P41B-01 

Venus Express

* Svedhem, H (H.Svedhem@esa.int), ESA/ESTEC, PB 299, Noordwijk, 2200AG, Netherlands Witasse, O (Olivier .Witasse@esa.int), ESA/ESTEC, PB 299, Noordwijk, 2200AG, Netherlands

Venus Express has now orbited Venus for more than two Venus sidereal days, i.e. 486 Earth days. The spacecraft remains in an excellent condition and more than 1 Terabit of science data has been downlinked to ground. The data returned from the mission during this period has been of extraordinary quality and has already led to new insights in several fields. Venus Express is the first mission fully exploiting the infrared spectral windows in order to map the atmosphere in three dimensions. The observations show a highly dynamic atmosphere, including close-ups of the southern polar double vortex with quickly moving fine structures at several different altitudes. For most of the time the atmosphere can be divided into three distinctly different dynamic regions. - The equatorial region, dominated by a turbulent atmosphere mainly driven by convection, a mid latitude region dominated by a smooth laminar like flow, and the polar region dominated by a cold collar and a vast complex vortex system. The dynamics is mainly studied by the Virtis and VMC instruments. Several minor species at various depths of the atmosphere, including D/H ratios as function of altitude are being characterised by the spectrometer SpicaV and the Virtis high-res spectral channel. The upper atmosphere and plasma environment and interaction between these is studied by the Aspera instrument, the Magnetometer and radio science by occultation. This talk will give a brief report of the status of the mission, a summary of the major findings from the first part of the mission, including during the Messenger fly-by, and an outline of the plans for the future activities.

P41B-02 INVITED 

MESSENGER's Venus Flyby: An Overview of Early Results

* Solomon, S C (scs@dtm.ciw.edu), Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, N.W., Washington, DC 20015, United States Ho, G C (george.ho@jhuapl.edu), The Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, United States Izenberg, N R (noam.izenberg@jhuapl.edu), The Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, United States Lawrence, D J (djlawrence@lanl.gov), Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87545, United States McClintock, W E (william.mcclintock@colorado.edu), University of Colorado, Laboratory for Atmospheric and Space Physics, Boulder, CO 80303, United States Neumann, G A (neumann@tharsis.gsfc.nasa.gov), NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, United States Prockter, L M (louise.prockter@jhuapl.edu), The Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, United States Raines, J M (jraines@umich.edu), University of Michigan, Department of Atmospheric, Oceanic and Space Sciences, Ann Arbor, MI 48109, United States Rhodes, E A (ed.rhodes@jhuapl.edu), The Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, United States Robinson, M S (mrobinson@asu.edu), Arizona State University, School of Earth and Space Exploration, Tempe, AZ 85287, United States Slavin, J A (james.a.slavin@nasa.gov), NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, United States Smith, D E (dsmith@tharsis.gsfc.nasa.gov), NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, United States Starr, R D (richard.starr@gsfc.nasa.gov), Catholic University of America, 620 Michigan Avenue, N.E., Washington, DC 20064, United States Zuber, M T (zuber@mit.edu), Massachusetts Institute of Technology, Department of Earth, Atmospheric and Planetary Sciences, Cambridge, MA 02139, United States MESSENGER Science Team, t

The MESSENGER spacecraft flew by Venus on 5 June 2007 for a gravity assist to its subsequent encounters with Mercury. Closest approach was at 338 km altitude over 12°S, 165°E, near the boundary between the lowland plains of Rusalka Planitia and the rifted uplands of Aphrodite Terra. All of the MESSENGER instruments operated during the flyby. The camera system imaged the night side in near-infrared bands and obtained color and higher-resolution monochrome mosaics of both the approaching and departing hemispheres. The ultraviolet and visible spectrometer obtained profiles of atmospheric species on the day and night sides as well as observations of the exospheric tail on departure. The visible and infrared spectrograph made observations of the Venus dayside near closest approach to gather compositional information on the upper atmosphere and clouds, and the laser altimeter carried out passive radiometry at 1064 nm and attempted to range to one or more cloud decks for several minutes near closest approach. The gamma-ray and neutron spectrometers observed gamma-rays and neutrons from the Venus atmosphere, providing information for planning the upcoming Mercury flybys and for calibration from a source of known composition. That the European Space Agency's Venus Express mission was operating at the time of the flyby permitted the simultaneous observation of the planet from two independent spacecraft, a situation of particular value for characterization of the particle and field environment at Venus. MESSENGER's energetic particle and plasma spectrometer observed charged particle acceleration at the Venus bow shock and elsewhere, and the magnetometer provided measurements of the upstream interplanetary magnetic field (IMF), bow shock signatures, and pick-up ion waves as a reference for energetic particle and plasma observations by both spacecraft. The encounter also enabled two-point measurements of IMF penetration into the Venus ionosphere, primary plasma boundaries, and the near-tail region.

P41B-03 

The Venus Express VIRTIS and MESSENGER teams

* Helbert, J (joern.helbert@dlr.de), Institute for Planetary Research DLR, Rutherfordstrasse 2, Berlin, 12489, Germany Robinson, M S (mrobinson@asu.edu), School of Earth and Space Exploration, Box 871404, Tempe, AZ 85287-1404, United States Muller, N (nils.mueller@dlr.de), Institute for Planetary Research DLR, Rutherfordstrasse 2, Berlin, 12489, Germany Prockter, L M (louise.prockter@jhuapl.edu), The Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, United States Head, J W (james_head_III@brown.edu), Department of Geological Sciences, Brown University, Providence, RI 02912, United States Izenberg, N R (noam.izenberg@jhuapl.edu), Department of Geological Sciences, Brown University, Providence, RI 02912, United States Solomon, S C (scs@dtm.ciw.edu), Department of Terrestrial Magnetism Carnegie Institution of Washington, 5241 Broad Branch Road, N.W, Washington, DC 20015, United States Svedhem, H (hsvedhem@esa.int), ESA, Keplerlaan 1, Noordwijk, 2200, Netherlands Piccioni, G (giuseppe.piccioni@iasf-roma.inaf.it), INAF - IASF Roma, Via del Fosso del Cavaliere 100, Roma, 00133, Italy Drossart, P (pierre.drossart@obspm.fr), LESIA - Observatoire de Paris, 61 avenue de l'observatoire, Paris, 75014, France MESSENGER team, T a

Because Venus Express has been in orbit around Venus since April 2006, MESSENGER's flyby of Venus on 5 June 2007 permitted a coordinated campaign of two-spacecraft observations of that planet. Here we report initial results from joint observations of the surface of Aphrodite Terra performed by the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) on Venus Express and the Mercury Dual Imaging System (MDIS) on MESSENGER. VIRTIS observed the region 13 hours before and 9 hours after the time of MESSENGER's closest approach (when Venus Express was on the opposite side of the planet). This timeline of nearly 24 hours allows the disentangling of variable atmospheric conditions from surface signals. Both instruments were able to observe the surface in the 1.02 μ m atmospheric window. At this wavelength the CO₂ atmosphere allows about 95% of the thermal radiation from the surface to escape. In addition VIRTIS could make observations in the atmospheric windows at 1.10 and 1.18 μ m, which are less transparent. Radiative transfer models were used to invert VIRTIS images at 1.02, 1.10, and 1.18 μ m for the thermal emission of the surface. Local atmospheric transmittance is derived from VIRTIS images at 1.31 μ m. The combined MDIS and VIRTIS data set covers almost the entire extent of southern Aphrodite Terra. Both instruments observed as expected a correlation between topography and thermal radiation, as the surface temperature on Venus is dominantly a function of altitude. There are, however, tentative indications of possible surface emissivity differences between highland material and the adjacent lowlands. Detailed data analysis and interpretation within the framework of the geology of the region are currently underway.

P41B-04 

Ranging to the Venus Atmosphere With the Mercury Laser Altimeter

* Smith, D E (dsmith@tharsis.gsfc.nasa.gov), NASA Goddard Space Flight Center, Solar System Exploration Division, Greenbelt, MD 20771, United States Zuber, M T (zuber@mit.edu), Massachusetts Institute of Technology, Dept Earth, Atmospheric and Planetary Sciences, Cambridge, MA 02139, United States Neumann, G A (neumann@tharsis.gsfc.nasa.gov), NASA Goddard Space Flight Center, Solar System Exploration Division, Greenbelt, MD 20771, United States Sun, X (xsun@pop900.gsfc.nasa.gov), NASA Goddard Space Flight Center, Solar System Exploration Division, Greenbelt, MD 20771, United States Cavanaugh, J F (John.F.Cavanaugh@nasa.gov), NASA Goddard Space Flight Center, Solar System Exploration Division, Greenbelt, MD 20771, United States McGarry, J (Jan McGarry ), NASA Goddard Space Flight Center, Solar System Exploration Division, Greenbelt, MD 20771, United States Solomon, S C (scs@dtm.ciw.edu), Department of Terrestrial Magnetism, Carnegie Institution of Washington 5421 Broad Branch Road, Washington, DC 20015, United States

During the flyby of Venus on 05 June 2007 by the MESSENGER spacecraft the Mercury Laser Altimeter (MLA) was operated for approximately 30 minutes, including approximately 8 minutes within 800 km of the planet's surface. With almost no expectation of receiving a return from the Venus surface the altimeter was targeted at the Venus atmosphere between 40 and 80 km above the surface, the altitude range of thickest clouds. Previous observations of the Venus atmosphere from nephelometry and particle size spectrometry indicated a structure of the clouds consisting of a haze that increases in opacity with depth, without discrete cloud tops. An objective of the MLA experiment was to attempt to identify heretofore undetected layering within the upper part of the Venus cloud deck. Although the MLA is a ranging device and not an atmospheric lidar, an instrument of similar design on the Mars Global Surveyor (MGS) spacecraft had obtained clear returns from layers within the Martian atmosphere at altitudes up to several tens of kilometers above the surface. At Venus, the MLA operated successfully in science ranging mode for the first time; the instrument recorded photon counts throughout the period of operation. We analyzed in detail a period of approximately 3 minutes when the spacecraft was closest to the planet at less than 400 km and when returns from the atmosphere would be most likely. When the backscattered signal is weak or non-existent, the altimeter dark noise dominates the detector count. Returns from cloud layers, if they exist, would appear as increased detector counts at the altitude of the cloud layer on top of the detector noise. The altimeter returns indicate a significant noise component throughout the 8-minute period of operation, including the 3 minutes bounding closest approach. Analysis of the data by three different methods suggest an increase in returns in two regions between 50 and 70 km altitude range, which, on the basis of statistical analysis, could be attributable to backscattered photons from the Venus atmosphere at a weak level of statistical significance. However, the experiment showed no evidence for discrete layering within the primary cloud deck.

P41B-05 

State of the Venus Atmosphere from Venus Express at the time of MESSENGER FLy- By

* Limaye, S S (SanjayL@ssec.wisc.edu), University of Wisconsin, Space Science and Engineering Ce nter 1225 West Dayton Street, Madison, WI 53706, United States Markiewicz, W J (mailto:markiewicz@linmpi.mpg.de), Max Planck Institute for Solar System Research, Max Planck Strasse 2, Katlenburg-Lindau, 17191, Germany Titov, D (titov@mps.mpg.de), Max Planck Institute for Solar System Research, Max Planck Strasse 2, Katlenburg-Lindau, 17191, Germany Piccione, G (giuseppe.piccioni@iasf-roma.inaf.it), Institute di Astrofisia Spaziale e Fisica Cosmica, Via del FOsseo del Cavaliere, Roma, 00133, Italy Baines, K H (blueskies4321@yahoo.com), Jet Propulsion Laboratory, 4800 Oark Grove Drive, Pasadena, CA 91109, United States Robinson, M (mark.s.robinson@asu.edu), Arizona State University, School of Earth and Space Exploration Box 871404, Tempe, AZ 85287, United States

The Venus Monitoring Camera (VMC) and the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) instruments on Venus Express spacecraft have been observing Venus since orbit insertion in April 2006. The state of the atmosphere in 2006 was in the form of a hemispheric vortex centered over the south pole, and presumably, another one in the northen hemisphere. The VMC and VIRTIS data have been used to determine cloud motions as well as the structure and organization of the atmospheric circulation from the the data collected since June 2006. In June 2007, the MESSENGER spacecraft flew-past Venus and also observed Venus on approach and departure from Venus. We report on the atmosphere of Venus as it appeared during this period.

P41B-06 

MESSENGER and Venus Express Observations of the Solar Wind Interaction with Venus: A Dual Spacecraft Study

* Slavin, J A (James.A.Slavin@nasa.gov), NASA GSFC, Heliophysics Science Division, Greenbelt, 20771, United States Acuña, M H), NASA GSFC, Solar System Exploration Division, Greenbelt, MD, United States Anderson, B J), The Johns Hopkins University, Applied Physics Laboratory, Laurel, 20723, United States Barabash, S), Swedish Institute of Space Physics, Swedish Institute of Space Physics, Kiruna, SE-981 28, Sweden Benna, M), NASA GSFC, Solar System Exploration Division, Greenbelt, MD, United States Boardsen, S A), NASA GSFC, Heliophysics Science Division, Greenbelt, 20771, United States Fraenz, M), Max Planck Institute for Solar System Research, Max Planck Institute for Solar System Research, Katlenburg-Lindau, 37191, Germany Gloeckler, G), University of Michigan, Department of Atmospheric, Oceanic, and Space Sciences, Ann Arbor, 48109, United States Gold, R E), The Johns Hopkins University, Applied Physics Laboratory, Laurel, 20723, United States Ho, G C), The Johns Hopkins University, Applied Physics Laboratory, Laurel, 20723, United States Korth, H), The Johns Hopkins University, Applied Physics Laboratory, Laurel, 20723, United States Krimigis, S M), The Johns Hopkins University, Applied Physics Laboratory, Laurel, 20723, United States McNutt, R L), The Johns Hopkins University, Applied Physics Laboratory, Laurel, 20723, United States Raines, J M), University of Michigan, Department of Atmospheric, Oceanic, and Space Sciences, Ann Arbor, 48109, United States Sarantos, M), NASA GSFC, Heliophysics Science Division, Greenbelt, 20771, United States Solomon, S C), Carnegie Institution, Department of Terrestrial Magnetism, Washington, 20015, United States Zhang, T L), Space Research Institute, Austrian Academy of Sciences, Graz, 8042, Austria Zurbuchen, T H), University of Michigan, Department of Atmospheric, Oceanic, and Space Sciences, Ann Arbor, 48109, United States

At 23:08 UT on 5 June 2007 the MESSENGER spacecraft reached its closest approach altitude (338 km) during its second flyby of Venus en route to its 2011 orbit insertion at Mercury. Whereas no measurements were collected during MESSENGER's first Venus flyby in October 2006, the Magnetometer (MAG) and the Energetic Particle and Plasma Spectrometer (EPPS) operated successfully throughout this second encounter. Venus provides the solar system's best example of a solar wind - ionosphere planetary interaction. Pioneer Venus Orbiter measurements have shown that this interaction affects the upper atmosphere and ionosphere down to altitudes of ~ 150 km. Here we present an initial overview of the MESSENGER observations during the ~ 4 hrs that the spacecraft spent within 10 planetary radii of Venus and, together with Venus Express measurements, examine the influence of solar wind plasma and interplanetary magnetic field conditions on the solar wind interaction at solar minimum.

P41B-07 

Modeling of the Interaction Between the Induced Magnetosphere of Venus and the Solar Wind During the MESSENGER Flyby.

* Benna, M (Mehdi.Benna@nasa.gov), NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, United States Slavin, J A (James.A.Slavin@nasa.gov), NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, United States Acuña, M H (Mario.H.Acuna@nasa.gov), NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, United States Anderson, B J (Brian.Anderson@jhuapl.edu), The Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, United States Barabash, S (stas@irf.se), Swedish Institute of Space Physics, Box 812, Kiruna, 98128, Sweden Boardsen, S A (Scott.A.Boardsen@nasa.gov), NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, United States Gloeckler, G (gglo@umich.edu), Atmospheric, Oceanic, and Space Science Department, University of Michigan, 2455 Hayward Street, Ann Arbor, MI 48109, United States Ho, G C (george.ho@jhuapl.edu), The Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, United States Korth, H (Haje.Korth@jhuapl.edu), The Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, United States Krimigis, S M (Tom.Krimigis@jhuapl.edu), The Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, United States McNutt, R L (Ralph.McNutt@jhuapl.edu), The Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, United States Raines, J M (jraines@umich.edu), Atmospheric, Oceanic, and Space Science Department, University of Michigan, 2455 Hayward Street, Ann Arbor, MI 48109, United States Sarantos, M (Menelaos.Sarantos@nasa,gov), NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, United States Solomon, S C (scs@dtm.ciw.edu), Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, N.W., Washington, DC 20015, United States Zhang, T (Tielong.Zhang@oeaw.ac.at), Space Research Institute, Austrian Academy of Sciences, Schmiedlstraße 6, Graz, 8042, Austria Zurbuchen, T H (thomasz@umich.edu), Atmospheric, Oceanic, and Space Science Department, University of Michigan, 2455 Hayward Street, Ann Arbor, MI 48109, United States

MESSENGER's second flyby of Venus on 5 June 2007 represents one of the key events in the spacecraft's journey toward Mercury. The favorable geometry of MESSENGER's trajectory and the presence of Venus Express in orbit around the planet provided a unique opportunity to make multi-point observations of solar wind interactions with Venus. To help understand the data gathered during this important milestone, we modeled the induced magnetosphere of Venus and its interaction with the solar wind at the time of the MESSENGER encounter with the planet. This paper reports the results of this modeling effort, shows the ionospheric conditions encountered by MESSENGER and Venus Express at the time of the flyby, and provides a comparison with the Magnetometer instrument data. Our model uses the capabilities of the time-dependant multi-fluid magnetohydrodynamic (MHD) numerical code that was developed during the past few years to study the interaction of the solar wind with unmagnetized bodies. This code is based on a three-fluid approach where ions, neutrals, and electrons are considered as separate interacting fluids. The MHD equations relative to these three fluids are solved using an adaptive Cartesian grid that is refined or relaxed as needed.

P41B-08 

Coherent Electromagnetic Waves Observed Upstream of the Venus Bow Shock Recorded by the MESSENGER Magnetometer Experiment

* Korth, H (haje.korth@jhuapl.edu), The Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Rd., Laurel, MD 20723, United States Anderson, B J (brian.anderson@jhuapl.edu), The Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Rd., Laurel, MD 20723, United States Acuna, M H (mario.acuna@nasa.gov), Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, United States Slavin, J A (james.a.slavin@nasa.gov), Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, United States Boardsen, S A (scott.a.boardsen.1@gsfc.nasa.gov), Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, United States

The MESSENGER gravity assist maneuver at Venus on 5 June 2007 provided an opportunity to observe the interaction of Venus with the solar wind along a unique trajectory through the Venus environment. Closest approach (CA) occurred near 23:08 UTC on 5 June, and the Magnetometer experiment identified the inbound shock crossing at 22:57:55 UTC on 5 June and the outbound crossing at 00:43:47 UTC on 6 June. The Magnetometer experiment operated at its maximum sampling rate for a 12-hour span centered on CA, providing continuous coverage of magnetic signatures of electromagnetic waves up to 10 Hz. Prior to the inbound shock crossing, three intense foreshock magnetic field intensifications, analogous to hot flow anomalies documented at Earth's bow shock, were observed from 22:56:40 to 22:57:35 UTC on 5 June. The first upstream waves were observed as early as 22:25 UTC, more than 30 minutes upstream of the shock crossing at distance of 3 Venus radii upstream of the shock. These waves occurred in two narrow frequency bands, one near 0.05 Hz corresponding to a gyrofrequency of ions with M/Q in the range 10 to 20, and another near 1 Hz corresponding to a gyrofrequency of ions with M/Q near 1. Both waves increased in intensity with decreasing distance from the shock, but the lower-frequency waves ceased around 22:47 UTC whereas the higher-frequency waves persisted up to the inbound shock crossing. The higher-frequency waves were observed again following the outbound shock crossing. We attribute the 1-Hz waves to an ion cyclotron instability excited by solar wind ions reflected upstream by the shock. The lower-frequency waves are consistent with heavy ions originating from the Venus ionosphere and accelerated upstream by the shock.

Author(s) (2007), Title, Eos Trans. AGU, 88(52), Fall Meet. Suppl., Abstract #####-##.