Valeria Mangano

High latitude peaks in Mercury's sodium exosphere: Spectral signature using THEMIS solar telescope

We present the first combined intensity and temperature maps of sodium in Mercurys exosphere, made possible by the use of the THEMIS solar telescope on Tenerife in the Canary Islands. The intensity maps clearly show high-latitude peaks, and temperatures inferred from spectral line widths suggest that these regions are either slightly hotter than the rest of the exosphere or much smaller than observed. These brighter, warmer regions are also observed, for the first time, to appear within few Earth hours which strongly suggest that they are produced by solar wind sputtering. This highly capable instrument obtained these data during daylight, highlighting the unique potential for THEMIS to undertake continuous multi-hour and multi-day datasets in conjunction with the MESSENGER mission to Mercury.

Low energy high angular resolution neutral atom detection by means of micro‐shuttering techniques: the BepiColombo SERENA/ELENA sensor

The neutral sensor ELENA (Emitted Low‐Energy Neutral Atoms) for the ESA cornerstone BepiColombo mission to Mercury (in the SERENA instrument package) is a new kind of low energetic neutral atoms instrument, mostly devoted to sputtering emission from planetary surfaces, from E∼20 eV up to E∼5 keV, within 1‐D (2°×76°). ELENA is a Time‐of‐Flight (TOF) system, based on oscillating shutter (operated at frequencies up to a 100 kHz) and mechanical gratings: the incoming neutral particles directly impinge upon the entrance with a definite timing (START) and arrive to a STOP detector after a flight path. After a brief dissertation on the achievable scientific objectives, this paper describes the instrument, with the new design techniques approached for the neutral particles identification and the nano‐techniques used for designing and manufacturing the nano‐structure shuttering core of the ELENA sensor. The expected count‐rates, based on the Hermean environment features, are shortly presented and discussed. Such d...

Properties of the lunar exosphere during the Perseid 2009 meteor shower

Abstract Influence of the meteoroid bombardment on properties of the lunar exosphere has been confirmed. Quick increase in the zenith column density of Na atoms above the lunar north pole on August 13, 2009 at 0–1 UT is detected and explained by numerous collisions of relatively small Perseid meteoroids (

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

We report the analysis of short-term ground-based observations of the exospheric Na emission (D1 and D2 lines) from Mercury, which was characterized by two high-latitude peaks confined near the magnetospheric cusp footprints. During a series of scheduled observations from the THEMIS telescope, achieved by scanning the whole planet, we implemented a series of extra measurements by recording the Na emission from a narrow North-South strip only, centered above the two emission peaks. Our aim was to inspect the existence of short-term variations, which were never analyzed before from ground-based observations, and their possible correlation with IMF variations. Though Mercury possesses a miniature magnetosphere, characterized by fast reconnection events that develops on a timescale of few minutes, ground-based observations show that the exospheric Na emission pattern can be globally stable for a prolonged period (some days), but also exhibits fluctuations in the time range of tens of minutes.

Solar control of sodium escape from Io

We report ground-based spectroscopic observations of the Io sodium cloud before and after eclipse by Jupiter, in a search for possible effects of sunlight on the total atomic sodium content in Ios exosphere. These observations test the importance of the Sun in maintaining the supply of atoms from the thicker atmosphere, which lies close to the surface, to the thinner, more extended, sodium cloud. We performed ground-based spectroscopy of the sodium doublet at 589 nm with a high-resolution echelle spectrograph on the Italian National Telescope Galileo on La Palma Island. We find that the total atomic sodium content immediately after eclipse falls by a factor of ~4 during eclipse and recovers to preeclipse values on a timescale of ~5 h. We evaluate potential causes of the precipitous drop including condensation of the atmosphere, collapse of the ionosphere, and changes in atmospheric chemistry. We conclude that most plausible cause of the drop in atomic sodium production is the interruption of photodissociation of sodium-bearing molecules during eclipse. We discuss further implications of this change in atmospheric chemistry.

Investigation of the possible effects of comet Encke's meteoroid stream on the Ca exosphere of Mercury

The MESSENGER observations of the seasonal variability of Mercurys Ca-exosphere are consistent with the general idea that the Ca-atoms originate from the bombardment of the surface by particles from comet 2P/Encke. The generating mechanism is believed to be a combination of different processes including the release of atomic and molecular surface particles and the photo-dissociation of exospheric molecules. Considering different generation and loss mechanisms, we perform simulations with a 3D Monte Carlo model based on the exosphere generation model by Mura et al. [2009]. We present for the first time the 3D spatial distribution of the CaO and Ca exospheres generated through the process of micrometeoroid impact vaporization and we show that the morphology of the latter is consistent with the available MESSENGER/MASCS observations. The results presented in this paper can be useful in the exosphere observations planning for BepiColombo, the upcoming ESA-JAXA mission to Mercury.

Mercury sodium exospheric emission as a proxy for solar perturbations transit

The first evidence at Mercury of direct relation between ICME transit and Na exosphere dynamics is presented, suggesting that Na emission, observed from ground, could be a proxy of planetary space weather at Mercury. The link existing between the dayside exosphere Na patterns and the solar wind-magnetosphere-surface interactions is investigated. This goal is pursued by analyzing the Na intensity hourly images, as observed by the ground-based THEMIS solar telescope during 10 selected periods between 2012 and 2013 (with seeing, σ < = 2″), when also MESSENGER data were available. Frequently, two-peak patterns of variable intensity are observed, located at high latitudes in both hemispheres. Occasionally, Na signal is instead diffused above the sub-solar region. We compare these different patterns with the in-situ time profiles of proton fluxes and magnetic field data from MESSENGER. Among these 10 cases, only in one occasion the Na signal is diffused above the subsolar region, when the MESSENGER data detect the transit of two ICMEs. The selected cases suggest that the Na emission patterns are well related to the solar wind conditions at Mercury. Hence, the exospheric Na emission patterns, observed from ground, could be considered as a ‘natural monitor’ of solar disturbances when transiting near Mercury.