9 research outputs found

    Discovery of Grooves on Gaspra

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    We report the discovery of grooves in Galileo high-resolution images of Gaspra. These features, previously seen only on Mars' satellite Phobos, are most likely related to severe impacts. Grooves on Gaspra occur as linear and pitted depressions, typically 100-200 m wide, 0.8 to 2.5 km long, and 10-20 m deep. Most occur in two major groups, one of which trends approximately parallel to the asteroid's long axis, but is offset by some 15 deg.; the other is approximately perpendicular to this trends. The first of extensive flat facets identified by Thomas et al., Icarus 107. The occurence of grooves on Gaspra is inconsistent with other indications (irregular shape, cratering record) that this asteroid has evolved through a violent collisional history. The bodywide congruence of major groove directions and other structural elements suggests that the present- day Gaspra is a globally coherent body

    Images of the Venus cloud deck from Galileo.

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    Images of Venus taken in spectral bands centered at 418 (violet) and 986 (NIR) nanometers show that the morphology and motions of large-scale features change with depth into the cloud deck. Equatorial zonal velocities of 101+-1 m.sec -1 are seen in the violet and 78+-2m.sec -1 in the NIR. Poleward meridional velocities are seen in both spectral regions but are much reduced in the NIR. Inthe south polar region the dominant markings in the two wavelength bands are strongly anticorrelated, while in the equatorial region the motion of a large-scale meridional NIR feature appears to be associated with the equatorial wave (Venus "horizontal" Y) feature seen in the violet. The images follow the changing state of the upper cloud layer downwind of the subsolar point, and several equatorial strucutres are seen to evolve rapidly. The zonal flow field shows a longitudinal periodicity that may be coupled to the initiation of limited regions of small scale markings near the subsolar region. In midlatitudes the shapes of small features are seen to evolve as they move along the region that forms the arms of the "Y", indicating that advection, and notsuperimposed wave motion, is the probable cause of the striated pattern that is seen there. Limb hazes between 83 and 96 km altitude show similar behavior at both wavelengths indicating that te particulates above the main cloud deck are at least a few tenth of a micron in size. The vertical structure is similar to that previously observed by Mariner 10 but displaced to higher altitudes with less prominent layering. A search was made for optical lightning but no events were detected. The limiting optical energy/flash for lightning to show in the SSI frames is estimated at 4.10^9 J

    Electroweak measurements in electron–positron collisions at w-boson-pair energies at lep

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    Contains fulltext : 121524.pdf (preprint version ) (Open Access

    Search for Charged Higgs bosons: Combined Results Using LEP Data

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    The four LEP collaborations, ALEPH, DELPHI, L3 and OPAL, have searched for pair-produced charged Higgs bosons in the framework of Two Higgs Doublet Models (2HDMs). The data of the four experiments are statistically combined. The results are interpreted within the 2HDM for Type I and Type II benchmark scenarios. No statistically significant excess has been observed when compared to the Standard Model background prediction, and the combined LEP data exclude large regions of the model parameter space. Charged Higgs bosons with mass below 80 GeV/c^2 (Type II scenario) or 72.5 GeV/c^2 (Type I scenario, for pseudo-scalar masses above 12 GeV/c^2) are excluded at the 95% confidence level

    Search for High-energy Neutrinos from Binary Neutron Star Merger GW170817 with ANTARES, IceCube, and the Pierre Auger Observatory

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    The Advanced LIGO and Advanced Virgo observatories recently discovered gravitational waves from a binary neutron star inspiral. A short gamma-ray burst (GRB) that followed the merger of this binary was also recorded by the Fermi Gamma-ray Burst Monitor (Fermi-GBM), and the Anticoincidence Shield for the Spectrometer for the International Gamma-Ray Astrophysics Laboratory (INTEGRAL), indicating particle acceleration by the source. The precise location of the event was determined by optical detections of emission following the merger. We searched for high-energy neutrinos from the merger in the GeV--EeV energy range using the ANTARES, IceCube, and Pierre Auger Observatories. No neutrinos directionally coincident with the source were detected within ±500\pm500 s around the merger time. Additionally, no MeV neutrino burst signal was detected coincident with the merger. We further carried out an extended search in the direction of the source for high-energy neutrinos within the 14-day period following the merger, but found no evidence of emission. We used these results to probe dissipation mechanisms in relativistic outflows driven by the binary neutron star merger. The non-detection is consistent with model predictions of short GRBs observed at a large off-axis angle.Comment: 22 pages, 2 figure
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