Search

The Mars Science Laboratory (MSL) recently discovered nitrates in Gale Crater (e.g., Stern et al., 2015; Sutter et al., 2017). One possible mechanism for ancient nitrate deposition on Mars is through HNOx formation and rain out in the atmosphere, for which lightning-induced NO is likely the fundamental source. This study investigates nitrogen (N₂) fixation in early Mars' atmosphere, with implications for early Mars' habitability. We consider a 1 bar atmosphere of background CO₂, with abundance of N₂, hydrogen, and methane varied from 1% to 10% to explore a swath of potential early Mars climates. We derive lightning-induced thermochemical equilibrium fluxes of NO and HCN by coupling the lightning-rate parametrization from the study of Romps et al. (2014) with chemical equilibrium with applications, and we use a Geant4 simulation platform to estimate the effect of solar energetic particle events. These fluxes are used as input into KINETICS, the Caltech/JPL coupled photochemistry and transport code, which models the chemistry of 50 species linked by 495 reactions to derive rain-out fluxes of HNOx and HCN. We compute equilibrium concentrations of cyanide and nitrate in a putative northern ocean at early Mars, assuming hydrothermal vent circulation and photoreduction act as the dominant loss mechanisms. We find average oceanic concentrations of ∼0.1–2 nM nitrate and ∼0.01–2 mM cyanide. HCN is critical for protein synthesis at concentrations >0.01 M (e.g., Holm and Neubeck, 2009), and our result is astrobiologically significant if secondary local concentration mechanisms occurred. Nitrates may act as high-potential electron acceptors for early metabolisms, although the minimum concentration required is unknown. Our study derives concentrations that will be useful for future laboratory studies to investigate the habitability at early Mars. The aqueous nitrate concentrations correspond to surface nitrate precipitates of ∼1–8 × 10⁻⁴ wt % that may have formed after the evaporation of surface waters, and these values roughly agree with recent MSL measurements.

The observation of a 266.94 GHz feature in the Venus spectrum has been attributed to PH$_3$ in the Venus clouds, suggesting unexpected geological, chemical or even biological processes. Since both PH$_3$ and SO$_2$ are spectrally active near 266.94 GHz, the contribution to this line from SO$_2$ must be determined before it can be attributed, in whole or part, to PH$_3$. An undetected SO$_2$ reference line, interpreted as an unexpectedly low SO$_2$ abundance, suggested that the 266.94 GHz feature could be attributed primarily to PH$_3$. However, the low SO$_2$ and the inference that PH$_3$ was in the cloud deck posed an apparent contradiction. Here we use a radiative transfer model to analyze the PH$_3$ discovery, and explore the detectability of different vertical distributions of PH$_3$ and SO$_2$. We find that the 266.94 GHz line does not originate in the clouds, but above 80 km in the Venus mesosphere. This level of line formation is inconsistent with chemical modeling that assumes generation of PH$_3$ in the Venus clouds. Given the extremely short chemical lifetime of PH$_3$ in the Venus mesosphere, an implausibly high source flux would be needed to maintain the observed value of 20$\pm$10 ppb. We find that typical Venus SO$_2$ vertical distributions and abundances fit the JCMT 266.94 GHz feature, and the resulting SO$_2$ reference line at 267.54 GHz would have remained undetectable in the ALMA data due to line dilution. We conclude that nominal mesospheric SO$_2$ is a more plausible explanation for the JCMT and ALMA data than PH$_3$., Comment: 12 pages, 5 figures, accepted to ApJL

We quantify the amount of nitrogen oxides (NOx) produced through lightning and photochemical processes in the Hadean atmosphere to be available in the Hadean ocean for the emergence of life. Atmospherically generated nitrate (NO_3−) and nitrite (NO_2−) are the most attractive high-potential electron acceptors for pulling and enabling crucial redox reactions of autotrophic metabolic pathways at submarine alkaline hydrothermal vents. The Hadean atmosphere, dominated by CO_2 and N_2, will produce nitric oxide (NO) when shocked by lightning. Photochemical reactions involving NO and H_2O vapor will then produce acids such as HNO, HNO_2, HNO_3, and HO_2NO_2 that rain into the ocean. There, they dissociate into or react to form nitrate and nitrite. We present new calculations based on a novel combination of early-Earth global climate model and photochemical modeling, and we predict the flux of NOx to the Hadean ocean. In our 0.1-, 1-, and 10-bar pCO_2 models, we calculate the NOx delivery to be 2.4 × 10^5, 6.5 × 10^8, and 1.9 × 10^8 molecules cm^(−2) s^(−1). After only tens of thousands to tens of millions of years, these NOx fluxes are expected to produce sufficient (micromolar) ocean concentrations of high-potential electron acceptors for the emergence of life.

New Horizons has granted us an unprecedented glimpse at the structure and composition of Pluto's atmosphere, which is comprised mostly of N_2 with trace amounts of CH_4, CO, and the photochemical products thereof. Through photochemistry, higher-order hydrocarbons are generated, coagulating into aerosols and resulting in global haze layers. Here we present a state-of-the-art photochemical model for Pluto's atmosphere to explain the abundance profiles of CH_4, C_2H_2, C_2H_4, and C_2H_6, the total column density of HCN, and to predict the abundance profiles of oxygen-bearing species. The CH_4 profile can be best matched by taking a constant-with-altitude eddy diffusion coefficient K_(zz) profile of 1 × 10^3 cm^2 s^(–1) and a fixed CH_4 surface mixing ratio of 4 × 10^(–3). Condensation is key to fitting the C_2 hydrocarbon profiles. We find that C_2H_4 must have a much lower saturation vapor pressure than predicted by extrapolations of laboratory measurements to Pluto temperatures. We also find best-fit values for the sticking coefficients of C_2H_2, C_2H_4, C_2H_6, and HCN. The top three precipitating species are C_2H_2, C_2H_4, and C_2H_6, with precipitation rates of 179, 95, and 62 g cm^(–2) s^(–1), respectively.

This study aims to assess the results of extended transforaminal lumbar interbody fusion (TLIF) for a two surgeon, single institution series. In total, extended TLIF with bilateral decompression was performed in 57 patients. Pain, American Spinal Injury Association scores, patient demographics, body mass index (BMI), perioperative indices and radiographic measurements were recorded and analysed. The surgeries were performed between February 2011 and January 2014 on 38 women and 19 men. The mean patient age was 62.86 years, and the mean BMI was 30.31 kg/m(2). In 49 patients, spondylolisthesis was the primary indication. The mean intraoperative time was 284.65 min, and this decreased as the series progressed. The median length of stay was 5 days (range: 2-9). The surgical complication rate was 19.3%. Two patients died from cardiopulmonary complications. Single level TLIF was performed in 78.9% of the cohort, with L4/5 the most commonly fused level. Significant pain reduction was achieved from a mean (± standard deviation) preoperative visual analogue scale (VAS) of 8.28 ± 1.39 to 1.50 ± 1.05 at 12 months postoperatively. No patients deteriorated neurologically. Spondylolisthesis was significantly corrected from a preoperative mean of 6.82 mm to 2.80 mm postoperatively. Although there is a learning curve associated with the procedure, extended TLIF with bilateral facet joint removal and decompression appeared to be a safe and effective alternative to other fusion techniques, and our results were comparable to other published case series. The stabilisation and correction of spinal deformity reduces pain, aids neurologic recovery and improves quality of life.

The Alice instrument on NASA's New Horizons spacecraft observed an ultraviolet solar occultation by Pluto's atmosphere on 2015 July 14. The transmission vs. altitude was sensitive to the presence of N_2, CH_4, C_2H_2, C_2H_4, C_2H_6, and haze. We derived line-of-sight abundances and local number densities for the 5 molecular species, and line-of-sight optical depth and extinction coefficients for the haze. We found the following major conclusions: (1) We confirmed temperatures in Pluto's upper atmosphere that were colder than expected before the New Horizons flyby, with upper atmospheric temperatures near 65–68 K. The inferred enhanced Jeans escape rates were (3–7) × 10^(22) N_2 s^(−1) and (4–8) × 10^(25) CH_4 s^(−1) at the exobase (at a radius of ∼ 2900 km, or an altitude of ∼1710 km). (2) We measured CH_4 abundances from 80 to 1200 km above the surface. A joint analysis of the Alice CH_4 and Alice and REX N_2 measurements implied a very stable lower atmosphere with a small eddy diffusion coefficient, most likely between 550 and 4000 cm^2 s^(−1). Such a small eddy diffusion coefficient placed the homopause within 12 km of the surface, giving Pluto a small planetary boundary layer. The inferred CH_4 surface mixing ratio was ∼ 0.28–0.35%. (3) The abundance profiles of the “C_2H_x hydrocarbons” (C_2H_2, C_2H_4, C_2H_6) were not simply exponential with altitude. We detected local maxima in line-of-sight abundance near 410 km altitude for C_2H_4, near 320 km for C_2H_2, and an inflection point or the suggestion of a local maximum at 260 km for C_2H_6. We also detected local minima near 200 km altitude for C_2H_4, near 170 km for C_2H_2, and an inflection point or minimum near 170–200 km for C_2H_6. These compared favorably with models for hydrocarbon production near 300–400 km and haze condensation near 200 km, especially for C_2H_2 and C_2H_4 (Wong et al., 2017). (4) We found haze that had an extinction coefficient approximately proportional to N_2 density.

International audience; Recent measurements of methane (CH4) by the Mars Science Laboratory (MSL) now confront us with robust data that demand interpretation. Thus far, the MSL data have revealed a baseline level of CH4 (*0.4 parts per billion by volume [ppbv]), with seasonal variations, as well as greatly enhanced spikes of CH4 with peak abundances of *7 ppbv. What do these CH4 revelations with drastically different abundances and temporal signatures represent in terms of interior geochemical processes, or is martian CH4 a biosignature? Discerning how CH4 generation occurs on Mars may shed light on the potential habitability of Mars. There is no evidence of life on the surface of Mars today, but microbes might reside beneath the surface. In this case, the carbon flux represented by CH4 would serve as a link between a putative subterranean biosphere on Mars and what we can measure above the surface. Alternatively, CH4 records modern geochemical activity. Here we ask the fundamental question: how active is Mars, geochemically and/or biologically? In this article, we examine geological, geochemical, and biogeo- chemical processes related to our overarching question. The martian atmosphere and surface are an over- whelmingly oxidizing environment, and life requires pairing of electron donors and electron acceptors, that is, redox gradients, as an essential source of energy. Therefore, a fundamental and critical question regarding the possibility of life on Mars is, ‘‘Where can we find redox gradients as energy sources for life on Mars?’’ Hence, regardless of the pathway that generates CH4 on Mars, the presence of CH4, a reduced species in an oxidant-rich environment, suggests the possibility of redox gradients supporting life and habitability on Mars. Recent missions such as ExoMars Trace Gas Orbiter may provide mapping of the global distribution of CH4. To discriminate between abiotic and biotic sources of CH4 on Mars, future studies should use a series of diagnostic geochemical analyses, preferably performed below the ground or at the ground/atmosphere interface, including measurements of CH4 isotopes, methane/ethane ratios, H2 gas concentration, and species such as acetic acid. Advances in the fields of Mars exploration and instrumentation will be driven, augmented, and supported by an improved un- derstanding of atmospheric chemistry and dynamics, deep subsurface biogeochemistry, astrobiology, planetary geology, and geophysics. Future Mars exploration programs will have to expand the integration of complementary areas of expertise to generate synergistic and innovative ideas to realize breakthroughs in advancing our under- standing of the potential of life and habitable conditions having existed on Mars. In this spirit, we conducted a set of interdisciplinary workshops. From this series has emerged a vision of technological, theoretical, and meth- odological innovations to explore the martian subsurface and to enhance spatial tracking of key volatiles, such as CH4.

The present study aims to assess the results of single-stage instrumentation and fusion at the time of surgical debridement of spinal infections; vertebral osteomyelitis or epidural abscess. Nine patients with spinal infection were treated with instrumentation and fusion after radical debridement in a single-stage operation. Predisposing factors and comorbidities, pain, American Spinal Injury Association motor scores, primary pathologies, microbiology and perioperative markers were recorded. Seven patients with pyogenic and two with tuberculous spinal infection were encountered; the most common pathogen was Staphylococcus aureus. Five patients were predisposed to infection because of diabetes mellitus. Duration of antibiotic therapy lasted up to 12 months. Six patients had thoracic infection, two lumbar and one cervical. No post-operative complications were encountered. There was a significant reduction in pain scores compared to pre-operatively. All patients with neurological deficits improved post-operatively. Despite introduction of hardware, no patients had a recurrence of their infection in the 12 month follow up period. Single-stage debridement and instrumentation appeared to be a safe and effective method of managing spinal infections. The combination of debridement and fusion has the dual benefit of removing a focus of infection and stabilising the spine. The current series confirms that placing titanium cages into an infected space is safe in a majority of patients. Stabilisation and correction of spinal deformity reduces pain, aids neurologic recovery and improves quality of life. The small patient population and retrospective nature limit the present study.

The New Horizons flyby of Pluto confirmed the existence of hazes in its atmosphere. Observations of a large high- to low- phase brightness ratio, combined with the blue color of the haze, suggest that the haze particles are fractal aggregates, analogous to the photochemical hazes on Titan. Therefore, studying the Pluto hazes can shed light on the similarities and differences between the Pluto and Titan atmospheres. We model the haze distribution using the Community Aerosol and Radiation Model for Atmospheres assuming that the distribution is shaped by sedimentation and coagulation of particles originating from photochemistry. Hazes composed of both purely spherical and purely fractal aggregate particles are considered. Agreement between model results and occultation observations is obtained with aggregate particles when the downward flux of photochemical products is equal to the column-integrated methane destruction rate ~1.2 $\times$ 10$^{-14}$ g cm$^{-2}$ s$^{-1}$, while for spherical particles the mass flux must be 2-3 times greater. This flux is nearly identical to the haze production flux of Titan previously obtained by comparing microphysical model results to Cassini observations. The aggregate particle radius is sensitive to particle charging, and a particle charge to radius ratio of 30 e-/{\mu}m is necessary to produce ~0.1-0.2 {\mu}m aggregates near Pluto's surface, in accordance with forward scattering measurements. Such a particle charge to radius ratio is 2-4 times higher than those previously obtained for Titan. Hazes composed of spheres with the same particle charge to radius ratio have particles that are 4 times smaller. These results further suggest that the haze particles are fractal aggregates. We also consider the effect of condensation of HCN, and C$_{2}$-hydrocarbons on the haze particles, which may play an important role in shaping their distributions., Comment: 30 pages, 6 figures. Accepted for publication in Icarus

This retrospective study investigated the early results of a single-stage posterolateral transpedicular corpectomy and fusion in the thoracolumbar spine. A modified technique with nerve preservation and bilateral expandable cage implantation is described. Four patients with vertebral metastasis and one patient with vertebral osteomyelitis were included in this series. Two patients underwent two level corpectomies, whereas three patients underwent single level corpectomy. The mean follow-up was 3.3 months. No perioperative complication was encountered. Improvement in neurological status was observed in patients with preoperative neurological deficits. Vertebral height and sagittal and coronal deformity were corrected using the current technique. Bilateral cage implantation offers an additional advantage of asymmetrical reconstruction of the ventral column in cases of hemicorpectomy. Single-stage posterolateral transpedicular corpectomy and fusion is a useful approach to treat ventral thoracolumbar pathologies.

This study aims to assess the results of a single-stage posterolateral transpedicular corpectomy and fusion in malignant spinal cord compression of the thoracolumbar spine.Sixteen cases of thoracolumbar metastases were treated with single-stage posterolateral transpedicular corpectomy and fusion. A modified technique of nerve preserving bilateral cage placement was described. Pain, American Spinal Injury Association (ASIA) scores, spinal deformity, primary pathologies, and survival were recorded.The most common primary pathology was lung, followed by renal and colorectal cancer. Significant pain reduction was achieved in all patients, regardless of previous nonsurgical treatment. No patient suffered neurological deterioration after surgery. For the 10 patients who presented with neurological deficits, 90% improved after surgery. Significant improvement in Cobb angle and vertebral height were observed postoperatively. A mean survival of 5·6 months was recorded at the completion of this manuscript.Single-stage posterolateral transpedicular corpectomy and fusion appeared to be a safe and an effective approach in malignant spinal cord compression. The current modified technique extends its application to lumbar spine by preserving all nerve roots. The significant improvement of pain and neurological deficits leads to better quality of life. The benefits of surgery in the overall survival remain to be investigated.

Observations made during the New Horizons flyby provide a detailed snapshot of the current state of Pluto's atmosphere. While the lower atmosphere (at altitudes, in Science 351, aad8866 (2016)

Objectives: The present study aims to assess the results of extended Transforaminal Lumbar Interbody Fusion (TLIF) for a two-surgeon, single institution series. Methods: 57 cases of extended TLIF with bilateral decompression were performed. Pain, ASIA scores, patient demographics, BMI, perioperative indices and radiographic measurements were recorded and analysed. Results: 57 operations were performed between February 2011 and January 2014, there were 38 female and 19 male patients. Mean patient age was 62.86 years, mean BMI was 30.31 kg/m2. In 49 patients spondylolisthesis was the primary indication. The mean intraoperative time was 284.65 min, this decreased as the series progressed. The median length of stay was 5 days, ranging from 2 to 9 days. The surgical complication rate was 22.8%. Two patients died from cardiopulmonary complications. 78.9% of the cohort had single-level TLIF, L4/5 was the most commonly fused level. Significant pain reduction was achieved from a mean Pre-operative VAS of 8.28 +/- 1.39 to post-op VAS of 1.50+/-1.05 at 12 months. No patients deteriorated neurologically. Spondylolisthesis was significantly corrected from a pre-operative mean of 6.82 mm to 2.80 mm post-operatively. There is a learning curve associated with the procedure. Discussion: TLIF with bilateral facet joint removal and decompression appeared to be a safe and effective alternative to other fusion techniques, and is comparable to other published case series. Stabilisation and correction of spinal deformity reduces pain, aids neurologic recovery and improves quality of life.

This review will outline the history of spinal fusion. It will compare the different approaches currently in use for interbody fusion. A comparison of the techniques, including minimally invasive surgery and graft options will be included. Lumbar interbody fusion is a commonly performed surgical procedure for a variety of spinal disorders, especially degenerative disease. Currently this procedure is performed using anterior, lateral, transforaminal and posterior approaches. Minimally invasive techniques have been increasing in popularity in recent years. A posterior approach is frequently used and has good fusion rates and low complication rates but is limited by the thecal and nerve root retraction. The transforaminal interbody fusion avoids some of these complications and is therefore preferable in some situations, especially revision surgery. An anterior approach avoids the spinal cord and cauda equina all together, but has issues with visceral exposure complications. Lateral lumbar interbody fusion has a risk of lumbar plexus injury with dissection through the psoas muscle. Studies show less intraoperative blood loss for minimally invasive techniques, but there is no long-term data. Iliac crest is the gold standard for bone graft, although adjuncts such as bone morphogenetic proteins are being used more frequently, despite their controversial history. More high-level studies are needed to make generalisations regarding the outcomes of one technique compared with another.

Objective Transcranial Doppler (TCD) flow velocity (FV) assessment may provide a useful index of autoregulatory impairment after severe head injury. It may define a therapeutic end point against which cerebral perfusion pressure (CPP) can be titrated. This study examines the relationship between cerebral blood flow (CBF) and TCD FV indices in a laboratory model before and after autoregulatory impairment. Methods CPP, CBF, and middle cerebral artery TCD FV were measured continuously in nine anesthetized and ventilated sheep. CPP was decreased by hemorrhagic hypotension. The process was repeated after impairment of autoregulation by cisternal infusion, which maintained CPP at 0 mm Hg for 15 minutes. Points of significant change (i.e., breakpoints) from baseline values for each of the measured flow parameters were identified by using a ratio of variance technique. Results Before any significant change in CBF or systolic TCD, diastolic TCD FV decreased (mean breakpoint, 69 mm Hg; range, 56-78 mm Hg) as CPP was reduced. This divergence of diastolic and systolic TCD FV, which occurred before autoregulatory failure, was associated with an increasing TCD pulsatility index (mean breakpoint, 63 mm Hg; range, 53-70 mm Hg). At diastolic TCD FV congruent with 10 cm/s, systolic TCD FV (mean breakpoint, 48 mm Hg; range, 46-53 mm Hg) and CBF (mean breakpoint, 49 mm Hg; range, 47-51 mm Hg) decreased rapidly, indicating autoregulatory failure. After autoregulatory impairment, the breakpoints for all four indices shifted to higher CPP values (mean, 16 mm Hg). Conclusion TCD FV assessment identified two CPP thresholds of autoregulatory loss. Before autoregulatory failure, an earlier phase of autoregulatory disturbance may be detected by divergent systolic and diastolic TCD FVs. It is important to note that this phase may be detected before CBF decreases. These TCD FV breakpoints depend on the state of autoregulatory impairment and may provide potential targets for CPP-directed therapy.