C. Plainaki

The Venus nighttime atmosphere as observed by the VIRTIS‐M instrument. Average fields from the complete infrared data set

We present and discuss here the average fields of the Venus atmosphere derived from the nighttime observations in the 1960–2350u2009cm−1 spectral range by the VIRTIS-M instrument on board the Venus Express satellite. These fields include: (a) the air temperatures in the 1–100u2009mbar pressure range (~85–65u2009km above the surface), (b) the altitude of the clouds top, and (c) the average CO mixing ratio. A new retrieval code based on the Bayesian formalism has been developed and validated on simulated observations, to statistically assess the retrieval capabilities of the scheme once applied to the VIRTIS data. The same code has then been used to process the entire VIRTIS-M data set. Resulting individual retrievals have been binned on the basis of local time and latitude, to create average fields. Air temperature fields confirm the general trends previously reported in Grassi et al. (2010), using a simplified retrieval scheme and a more limited data set. At the lowest altitudes probed by VIRTIS (~65u2009km), air temperatures are strongly asymmetric around midnight, with a pronounced minima at 3LT, 70°S. Moving to higher levels, the air temperatures first become more uniform in local time (~75u2009km), then display a colder region on the evening side at the upper boundary of VIRTIS sensitivity range (~80u2009km). As already shown by Ignatiev et al. (2008) for the dayside, the cloud effective altitude increases monotonically from the south pole to the equator. However, the variations observed in night data are consistent with an overall variation of just 1u2009km, much smaller than the 4u2009km reported for the dayside. The cloud altitudes appear slightly higher on the evening side. Both observations are consistent with a less vigorous meridional circulation on the nightside of the planet. Carbon monoxide is not strongly constrained by the VIRTIS-M data. However, average fields present a clear maximum of 80u2009ppm around 60°S, well above the retrieval uncertainty. Once the intrinsic low sensitivity of VIRTIS data in the region of cold collar is kept in mind, this datum is consistent with a [CO] enrichment toward the poles driven by meridional circulation.

Neutral particle release from Europa's surface

Abstract In this paper, we look at space weathering processes on the icy surface of Jupiter’s moon Europa. The heavy energetic ions of the jovian plasma (H + , O + , S + , C + ) can erode the surface of Europa via ion sputtering (IS), ejecting up to 1000 H 2 O molecules per ion. UV photons impinging the Europa’s surface can also result in neutral atom release via photon-stimulated desorption (PSD) and chemical change (photolysis). In this work, we study the efficiency of the IS and PSD processes for ejecting water molecules, simulating the resulting neutral H 2 O density. We also estimate the contribution to the total neutral atom release by the Ion Backscattering (IBS) process. Moreover, we estimate the possibility of detecting the sputtered high energy atoms, in order to distinguish the action of the IS process from other surface release mechanisms. Our main results are: (1) The most significant sputtered-particle flux and the largest contribution to the neutral H 2 O density come from the incident S + ions; (2) the H 2 O density produced via PSD is lower than that due to sputtering by ∼1.5 orders of magnitude; (3) in the energy range below 1xa0keV, the IBS can be considered negligible for the production of neutrals, whereas in the higher energy range it becomes the dominant neutral emission mechanism; (4) the total sputtering rate for Europa is 2.0xa0×xa010 27 xa0H 2 Oxa0s −1 ; and (5) the fraction of escaping H 2 O via IS is 22% of the total sputtered population, while the escape fraction for H 2 O produced by PSD is 30% of the total PSD population. Since the PSD exosphere is lower than the IS one, the major agent for Europa’s surface total net erosion is IS on both the non-illuminated and illuminated side. Lastly, the exospheric neutral density, estimated from the Galileo electron density measurements appears to be higher than that calculated for H 2 O alone; this favors the scenario of the presence of O 2 produced by radiolysis and photolysis.

THE GROUND-LEVEL ENHANCEMENT OF 2012 MAY 17: DERIVATION OF SOLAR PROTON EVENT PROPERTIES THROUGH THE APPLICATION OF THE NMBANGLE PPOLA MODEL

In this work, we apply an updated version of the Neutron Monitor (NM) Based Anisotropic GLE Pure Power Law (NMBANGLE PPOLA) model, in order to derive the characteristics of the ground-level enhancement (GLE) on 2012 May 17 (GLE71), the spectral properties of the related solar energetic particle (SEP) event, the spatial distributions of the high-energy solar cosmic ray fluxes at the top of the atmosphere, and the time evolution of the locationoftheGLEsource.Ourmodeling,baseduniquelyontheuseofground-levelNMdata,leadstothefollowing mainresults.TheSEPspectrumrelatedtoGLE71wasrathersoftduringthewholedurationoftheevent,manifesting some weak acceleration episodes only during the initial phase (at 01:55‐02:00UT) and at 02:30‐02:35UT and 02:55‐03:00UT. The spectral index of the modeled SEP spectrum supports the coronal mass ejection‐shock driven particle acceleration scenario, in agreement with past results based on the analysis of satellite measurements. During the initial phase of GLE71, the solar proton source at the top of the atmosphere was located above the northernhemisphere,implyingthattheasymptoticdirectionsofviewingofthenorthernhemisphereNMsweremore favorably located for registering the event than the southern ones. The spatial distribution of the solar proton fluxes at the top of the atmosphere during the main phase manifested a large variation along longitude and latitude. At the rigidity of 1GV, the maximum primary solar protonflux resulted on the order of 3# 10 4 part. m

The comparative exploration of the ice giant planets with twin spacecraft: Unveiling the history of our Solar System

2 s

Water Ice Radiolytic O2, H2, and H2O2 Yields for Any Projectile Species, Energy, or Temperature: A Model for Icy Astrophysical Bodies

1 sr

Space weather forecasting at the new Athens center: the recent extreme events of January 2005

1 GV

Clusters of cyclones encircling Jupiter’s poles

1 .

The influence of space environment on the evolution of Mercury

Abstract In the course of the selection of the scientific themes for the second and third L-class missions of the Cosmic Vision 2015–2025 program of the European Space Agency, the exploration of the ice giant planets Uranus and Neptune was defined “a timely milestone, fully appropriate for an L class mission”. Among the proposed scientific themes, we presented the scientific case of exploring both planets and their satellites in the framework of a single L-class mission and proposed a mission scenario that could allow to achieve this result. In this work we present an updated and more complete discussion of the scientific rationale and of the mission concept for a comparative exploration of the ice giant planets Uranus and Neptune and of their satellite systems with twin spacecraft. The first goal of comparatively studying these two similar yet extremely different systems is to shed new light on the ancient past of the Solar System and on the processes that shaped its formation and evolution. This, in turn, would reveal whether the Solar System and the very diverse extrasolar systems discovered so far all share a common origin or if different environments and mechanisms were responsible for their formation. A space mission to the ice giants would also open up the possibility to use Uranus and Neptune as templates in the study of one of the most abundant type of extrasolar planets in the galaxy. Finally, such a mission would allow a detailed study of the interplanetary and gravitational environments at a range of distances from the Sun poorly covered by direct exploration, improving the constraints on the fundamental theories of gravitation and on the behavior of the solar wind and the interplanetary magnetic field.

Space weathering on near-Earth objects investigated by neutral-particle detection

O2, H2, and H2O2 radiolysis from water ice is pervasive on icy astrophysical bodies, but the lack of a self-consistent, quantitative model of the yields of these water products versus irradiation projectile species and energy has been an obstacle to estimating the radiolytic oxidant sources to the surfaces and exospheres of these objects. A major challenge is the wide variation of O2 radiolysis yields between laboratory experiments, ranging over 4 orders of magnitude from 5xa0×xa010−7 to 5xa0×xa010−3 molecules/eV for different particles and energies. We revisit decades of laboratory data to solve this long-standing puzzle, finding an inverse projectile range dependence in the O2 yields, due to preferential O2 formation from an ~30xa0A thick oxygenated surface layer. Highly penetrating projectile ions and electrons with ranges ≳30xa0A are therefore less efficient at producing O2 than slow/heavy ions and low-energy electrons (≲ 400xa0eV) which deposit most energy near the surface. Unlike O2, the H2O2 yields from penetrating projectiles fall within a comparatively narrow range of (0.1–6)xa0×xa010−3 molecules/eV and do not depend on range, suggesting that H2O2 forms deep in the ice uniformly along the projectile track, e.g., by reactions of OH radicals. We develop an analytical model for O2, H2, and H2O2 yields from pure water ice for electrons and singly charged ions of any mass and energy and apply the model to estimate possible O2 source rates on several icy satellites. The yields are upper limits for icy bodies on which surface impurities may be present.

Short‐term observations of double‐peaked Na emission from Mercury's exosphere

From the beginning of this year a new data analysis center [Athens Neutron Monitor Data Processing (ANMODAP) Center] is operated in Athens University producing a real-time prediction of space weather phenomena. At this moment there has been a multi-sided use of twenty-three neutron monitors providing real-time data on the Internet. Moreover, interplanetary space parameters data from Geostationary Orbiting Environmental Satellite and Advanced Composition Explorer (ACE) satellite are also collected in this center. The ANMODAP Center in real-time is of high potential interest, as it is expected to give alerts for ground level enhancements (GLEs) of solar cosmic rays (CRs) and geomagnetic storms and therefore to provide crucial information for Space Weather applications. Forecasting of the last GLE and the geomagnetic variations of CRs on January 2005, is presented.