Lorenz Roth^1,2,*,†, Joachim Saur^2,†, Kurt D. Retherford¹, Darrell F. Strobel^3,4, Paul D. Feldman⁴, Melissa A. McGrath⁵, Francis Nimmo⁶

¹Southwest Research Institute, San Antonio, TX, USA.
²Institute of Geophysics and Meteorology, University of Cologne, Germany.
³Department of Earth and Planetary Science, The Johns Hopkins University, Baltimore, MD, USA.
⁴Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD, USA.
⁵NASA Marshall Space Flight Center, Huntsville, AL, USA.
^† These authors contributed equally to this work.

In November and December 2012, the Hubble Space Telescope (HST) imaged Europa’s ultraviolet emissions in the search for vapor plume activity. We report statistically significant coincident surpluses of hydrogen Lyman-α and oxygen OI 130.4-nanometer emissions above the southern hemisphere in December 2012. These emissions were persistently found in the same area over the 7 hours of the observation, suggesting atmospheric inhomogeneity; they are consistent with two 200-km-high plumes of water vapor with line-of-sight column densities of about 1020 per square meter. Nondetection in November 2012 and in previous HST images from 1999 suggests varying plume activity that might depend on changing surface stresses based on Europa’s orbital phases. The plume was present when Europa was near apocenter and was not detected close to its pericenter, in agreement with tidal modeling predictions.

Reference
Roth L, Joachim Saur J, Retherford KD, Strobel DF, Feldman PD, McGrath MA and Nimmo F (2014) Transient Water Vapor at Europa’s South Pole. Science 343:171-174.
[doi:10.1126/science.1247051]
Reprinted with permission from AAAS

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John R. Spencer

Southwest Research Institute, 1050 Walnut Street, Boulder, CO 80302, USA.

Second-closest to Jupiter (after Io) of the four large Galilean satellites, icy Europa is one of the strangest objects in the solar system (1). On page 171 of this issue, Roth et al. (2) present strong evidence for ongoing eruptions of plumes of water vapor from Europa’s surface. This is a potentially major discovery, making Europa only the fourth object in the solar system known to exhibit ongoing internally powered geological activity, after Earth, Europa’s volcanic neighbor moon Io, and Saturn’s icy moon Enceladus.

Reference
Spencer JR (2014) Glimpsing Eruptions on Europa. Science 343:148-149.
[doi:10.1126/science.1248879]
Reprinted with permission from AAAS

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E. Stokan and M.D. Campbell-Brown

Department of Physics and Astronomy, University of Western Ontario, London, Canada, N6A 3K7

Nine fragmenting, faint meteors (peak magnitude ∼+1, mass <10^-4 kg) were observed with the Canadian Automated Meteor Observatory (CAMO). Fragments for eight of the nine meteors exhibited significant transverse motion, perpendicular to the meteor velocity. Transverse speeds of the order 100 m s^-1 were observed, while models of aerodynamic loading predict speeds of the order 0.5 m s^-1. Acceleration of the fragments in the transverse direction was negligible. Alternate methods of fragmentation, namely rotation and electrostatic charge accumulation, were examined through basic models to explain the observed transverse speeds. Meteoroid strengths of the order 10⁶ Pa were derived, matching observed strengths of larger, brighter meteors.

Reference
Stokan E and Campbell-Brown MD (in press) Transverse motion of fragmenting faint meteors observed with the Canadian Automated Meteor Observatory. Icarus
[doi:10.1016/j.icarus.2014.01.002]
Copyright Elsevier

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Paul D. Spudis^1,*, Dayl J. P. Martin^1,2 and Georgiana Kramer¹

¹Lunar and Planetary Institute, Houston, Texas, USA
²School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Manchester, UK

The Orientale Basin is one of the largest (930 km diameter) and youngest (~3.8 Ga) impact craters on the Moon. As the basin is only partly flooded by mare lava, its floor materials expose a major portion of the basin impact melt sheet, which some previous work has suggested might have undergone igneous differentiation. To test this idea, we remapped the geology of the Orientale Basin using images and topography from the Lunar Reconnaissance Orbiter, mineralogical information from the Chandrayaan-1 Moon Mineralogy Mapper, and elemental concentration maps from Clementine multispectral imaging and Lunar Prospector gamma ray data. The Maunder Formation (impact melt sheet of the basin) is uniform in chemical composition (equivalent to “anorthositic norite”) in at least the upper 2 km of the deposit. The deepest sampling of the basin melt sheet (maximum depths of ~3–5 km by the crater Maunder, 55 km in diameter) shows a variety of lithologies, but these rock types (anorthosite, anorthositic norite melt rocks, mare basalt, and gabbro) are not those predicted by the differentiation model. We conclude that no differentiation of the Orientale Basin melt sheet has occurred and that such a process is not evident from new remote sensing data for the Moon or in the Apollo lunar samples.

Reference
Spudis PD, Martin DJP and Kramer G (in press) Geology and composition of the Orientale Basin impact melt sheet. Journal of Geophysical Research: Planets
[doi:10.1002/2013JE004521]
Published by arrangement with John Wiley & Sons

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