Differentiation in impact melt sheets as a mechanism to produce evolved magmas on Mars

Asteroid bombardment contributed to extensive melting and resurfacing of ancient (\u3e 3 Ga) Mars, thereby influencing the early evolution of the Martian crust. However, information about how impact melting has altered Mars’ crustal petrology is limited. Evidence from some of the largest impact structures on Earth, such as Sudbury and Manicouagan, suggests that some impact melt sheets experience chemical differentiation. If these processes occur on Mars, we expect to observe differentiated igneous materials in some exhumed rock samples. Some rocks observed in Gale crater are enriched in alkalis (up to 14 wt% Na2O + K2O) and silica (up to 67 wt% SiO2) with low (\u3c 5wt%) MgO. This alkaline differentiation trend has previously been attributed to fractional crystallization of magmas resulting from low-degree mantle melting analogous to ocean island or rift settings on Earth. In this study, we investigate the hypothesis that differentiation of impact-generated melts provides a viable alternative explanation for the petrogenesis of some evolved rocks on Mars. We scaled melt volumes and melt sheet thicknesses for a range of large impact magnitudes and employed the MELTS algorithm to model mineral phase equilibria in those impact-generated melts. Model runs consider a range of possible oxidation states (IW to QFM), crystallization regimes (batch, fractional and liquid segregation), and volatile contents (initially water-saturated and nominally anhydrous). Moderate pressure and water are required to produce alkaline differentiation trends in mafic melts. Large impacts that melt a water-bearing early basaltic crust provide a mechanism to generate wetter magmas on Mars, consistent with some observed Martian differentiation trends. Low-degree partial melting and/or an alkali-enriched source are required to generate the most alkaline observed compositions, motivating future work to examine partial melting regimes during large impacts

Discovery of an Apparent High Latitude Galactic Supernova Remnant

Deep H$\alpha$ images of a faint emission complex 4.0 x 5.5 degrees in angular extent and located far off the Galactic plane at l = 70.0 degrees, b=-21.5 degrees reveal numerous thin filaments suggestive of a supernova remnant's shock emission. Low dispersion optical spectra covering the wavelength range 4500 - 7500 A show only Balmer line emissions for one filament while three others show a Balmer dominated spectrum along with weak [N I] 5198, 5200 A, [O I] 6300, 6364 A, [N II] 6583 A, [S II] 6716, 6731 A and in one case [O III] 5007 A line emission. Many of the brighter H$\alpha$ filaments are visible in near UV GALEX images presumably due to C III] 1909 A line emission. ROSAT All Sky Survey images of this region show a faint crescent shaped X-ray emission nebula coincident with the portion of the H$\alpha$ nebulosity closest to the Galactic plane. The presence of long, thin Balmer dominated emission filaments with associated UV emission and coincident X-ray emission suggests this nebula is a high latitude Galactic supernova remnant despite a lack of known associated nonthermal radio emission. Relative line intensities of the optical lines in some filaments differ from commonly observed [S II]/H$\alpha$ > 0.4 radiative shocked filaments and typical Balmer filaments in supernova remnants. We discuss possible causes for the unusual optical SNR spectra.Comment: 12 pages, 10 figures, accepted to the Astrophysical Journa

A fragile record of fleeting water on Mars: data

This dataset accompanies the manuscript "A fragile record of fleeting water on Mars" by Koeppel et al., published in 2021 in the journal Geology

Intermittent ischaemia maintains function after ischaemia reperfusion in steatotic livers

INT is more effective than IPC in restoring liver function in the acute phase of IR in steatotic livers. In obese patients, INT may be useful in promoting better liver function after IR after liver resection

New Frontiers Titan Orbiter

International audienceAs one of two planetary objects (other than Earth) that have solid surfaces, thick atmospheres, and astrobiological significance, Titan, like Mars, merits ongoing study with multiple spacecraft. We propose that a Titan orbiter dedicated to geophysics, geology, and atmospheric science be added to the New Frontiers menu for the coming decade