GGD 37: An Extreme Protostellar Outflow

We present the first Spitzer-IRS spectral maps of the Herbig-Haro flow GGD 37 detected in lines of [Ne III], [O IV], [Ar III], and [Ne v]. The detection of extended [O IV] (55 eV) and some extended emission in [Ne v] (97 eV) indicates a shock temperature in excess of 100,000 K, in agreement with X-ray observations, and a shock speed in excess of 200 km s(-1). The presence of an extended photoionization or collisional ionization region indicates that GGD 37 is a highly unusual protostellar outflow.Jet Propulsion Laboratory, under NASA 1407NASA 1257184Jet Propulsion Laboratory (JPL) 960803University of Rochester 31419-5714Astronom

Upstream Ultra‐Low Frequency Waves Observed by MESSENGER’s Magnetometer: Implications for Particle Acceleration at Mercury’s Bow Shock

We perform the first statistical analysis of the main properties of waves observed in the 0.05–0.41 Hz frequency range in the Hermean foreshock by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) Magnetometer. Although we find similar polarization properties to the “30 s” waves observed at the Earth’s foreshock, the normalized wave amplitude (δB/|B0|∼0.2) and occurrence rate (∼0.5%) are much smaller. This could be associated with relatively lower backstreaming proton fluxes, the smaller foreshock size and/or less stable solar wind (SW) conditions around Mercury. Furthermore, we estimate that the speed of resonant backstreaming protons in the SW reference frame (likely source for these waves) ranges between 0.95 and 2.6 times the SW speed. The closeness between this range and what is observed at other planetary foreshocks suggests that similar acceleration processes are responsible for this energetic population and might be present in the shocks of exoplanets.Key PointsWe perform the first statistical analysis (4,536 events) of the main properties of the lowest‐frequency waves in the Hermean foreshockSmall normalized wave amplitude (0.2) and occurrence (0.5%) are likely due to low backstreaming proton flux and variable external conditionsThe normalized backstreaming protons speed (∼0.95–2.6) suggests similar acceleration processes occur at several planetary shocksPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/155492/1/grl60476.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/155492/2/grl60476_am.pd

Simvastatin reduces MMP1 expression in human smooth muscle cells cultured on polymerized collagen by inhibiting Rac1 activation

OBJECTIVE: Activation of collagen receptors expressed by smooth muscle cells induces matrix metalloproteinase (MMP) expression. The 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) have been shown to interfere with integrin signaling, but their effects on collagen receptor-mediated MMP expression have not been investigated. METHODS AND RESULTS: In the present study, we show that simvastatin (3 micromol/L) reduces MMP1 expression and secretion in human smooth muscle cells cultured on polymerized type I collagen by 39.9+/-11.2% and 36.0+/-2.3%, respectively. Reduced MMP1 protein levels correlate with a similar decrease in MMP1 promoter activity (-33.0+/-8.9%), MMP1 mRNA levels (-37.8+/-10.5%), and attenuation of smooth muscle cell collagen degradation (-34.2+/-6.1%). Mevalonate, and the isoprenoid derivative geranylgeraniol, precursors of geranylgeranylated proteins, completely prevent the inhibitory effect of simvastatin on MMP1. Moreover, the protein geranylgeranyltransferase inhibitor GGTI-286 significantly decreases MMP1 expression. Retroviral overexpression of dominant-negative mutants of geranylgeranylated Rac1 lead to a reduction of MMP1 protein (-50.4+/-5.4%) and mRNA levels (-97.9+/-1.0%), and knockdown of Rac1 by small interfering RNA downregulates MMP1 expression. Finally, simvastatin reduces GTP-bound Rac1 expression levels in smooth muscle cells cultured on polymerized collagen. CONCLUSIONS: These results demonstrate that simvastatin, by inhibiting Rac1 activity, reduces MMP1 expression and collagen degradation in human smooth muscle cells

Ion kinetic properties in Mercury's pre-midnight plasma sheet

With data from the Fast Imaging Plasma Spectrometer sensor on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging spacecraft, we demonstrate that the average distributions for both solar wind and planetary ions in Mercury’s pre-midnight plasma sheet are well-described by hot Maxwell-Boltzmann distributions. Temperatures and densities of the H+ ranges ~1–10 cm3 and ~5–30 MK, respectively, maintain thermal pressures of ~1 nPa. The dominant planetary ion, Na+ abundances with respect to H+ and exhibit mass-proportional ion temperatures, indicative of a reconnection-dominated heating in the magnetosphere. Conversely, planetary ion species are accelerated to similar average energies greater by a factor of ~1.5 than that of H+ acceleration in an electric potential, consistent with the presence of a strong centrifugal acceleration process in Mercury’s magnetosphere

Magnetic flux pileup and plasma depletion in Mercury’s subsolar magnetosheath

Measurements from the Fast Imaging Plasma Spectrometer (FIPS) and Magnetometer (MAG) on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging spacecraft during 40 orbits about Mercury are used to characterize the plasma depletion layer just exterior to the planet’s dayside magnetopause. A plasma depletion layer forms at Mercury as a result of piled-up magnetic flux that is draped around the magnetosphere. The low average upstream Alfvénic Mach number (MA ~3–5) in the solar wind at Mercury often results in large-scale plasma depletion in the magnetosheath between the subsolar magnetopause and the bow shock. Flux pileup is observed to occur downstream under both quasi-perpendicular and quasi-parallel shock geometries for all orientations of the interplanetary magnetic field (IMF). Furthermore, little to no plasma depletion is seen during some periods with stable northward IMF. The consistently low value of plasma β, the ratio of plasma pressure to magnetic pressure, at the magnetopause associated with the low average upstream MA is believed to be the cause for the high average reconnection rate at Mercury, reported to be nearly 3 times that observed at Earth. Finally, a characteristic depletion length outward from the subsolar magnetopause of ~300 km is found for Mercury. This value scales among planetary bodies as the average standoff distance of the magnetopause

Particles and Photons as Drivers for Particle Release from the Surfaces of the Moon and Mercury

The Moon and Mercury are airless bodies, thus they are directly exposed to the ambient plasma (ions and electrons), to photons mostly from the Sun from infrared range all the way to X-rays, and to meteoroid fluxes. Direct exposure to these exogenic sources has important consequences for the formation and evolution of planetary surfaces, including altering their chemical makeup and optical properties, and generating neutral gas exosphere. The formation of a thin atmosphere, more specifically a surface bound exosphere, the relevant physical processes for the particle release, particle loss, and the drivers behind these processes are discussed in this review

Myosin X and its motorless isoform differentially modulate dendritic spine development by regulating trafficking and retention of vasodilator-stimulated phosphoprotein

Myosin X (Myo10) is an unconventional myosin with two known isoforms: full-length (FL)-Myo10 that has motor activity, and a recently identified brain-expressed isoform, headless (Hdl)-Myo10, which lacks most of the motor domain. FL-Myo10 is involved in the regulation of filopodia formation in non-neuronal cells; however, the biological function of Hdl-Myo10 remains largely unknown. Here, we show that FL- and Hdl-Myo10 have important, but distinct, roles in the development of dendritic spines and synapses in hippocampal neurons. FL-Myo10 induces formation of dendritic filopodia and modulates filopodia dynamics by trafficking the actin-binding protein vasodilator-stimulated phosphoprotein (VASP) to the tips of filopodia. By contrast, Hdl-Myo10 acts on dendritic spines to enhance spine and synaptic density as well as spine head expansion by increasing the retention of VASP in spines. Thus, this study demonstrates a novel biological function for Hdl-Myo10 and an important new role for both Myo10 isoforms in the development of dendritic spines and synapses

A Mercury Lander Mission Concept Study for the Next Decadal Survey

Mariner 10 provided our first closeup reconnaissance of Mercury during its three flybys in 1974 and 1975. MESSENGERs 20112015 orbital investigation enabled numerous discoveries, several of which led to substantial or complete changes in our fundamental understanding of the planet. Among these were the unanticipated, widespread presence of volatile elements (e.g., Na, K, S); a surface with extremely low Fe abundance whose darkening agent is likely C; a previously unknown landformhollows that may form by volatile sublimation from within rocks exposed to the harsh conditions on the surface; a history of expansive effusive and explosive volcanism; substantial radial contraction of the planet from interior cooling; offset of the dipole moment of the internal magnetic field northward from the geographic equator by ~20% of the planets radius; crustal magnetization, attributed at least in part to an ancient field; unexpected seasonal variability and relationships among exospheric species and processes; and the presence in permanently shadowed polar terrain of water ice and other volatile materials, likely to include complex organic compounds. Mercurys highly chemically reduced and unexpectedly volatile-rich composition is unique among the terrestrial planets and was not predicted by earlier hypotheses for the planets origin. As an end-member of terrestrial planet formation, Mercury holds unique clues about the original distribution of elements in the earliest stages of the Solar System and how planets (and exoplanets) form and evolve in close proximity to their host stars. The BepiColombo mission promises to expand our knowledge of this planet and to shed light on some of the mysteries revealed by the MESSENGER mission. However, several fundamental science questions raised by MESSENGERs pioneering exploration of Mercury can only be answered with in situ measurements from the planets surface

Space environment of Mercury at the time of the first MESSENGER flyby: Solar wind and interplanetary magnetic field modeling of upstream conditions

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94712/1/jgra19984.pd

Distribution and compositional variations of plasma ions in Mercury's space environment: The first three Mercury years of MESSENGER observations

We have analyzed measurements of planetary ions near Mercury made by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) Fast Imaging Plasma Spectrometer (FIPS) over the first three Mercury years of orbital observations (25 March 2011 through 31 December 2011). We determined the composition and spatial distributions of the most abundant species in the regions sampled by the MESSENGER spacecraft during that period. In particular, we here focus on altitude dependence and relative abundances of species in a variety of spatial domains. We used observed density as a proxy for ambient plasma density, because of limitations to the FIPS field of view. We find that the average observed density is 3.9 × 10 –2  cm –3 for He 2+ , 3.4 × 10 –4  cm –3 for He + , 8.0 × 10 –4  cm –3 for O + ‐group ions, and 5.1 × 10 –3  cm –3 for Na + ‐group ions. Na + ‐group ions are particularly enhanced over other planetary ions (He + and O + group) in the northern magnetospheric cusp (by a factor of ~2.0) and in the premidnight sector on the nightside (by a factor of ~1.6). Within 30° of the equator, the average densities of all planetary ions are depressed at the subsolar point relative to the dawn and dusk terminators. The effect is largest for Na + ‐group ions, which are 49% lower in density at the subsolar point than at the terminators. This depression could be an effect of the FIPS energy threshold. The three planetary ion species considered show distinct dependences on altitude and local time. The Na + group has the smallest e ‐folding height at all dayside local times, whereas He + has the largest. At the subsolar point, the e ‐folding height for Na + ‐group ions is 590 km, and that for the O + group and He + is 1100 km. On the nightside and within 750 km of the geographic equator, Na + ‐group ions are enhanced in the premidnight sector. This enhancement is consistent with nonadiabatic motion and may be observational evidence that nonadiabatic effects are important in Mercury's magnetosphere. Key Points Na+-group ions are enhanced in northern cusp and pre‐midnight sector Planetary ion species show distinct dependences on altitude and local time May be first observation of non‐adiabatic effects in Mercury's magnetospherePeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98388/1/jgra50016.pd