em>J Geophys Res</em> 108(E12), 8067. [5] Morris et al (2019) in <em>Remote Compositional Analysis: Techniques for Understanding Spectroscopy, Mineralogy, and Geochemistry of Planetary Surfaces</em>, pp. 538-554, Cambridge University Press. [6] Rampe et al (2017) <em>Earth Planet Sci Lett</em> 471, 172–185. [7] Tan et al (2021) <em>Astrobiology</em> 21, 199-218. [8] Royle et al (2021) <em>Astrobiology</em> in press. </p>