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SUDA: A Dust Mass Spectrometer for Compositional
Surface Mapping for a Mission to Europa
S. Kempf, N. Altobelli, Christelle Briois, E. Grün, M. Horányi, F. Postberg, J.
Schmidt, R. Srama, Z. Sternovsky, Tobie G., et al.
To cite this version:
S. Kempf, N. Altobelli, Christelle Briois, E. Grün, M. Horányi, et al.. SUDA: A Dust Mass
Spec-trometer for Compositional Surface Mapping for a Mission to Europa. European Planetary Science
Congress, Sep 2014, Cascais, Portugal. EPSC2014-229 (2 p.). �insu-02922799�
SUDA: A Dust Mass Spectrometer for Compositional Surface
Mapping for a Mission to Europa
S. Kempf (1), N. Altobelli (2), C. Briois (3), E. Grün (1), M. Horanyi (1), F. Postberg (4), J. Schmidt (5), R. Srama (4), Z. Sternovsky (1), G. Tobie (6), and M. Zolotov (7)
(1) LASP, University of Colorado at Boulder, Boulder, USA (sascha.kempf@lasp.colorado.edu), (2) ESA, ESAC, Spain, (3) LPC2E, Orleans, France, (4) IRS, Stuttgart University, Stuttgart, Germany, (5) University of Oulu, Finland, (6) LPGN, Nantes, France, (7) Arizona State University, Tempe, USA
Abstract
We developed a dust mass spectrometer to measure the composition of ballistic dust particles populating the thin exospheres that were detected around each of the Galilean moons. Since these grains are direct samples from the moons’ icy surfaces, unique composition data will be obtained that will help to define and constrain the geological activities on and below the moons? sur-face. The proposed instrument will make a vital con-tribution to NASA’s planned Europa Clipper mission and provide key answers to its main scientific ques-tions about the surface composition, habitability, the icy crust, and exchange processes with the deeper in-terior of the Jovian icy moon Europa.
The SUrface Dust Aanalyser (SUDA) is a time-of-flight, reflectron-type impact mass spectrometer, opti-mised for a high mass resolution which only weakly depends on the impact location. The small size (268 ×
250×171 mm3), low mass (< 4 kg) and large sensitive
area (220 cm2) makes the instrument well suited for
the challenging demands of the Europa Clipper mis-sion. A full-size prototype SUDA instrument was built in order to demonstrate its performance through cali-bration experiments at the dust accelerator at NASA’s IMPACT institute at Boulder, CO with a variety of cos-mochemically relevant dust analogues. The effective mass resolution of m/∆m of 200-250 is achieved for mass range of interest m = 1-250.
1. Dust Exoclouds
The basic idea of compositional mapping [1, 6] is that moons without an atmosphere are ensgulfed in clouds of dust particles released from their surfaces by mete-oroid bombardment. The ejecta cloud particles can be detected and their composition analyzed from orbit or during a spacecraft flyby. The ejecta duction
pro-cess is very efficient: a typical interplanetary 10−8kg
micrometeoroid impact on a Jovian moon produces a large number of ejecta particles whith a total mass on the order of a few thousand times of that of the im-pactor [2]. These ejecta particles move on ballistic tra-jectories and most of them re-collide with the satellite due to the lower initial speed. As a consequence, an almost isotropic dust exosphere is present around the moon [3, 7].
In 1999, the Galileo dust instrument measured the density profiles of the tenuous dust exospheres around the Galilean satellites Callisto, Ganymede, and Europa [4]. The cloud density decreases asymptotically with
radial distance as r−5/2, i.e. the cloud extent is only
of a few moon radii. However, a spacecraft during a close flyby at Europa will detect a substantial number of ejecta particles. The initial speed of most ejecta par-ticles is smaller than the escape velocity, which in turn is much smaller than the speed of an orbiting space-craft. The ejecta particles thus hit the dust detector with the velocity of the spacecraft and arrive from the apex direction. The dynamic properties of the parti-cles forming the ejecta cloud are unique and can be clearly distinguished from any other kind of cosmic dust likely to be detected in the vicinity of the satel-lite.
2. Instrument description
The SUrface Dust Analyser (SUDA) is a reflectron-type, time-of-flight impact mass spectrometer, which has heritage from the Cassini CDA and the Stardust CIDA instruments. The main challenge for the design of a dust mass spectro-meter is to achieve simultane-ously a high mass resolution, a sufficiently large sensi-tive area, and a compact design. The plasma ions pro-duced by the hypervelocity impact may have a broad energy distributions of up to 100 eV, which limits the mass resolution of linear TOF dust spectrometer of reasonable size to about m/∆m = 50. The effect of EPSC Abstracts
Vol. 9, EPSC2014-229, 2014
European Planetary Science Congress 2014 c
Entrance Grid Signal
Acceleration Grid Signal
Ion Grid Signal
TOF Signal Ejecta Particle Ions Accelerating E field Reflecting E field +2500V / -3000V / Target Ion Sensor log Amplitude 2010−139/15:07:04 2 4 Time (µs)6 8 10 12 (c)MPI−K SpectrumGui * 2012 −08−30T20:42:44 <SUDA_LatexPPY_Au_2900VReflectron_1to120kms.bin> Time Dust Time of Flight
Impact Charge Ion Charge Dust Charge Impa ct Ti me +3000V -2500V Acceleration Grid Reflectron Grid
Figure 1: Function principle of the SUDA impact mass spectrometer.
the initial energy spread on the mass resolution is sig-nificantly reduced by employing a so-called reflectron acting as an electrostatic mirror [5]. The ion optics of large area reflectron mass spectrometers can be de-signed using optimization methods to ensure simulta-neously the good spatial and time focus-ing of ions. The combination of a plane target, a set of ring elec-trodes and an hemispherical reflectron grid yields a good performance instruments (Fig. 1). The
instru-ment size is 268 × 250 × 171 mm3 and the weight
of 5 kg. Dust particles enter the aperture and fly through a set of shielding grids and reflectron grid be-fore impacting on the planar, ring shaped target (Fig. 1). Even a relatively slow dust impact of typically 1.6 km/s generates a sufficient amount amount of atomic and molecular ions for the in-situ mass analysis of the grain?s material. A strong electric field generated by the 2.5 kV bias potential on the target accelerates the ions toward the ions detector, where they are detected in a time-of-flight fashion focusing by the reflectron. The acquisiton of the mass spectra is triggered by the impact generated charge pulse detected by the charge sensitive electronics connected to the target. The re-tarding field of the reflectron was optimized to achieve the best spatial and time focusing at the ion detector area in the center of the instrument.
3. Instrument Performance
SUDA was tested using the IMPACT 3 MV dust ac-celerator to simulate hyper-velocity impacts of cos-mic dust particles. We performed calibration experi-ments with powders of orthopyroxene and latex parti-cles. This choice of test particles covers a broad vari-ety of materials representive for cosmic dust grains of
25 30 35 40 45 50 25 30 35 40 45 50 log Amplitude 2010−05−19T14:50:31 50 100 150 200 Mass (u) (c)MPI −K SpectrumGui * 2012 −06 −28T07:25:25 <SUDA_LatexPPY_Au_2800VReflectron_1to120kms.bin> 22 24 26 28 30 32 34 22 24 26 28 30 32 34 log Amplitude 50 100 150 200 Mass (u) (c)MPI −K SpectrumGui * 2012 −06 −27T18:28:46 <suda_pyroxene_Ag_2500V.bin> 107 Ag 109 Ag 107 Ag Mg 109 Ag Mg C4 H9 56Fe 39K 40Ca 41K 12C CH 7Li 56Fe 56Fe H 3 H 2 H ( 107 Ag ) 2 ( 109 Ag )2 107 Ag 109 Ag 25Mg 26Mg 27Al 28Si 29Si 30Si O2 24Mg 23Na Pt-coated Pyroxene PPy-PMPV latex 197 Au 12C H H 2 H 3 CH CH 2 23Na 23Na 23Na C 2 C2 H C2 H2 C 2 H 3 C 2 H 4 C2 H5 32S/ O 2 34S C 3 C 3 H C 3 H 2 39K 40Ca 41K C 4C4H C 4 H 2 C 4 H 3 H C S? H C S? C5 H C 6 H C5 C 6 C 7 H C7 32S/ O2 C 5 H 39K C3 H C 3 C4 H C4
Figure 2: Example spectra of a pyroxene particle im-pact on a silver target and of a latex particle on a gold target recorded with SUDA.
planetary, interplanetary, and interstellar origin. The vast majority of the dust impacts were slower than 4 km/s, which is similar to the typical ejecta impact speeds onto a detector during the Europa Clipper fly-bys at Europa. Fig. 2 shows two typical examples of SUDA impact spectra.
References
[1] S. Kempf et al. Dust Spectroscopy of Jovian Satellite Surface Composition. In European Planetary Science Congress 2009, pages 472–473, 2009.
[2] D. Koschny and E. Grün. Impacts into Ice-Silicate Mix-tures: Ejecta Mass and Size Distributions. Icarus, 154, 402–411, 2001.
[3] A. V. Krivov et al. Impact-generated dust clouds around planetary satellites: spherically symmetric case. Planet. Space Sci., 51, 251–269, 2003.
[4] H. Krüger et al. Detection of an impact-generated dust cloud around ganymede. Nature, 399, 558–560, 1999. [5] B. A. Mamyrin et al. The mass-reflectron, a new
non-magnetic time-of-flight mass spectrometer with high res-olution. JETP, 37, 45, 1973.
[6] F. Postberg et al. Compositional mapping of plane-tary moons by mass spectrometry of dust ejecta. Planet. Space Sci., 2011.
[7] M. Sremˇcevi´c, A. V. Krivov, and F. Spahn. Impact-generated dust clouds around planetary satellites: asym-metry effects. Planet. Space Sci., 51, 455–471, 2003.
