Geologic Mapping and Age Determinations of Tsiolkovskiy Crater

Tsiolkovskiy is a ~200 km diameter crater presenting one of the few mare deposits of the lunar far side. In this work, we perform a geological study of the crater by means of morpho-stratigraphic and color-based spectral mappings, and a detailed crater counting age determination. The work aims at characterizing the surface morphology and compositional variation observed from orbital data including the Lunar Reconnaissance Orbiter Wide Angle Camera and Clementine UVVIS Warped Color Ratio mosaics, and attempts a reconstruction of the evolutionary history of the Tsiolkovskiy crater through both relative and absolute model age determinations. The results show a clear correlation between the geologic and spectral units and an asymmetric distribution of these units reflecting the oblique impact origin of the crater. Crater counts performed using the spectral units identified on the smooth crater floor returned distinct age ranges, suggesting the occurrence of at least three different igneous events, generating units characterized by particular compositions and/or degree of maturity. This work demonstrates the scientific value of Tsiolkovskiy crater for a better understanding of the volcanic evolution of the Moon and, in particular, of its far side.

Kīlauea -Leilani 2018 lava flow delineation by using Sentinel2 and Landsat8 images

Kīlauea is a broad shield volcano built against the southeastern slope of Mauna Loa. The summit presently has a caldera that is roughly 4km by 3.2km wide, and walls of between 0 m and 120 m high. In late April 2018, an eruption interesting both the summit crater and the lower East Rift Zone (LERZ) occurred. In this work a quasi real time estimation of the evolution of radiant lava flow extension starting from May 2018 for Kīlauea -Leilani eruption using satellite image data is presented. The active lava flow evolution is obtained by using Copernicus Sentinel2 (S2) and USGS-Landsat8 (L8) polar satellites acquiring medium/high spatial resolution images (20mx20m and 30mx30m respectively) in the VIS-SWIR-TIR spectral range. Because of the Kīlauea eruption extension and duration, a multi sensor approach has been used in order to improve the timing of the information derived by high spatial resolution remote sensed data merging two missions with different revisit time. The 2018 eruptions at Hawaii's Kīlauea Volcano developed rapidly, after the initial activity centered on the Púu ′Ō′ō crater floor on 1 May followed by draining of the lava lake at Halemáumáu (HMM) Overlook Crater in the next days. During the magma extrusion from the summit, earthquake swarms and ground cracking hit the Leilani Estates neighborhood on 2 May. With the S2 and L8 sensors we followed the lava flow by 5th of May up to mid of August, considering also that the activity started to decline from the beginning of August. At the end of activity, Kīlauea Volcano experienced its largest LERZ eruption and caldera collapse in at least 200 years.

Mars Methane Sources in Northwestern Gale Crater Inferred from Back-Trajectory Modeling

During its five years of operation, the Sample Analysis at Mars (SAM) Tunable Laser Spectrometer (TLS) on board the Curiosity rover has detected six methane spikes above a low background abundance in Gale crater. The methane spikes are likely the consequence of nearby surface emission. Here we use inverse Lagrangian modeling techniques to identify probable upstream emission regions for these methane spikes at an unprecedented spatial resolution. Inside Gale crater, the northwestern crater floor casts the strongest influence on the detections. Outside Gale crater, the emission region with the strongest influence extends towards the north. The contrasting results from two consecutive methane measurements point to an active emission region to the west and the southwest of the Curiosity rover on the northwestern crater floor. The observed spike magnitude and frequency also favor emission sites on the northwestern crater floor, unless fast methane removal mechanisms that are unknown to date are at work.

Impacts may provide heat for aqueous alteration and organic solid formation on asteroid parent bodies

Chemical reactions on asteroid parent bodies, such as aqueous alteration and the formation of organic solids, require a heat source. Radioactive decay in the interiors of these bodies is generally considered the most important heat source, but impact-generated heating is also likely to play a role. Here we present high-velocity impact cratering experiments using thermocouples embedded in the target material to directly measure the spatial and temporal evolution of temperature throughout each impact experiment. We find that the maximum temperature below the crater floor scales with the distance from the impact point, while the duration of temperature rise is scaled by the thermal diffusion time. We use numerical modelling to suggest that, at distances within 2 astronomical units, impacts producing craters of >20 km radius can facilitate aqueous alteration in the material below the crater, while those which produce craters of 1 km radius can support organic solid formation.

Detailed age determinations for Tsiolkovskiy crater floor

<p>With respect to its counterpart, the lunar farside is characterized by few basaltic mare exposures. One of these, with a total surface area of approximately 12 000 km<sup>2</sup>, covers the floor of the ~200 km diameter Tsiolkovskiy crater (20.4° S, 129.1° E) [1].</p><p>The crater size frequency distributions (CSFDs) calculated for this crater led to different results. The age determination performed on the mare infilling resulted in an Imbrian-Erathostenian age of about 3.2 Ga [2], while a 3.6 Ga Late Imbrian age was derived from areas scattered on top of a long run-out landslide generated from the western rim and its surroundings [3-4].</p><p>The spectral map produced for Tsiolkovskiy crater [5-6], performed on the ~200 m/pixel Clementine UVVIS color ratio mosaic [7] (R: 750/415 nm; G: 750/1000 nm; B: 415/750 nm), and recently updated suggests for the crater floor the presence of three color units, characteristics of higher 415/750 nm ratio, higher 750/415 nm ratio and average 750/415 nm and 750/1000 nm ratios, defined by a different composition and/or age formation.</p><p>In order to discriminate possible age differences ascribable to different eruptive events, on the basis of the spectral mapping we defined several areas for measuring the crater size-frequency distributions of the different color units on the crater floor. In addition, we calculated the age formation of Tsiolkovskiy crater itself by means of hummocky areas interpreted as impact melt identified in accordance to the geological mapping [5-6] performed on the ~100 m/pixel LRO-WAC [8] global mosaic.</p><p>The CSFDs measurements have been performed on areas of at least 100 km<sup>2</sup> using the CraterTools add-on [9] in the ArcGIS software on LRO-NAC [8] images with resolution ranging between 0.5 and 1.5 m/pixel. The exported data have then been plotted in the Craterstats2 software [10].</p><p>The obtained results highlight that i) Tsiolkovskiy crater formed around 3.6 Ga, in agreement with [3], ii) three different age ranges are discernible and iii) these age ranges are correlated to each one of the three color units of the crater floor.</p><p>This allows to reconstruct the evolution history of the crater and in particular of its crater floor, with particular focus also on its compositional variegation.</p><p> </p><p>Acknowledgments</p><p>This research was supported by the European Union’s Horizon 2020 under grant agreement No 776276-PLANMAP.</p><p>References</p><p>[1] Whitford-Stark, J.L. & Hawke, B.R., XXXIII LPSC, pp. 861-862, 1982  [2] Pasckert, J.H. et al., Icarus, Vol. 257, pp. 336-354, 2015  [3] Boyce, J.M. et al., XXXXVII LPSC, 2471, 2016  [4] Boyce, J.M. et al., Icarus, Vol. 337, 2020  [5] Tognon, G. et al., EGU, 733, 2020  [6] Tognon, G. et al., EPSC, 581, 2020  [7] Lucey, P.G. et al., JGR, Vol. 105, pp. 20377-20386, 2000  [8] Robinson, M.S. et al., Space Sci. Rev., Vol. 150, pp. 81–124, 2010  [9] Kneissl, M. et al., Plan. Space Sci., Vol. 59, pp. 1243-1254, 2011  [10] Michael G.G. & Neukum, G., Earth and Plan. Sci. Letters, Vol. 294, pp. 223-229, 2010</p>

Identification and interpretation of seismic short-duration events inside the Kolumbo submarine volcano in the Southern Aegean

<p>Kolumbo represents one of the most hazardous, currently active, volcanoes in the eastern Mediterranean. Its last eruption in 1650 AD was associated with a vast explosion, causing a tsunami of regionally devastating impact. The eruption was also associated with the voluminous and rapid release of toxic gases asphyxiating humans and animals on the nearby Islands. Earthquake records from the recent decades document on-going unrest beneath the volcano. Remotely operated vehicle dives revealed several hydrothermal vent sites and bacterial mats at the crater floor, which are concentrated near the northern crater wall. The vents emit mainly CO<sub>2</sub>, leading to the accumulation of acidic waters in the crater. Accordingly, one of the main volcanic hazards associated with Kolumbo is that rapid overturning of water in the crater may release harmful amounts of toxic gases. Monitoring the hydrothermal processes inside the Kolumbo crater will provide an important contribution to the understanding and evaluation of this and other volcanic hazards.</p><p>In October 2019, we deployed an ocean bottom seismometer and hydrophone (OBS/H) inside the Kolumbo crater. During the four days of passive recording we identified about 100 so-called short duration seismic events, which were only present on the seismometer channels, while generally being absent on the hydrophone channels. The events have durations of less than one second with dominant frequencies between 5 to 30 Hz. Most of the events represent well-polarized seismic phases, which enables us to determine their azimuth angle (with a 180-degree bias) and angle of incidence at the OBS/H. We cross-correlated all polarized seismic waveforms and subsequently used the cross-correlation coefficients for a hierarchical cluster analysis to elaborate whether the events have a random origin or originated from a common origin. Our analysis revealed that the majority of events is associated with two clusters. The azimuth angles of all events in the largest cluster coincide with the azimuth angle between station and the field of hydrothermal vents and bacterial mats inside the crater. This coincidence suggests that the origin of the short duration events is associated with the sub-seafloor migration of fluids or the fluid discharge process at the crater floor. In fact, short-duration events of similar characteristics, recorded by OBS/H, were previously attributed to sub-seafloor fluid migration and the discharge of fluids at the seafloor. Our analyses indicate that seismic monitoring of submarine volcanoes should include the detection and analysis of short duration events, which may act as a novel tool in the characterization of volcanic unrests and volcanogenic geohazard monitoring in general.</p>

Post-Impact Faulting of the Holfontein Granophyre Dike of the Vredefort Impact Structure, South Africa, Inferred from Remote Sensing, Geophysics, and Geochemistry

Better characterization features borne from long-term crustal modification processes is essential for understanding the dynamics of large basin-forming impact structures on Earth. Within the deeply eroded 2.02 Ga Vredefort Impact Structure in South Africa, impact melt dikes are exposed at the surface. In this study, we utilized a combination of field, remote sensing, electrical resistivity, magnetic, petrographical, and geochemical techniques to characterize one such impact melt dike, namely, the Holfontein Granophyre Dike (HGD), along with the host granites. The HGD is split into two seemingly disconnected segments. Geophysical modeling of both segments suggests that the melt rock does not penetrate below the modern surface deeper than 5 m, which was confirmed by a later transecting construction trench. Even though the textures and clast content are different in two segments, the major element, trace element, and O isotope compositions of each segment are indistinguishable. Structural measurements of the tectonic foliations in the granites, as well as the spatial expression of the dike, suggest that the dike was segmented by an ENE–WSW trending sinistral strike-slip fault zone. Such an offset must have occurred after the dike solidified. However, the Vredefort structure has not been affected by any major tectonic events after the impact occurred. Therefore, the inferred segmentation of the HGD is consistent with long-term crustal processes occurring in the post-impact environment. These crustal processes may have involved progressive uplift of the crater floor, which is consistent with post-impact long-term crustal adjustment that has been inferred for craters on the Moon.