Sulfate-rich eolian and wet interdune deposits, Erebus crater, Meridiani Planum, Mars

This study investigates three bedrock exposures at Erebus crater, an ~ 300 m diameter crater approximately 4 km south of Endurance crater on Mars. These outcrops, called Olympia, Payson, and Yavapai, provide additional evidence in support of the dune–interdune model proposed for the formation of the deposits at the Opportunity landing site in Meridiani Planum. There is evidence for greater involvement of liquid water in the Olympia outcrop exposures than was observed in Eagle or Endurance craters. The Olympia outcrop likely formed in a wet interdune and sand sheet environment. The facies observed within the Payson outcrop, which is likely stratigraphically above the Olympia outcrop, indicate that it was deposited in a damp-wet interdune, sand sheet, and eolian dune environment. The Yavapai outcrop, which likely stratigraphically overlies the Payson outcrop, indicates that it was deposited in primarily a sand sheet environment and also potentially in an eolian dune environment. These three outcrop exposures may indicate an overall drying-upward trend spanning the stratigraphic section from its base at the Olympia outcrop to its top at the Yavapai outcrop. This contrasts with the wetting-upward trend seen in Endurance and Eagle craters. Thus, the series of outcrops seen at Meridiani by Opportunity may constitute a full climatic cycle, evolving from dry to wet to dry conditions

Hot Interstellar Gas and Stellar Energy Feedback in the Antennae Galaxies

We have analyzed Chandra archival observations of the Antennae galaxies to study the distribution and physical properties of its hot interstellar gas. Eleven distinct diffuse X-ray emission regions are selected according to their underlying interstellar structures and star formation activity. The X-ray spectra of these regions are used to determine their thermal energy contents and cooling timescales. Young star clusters in these regions are also identified and their photometric measurements are compared to evolutionary stellar population synthesis models to assess their masses and ages. The cluster properties are then used to determine the stellar wind and supernova energies injected into the ISM. Comparisons between the thermal energy in the hot ISM and the expected stellar energy input show that young star clusters are sufficient to power the X-ray-emitting gas in some, but not all, active star formation regions. Super-star clusters, with masses >= 1x10^5 M_sol, heat the ISM, but the yield of hot interstellar gas is not directly proportional to the cluster mass. Finally, there exist diffuse X-ray emission regions which do not show active star formation or massive young star clusters. These regions may be powered by field stars or low-mass clusters formed within the last ~100 Myr.Comment: 36 pages, 6 figures, 8 tables, 2 appendices, to appear in the Astrophysical Journal, April 20 issu

Deep-water incised valley deposits at the ediacaran-cambrian boundary in southern Namibia contain abundant treptichnus pedum

Valley-filling deposits of the Nama Group, southern Namibia, record two episodes of erosional downcutting and backfill, developed close together in time near the Ediacaran-Cambrian boundary. Geochronological constraints indicate that the older valley fill began 539.4 ± 1 Ma or later; the younger of these deposits contains unusually well-preserved populations of the basal Cambrian trace fossil Treptichnus pedum. Facies analysis shows that T. pedum is closely linked to a nearshore sandstone deposit, indicating a close environmental or taphonomic connection to very shallow, mud-draped sandy seafloor swept by tidal currents. Facies restriction may limit the biostratigraphic potential of T. pedum in Namibia and elsewhere, but it also illuminates functional and ecological interpretation. The T. pedum tracemaker was a motile bilaterian animal that lived below the sediment-water interface—propelling itself forward in upward-curving projections that breached the sediment surface. The T. pedum animal, therefore, lived infaunally, perhaps to avoid predation, surfacing regularly to feed and take in oxygen. Alternatively, the T. pedum animal may have been a deposit feeder that surfaced largely for purposes of gas exchange, an interpretation that has some support in the observed association of T. pedum with mud drapes. Treptichnus pedum provides our oldest record of animals that combined anatomical and behavioral complexity. Insights from comparative biology suggest that basal Cambrian T. pedum animals already possessed the anatomical, neurological, and genetic complexity needed to enable the body plan and behavioral diversification recorded by younger Cambrian fossils

Sublacustrine depositional fans in southwest Melas Chasma

Two depositional fan complexes have been identified on the floor of southwest Melas Chasma. The western fan complex is located near the center of an enclosed basin in southwest Melas Chasma and is composed of multiple lobes with dendritic finger-like terminations. These fans are very flat and have a morphology unlike any other fan that has been previously identified on Mars. On the basis of the morphologic similarity of the western fan complex to the Mississippi submarine fan complex, we suggest that it may be a deep subaqueous fan depositional system. There are numerous channels on the surface of the western fan complex, and measurements of channel length, width, and sinuosity are consistent with channels observed on terrestrial submarine fans. The eastern Melas depositional fans are less well preserved and may be of deltaic or sublacustrine origin. Recognition of the fans supports earlier suggestions for the presence of a former lake in Melas Chasma and indicates that a significant body of water was present and stable at the surface of Mars for at least 10^2 to 10^4 years

Sedimentary Textures Formed By Aqueous Processes, Erebus Crater, Meridiani Planum, Mars

New observations at Erebus crater (Olympia outcrop) by the Mars Exploration Rover Opportunity between sols 671 and 735 (a sol is a martian day) indicate that a diverse suite of primary and penecontemporaneous sedimentary structures is preserved in sulfate-rich bedrock. Centimeter-scale trough (festoon) cross-lamination is abundant, and is better expressed and thicker than previously described examples. Postdepositional shrinkage cracks in the same outcrop are interpreted to have formed in response to desiccation. Considered collectively, this suite of sedimentary structures provides strong support for the involvement of liquid water during accumulation of sedimentary rocks at Meridiani Planum.Organismic and Evolutionary Biolog

The High Resolution Imaging Science Experiment (HiRISE) during MRO’s Primary Science Phase (PSP)

The High Resolution Imaging Science Experiment (HiRISE) on the Mars Reconnaissance Orbiter (MRO) acquired 8 terapixels of data in 9137 images of Mars between October 2006 and December 2008, covering ~0.55% of the surface. Images are typically 5–6 km wide with 3-color coverage over the central 20% of the swath, and their scales usually range from 25 to 60 cm/pixel. Nine hundred and sixty stereo pairs were acquired and more than 50 digital terrain models (DTMs) completed; these data have led to some of the most significant science results. New methods to measure and correct distortions due to pointing jitter facilitate topographic and change-detection studies at sub-meter scales. Recent results address Noachian bedrock stratigraphy, fluvially deposited fans in craters and in or near Valles Marineris, groundwater flow in fractures and porous media, quasi-periodic layering in polar and non-polar deposits, tectonic history of west Candor Chasma, geometry of clay-rich deposits near and within Mawrth Vallis, dynamics of flood lavas in the Cerberus Palus region, evidence for pyroclastic deposits, columnar jointing in lava flows, recent collapse pits, evidence for water in well-preserved impact craters, newly discovered large rayed craters, and glacial and periglacial processes. Of particular interest are ongoing processes such as those driven by the wind, impact cratering, avalanches of dust and/or frost, relatively bright deposits on steep gullied slopes, and the dynamic seasonal processes over polar regions. HiRISE has acquired hundreds of large images of past, present and potential future landing sites and has contributed to scientific and engineering studies of those sites. Warming the focal-plane electronics prior to imaging has mitigated an instrument anomaly that produces bad data under cold operating conditions