We present g, r, and i band photometric observations of Comet 13P/Olbers obtained between 2024 August 31 and October 10, after its perihelion passage. These observations are used to investigate the evolution of the coma morphology, dust activity, and optical properties during the post-perihelion phase. Enhanced images reveal faint jet-like structures within the coma. The dust production proxy A(0)fρ decreases from ∼1.1×104 cm to ∼4.3×103 cm over the observed heliocentric distance range of 1.5–1.9 au. The radial profile of Afρ shows a deviation from the steady-state expectation, exhibiting a pronounced maximum near ∼1.5×104 km. The measured coma colors have mean values of g−r=0.62±0.10 and r−i=0.20±0.08, with reddening slopes of 6%–10% per 103 Å. The coma colors become marginally less red with increasing aperture size, suggesting weak radial evolution of the dust population within the coma. Overall, Comet 13P/Olbers exhibits a gradual decrease in dust activity after perihelion, while the radial Afρ profiles suggest possible evolution of the dust coma with cometocentric distance.
Lunar exploration, at present and in the immediately foreseeable future, is primarily focused on the surface of the Moon, which is covered by a layer of lunar regolith. Therefore, the physical and mechanical properties of lunar regolith, particularly the shear properties as a geomaterial, are of critical importance. However, due to the scarcity of authentic lunar regolith samples, pertinent tests and experiments are usually conducted on various lunar regolith simulants, most of which are developed based on the lunar samples from the Apollo missions. Nevertheless, after the Chang’E−5 probe successfully retrieved a batch of lunar regolith in 2020, simulants of this novel origin have gradually emerged. In this study, the shear properties of Apollo- and Chang’E-based lunar regolith simulants, TJ-1 and TJC-1, are compared. To this end, direct shear tests are conducted on the simulants and their contact interface with TC4 titanium alloy. The shear stress-relative lateral displacement curves of TJ-1 have strain-softening characteristics, while the curves of TJ-1 in contact with the surface of TC4 titanium alloy exhibit strain-hardening behavior, both of which can be described by the simplified Duncan-Chang model considering structure damage of the soil. On the other hand, TJC-1 and its contact with the surface of TC4 titanium alloy have strain-hardening characteristics, which could be described by the Gompertz model. Additionally, direct shear tests are conducted between the simulants and jagged titanium discs, during which two kinds of shearing processes occur simultaneously, i.e., the interface shear between the simulant and the smooth surface of the TC4 titanium alloy and the shear of the simulant itself. However, the final shear strength is also influenced by the surface morphology of the titanium disc.
Mars is a primary target in the search for extraterrestrial life, and biologically informative organic molecules are key candidates for molecular biosignatures. However, the stability and transformation pathways of specific biological molecules under Mars-relevant surface stressors remain insufficiently constrained. Lycopene, a widespread carotenoid and possible precursor of geologically persistent carotenoid derivatives, was selected here as a model biomolecule. We used laboratory irradiation experiments to examine lycopene photodegradation in dry and solution states and in association with representative mineral matrices (quartz, montmorillonite, and jarosite) and oxychlorine salts (chlorite, chlorate, and perchlorate). UV-Vis spectroscopy and first-order kinetic fitting show that dry lycopene is markedly more stable than lycopene in ethyl acetate solution. Among the tested mineral matrices, montmorillonite provides the strongest protective effect, whereas quartz provides little buffering capacity. Oxychlorine effects are compound- and matrix-dependent: chlorite and chlorate generally accelerate degradation, whereas perchlorate shows a weaker, more context-dependent effect. Jarosite-oxychlorine mixtures produce particularly complex spectral changes, including rapid transformation in the jarosite-chlorite system and extended apparent preservation in the jarosite-perchlorate system. These results indicate that lycopene preservation under Mars-relevant conditions cannot be predicted from individual stressors alone and depends on coupled mineral-oxidant interactions. Because the experiments were conducted under terrestrial atmospheric conditions and product identities were not determined by molecular analyses, the results should be interpreted as comparative laboratory constraints rather than as direct estimates of Martian surface lifetimes.
We assess the potential of rocks from the Semail Ophiolite in the northern Al-Hajar Mountains of the southeast Arabian peninsula for use as lunar and Martian simulants. Ten rock samples were collected from the United Arab Emirates (UAE) and one from Oman, and we characterized their geochemistry, mineralogy, and spectral characteristics. We proposed mixing recipes of Semail rocks to synthetically make our unique simulants. Our synthetic mixtures’ effectiveness was evaluated according to goodness of model fit to existing lunar and Martian rock/soil data and Simulant Suitability Score (SSS) comparisons to well-known lunar and Martian simulants. Our lunar mare rock and soil simulants had the highest model fit (root-mean-square error less than 10) and highest SSS (78). Spectra of synthetic simulants and spectral indices of major minerals common to Semail samples, the Moon, and Mars (feldspar and pyroxenes) were also computed, serving as inputs to map suitable locations for simulant sourcing using Hyperion hyperspectral and Sentinel-2 multispectral imagery. Results indicate that regions of interest are found around southern Ras al-Khaimah, Ajman Emirate, and Dubai area of UAE. Our findings contribute to the efforts to make and characterize various simulants supporting planetary science and exploration.
