The structure of the asteroid 4 Vesta as revealed by models of planet-scale collisions

Asteroid 4Vesta seems to be a major intact protoplanet, with a surface composition similar to that of the HED (howardite-eucrite-diogenite) meteorites. The southern hemisphere is dominated by a giant impact scar, but previous impact models have failed to reproduce the observed topography. The recent discovery that Vesta's southern hemisphere is dominated by two overlapping basins provides an opportunity to model Vesta's topography more accurately. Here we report three-dimensional simulations of Vesta's global evolution under two overlapping planet-scale collisions. We closely reproduce its observed shape, and provide maps of impact excavation and ejecta deposition. Spiral patterns observed in the younger basin Rheasilvia, about one billion years old, are attributed to Coriolis forces during crater collapse. Surface materials exposed in the north come from a depth of about 20kilometres, according to our models, whereas materials exposed inside the southern double-excavation come from depths of about 60-100kilometres. If Vesta began as a layered, completely differentiated protoplanet, then our model predicts large areas of pure diogenites and olivine-rich rocks. These are not seen, possibly implying that the outer 100kilometres or so of Vesta is composed mainly of a basaltic crust (eucrites) with ultramafic intrusions (diogenites).

Observations of the northern seasonal polar cap on Mars: I. Spring sublimation activity and processes

Spring sublimation of the seasonal CO2 northern polar cap is a dynamic process in the current Mars climate. Phenomena include dark fans of dune material propelled out onto the seasonal ice layer, polygonal cracks in the seasonal ice, sand flow down slipfaces, and outbreaks of gas and sand around the dune margins. These phenomena are concentrated on the north polar erg that encircles the northern residual polar cap. The Mars Reconnaissance Orbiter has been in orbit for three Mars years, allowing us to observe three northern spring seasons. Activity is consistent with and well described by the Kieffer model of basal sublimation of the seasonal layer of ice applied originally in the southern hemisphere. Three typical weak spots have been identified on the dunes for escape of gas sublimed from the bottom of the seasonal ice layer: the crest of the dune, the interface of the dune with the interdune substrate, and through polygonal cracks in the ice. Pressurized gas flows through these vents and carries out material entrained from the dune. Furrows in the dunes channel gas to outbreak points and may be the northern equivalent of southern radially-organized channels ("araneiform" terrain), albeit not permanent. Properties of the seasonal CO2 ice layer are derived from timing of seasonal events such as when final sublimation occurs. Modification of dune morphology shows that landscape evolution is occurring on Mars today, driven by seasonal activity associated with sublimation of the seasonal CO2 polar cap.

Last interglacial temperature evolution — a model inter-comparison

There is a growing number of proxy-based reconstructions detailing the climatic changes that occurred during the last interglacial period (LIG). This period is of special interest, because large parts of the globe were characterized by a warmer-than-present-day climate, making this period an interesting test bed for climate models in light of projected global warming. However, mainly because synchronizing the different palaeoclimatic records is difficult, there is no consensus on a global picture of LIG temperature changes. Here we present the first model inter-comparison of transient simulations covering the LIG period. By comparing the different simulations, we aim at investigating the common signal in the LIG temperature evolution, investigating the main driving forces behind it and at listing the climate feedbacks which cause the most apparent inter-model differences. The model inter-comparison shows a robust Northern Hemisphere July temperature evolution characterized by a maximum between 130–125 ka BP with temperatures 0.3 to 5.3 K above present day. A Southern Hemisphere July temperature maximum, −1.3 to 2.5 K at around 128 ka BP, is only found when changes in the greenhouse gas concentrations are included. The robustness of simulated January temperatures is large in the Southern Hemisphere and the mid-latitudes of the Northern Hemisphere. For these regions maximum January temperature anomalies of respectively −1 to 1.2 K and −0.8 to 2.1 K are simulated for the period after 121 ka BP. In both hemispheres these temperature maxima are in line with the maximum in local summer insolation. In a number of specific regions, a common temperature evolution is not found amongst the models. We show that this is related to feedbacks within the climate system which largely determine the simulated LIG temperature evolution in these regions. Firstly, in the Arctic region, changes in the summer sea-ice cover control the evolution of LIG winter temperatures. Secondly, for the Atlantic region, the Southern Ocean and the North Pacific, possible changes in the characteristics of the Atlantic meridional overturning circulation are crucial. Thirdly, the presence of remnant continental ice from the preceding glacial has shown to be important when determining the timing of maximum LIG warmth in the Northern Hemisphere. Finally, the results reveal that changes in the monsoon regime exert a strong control on the evolution of LIG temperatures over parts of Africa and India. By listing these inter-model differences, we provide a starting point for future proxy-data studies and the sensitivity experiments needed to constrain the climate simulations and to further enhance our understanding of the temperature evolution of the LIG period.

Two-phase change in CO2, Antarctic temperature and global climate during Termination II

The end of the Last Glacial Maximum (Termination I), roughly 20 thousand years ago (ka), was marked by cooling in the Northern Hemisphere, a weakening of the Asian monsoon, a rise in atmospheric CO2 concentrations and warming over Antarctica. The sequence of events associated with the previous glacial–interglacial transition (Termination II), roughly 136 ka, is less well constrained. Here we present high-resolution records of atmospheric CO2 concentrations and isotopic composition of N2—an atmospheric temperature proxy—from air bubbles in the EPICA Dome C ice core that span Termination II. We find that atmospheric CO2 concentrations and Antarctic temperature started increasing in phase around 136 ka, but in a second phase of Termination II, from 130.5 to 129 ka, the rise in atmospheric CO2 concentrations lagged that of Antarctic temperature unequivocally. We suggest that during this second phase, the intensification of the low-latitude hydrological cycle resulted in the development of a CO2 sink, which counteracted the CO2 outgassing from the Southern Hemisphere oceans over this period.

Paleoclimate data-model comparison and the role of climate forcings over the past 1500 years

The past 1500 years provide a valuable opportunity to study the response of the climate system to external forcings. However, the integration of paleoclimate proxies with climate modeling is critical to improving the understanding of climate dynamics. In this paper, a climate system model and proxy records are therefore used to study the role of natural and anthropogenic forcings in driving the global climate. The inverse and forward approaches to paleoclimate data–model comparison are applied, and sources of uncertainty are identified and discussed. In the first of two case studies, the climate model simulations are compared with multiproxy temperature reconstructions. Robust solar and volcanic signals are detected in Southern Hemisphere temperatures, with a possible volcanic signal detected in the Northern Hemisphere. The anthropogenic signal dominates during the industrial period. It is also found that seasonal and geographical biases may cause multiproxy reconstructions to overestimate the magnitude of the long-term preindustrial cooling trend. In the second case study, the model simulations are compared with a coral δ18O record from the central Pacific Ocean. It is found that greenhouse gases, solar irradiance, and volcanic eruptions all influence the mean state of the central Pacific, but there is no evidence that natural or anthropogenic forcings have any systematic impact on El Niño–Southern Oscillation. The proxy climate relationship is found to change over time, challenging the assumption of stationarity that underlies the interpretation of paleoclimate proxies. These case studies demonstrate the value of paleoclimate data–model comparison but also highlight the limitations of current techniques and demonstrate the need to develop alternative approaches.

Can the carbon isotopic composition of methane be reconstructed from multi-site firn air measurements?

Methane is a strong greenhouse gas and large uncertainties exist concerning the future evolution of its atmospheric abundance. Analyzing methane atmospheric mixing and stable isotope ratios in air trapped in polar ice sheets helps in reconstructing the evolution of its sources and sinks in the past. This is important to improve predictions of atmospheric CH4 mixing ratios in the future under the influence of a changing climate. The aim of this study is to assess whether past atmospheric δ13C(CH4) variations can be reliably reconstructed from firn air measurements. Isotope reconstructions obtained with a state of the art firn model from different individual sites show unexpectedly large discrepancies and are mutually inconsistent. We show that small changes in the diffusivity profiles at individual sites lead to strong differences in the firn fractionation, which can explain a large part of these discrepancies. Using slightly modified diffusivities for some sites, and neglecting samples for which the firn fractionation signals are strongest, a combined multi-site inversion can be performed, which returns an isotope reconstruction that is consistent with firn data. However, the isotope trends are lower than what has been concluded from Southern Hemisphere (SH) archived air samples and high-accumulation ice core data. We conclude that with the current datasets and understanding of firn air transport, a high precision reconstruction of δ13C of CH4 from firn air samples is not possible, because reconstructed atmospheric trends over the last 50 yr of 0.3–1.5 ‰ are of the same magnitude as inherent uncertainties in the method, which are the firn fractionation correction (up to ~2 ‰ at individual sites), the Kr isobaric interference (up to ~0.8 ‰, system dependent), inter-laboratory calibration offsets (~0.2 ‰) and uncertainties in past CH4 levels (~0.5 ‰).

Inter-hemispheric temperature variability over the past millennium

The Earth’s climate system is driven by a complex interplay of internal chaotic dynamics and natural and anthropogenic external forcing. Recent instrumental data have shown a remarkable degree of asynchronicity between Northern Hemisphere and Southern Hemisphere temperature fluctuations, thereby questioning the relative importance of internal versus external drivers of past as well as future climate variability1, 2, 3. However, large-scale temperature reconstructions for the past millennium have focused on the Northern Hemisphere4, 5, limiting empirical assessments of inter-hemispheric variability on multi-decadal to centennial timescales. Here, we introduce a new millennial ensemble reconstruction of annually resolved temperature variations for the Southern Hemisphere based on an unprecedented network of terrestrial and oceanic palaeoclimate proxy records. In conjunction with an independent Northern Hemisphere temperature reconstruction ensemble5, this record reveals an extended cold period (1594–1677) in both hemispheres but no globally coherent warm phase during the pre-industrial (1000–1850) era. The current (post-1974) warm phase is the only period of the past millennium where both hemispheres are likely to have experienced contemporaneous warm extremes. Our analysis of inter-hemispheric temperature variability in an ensemble of climate model simulations for the past millennium suggests that models tend to overemphasize Northern Hemisphere–Southern Hemisphere synchronicity by underestimating the role of internal ocean–atmosphere dynamics, particularly in the ocean-dominated Southern Hemisphere. Our results imply that climate system predictability on decadal to century timescales may be lower than expected based on assessments of external climate forcing and Northern Hemisphere temperature variations5, 6 alone.

A 12,000 Year Record of Explosive Volcanism in the Siple Dome Ice Core, West Antarctica

Air mass trajectories in the Southern Hemisphere provide a mechanism for transport to and deposition of volcanic products on the Antarctic ice sheet from local volcanoes and from tropical and subtropical volcanic centers. This study extends the detailed record of Antarctic, South American, and equatorial volcanism over the last 12,000 years using continuous glaciochemical series developed from the Siple Dome A (SDMA) ice core, West Antarctica. The largest volcanic sulfate spike ( 280 mu g/L) occurs at 5881 B. C. E. Other large signals with unknown sources are observed around 325 B. C. E. ( 270 mu g/L) and 2818 B. C. E. ( 191 mu g/L). Ages of several large equatorial or Southern Hemisphere volcanic eruptions are synchronous with many sulfate peaks detected in the SDMA volcanic ice chemistry record. The microprobe "fingerprinting'' of glass shards in the SDMA core points to the following Antarctic volcanic centers as sources of tephra found in the SDMA core: Balenny Island, Pleiades, Mount Berlin, Mount Takahe, and Mount Melbourne as well as Mount Hudson and possibly Mount Burney volcanoes of South America. Identified volcanic sources provide an insight into the poorly resolved transport history of volcanic products from source volcanoes to the West Antarctic ice sheet.

Solar Forcing of the Polar Atmosphere

We present highly resolved, annually dated, calibrated proxies for atmospheric circulation from several Antarctic ice cores (ITASE (International Trans-Antarctic Scientific Expedition), Siple Dome, Law Dome) that reveal decadal-scale associations with a South Pole ice-core Be-10 proxy for solar variability over the last 600 years and annual-scale associations with solar variability since AD 1720. We show that increased (decreased) solar irradiance is associated with increased (decreased) zonal wind strength near the edge of the Antarctic polar vortex. The association is particularly strong in the Indian and Pacific Oceans and as such may contribute to understanding climate forcing that controls drought in Australia and other Southern Hemisphere climate events. We also include evidence suggestive of solar forcing of atmospheric circulation near the edge of the Arctic polar vortex based on ice-core records from Mount Logan, Yukon Territory, Canada, and both central and south Greenland as enticement for future investigations. Our identification of solar forcing of the polar atmosphere and its impact on lower latitudes offers a mechanism for better understanding modern climate variability and potentially the initiation of abrupt climate-change events that operate on decadal and faster scales.

Antarctic Climate Change and the Environment

The Antarctic climate system varies on timescales from orbital, through millennial to sub-annual, and is closely coupled to other parts of the global climate system. We review these variations from the perspective of the geological and glaciological records and the recent historical period from which we have instrumental data (similar to the last 50 years). We consider their consequences for the biosphere, and show how the latest numerical models project changes into the future, taking into account human actions in the form of the release of greenhouse gases and chlorofluorocarbons into the atmosphere. In doing so, we provide an essential Southern Hemisphere companion to the Arctic Climate Impact Assessment.

The 1452 or 1453 A.D. Kuwae Eruption Signal Derived from Multiple Ice Core Records: Greatest Volcanic Sulfate Event of the Past 700 Years

We combined 33 ice core records, 13 from the Northern Hemisphere and 20 from the Southern Hemisphere, to determine the timing and magnitude of the great Kuwae eruption in the mid-15th century. We extracted volcanic deposition signals by applying a high-pass loess filter to the time series and examining peaks that exceed twice the 31 year running median absolute deviation. By accounting for the dating uncertainties associated with each record, these ice core records together reveal a large volcanogenic acid deposition event during 1453 - 1457 A. D. The results suggest only one major stratospheric injection from the Kuwae eruption and confirm previous findings that the Kuwae eruption took place in late 1452 or early 1453, which may serve as a reference to evaluate and improve the dating of ice core records. The average total sulfate deposition from the Kuwae eruption was 93 kg SO4/km(2) in Antarctica and 25 kg SO4/km(2) in Greenland. The deposition in Greenland was probably underestimated since it was the average value of only two northern Greenland sites with very low accumulation rates. After taking the spatial variation into consideration, the average Kuwae deposition in Greenland was estimated to be 45 kg SO4/km(2). By applying the same technique to the other major eruptions of the past 700 years our result suggests that the Kuwae eruption was the largest stratospheric sulfate event of that period, probably surpassing the total sulfate deposition of the Tambora eruption of 1815, which produced 59 kg SO4/km(2) in Antarctica and 50 kg SO4/km(2) in Greenland.

Antarctic Temperatures Over the Past Two Centuries from Ice Cores

We present a reconstruction of Antarctic mean surface temperatures over the past two centuries based on water stable isotope records from high-resolution, precisely dated ice cores. Both instrumental and reconstructed temperatures indicate large interannual to decadal scale variability, with the dominant pattern being anti-phase anomalies between the main Antarctic continent and the Antarctic Peninsula region. Comparative analysis of the instrumental Southern Hemisphere (SH) mean temperature record and the reconstruction suggests that at longer timescales, temperatures over the Antarctic continent vary in phase with the SH mean. Our reconstruction suggests that Antarctic temperatures have increased by about 0.2 degrees C since the late nineteenth century. The variability and the long-term trends are strongly modulated by the SH Annular Mode in the atmospheric circulation.

The role of brand marketing in snowboarding: A comparative study of Switzerland and New Zealand

Introduction: Brands play an essential role in the organizational structure of snowboarding by sponsoring athletes, arranging events, contributing to product development and developing long-term partnerships with other key actors. However, the specialities of their role in scene sports, such as creating identities, networking and brand marketing strategies, have not been extensively researched. This study aims to provide an analysis of the function of brands within the snowboarding subculture by comparing how the sport is organized in Switzerland and New Zealand. Sociological theories of subcultures (Hitzler & Niederbacher, 2010) and social networks (Stegbauer, 2008) are used to defi ne the structures of the sport, whereas marketing and branding theories (Adjouri & Stastny, 2006) help to understand the role of the brands. Snowboarding will be defi ned as an alternative sports subculture based on characteristics such as aesthetics, adventure and new resources of performance (Schwier, 2006). Such a defi nition also begs for a novel form of analyzing its organization. Unlike more conventional structures, the organization of snowboarding allows a variety of actors to get involved in leading the sport. By portraying and encouraging differentiated identities and lifestyles, athletes provide a space for other actors to fi nd their place within the sport (Wheaton, 2005). According to Stegbauers network theory, individual actors are able to obtain high positions and defi ne their identity depending on their ties to actors and networks within the subculture (Stegbauer, 2008). For example, social capital, contacts within the sport and insider knowledge on subculture-related information enable actors to get closer to the core (Hitzler & Niederbacher, 2010). Actors who do not have close networks and allies within the subculture are less likely to engage successfully in the culture, whether as an individual or as a commercial actor (Thorpe, 2011). This study focuses on the organizational structure of snowboarding by comparing the development of the sport in Switzerland and New Zealand. An analysis of snowboarding in two nations with diverse cultures and economic systems allows a further defi nition of the structural organization of the sport and explains how brands play an important role in the sport. Methods: The structural organization of the sport will be analyzed through an ethnographic approach, using participant observation at various leading events in Switzerland (Freestyle.ch, European Open) and New Zealand (World Heli Challenge, New Zealand Open, New Zealand Winter Games). The data is analyzed using grounded theory (Glaser & Strauss 1967) and gives an overview of the actors that are playing an important role in the local development of snowboarding. Participant observation was also used as a tool to get inside the sport culture and opened up the possibility to make over 40 semi-structured qualitative expert interviews with international core actors from 11 countries. Obtaining access to one actor as a partner early on helped to get inside the local sport culture. The ‘snowball effect’ allowed the researcher to acquire access, build trust and conduct interviews with experts within the core scene. All the interviewed actors have a direct infl uence on the sport in one or both countries, which permit a cross-analysis. The data of the interviews was evaluated through content analysis (Mayring 2010). The two methods together provided suffi cient data to analyze the organizational structure and discuss the role of brand marketing within snowboarding. Results: An actors mapping by means of a center-periphery framework has identifi ed fi ve main core groups: athletes, media representatives, brand-marketing managers, resort managers and event organizers. In both countries the same grouping of actors were found. Despite possessing different and frequently multiple roles and responsibilities, core actors appear to have a strong common identifi cation as ‘snowboarders’, are considered to be part of the organizational elite of the sport and tend to advocate similar goals. The author has found that brands in Switzerland tend to have a larger impact on the broader snowboarding culture due to a number of factors discussed below. Due to a larger amount of snowboarders and stronger economic power in Europe, snowboarders are making attempts to differentiate themselves from other winter sports, while competing with each other to develop niche markets. In New Zealand, on the other hand, the smaller market enables more cooperation and mutual respect within snowboarders. Further they are more closely linked to other winter sports and are satisfi ed with being lumped together. In both countries, brands have taken up the role of supporting young athletes, organizing competitions and feeding media with subculture-related content. Brands build their image and identity through the collaboration with particular athletes who can represent the values of the brand. Local and global communities with similar lifestyles and interests are being built around brands that share a common vision of the sport. The dominance of brands in snowboarding has enabled them with the power to organize and rule the sport through its fan base and supporters. Brands were defi ned by interviewees as independent institutions led by insiders who know the codes and symbols of the sport and were given trust and credibility. The brands identify themselves as the engines of the sport by providing the equipment, opportunities for athletes to get exposure, allowing media to get exclusive information on activities, events and sport-related stories. Differences between the two countries are more related to the economic system. While Switzerland is well integrated in the broader European market, New Zealand’s geographical isolation and close proximity to Australia tends to limit its market. Further, due to different cultural lifestyles, access to resorts and seasonal restrictions, to name a few, the amount of people practicing winter sports in New Zealand is much smaller than in Switzerland. However, this also presents numerous advantages. For example, the short southern hemisphere winter season in New Zealand enables them to attract international sports athletes, brands and representatives in a period when Europe and North America is in summer. Further, the unique snow conditions in New Zealand and majestic landscape is popular for attracting world renowned photo- and cinematographers. Another advantage is the less populated network as it provides the opportunity for individuals to gain easier access to the core of the sport, obtain diverse positions and form a unique identity and market. In Switzerland, on the other hand, the snowboarding network is dense with few positions available for the taking. Homegrown brands with core recognition are found in both countries. It was found that the Swiss brands tend to have a larger impact on the market, whereas in New Zealand, the sport is more dependent on import products by foreign brands. Further, athletes, events and resorts in New Zealand are often dependent on large brand sponsorships from abroad such as from brand headquarters in the Unites States. Thus, due to its location in the centre of Europe, Swiss brands can take advantage of brands which are closer in proximity and culture to sponsor athletes and events. In terms of media coverage, winter sports in New Zealand tend to have a minor coverage and tradition in local mass media, which leads to less exposure, recognition and investment into the sport. This is also related to how snowboarding is more integrated into other winter sports in New Zealand. Another difference is the accessibility of the ski resort by the population. While in Switzerland the resorts are mostly being visited by day-travelers, ‘weekend warriors’ and holiday makers, the location of the resorts in New Zealand make it diffi cult to visit for one day. This is in part due to the fact that Swiss ski resorts and villages are usually the same location and are accessible through public transportation, while the ski resorts in New Zealand have been built separately from the villages. Further, the villages have not been built to accommodate to high tourist arrivals. Thus, accommodation and food facilities are limited and there is a lack of public transportation to the resorts. Discussion: The fi ndings show that networks and social relations combined with specifi c knowledge on scene-related attributes are crucial in obtaining opportunities within the sport. Partnerships as well as competition between these different actors are necessary for core acceptance, peer credibility and successful commercial interests. Brands need to maintain effective marketing strategies and identities which incorporate subcultural forms of behavior and communication. In order to sustain credibility from its fans, athletes and other snowboarding actors, brands need to maintain their insider status through social networks and commercial branding strategies. The interaction between all actors is a reciprocated process, where social capital, networks and identities are being shared. While the overall structure of snowboard subcultures in Europe and New Zealand are similar, there are some distinct characteristics which make each one unique. References Adjouri, N. & Stastny, P. (2006). Sport-Branding: Mit Sport-Sponsoring zum Markenerfolg. Wiesbaden: Gabler. Glaser, B. & Strauss, K. (1967). The discovery of grounded theory: Strategies for qualitative research. Chicago: Aldine. Hebdige, D. (2009). Subculture; The meaning of style. New York: Routledge. Hitzler, R. & Niederbacher, A. (2010). Leben in Szenen: Formen juveniler Vergemeinschaftung heute. Wiesbaden: Verlag für Sozialwissenschaften. Mayring, P. (2010). Qualitative Inhaltsanalyse: Grundlagen und Techniken. Weinheim: Beltz. Schwier, J. (2006). Repräsentationen des Trendsports. Jugendliche Bewegungskulturen, Medien und Marketing. In: Gugutzer, R. (Hrsg.). body turn. Perspektiven der Soziologie des Körpers und des Sports. Bielefeld: transcript (S. 321-340). Stegbauer, C. (2008). Netzwerkanalyse und Netzwerktheorie. Ein neues Paradigma in den Sozialwissenschaften. Wiesbaden: VS Verlag für Sozialwissenschaften. Thorpe, H. (2011). Snowboarding bodies in theory and practice. Basingstoke: Palgrave Macmillan. Wheaton, B. (2005). Understanding lifestyle sports; consumption, identity and difference. New York: Routledge.

Lutetia׳s lineaments

The European Space Agency׳s Rosetta spacecraft flew by asteroid (21) Lutetia on July 10, 2010. Observations through the OSIRIS camera have revealed many geological features. Lineaments are identified on the entire observed surface of the asteroid. Many of these features are concentric around the North Pole Crater Cluster (NPCC). As observed on (433) Eros and (4) Vesta, this analysis of Lutetia assesses whether or not some of the lineaments could be created orthogonally to observed impact craters. The results indicate that the orientation of lineaments on Lutetia׳s surface could be explained by three impact craters: the Massilia and the NPCC craters observed in the northern hemisphere, and candidate crater Suspicio inferred to be in the southern hemisphere. The latter has not been observed during the Rosetta flyby. Of note, is that the inferred location of the Suspicio impact crater derived from lineaments matches locations where hydrated minerals have been detected from Earth-based observations in the southern hemisphere of Lutetia. Although the presence of these minerals has to be confirmed, this analysis shows that the topography may also have a significant contribution in the modification of the spectral shape and its interpretation. The cross-cutting relationships of craters with lineaments, or between lineaments themselves show that Massilia is the oldest of the three impact feature, the NPCC the youngest, and that the Suspicio impact crater is of intermediate age that is likely occurred closer in time to the Massilia event.

Backscattered energetic neutral atoms from the Moon in the Earth's plasma sheet observed by Chandarayaan-1/Sub-keV Atom Reflecting Analyzer instrument

We present the observations of energetic neutral atoms (ENAs) produced at the lunar surface in the Earth's magnetotail. When the Moon was located in the terrestrial plasma sheet, Chandrayaan-1 Energetic Neutrals Analyzer (CENA) detected hydrogen ENAs from the Moon. Analysis of the data from CENA together with the Solar Wind Monitor (SWIM) onboard Chandrayaan-1 reveals the characteristic energy of the observed ENA energy spectrum (the e-folding energy of the distribution function) ∼100 eV and the ENA backscattering ratio (defined as the ratio of upward ENA flux to downward proton flux) <∼0.1. These characteristics are similar to those of the backscattered ENAs in the solar wind, suggesting that CENA detected plasma sheet particles backscattered as ENAs from the lunar surface. The observed ENA backscattering ratio in the plasma sheet exhibits no significant difference in the Southern Hemisphere, where a large and strong magnetized region exists, compared with that in the Northern Hemisphere. This is contrary to the CENA observations in the solar wind, when the backscattering ratio drops by ∼50% in the Southern Hemisphere. Our analysis and test particle simulations suggest that magnetic shielding of the lunar surface in the plasma sheet is less effective than in the solar wind due to the broad velocity distributions of the plasma sheet protons.