Geology of Mars after the first 40 years of exploration

The knowledge of Martian geology has increased enormously in the last 40 yr. Several missions orbiting or roving Mars have revolutionized our understanding of its evolution and geological features, which in several ways are similar to Earth, but are extremely different in many respects. The impressive dichotomy between the two Martian hemispheres is most likely linked to its impact cratering history, rather than internal dynamics such as on Earth. Mars' volcanism has been extensive, very long-lived and rather constant in its setting. Water was available in large quantities in the distant past of Mars, when a magnetic field and more vigorous tectonics were active.Exogenic forces have been shaping Martian landscapes and have led to a plethora of landscapes shaped by wind, water and ice. Mars' dynamical behavior continues, with its climatic variation affecting climate and geology until very recent times. This paper tries to summarize major highlights in Mars' Geology, and points to deeper and more extensive sources of important scientific contributions and future exploration.     

A multidisciplinary approach to reveal the Sicily Climate and Environment over the last 20 000 years

We present a thorough review of the knowledge on the climate and environment in Sicily over the last 20 000 years, taking into account results of several studies carried using terrestrial and marine records. We obtain a coherent framework of the most important changes succeeded in the island, even if some points need further investigation. All the reconstructions of surface temperatures of the seas and the air surrounding Sicily point out severe climatic conditions during the last glacial period. The steppe- and semisteppe-like vegetation pattern testifies, together with additional evidence from geochemical data of lacustrine evidence, markedly arid conditions. Fi-nally, significant episodes of sea level drop connected Sicily to the Italian Peninsula and favoured the dispersion of faunal elements from southern Italy. The transition between the last glacial and the Holocene was not characterized by a gradual warming but was punctuated by two abrupt suborbital climatic fluctuations: Bølling-Allerød (warm) and Younger Dryas (cold), as recognized in the sediments recovered close to the northern and southern coast of Sicily. A denser arboreal cover is possibly indicated by the occurrence of dormouse and Arvicola remains. Finally the sensitivity of Sicily to climate perturbations is demonstrated by the occurrence of repeated subtle climatic anomalies during the Holocene, including the Little Ice Age, also known from historical chronicles. Forests, woods and Mediterranean maquis developed in the early-middle Holocene. Thereafter was a general decline of arboreal vegetation, following a general aridification trend that seems to be a common feature in southern Europe and North Africa. Science Greek colonization (7^th century before Christ), the landscape was intensively modelled for agriculture and breeding, leading to a significant loss of vegetation cover.     

Precipitable water evaluations from infrared sun‐photometric measurements analyzed using the atmospheric hygrometry technique

Measurements of direct solar irradiance were taken employing 4 different sun‐photometers at near infrared wavelengths, suitable for use in atmospheric hygrometry. This technique utilising a set of spectral ratios, in and out of selected water vapour absorption bands, was applied to the measurements to obtain accurate evaluations of precipitable water. For all the hygrometric ratios given by the 4 sun‐photometers used at the 3 stations of Sagres, Monchique and Mt. Foia, during the CLEARCOLUMN experiment, we determined the calibration curves by correcting them for the Rayleigh scattering effects and, then, plotting the natural logarithms of such corrected ratios versus the square root of the water vapour mass present along the atmospheric slant path. The regression lines drawn for the various scatter diagrams were estimated to give evaluations of precipitable water with an uncertainty of less than 5%, 3% and 10% at the 3 stations, respectively. The calibration curves of the sun‐photometer located at the Sagres station were determined using the precipitable water evaluations obtained from the local radiosounding measurements taken on 5 clear‐sky days. Those of the sun‐photometers used at the Monchique and Mt. Foia stations were instead determined through intercomparison between subsets of measurements simultaneously taken with various instruments at Sagres and Mt. Foia. Using these calibration curves, we examined all the field measurements determining the time‐patterns of precipitable water at the 3 stations. During the period from 16 June to 25 July 1997, precipitable water was found to vary between 1.1 and 3.7 g cm⁻² at the Sagres station (with an accuracy within ±13%), between 1.0 and 2.8 g cm⁻² at Monchique (±11%) and between 0.8 and 3.0 g cm⁻² at the top of Mt. Foia (±26%).     

Shock melts in QUE 94411, Hammadah al Hamra 237, and Bencubbin: Remains of the missing matrix?

Abstract— We have studied the CB carbonaceous chondrites Queen Alexandra Range (QUE) 94411, Hammadah al Hamra (HH) 237, and Bencubbin with an emphasis on the petrographical and mineralogical effects of the shock processing that these meteorite assemblages have undergone. Iron‐nickel metal and chondrule silicates are the main components in these meteorites. These high‐temperature components are held together by shock melts consisting of droplets of dendritically intergrown Fe,Ni‐metal/sulfide embedded in silicate glass, which is substantially more FeO‐rich (30–40 wt%) than the chondrule silicates (FeO <5 wt%). Fine‐grained matrix material, which is a major component in most other chondrite classes, is extremely scarce in QUE 94411 and HH 237, and has not been observed in Bencubbin. This material occurs as rare, hydrated matrix lumps with major and minor element abundances roughly similar to the ferrous silicate shock melts (and CI). We infer that hydrated, fine‐grained material, compositionally similar to these matrix lumps, was originally present between the Fe,Ni‐metal grains and chondrules, but was preferentially shock melted. Other shock‐related features in QUE 94411, HH 237, and Bencubbin include an alignment and occasionally strong plastic deformation of metal and chondrule fragments. The existence of chemically zoned and metastable Fe,Ni‐metal condensates in direct contact with shock melts indicates that the shock did not substantially increase the average temperature of the rock. Because porphyritic olivine‐pyroxene chondrules are absent in QUE 94411, HH 237, and Bencubbin, it is difficult to determine the precise shock stage of these meteorites, but the shock was probably relatively light (S2–S3), consistent with a bulk temperature increase of the assemblages of less than ?300 °C. The apparently similar shock processing of Bencubbin, Weatherford, Gujba (CB_a) and QUE 94411/HH 237 (CB_b) supports the idea of a common asteroidal parent body for these meteorites.     

Magnetometer survey of the proposed Sirente meteorite crater field,central Italy: Evidence for uplifted crater rims and buried meteorites

Abstract— The Sirente crater field consists of a 120 m wide, rimmed main depression flanked to the northwest by about 30 smaller depressions. It has been dated to the first centuries A.D. An impact origin is suggested, but not confirmed. The small size combined with the properties of the target material (carbonate mud) would neither allow shock features diagnostic of impact, nor projectile vaporization. Consequently, a meteoritic component in the sediments would be very localized. At impacts of this size the projectile most likely is an iron meteorite. Any iron meteorites on the ground surface would, in Iron Age Europe, have been removed shortly after the event. However, if the depressions are of impact origin they should contain meteorites at great depth in analogy with known craters. The magnetic properties of iron meteorites differ distinctly from the very low magnetic sediments and sedimentary rocks of the Sirente area. We have used a proton precession magnetometer/gradiometer to produce magnetic anomaly maps over four of the smaller depressions (～8 m diameter), as well as two crossing profiles over a fifth depression (～22 m diameter). All show distinct magnetic anomalies of about 20 nT, the larger depression up to 100 nT. Magnetic modeling shows a best fit for structures with upturned strata below their rims, excluding a karstic origin but supporting an explosive formation. The 100 nT anomaly can only be explained by highly‐magnetic objects at a few meters depth. All together, the magnetic data provides a strong indication for an impact origin of the crater field.     

Vertical distribution of two sympatric labrid fishes in the Western Mediterranean and Eastern Atlantic rocky subtidal: local shore topography does matter

Changes in the shore topography (e.g. slope) occur at a scale of hundreds of meters in several locations in the Lusitanian and the Mediterranean Sea provinces. We tested whether differences in the bottom inclination might affect the vertical distribution patterns of two sympatric coastal labrid fishes, the rainbow wrasse Coris julis and the ornate wrasse Thalassoma pavo. Visual censuses were used to determine the distribution and abundance of these labrid species in high (≥30°) and low (≤3°) slope rocky substrates covered by brown macroalgae and at two different depths (shallow, 4–7 m, and deep 14–20 m). Pectoral fin aspect ratio was used as an estimate of swimming performance to potentially explain the patterns observed. Despite the intrinsic biogeographical differences in the overall density of T. pavo and C. julis, on steep coasts the ornate wrasse dominated in shallow waters, whereas the two species coexisted both in shallow and deeper depths on gentle slope coasts. These distribution patterns were consistent across locations, and fin aspect ratio was not a good predictor of between‐habitat use for wrasses. We show that, under specific topographical conditions, the depth segregation pattern seems to be an interactive segregation (likely related to resource competition) rather than a result of selective segregation due to morphological differences in the pectoral fin. Significant ecological changes might occur in locations where the density of T. pavo has recently increased as a result of water warming.     

New constraints on the Messinian sealevel drawdown from 3D seismic data of the Ebro Margin,western Mediterranean

We present new 3D seismic and well data from the Ebro Margin, NW Mediterranean Sea, to shed new light on the processes that formed the Messinian Erosion Surfaces (MES) of the Valencia Trough (Mediterranean Sea). We combine these data with backstripping techniques to provide a minimum estimate of the Messinian sea level fall in the EBRO Margin, as well as coupled isostasy and river incision and transport modeling to offer new constraints on the evolution of the adjacent subaerial Ebro Basin. Four major seismic units are identified on the Cenozoic Ebro Margin, based on the seismic data, including two major prograding megasequences that are separated by a major unconfirmity: the MES. The 3D seismic data provide an unprecedented view of the MES and display characteristic features of subaerial incision, including a drainage network with tributaries of at least five different orders, terraces and meandering rivers. The Messinian landscape presents a characteristic stepped‐like profile that allows the margin to be subdivided in three different regions roughly parallel to the coastline. No major tectonic control exists on the boundaries between these regions. The boundary between the two most distal regions marks the location of a relatively stable base level, and this is used in backstripping analysis to estimate the magnitude of sea level drop associated with the Messinian Salinity Crisis on the Ebro Margin. The MES on the Ebro Margin is dominated by a major fluvial system, that we identify here as the Messinian Ebro River. The 3D seismic data, onshore geology and modeling results indicate that the Ebro River drained the Ebro Basin well in advance of the Messinian.     

Water production and release in Comet 153P/Ikeya-Zhang (C/2002 C1): accurate rotational temperature retrievals from hot-band lines near 2.9-μm

Multiple non-resonance fluorescence lines of water (H₂O) were detected in Comet 153/P Ikeya-Zhang (2002 C1) between UT 2002 March 21.9 (R_h=0.51 AU) and April 13.9 (R_h=0.78 AU), using the Cryogenic Echelle Spectrometer (CSHELL) at the NASA Infrared Telescope Facility. Analysis of 2.9-μm water lines enabled accurate determination of rotational temperatures on three dates. The derived H₂O rotational temperatures were 138⁺⁶₋₅, 141⁺¹⁰₋₉, and 94±3 K on UT 2002 March 22.0, March 23.0, and April 13.8, respectively. Water production rates were retrieved from spectral lines measured in nineteen separate grating settings over seven observing periods. The derived heliocentric dependence of the water production rate was Q=(9.2±1.1)×10²⁸[R_h^{(−3.21±0.26)}] molecules s⁻¹. The spatial distribution of H₂O in the coma was consistent with its release directly from the nucleus (as a native source) on all dates.     

Chemometric study of functional groups in different layers of Trigonocarpus grandis ovules (Pennsylvanian seed fern, Canada)

We examined four dispersed, coalified ovules, Trigonocarpus grandis, of medullosalean seed-fern affinity from the Late Pennsylvanian age Sydney Coalfield, Canada, which represent the larger type of the 7–8 cm trigonocarpalean form species. At first glance it appears that the ovules are preserved like the usual Carboniferous foliar compressions, i.e. one coalified layer with one preserved anatomical tissue, the cuticle. However, careful sample preparation uncovered at least three coalified layers, and Schulze’s oxidative maceration process, which dissolves the coalified material, revealed several tissue layers. Altogether, eight sample forms were defined: (i) coalified layer, (ii) cuticle A, (iii) cupric + vitrain, (iv) vitrain, (v) cupric, (vi) cuticle B, (vii) alkaline solution and (viii) added coal seam material. The purpose of the study was twofold: first, to systematically analyze the forms by way of Fourier transform infrared (FTIR) spectrometry to fill a gap in chemical information that exits for coalified trigonocarpalean ovules of Carboniferous seed ferns; second, to use principal component analysis to focus on groupings as a function of chemical structure (functional groups) and to assess the different fossil forms in terms of FTIR chemical parameters, based on a 8 × 49 data matrix.Results include distinction among the three coaly sample forms, coalified layer (i), cupric + vitrain (iii) and cupric (v), based mainly, but not exclusively, on differences in carbonyl content, as well as length and branching of the polymethylenic chains. Important to note is the high aliphatic content of the cuticles as a signature of the biomacromolecules cutan/cutin. In particular, new insights into the structure of the original ovule are presented, and differences in chemistry are mainly a result of the complex structure of the precursor plant organ.