ABSTRACT
The deuterium-to-hydrogen (D/H) ratio in strongly bound water or hydroxyl groups in ancient martian clays retains the imprint of the water of formation of these minerals. Curiosity's Sample Analysis at Mars (SAM) experiment measured thermally evolved water and hydrogen gas released between 550° and 950°C from samples of Hesperian-era Gale crater smectite to determine this isotope ratio. The D/H value is 3.0 (±0.2) times the ratio in standard mean ocean water. The D/H ratio in this ~3-billion-year-old mudstone, which is half that of the present martian atmosphere but substantially higher than that expected in very early Mars, indicates an extended history of hydrogen escape and desiccation of the planet.
ABSTRACT
Samples from the Rocknest aeolian deposit were heated to ~835°C under helium flow and evolved gases analyzed by Curiosity's Sample Analysis at Mars instrument suite. H2O, SO2, CO2, and O2 were the major gases released. Water abundance (1.5 to 3 weight percent) and release temperature suggest that H2O is bound within an amorphous component of the sample. Decomposition of fine-grained Fe or Mg carbonate is the likely source of much of the evolved CO2. Evolved O2 is coincident with the release of Cl, suggesting that oxygen is produced from thermal decomposition of an oxychloride compound. Elevated δD values are consistent with recent atmospheric exchange. Carbon isotopes indicate multiple carbon sources in the fines. Several simple organic compounds were detected, but they are not definitively martian in origin.
ABSTRACT
Water has supposedly marked the surface of Mars and produced characteristic landforms. To understand the history of water on Mars, we take a close look at key locations with the High-Resolution Imaging Science Experiment on board the Mars Reconnaissance Orbiter, reaching fine spatial scales of 25 to 32 centimeters per pixel. Boulders ranging up to approximately 2 meters in diameter are ubiquitous in the middle to high latitudes, which include deposits previously interpreted as finegrained ocean sediments or dusty snow. Bright gully deposits identify six locations with very recent activity, but these lie on steep (20 degrees to 35 degrees) slopes where dry mass wasting could occur. Thus, we cannot confirm the reality of ancient oceans or water in active gullies but do see evidence of fluvial modification of geologically recent mid-latitude gullies and equatorial impact craters.
Subject(s)
Mars , Water , Extraterrestrial Environment , Geological Phenomena , GeologyABSTRACT
BACKGROUND: Secretin is a gastro-intestinal hormone which has been presented as an effective treatment for autism based on anecdotal evidence. OBJECTIVES: To determine if intravenous secretin:1. improves the core features of autism (social interaction, communication and behaviour problems); 2. improves the non-core aspects of behaviour or function such as self injurious behaviour;3. improves the quality of life of affected individuals and their carers; 4. has short term and long term effects on outcome; 5. causes harm. SEARCH STRATEGY: Results of electronic searches of CENTRAL, MEDLINE, EMBASE, PsycINFO, CINAHL, ERIC, HealthStar and Sociofile (1998 - March 2005) were independently examined by two authors. Reference lists of trials and reviews were searched; experts and trialists were contacted to find unpublished studies. SELECTION CRITERIA: Randomised controlled trials of intravenous secretin comparing secretin with a placebo treatment in children or adults diagnosed with autism spectrum disorders, where at least one standardised outcome measure was reported. DATA COLLECTION AND ANALYSIS: Fourteen studies met inclusion criteria. All outcome data were continuous. Where trials used cross-over designs, analysis was conducted on results from first treatment phase, allowing combined analysis with parallel design trials. Where standardised assessment tools generated scores as outcome measures, comparisons were made between means of these scores. Where baseline means were reported, differences between treatment and control were determined to assess possible bias. Where mean change from baseline was reported, this was used in preference to post-treatment scores for meta-analyses or forest plots. As meta-analysis was possible for only one outcome (Childhood Autism Rating Scale), it was impossible to use sensitivity or subgroup analyses to assess impact of study quality, clinical differences in the intervention, or clinically relevant differences between groups, such as age or presence of gastrointestinal symptoms. MAIN RESULTS: Twenty-five established standardised outcome measures were reported to assess core features of autism, communication, behaviour, visio-spatial skills, affect and adverse events within fourteen included studies. No more than four studies used any one outcome measure similarly. Outcomes were reported between three and six weeks. RCTs of efficacy of secretin in autism have not shown improvements for core features of autism. AUTHORS' CONCLUSIONS: There is no evidence that single or multiple dose intravenous secretin is effective and as such it should not currently be recommended or administered as a treatment for autism. Further experimental assessment of secretin's effectiveness for autism can only be justified if methodological problems of existing research can be overcome.
