Jovian dust streams: Probes of the Io plasma torus

Jupiter was discovered to be a source of high speed dust particles by the Ulysses spacecraft in 1992. These dust particles originate from the volcanic plumes on Io. They collect electrostatic charges from the plasma environment, gain energy from the co-rotating electric field of the magnetosphere, and leave Jupiter with escape speeds over $\rm 200 km s^{-1}$. The dust streams were also observed by the Galileo and Cassini spacecraft. While Ulysses and Cassini only had a single encounter with Jupiter, Galileo has continuously monitored the dust streams in the Jovian magnetosphere since 1996. The observed dust fluxes exhibit large orbit-to-orbit variability due to both systematic and stochastic changes. By combining the entire data set, the variability due to stochatic processes can be approximately removed and a strong variation with Jovian local time is found. This result is consistent with theoretical expectations and confirms that the majority of the Jovian dust stream particles originate from Io rather than other potential sources.Comment: 4 pages, 1 b/w figure, 2 color figures, accepted for Geophysical Research Letter

Modeling Meteoroid Impacts on the Juno Spacecraft

Events which meet certain criteria from star-tracker images on board the Juno spacecraft have been proposed to be due to interplanetary dust particle impacts on its solar arrays. These events have been suggested to be caused by particles with diameters larger than 10 &mu;m. Here, we compare the reported event rates to expected dust-impact rates using dynamical meteoroid models for the four most abundant meteoroid/dust populations in the inner solar system. We find that the dust-impact rates predicted by dynamical meteoroid models are not compatible with either the Juno observations in terms of the number of star-tracker events per day, or with the variations of dust flux on Juno's solar panels with time and position in the solar system. For example, the rate of star-tracker events on Juno's antisunward surfaces is the largest during a period in which Juno is expected to experience the peak impact fluxes on the opposite, sunward hemisphere. We also investigate the hypothesis of dust leaving the Martian Hill sphere originating either from the surface of Mars itself or from one of its moons. We do not find such a hypothetical source to be able to reproduce the star-tracker event-rate variations observed by Juno. We conclude that the star-tracker events observed by Juno are unlikely to be the result of instantaneous impacts from the zodiacal cloud. &nbsp;</p

A szél hatása a késő-neogén–negyedidőszaki üledékképződésre és a domborzat alakulására a Magyar-középhegységben és előterében = The effect of the wind on the late Neogene and Quaternary sedimentation and morphological evolution of the Hungarian Central Range and of its foreland

Legfontosabb kutatási eredményeink: az eolikus üledékek és felszínek elterjedésének és korának meghatározása, megayardangok és plató helyzetű eolikus képződmények leírása, valamint a defláció meghatározó szerepének kimutatása a Dunántúl mai domborzatának, így a zalai és somogyi ún. meridionális völgyrendszer kialakításában is. A szélmarta kőzetfelszínek kozmogén 10Be izotópos korát a mélységprofilok menti mintavételezési módszer alkalmazásával sikerült meghatároznunk. Ezt a módszert korábban szélcsiszolta kőzetfelszíneken még nem alkalmazták; elsőként sikerült 1,5 millió éves szélcsiszolta sziklafelszínt datálnunk Európában. A Tapolcai- és Káli-medencék negyedidőszaki deflációs alacsonyodási rátája 40-75 m/My volt, ugyanakkor a kipreparálódó kvarcittömbök csupán 2-4 m-t pusztulnak évmilliónként. A különböző korú szélmarta felszíneken mért szélkarc irányok megfeleltek a mai ÉNy-ias széliránynak. Ezzel igazoltuk az állandónak tekinthető uralkodó szélirányt a negyedidőszak során. Az OSL kormeghatározással 8-80 ezer éves üledékeket sikerült datálnunk a Vértes környezetében. Az üledékanyag szemcséit a betemetődés előtt nem érte elegendő fény ahhoz, hogy a lumineszcens szignál teljesen lenullázódjon. Ezt valószínűleg a rövid szállítási távolság okozhatta. Ezzel magyarázható, hogy a vizsgált üledékek esetében a geomorfológia és a korábbi koradatok tükrében többnyire a centrális OSL kor adja meg a betemetődés korát. | Our most important results are: determination of the distribution and age of aeolian landforms and sediments and description of megayardangs and aeolian formations in plateau position. We demonstrated that deflation played a definitive role in the formation of the topography of Transdanubia and in the development of the radial valley system of Zala and Somogy countries. Age and denudation rate of the wind-abraded rock surfaces was determined using in situ produced 10Be depth profiles. This was the first application of this method on wind-polished rock surfaces, and the first time when a 1.5 million years old wind-abraded surface was dated in Europe. Quaternary deflational surface lowering of the Tapolca and Kál Basins was 40-75 m/My, while denudation rate of the cemented quartzite rock surfaces was only 2-4 m/My. We proved long term stability of north-westerly winds by the measurement of the direction of wind striations rock surfaces of different age. OSL ages of aeolian sediments in the Vértes foreland were 8-80 ky old. The sediments were not exposed to sunlight for enough time to anneal completely the luminescence signal, most probably because of the short distance of transportation. This is the reason why the central OSL ages provide the age of sedimentation, considering the geomorphology and previous age data as well

Detecting meteoroid streams with an in-situ dust detector above an airless body

AbstractThe Lunar Dust Experiment (LDEX), aboard NASA’s Lunar Atmosphere and Dust Environment Explorer (LADEE) successfully mapped the dust density distribution over the lunar surface up to an altitude of ∼ 250 km. LDEX detected dust grains launched off the surface in ejecta plumes generated by impacts of cometary and asteroidal micrometeoroids striking the Moon. While on average LDEX detected particles at a rate of 1 min−1, periodically it measured bursts of particles at a rate exceeding the average value by up to two orders of magnitude. The timing and location of the most intense period of bursts is used here to independently determine the radiant for the Geminids meteoroid stream. The method is proposed to be of general interest to characterize meteoroid streams bombarding any of the airless bodies in the solar system using in-situ dust detectors

Analyzing LDEX's Current Measurements in Lunar Orbit

The Lunar Dust Experiment (LDEX) on board the Lunar Atmosphere and Dust Environment Explorer mission orbited the Moon from 2014 September to 2015 April and observed a dynamic, permanently present dust cloud produced by continual meteoroid bombardment. In addition to measuring individual ejecta with radii >0.3 μ m, LDEX also recorded an integrated current of the collective signal generated by the impacts of smaller ejecta particles. From this signal, we explore the potential for electrostatic dust lofting via twilight craters through correlation with changes in lunar topography. As the integrated current can contain numerous background contributions, we start by isolating regions of transient enhancements of this signal. A consistent lunar dayside enhancement is identified, with solar wind ions reflected as energetic neutral atoms shown to be a feasible source. We do not detect any enhanced integrated current correlated with the antihelion meteoroid bombardment or discernible enhancement due to electrostatic lofting via twilight craters, suggesting that electrostatic dust lofting does not contribute to the lunar dust environment at high altitudes (≫1 km)

Laboratory Investigation Of The Effect Of Surface Roughness On Photoemission From Surfaces In Space

Surfaces in space collect charges due to exposure of solar ultraviolet (UV) radiation, electrons, and ions. Throughout the solar system, UV-generated photoelectrons dominate the charging balance and exposed surfaces tend to charge positively. The surface potential of exposed objects depends on the material properties of their surfaces. Composition and particle size primarily affect the quantum efficiency of photoelectron generation; however, surface roughness can also control the charging process. Here we examine the role of surface roughness in generating photoelectrons in dedicated laboratory experiments using solid and dusty surfaces of the same composition. Using Langmuir probe measurements, we explore the measured plasma conditions above insulating surfaces exposed to UV, and we show that the photoemission current from a dusty surface is largely reduced due to its higher surface roughness, which causes a significant fraction of the emitted photoelectrons to be re-absorbed within the surface

A fully kinetic perspective of electron acceleration around a weakly outgassing comet: Ohm's law

International audienceWhen a comet is sufficiently close to the Sun, the sublimation of ice leads to outgassing and the formation of a coma of gas and dust. Ionisation of the outgassing material then results in mass-loading of the solar wind and magnetic field draping around the cometary nucleus. Here we present three-dimensional fully kinetic simulations of the solar wind interaction with comet 67P/Churyumov- Gerasimenko at a low-activity regime, before collisions have any impact on the plasma dynamics. The interaction scales are well below the relevant ion gyroradii. Non-equilibrium electron distributions develop. To first order, the dynamical interaction is representative of a four-fluid coupled system [Deca et al., PRL 2017, Divin et al., submitted]. Our approach is self-consistent and allows to distill Ohm's law directly from the electron dynamics in the simulation, rather than imposing it beforehand. In the vicinity of the cometary nucleus, the balance changes between the different terms in the equation. Deciphering the relative importance of each term allows to identify the driving physics in the various regions of the cometary plasma environment. For example, we find that close to the outgassing nucleus the electron pressure gradient dominates; that at sub-ion scales, the total electric field is a superposition of the solar wind convective electric field, where electrons are frozen-in, and the ambipolar electric field; that the latter accelerates electrons parallel to the magnetic field and is the source of/provides feedback to the electron pressure gradient that balances the Ohm's law perpendicular to the magnetic field, and that the role of electron inertia is negligible to balance the electric field. In conclusion, Ohm's law shows us what happens to all ion and electron species, and why