europhysicsnews number 3 • volume 39 • 27 features [PHYSICS IN SPACE] DUST IN SPACE >>> DOI 10.1051/EPN:2008303 J. Blum 1 , A.-C. Levasseur-Regourd 2 , O. Muñoz 3 , R. J. Slobodrian 4 and A. Vedernikov 5 1 TU Braunschweig, 2 UPMC Univ. Paris 06 / CNRS-ISPL, 3 Univ. Granada, 4 Univ. Laval, Quebec, 5 ULB Brussels pace is far from being empty. Besides stars and galaxies, microscopic dust particles, often immersed in a gaseous medium,areubiquitousandplayanimportantroleinavari- ety of cosmic and atmospheric environments. Nanometer- to micrometer-sized particles can be observed in different situa- tionssuchas: • stellar outflows, in which freshly-bred material is provided to thechemicalreservoirofagalaxy, • molecularclouds,thecradlesofstarformation, • protoplanetarydiscs,inwhichplanetsareborn, • planetary atmospheres and in Earth’s atmosphere, where they determine the chemistry and temperature distribution and, thus,climateandweatheroftheplanet,and • cometarycomaeandtails,thebestsourceforpristinesolar-sys- tem material. Incontrastwiththemuchlargerdustparticlesfoundonthe surfaces of solid planetary bodies and in Saturn’s rings, small dust grains always experience considerable attractive van-der- Waals or hydrogen-bonding forces whenever they collide with each other. The presence of a gaseous environment generally dampstherelativespeedssomuchthatatleastsomeoftheinter- particle collisions can result in the sticking of the grains. The dustagglomeratessoformedexhibitinterestingmorphological, mechanical,andopticalproperties.Systematicinvestigationsof these quantities can help to understand the cosmic material cycle,theformationofthefirstsolidbodiesinthesolarsystem, theevolutionofplanetaryatmospheres,andthecometarycom- position,activityandevolutionatsuccessiveperihelionpassages. Inaddition,futurespacemissionstotheMoon,Mars,oraster- oidscanbenefitfromknowledgeaboutthephysicalinteractions of small dust particles.Technical questions of how deep space probessinkinorhowwellroverscandriveonregolith-covered surfacescanonlybeansweredifthefundamentalpropertiesof the small solid particles and their behaviour under different gravityconditionsareknown.Inourownatmosphere,aerosols influence the global energy budget and cause the formation of rain drops, which efficiently cleanse the atmosphere of pollu- tants, and are thus of important environmental interest. More investigationsarealsorequiredtobetterunderstandtheroleof aerosolsinglobalclimatechange. Why long-duration microgravity conditions? Laboratoryandtheoreticalstudieshaveshownthatcollisionve- locitiesrequiredfortheformationofcosmicdustagglomerates are typically well below 1 ms -1 . Most of the above-mentioned astrophysicalandplanetaryenvironmentsexhibitratherlowgas densitiesandgravitationalaccelerations.Ground-basedlabora- toryexperimentsinvolvingensemblesofdustparticleswithdif- S  FIG. 1: Four examples of dust aggregates grown by Brownian-motion-induced collisions [2]. The displayed dust aggregates were recon- structed from three-dimensional micro- scopic images in a space-shuttle experiment and consist of SiO 2 spheres with 1.9 μm diameter. The centre of the image shows a trajectory of a single SiO 2 sphere with 1.5 μm diameter, recorded in a drop-tower experiment [4]. The trajecto- ry consists of 1024 position measurements and has a total duration of 2.2 seconds. The gas pressure in the experi- ment was 100 Pa. Article available at http://www.europhysicsnews.org or http://dx.doi.org/10.1051/epn:2008303