Workshop on the Habitability of Icy Worlds (2014) 4052.pdf

COMPOSITIONAL MAPPING OF ’S SURFACE WITH A DUST MASS SPECTROMETER. S. Kempf1, N. Altobelli2, C. Briois3, T. Cassidy1, E. Grün1, M. Horányi1, F. Postberg4, J. Schmidt5, S. Shasharina6, R. Srama4, and Z. Sternovsky1 1LASP, CU Boulder, USA, 2ESA, ESAC, Spain, 3LPC2E, Orléans, France, 4IRS, Universität Stuttgart, Germany, 6University of Oulu, Finland, 6Tech-X Corporation, Boulder, CO, USA

Introduction: We developed a dust mass spec- components, including both major and trace com- trometer (SUrface Dust Analyser - SUDA) to measure pounds, with a single instrument. the composition of ballistic dust particles populating 860 km the thin exosphere that was detected around Europa. Probability for origin inside contour lines: Because these grains are samples from the moon’s icy surface, unique information will be obtained about the grains’ composition, constraining geological activities on and below the moon’s surface. The instrument will contribute significantly to answer main scientific ques- tions of NASA’s mission, in particular about the surface composition, habitability, the icy

crust, and exchange processes with the deeper interior 980 km of Jovian icy moon Europa. Dust Exoclouds: The basic idea of compositional 20% mapping [1] [2] is that moons without an atmosphere 50% are wrapped in clouds of dust particles ejected by me- 70% 90% teoroid impacts from the moon's surfaces, whose com- position can be analysed by and detected by an orbiter 420 km instrument. The ejecta production process is very effi- Fig. 1 The Monte Carlo simulation of ejecta dust particles -8 cient: a typical interplanetary 10 kg micrometeoroid shows that geological features (.e.g., Thrace Macula ,140 km impact on Europa produces a large number of dust in diameter, circled) can be mapped compositionally by particles with a total mass about 18 thousand times of SUDA. The indicated trajectory is Clipper’s 25km E16 flyby. the imp actor’s mass [3]. The so-called ejecta particles move on ballistic trajectories and most of them recol- Compositional Analysis: Measuring the composition lide with the moon. As a consequence, an almost iso- of cosmic dust provides unique insight into the physi- tropic dust cloud forms around the moon [4] [5]. cal and chemical conditions at its origin as demonstrat- In 1999, the dust instrument measured the ed recently by Cassini dust detector [7]. Information density profiles of the tenuous dust exospheres around about the geological activities on and below a moon’s each of the Galilean satellites [6]. The cloud density surface, in particular about the material exchange be- -5/2 declines asymptotically with the distance as r . This tween the interior and the surface, is contained in the implies that a spacecraft in close orbits around Europa types and amounts of organic and inorganic compo- will be hit by a substantial number of eject arriving nets embedded in the dominant surface material. Relat- from apex direction with approximately spacecraft ing composition to subsurface habitability requires speed. The dynamic properties of the cloud particles knowledge of both the organic and inorganic inventory are clearly distinct from any other kind of cosmic dust in surface materials. SUDA is uniquely capable of likely to be detected in the vicinity of the satellite. providing both and will detect a wide variety of com- Compositional Mapping: For every dust particle pounds from the European surface over a concentration detected in the vicinity of the moon, the SUDA in- range of percent to ppm, and connect them to their strument is capable of constraining the location of origin on the surface. origin on the surface. This enables the correlation of the measured dust composition to geologic features on References: [1] S. Kempf et al. (2009) EPSC, 472– the surface. This is accomplished by measuring the 473, [2] F. Postberg et al. (2011) Planet. Space Sci., particles’ velocity along the instrument axis to infer the 371, [3] D. Koschny & E. Grün (2001) Icarus, 154, [4] most likely distance of the particle origin from the sub- A. V. Krivov et al. (2003) Planet. Space Sci. 51, [5] M. spacecraft point with a possible resolution of a few Sremcevic et al. (2003) Planet. Space Sci. 51, [6] H. tens of kilometers (Fig. 1). This allows simultaneous Krüger et al. (1999) Nature, 399. [7] F. Postberg et al. compositional mapping of many organic and inorganic (2009) Nature, 459.