SH13B-01 INVITED 

Prospects of the Solar System Environment Observation via ENA Measurements: towards Mercury and the Sun with BepiColombo and Solar Orbiter

* ORSINI, S (stefano.orsini@ifsi-roma.inaf.it), INAF/IFSI, via del Fosso del Cavaliere, 100, ROMA, 00133, Italy MILILLO, A \ (anna.milillo@ifsi-roma.inaf.it), INAF/IFSI, via del Fosso del Cavaliere, 100, ROMA, 00133, Italy DI LELLIS, A M (amdlspace@gmail.com), AMDL, viale Somalia 133, ROMA, 00199, Italy MURA, A (alessandro.mura@ifsi-roma.inaf.it), INAF/IFSI, via del Fosso del Cavaliere, 100, ROMA, 00133, Italy MASSETTI, S (stefano.massetti@ifsi-roma.inaf.it), INAF/IFSI, via del Fosso del Cavaliere, 100, ROMA, 00133, Italy DE ANGELIS, E (elisabetta.deangelis@ifsi-roma.inaf.it), INAF/IFSI, via del Fosso del Cavaliere, 100, ROMA, 00133, Italy

Nowadays, more and more interest is growing about the capabilities of investigating crucial aspects of the particle regimes present in the solar system by means of detection of escaping neutral particle fluxes. Such studies range form the properties of the expanding corona, to the escape of matter from the planetary surfaces; from the plasma distributions in the magnetospheres to the interaction between solar and interstellar matter; from the characteristics of escaping fractions of the planetary atmospheres, to the transfer of energy to the internal atmospheric regions. Generally speaking, escaping neutral fluxes carry significant information that allow to study these phenomena in terms of their dynamics. Such an increase of interest in ENA signal detection is pushing the technological community to produce more and more sophisticated devices, able to accomplish the scientific goals over a wide spectrum of energies and mass species. This presentation will resume the present situation and will try to figure the way such aspects will develop in the near future, in view of the next missions BepiColombo and Solar Orbiter, to explore Mercury and the Sun.

SH13B-02 INVITED 

Lunar atmosphere and surface analysis through in situ pickup ions

* Zurbuchen, T H (thomasz@umich.edu), University of Michigan Department of AOSS, 2455 Hayward Street, Ann Arbor, MI 48109, United States Lundgren, R (rlundgre@umich.edu), University of Michigan Department of AOSS, 2455 Hayward Street, Ann Arbor, MI 48109, United States Keller, J (john.w.keller@nasa.gov), Goddard Space Flight Center, Code 692, Greenbelt, MD 20771, United States Baragiola, R (raul@virginia.edu), University of Virginia, Thornton Hall, Charlottesville, VA 22904, United States Collier, M (michael.r.collier@nasa.gov), Goddard Space Flight Center, Code 692, Greenbelt, MD 20771, United States Delory, G (gdelory@ssl.berkeley.edu), University of California Berkeley, Space Science Laboratory, Berkeley, CA 94720, United States Gloeckler, G (gglo@umich.edu), University of Michigan Department of AOSS, 2455 Hayward Street, Ann Arbor, MI 48109, United States Hartle, R (richard.E.Hartle@nasa.gov), Goddard Space Flight Center, Code 692, Greenbelt, MD 20771, United States Johnson, R (rej@virginia.edu), University of Virginia, Thornton Hall, Charlottesville, VA 22904, United States Killen, R (rkillen@astro.umd.edu), University of Maryland, Computer & Space Science Building, College Park, MD 20742, United States Lin, R (rlin@ssl.berkeley.edu), University of California Berkeley, Space Science Laboratory, Berkeley, CA 94720, United States

The exploration of the lunar atmosphere and its relation to physical processes that dominate the interaction between the moon its space environment is enabled by the analysis of charged and neutrals from a near-lunar orbit. The Moon has an atmosphere, a collisionless exosphere in which material released from the surface is gravitationally bound. It is very tenuous and very fragile, very much affected and expected to be very much affected by the anticipated lunar exploration program. It is the purpose to this talk to outline the breakthrough science that can be done from a platform in a near-lunar orbit, detecting pickup ions from surface and atmospheric sources. We will discuss expected sources and sinks of these species. We will also focus on transient events from lunar quakes and from meteoritic impacts. Finally, we discuss a possible implementation of an instrument that could do these breakthrough measurements.

SH13B-03 INVITED 

ENAs from the Moon

* Futaana, Y (futaana@irf.se), Swedish Institute of Space Physics, Box 812, Kiruna, 98128, Sweden Barabash, S (stas@irf.se), Swedish Institute of Space Physics, Box 812, Kiruna, 98128, Sweden Wieser, M (wieser@irf.se), Swedish Institute of Space Physics, Box 812, Kiruna, 98128, Sweden Bhardwaj, A (anil_bhardwaj@vssc.gov.in), Space Physics Laboratory, Vikram Sarabhai Space Centre, Trivandrum 695022, Trivandrum, 695022, India Holmstrom, M (matsh@irf.se), Swedish Institute of Space Physics, Box 812, Kiruna, 98128, Sweden Wurz, P (peter.wurz@soho.unibe.ch), Physikalisches Institut, University of Bern, Sidlerstrasse 5, Bern, CH-3012, Switzerland Lundin, R (rickard@irf.se), Swedish Institute of Space Physics, Box 812, Kiruna, 98128, Sweden

Because the Moon has no magnetosphere and no atmosphere, it exhibits quite different characteristics of interaction with the solar wind compared with those of the Earth, Mars, and Venus. Energetic neutral atom (ENA) environment is obviously quite different from them, therefore, ENA measurement have new possibilities of contributions to lunar sciences. This presentation reviews ENA generation mechanisms at the Moon, and discusses feasible applications of ENA measurement to lunar sciences. Owing to the lack of the magnetosphere and atmosphere, the solar wind can directly reach the lunar surface, and surface atoms are sputtered to space. The sputtered atoms are thought to conserve the surface composition. This means that we can introduce new technology for investigating the lunar surface composition by measuring lunar ENAs from space. In addition to the sputtered ENAs, solar wind particles reflected at the surface can be measured by ENA instrument (most of the protons are converted to neutral hydrogens during the reflection). They enable us to investigate coupling among penetration, implantation and reflection of the solar wind particles at the lunar surface. One application is that we can use the reflected neutral atom in order to study the correlation between the existence of the magnetic anomalies and characteristic albedo structure.

SH13B-04 INVITED 

A Review on the First ENA Observations at Mars and Venus

* Galli, A (galli@space.unibe.ch), University of Bern, Sidlerstrasse 5, Bern, 3012, Switzerland Fok, M (mei-ching.h.fok@nasa.gov), NASA Goddard Space Flight Center, 8800 Greenbelt Road, Code 673, Greenbelt, MD 20771, United States Wurz, P (peter.wurz@space.unibe.ch), University of Bern, Sidlerstrasse 5, Bern, 3012, Switzerland Barabash, S (stas@irf.se), Swedish Institute of Space Physics, P.O. Box 812, Kiruna, 981 28, Sweden Grigoriev, A (aug@irf.se), Swedish Institute of Space Physics, P.O. Box 812, Kiruna, 981 28, Sweden Futaana, Y (futaana@irf.se), Swedish Institute of Space Physics, P.O. Box 812, Kiruna, 981 28, Sweden Holmstrom, M (matsh@irf.se), Swedish Institute of Space Physics, P.O. Box 812, Kiruna, 981 28, Sweden Gunell, H (hegunell@mail.wvu.edu), Department of Physics, West Virginia University, P.O. Box 6315, 209 Hodges Hall, Morgantown, WV 26506, United States

The ASPERA-3/4 instruments on the two ESA spacecraft Mars Express and Venus Express have provided the first measurements ever of energetic neutral atoms (ENAs) from Mars and Venus. Here we review the first years of ENA observations. We will present an overview of the observed ENA sources in the Mars and Venus environment and compare them to model results. These comparisons are a vital test for the models and for our general understanding of the interaction of the solar wind with non-magnetized planets. Finally, we will summarize the lessons learned for future ENA imaging missions.

SH13B-05 

Energetic Neutral Atom Emissions From Venus: VEX Observations and Theoretical Modeling

* Fok, M (Mei-Ching.h.fok@nasa.gov), NASA Goddard Space Flight Center, Heliophysics Science Division Code 670, Greenbelt, MD 20771, United States Galli, A (andre.galli@space.unibe.ch), University of Bern, Physikalisches Institut Sidlerstrasse, Bern, 5, CH-3012, Switzerland Tanaka, T (tatanaka@geo.kyushu-u.ac.jp), Kyushu University, Department of Earth and Planetary Science, Hakozaki, 6-10-1, Japan Moore, T E (thomas.e.moore@nasa.gov), NASA Goddard Space Flight Center, Heliophysics Science Division Code 670, Greenbelt, MD 20771, United States Wurz, P (peter.wurz@space.unibe.ch), University of Bern, Physikalisches Institut Sidlerstrasse, Bern, 5, CH-3012, Switzerland Holmstrom, M (matsh@irf.se), Swedish Institute of Space Physics, PO Box 812, Kiruna, SE-981 28, Sweden

Venus has almost no intrinsic magnetic field to shield itself from its surrounding environment. The solar wind thus directly interacts with the planetary ionosphere and atmosphere. One of the by-products of this close encounter is the production of energetic neutral atom (ENA) emissions. Theoretical studies have shown that significant amount of ENAs are emanated from the planet. The launch of the Venus Express (VEX) in 2005 provided the first light ever of the Venus ENA emissions. The observed ENA flux level and structure are in pretty good agreement with the theoretical studies. In this paper, we present VEX ENA data and the comparison with numerical simulations. We seek to understand the solar wind interaction with the planet and the impacts on its atmospheres.

SH13B-06 

Motion of the Earth's magnetopause: Estimation from low-energy neutral atom emissions

* Hosokawa, K (hosokawa@ice.uec.ac.jp), The University of Electro-Communications, Chofugaoka 1-5-1, Chofu-shi, Tokyo, 182-8585, Japan Taguchi, S (taguchi@ice.uec.ac.jp), The University of Electro-Communications, Chofugaoka 1-5-1, Chofu-shi, Tokyo, 182-8585, Japan Suzuki, S (shin.s@ice.uec.ac.jp), The University of Electro-Communications, Chofugaoka 1-5-1, Chofu-shi, Tokyo, 182-8585, Japan Nishizawa, R (nishizawa@ice.uec.ac.jp), The University of Electro-Communications, Chofugaoka 1-5-1, Chofu-shi, Tokyo, 182-8585, Japan Collier, M R (michael.r.collier@nasa.gov), NASA/Goddard Space Flight Center, Greenbelt, Maryland, 20771, United States Moore, T E (thomas.e.moore@gsfc.nasa.gov), NASA/Goddard Space Flight Center, Greenbelt, Maryland, 20771, United States Thomsen, M F (mthomsen@lanl.gov), Los Alamos National Laboratory, Los Alamos, New Mexico, 87545, United States

On April 13, 2001 the high pressure solar wind impinged on the Earth and moved the magnetopause inside of geosynchronous orbit. During this interval, the Low Energy Neutral Atom (LENA) imager onboard the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) spacecraft observed significant amount of ENA flux in the direction of the dayside low-latitude magnetosheath. This ENA flux is primarily a result of enhanced charge exchange between the increased solar wind plasma and the exospheric hydrogen neutral. We have developed a method of deriving the stand-off distance of the dayside magnetopause directly from this ENA emission, which enables subsolar distance of the magnetopause to be monitored continuously for an hour. Location of the magnetopause estimated from ENA measurements is found to be well consistent with the in-situ measurement of the magnetopause crossings by the LANL-01A spacecraft on geosynchronous orbit. We also estimated velocity of the inward/outward motion of the dayside magnetopause. Estimated velocities of the magnetopause are typically in between -50 to 50 km/s during this interval, which are very close to the values derived from the recent multi-spacecraft observations of the magnetopause. Our result also shows that the motion of the boundary can be changing very rapidly and that its speed sometimes reaches the order of 100 km/s in response to the arrival of the interplanetary shock, demonstrating that the dayside magnetopause moves at very high acceleration.

SH13B-07 

Measurements of the Kinematics of Energetic Neutral Atom Collisions with Surfaces

* Hughes, P W (phughes@glue.umd.edu), University of Maryland, IPST, College Park, MD 20742, United States DeFazio, J), University of Denver, Department of Physics, Denver, Cco 20742, United States Collier, M (michael.r.collier@nasa.gov), Goddard Space Flight Center, Heliospheric Science Division, Greenbelt, MD 20771, United States Shappirio, M (m.d.shappirio@nasa.gov), Goddard Space Flight Center, Heliospheric Science Division, Greenbelt, MD 20771, United States Ogilvie, K W (keith.w.ogilvie@gsfc.nasa.gov), Goddard Space Flight Center, Heliospheric Science Division, Greenbelt, MD 20771, United States Coplan, M A (coplan@umd.edu), University of Maryland, IPST, College Park, MD 20742, United States Chornay, D (dennis.chornay@gsfc.nasa.gov), University of Maryland, IPST, College Park, MD 20742, United States

The use of energetic neutral atoms to image plasma structures in interplanetary space has proved to be a very useful alternative to direct in situ measurements of the plasma ions*. In order for a neutral atom imager to be effective, it must have the capability of efficiently measuring both the angular and energy distributions of the detected neutral atoms. The critical element in neutral imagers is the surface that is used to convert neutral atoms to negative ions. We have examined in detail the conversion of hydrogen atoms to negatively charged hydrogen ions on tungsten and diamond-like carbon surfaces. The measurements covered a range of neutral atom kinetic energies from 20 eV to 925 eV and angles of incidence from 70° to 84°. The angular and energy distributions of the negative ions generated at the surfaces were measured both at room temperature and elevated temperatures. Total conversion efficiencies were calculated from the data. It was found that in general the angle of incidence and kinetic energy of the incident neutral atoms were accurately represented in the angular and energy distributions of the negative ions. Furthermore, conversion efficiency increased as the angle on incidence of the neutral atoms increased for a fixed incident kinetic energy. The conversion efficiency of heated surfaces was always less than that of room temperature surfaces leading to the conclusion that surface adsorbates have a large role in neutral to negative ion conversion. The application of the measurements to the design of neutral atoms imagers will be discussed. *T.E. Moore et al., Geophys. Res. Lett., 28:1143, 2001

SH13B-08 

STROFIO: Exospheric Sampling of Mercury's Surface Composition

* Livi, S A (Stefano.Livi@swri.edu), Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78228, United States Ho, G (George.Ho@jhuapl.edu), Johns Hopkins University - Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, United States Haggerty, D (Dennis.Haggerty@jhuapl.edu), Johns Hopkins University - Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, United States

ESA's BepiColombo mission to the planetary Mercury includes a comprehensive set of advanced instruments. Strofio, one of the instruments on the SERENA neutral and ionizing particle suite on the Mercury Planet Orbit (MPO), is a high mass resolution, time-of-flight system for low energy neutral particles. Key questions addressed by Strofio are: * What are the composition, isotopic abundance, spatial distribution, and temporal variability of the neutral particles in Mercury's exosphere? * How do the surface, exosphere, and magnetosphere interact? * What is the chemical composition of Mercury's surface? Strofio takes advantage of the direct coupling between the neutral atoms in the exosphere and their source regions in the outer layers of the regolith to answer fundamental questions about Mercury, its highly variable exosphere and its small but dynamic magnetosphere. In each case Strofio is either the only proposed BepiColombo investigation that can make these discoveries or it is the investigation that can return the highest quality, most definitive result. The MPO spacecraft's low-altitude (400 × 1500 km) polar orbit provides Strofio a unique opportunity to measure the in situ composition of the very tenuous and highly variable Mercurian exosphere. In Mercury's surface- bounded exosphere, the neutral particles move on Keplerean trajectories and mostly return to the surface. Strofio will obtain the first direct measurements of the absolute abundances, both chemical and isotopic, of all exospheric neutral particles. The temporal and spatial variability of the exosphere will be integrated within models of the coupled system (surface, exosphere, magnetosphere). These data-driven models will enable us to understand the different processes responsible for ejecting the atoms from the surface, and ultimately will allow us to infer Mercury's surface composition.

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