The Lunar Dust Cloud. Sascha Kempf 1,2, Mihaly Horanyi 1,2, Zoltan Sternovsky 1,2, Jürgen Schmidt 3, and Ralf Srama 4. Tuesday, June 26, 12

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1 The Lunar Dust Cloud Sascha Kempf 1,2, Mihaly Horanyi 1,2, Zoltan Sternovsky 1,2, Jürgen Schmidt 3, and Ralf Srama 4

2 LDEX

3 LDEX Prediction Impact Rate (1/s) Terminators Altitude (km) r d > 0.1 micron Sternovsky, NLSI Meeting, 2009

4 LDEX Prediction Impact Rate (1/s) Terminators Cloud Altitude (km) r d > 0.1 micron Sternovsky, NLSI Meeting, 2009

5 How is the Lunar dust produced?

6 Dust Production Meteoroid Impacts Produce Ejecta Sremcevic et al., Icarus, 2005 Lunar Mass Yield ~ 1000 Koschny & Grün, Icarus, 2001; Krivov et al., Icarus, 2003

7 Dust Production Meteoroid Impacts Produce Ejecta Gravitationally Bound Ejecta Populate Cloud Sremcevic et al., Icarus, 2005 Lunar Mass Yield ~ 1000 Koschny & Grün, Icarus, 2001; Krivov et al., Icarus, 2003

8 Dust Production Meteoroid Impacts Produce Ejecta Gravitationally Bound Ejecta Populate Cloud Some Ejecta Escape: Sremcevic et al., Icarus, 2005 Lunar Mass Yield ~ 1000 Koschny & Grün, Icarus, 2001; Krivov et al., Icarus, 2003

9 Dust Production Meteoroid Impacts Produce Ejecta Gravitationally Bound Ejecta Populate Cloud Some Ejecta Escape: Feed Rings Sremcevic et al., Icarus, 2005 Lunar Mass Yield ~ 1000 Koschny & Grün, Icarus, 2001; Krivov et al., Icarus, 2003

10 Dust Production Meteoroid Impacts Produce Ejecta Gravitationally Bound Ejecta Populate Cloud Some Ejecta Escape: Feed Rings Sremcevic et al., Icarus, 2005 Moon Mass Loss Mechanism Lunar Mass Yield ~ 1000 Koschny & Grün, Icarus, 2001; Krivov et al., Icarus, 2003

11 Dust Moon at Work Jupiter s Gossamer Rings Burns et al., Science, 1999

12 Dust Moon at Work Jupiter s Gossamer Rings Amalthea Burns et al., Science, 1999

13 Dust Moon at Work Jupiter s Gossamer Rings Amalthea Thebe Burns et al., Science, 1999

14 Ejecta Clouds Galileo Dust Detector: Galilean Satellites Wrapped in Dust Clouds (Krüger et al., Nature, 1999)

15 Ejecta Clouds Krivov et al., PSS, 2003 Galileo Dust Detector: Galilean Satellites Wrapped in Dust Clouds (Krüger et al., Nature, 1999) Almost Isotropic Clouds Composed of Surface Ejecta

16 Evidence for Enceladus Dust Exosphere Kempf et. al., Icarus, 2010

17 Evidence for Enceladus Dust Exosphere Kempf et. al., Icarus, 2010

18 Rhea Dust Exosphere Model: Isotropic Impactors Sun vrhea :45 4:50 4:55 5:00 5:05 Rhea Radii

19 Evidence Lunar Exosphere? Iglseder et al., 2006, Adv. Space Res.

20 Evidence Lunar Exosphere? Hiten was the only Lunar orbiter equipped with a dust detector (MDC) Iglseder et al., 2006, Adv. Space Res.

21 Evidence Lunar Exosphere? Hiten was the only Lunar orbiter equipped with a dust detector (MDC) Orbit was not favourable for detecting Lunar ejecta (Altitude: km km) Iglseder et al., 2006, Adv. Space Res.

22 Evidence Lunar Exosphere? Hiten was the only Lunar orbiter equipped with a dust detector (MDC) Orbit was not favourable for detecting Lunar ejecta (Altitude: km km) Iglseder et al., 2006, Adv. Space Res.

23 Evidence Lunar Exosphere? Hiten was the only Lunar orbiter equipped with a dust detector (MDC) Orbit was not favourable for detecting Lunar ejecta (Altitude: km km) Iglseder et al., 2006, Adv. Space Res. Trajectory and dust data are lost!

24 Prediction is very difficult,

25 Prediction is very difficult, especially about the future Nils Bohr

26 Ballistic Dust Clouds Spahn, 2001

27 Ballistic Dust Clouds Spahn, 2001

28 Ballistic Dust Clouds Spahn, 2001

29 Ballistic Dust Clouds Index of speed distribution only matters at low altitudes Spahn, 2001

30 Ballistic Dust Clouds Index of speed distribution only matters at low altitudes Spahn, 2001

31 Reproduces Cloud Data 10-2 Europa Dust Cloud Number Density (m -3 ) RE Krüger et al., PSS, 2003

32 Enceladus Dust Plume Altitude = 246 km VIMS Images of Enceladus Equivalent Width Altitude = 181km Altitude = 115km Altitude = 49km 1µm 2µm 3µm 4µm 5µm Wavelength Hedman et. al., AJ, 2009

33 Enceladus Dust Plume Particles per Unit Area (10 18 /m 2 ) micron particles n~r -5/2 2 micron particles 3 micron particles VIMS Images of Enceladus Density Profile of 3 µm 0 0km 100km 200km 300km Altitude Grains is much Steeper

34 General Case Include ejectas angular distribution: ψ 0 ψ u r M r θ v Moon n(r, v, )= N r 2 1 ṙ 1 v 2 sin f(u, ) (u, ) (v, ) Krivov et al., 2003 Sremcevic et al., 2003, 2005

35 Ejecta Cloud Profile Bound Ejecta: n b (r) = N + 2 r 2 M v esc u 0 r 5/2 K b (r) Unbound Ejecta: n u (r) = N + 4 r 2 M v esc u 0 r 2 c 0 ( )K b (r) Krivov et al., 2003 Sremcevic et al., 2003, 2005

36 Angular Distribution Bound Ejecta: Unbound Ejecta: Kbound-1 1-Kunbound r/rsat r/rsat

37 Angular Distribution Bound Ejecta: Unbound Ejecta: Kbound-1 1-Kunbound r/rsat r/rsat Angular Distribution can be Deduced from Density Profile

38 How About the Impactor Flux?

39 1985: Interplanetary 1 AU Grün et al., Icarus,1985 Taylor, Adv. Space Res.,1995 Cumulative mass flux on plate spinning orthogonally to ecliptic plane based on spacecraft data and lunar crater size distribution derived from radio meteors data mean speed: ~ 17 km/s

40 Mass 1 AU Spatial mass density: Grün flux and Taylor speed distribution the largest fraction of the IDP mass is in particles of mass kg to 10-4 kg

41 Isotropic Impactor Flux - Really? Sremcevic et al., (2003, 2005)

42 Induced Dust Cloud Anisotropy

43 Induced Dust Cloud Anisotropy Anisotropic impactor flux causes anisotropic ejecta clouds:

44 Induced Dust Cloud Anisotropy Anisotropic impactor flux causes anisotropic ejecta clouds: Anisotropy provides information about the directionality of the impactor flux

45 Induced Dust Cloud Anisotropy Anisotropic impactor flux causes anisotropic ejecta clouds: Anisotropy provides information about the directionality of the impactor flux Example: Ejecta cloud of the Jovian moon Europa:

46 Induced Dust Cloud Anisotropy Anisotropic impactor flux causes anisotropic ejecta clouds: Anisotropy provides information about the directionality of the impactor flux Example: Ejecta cloud of the Jovian moon Europa: generated by IDPs with an isotropic speed distribution and Sremcevic et al., PSS 53, 2006 by IDPs in retrograde orbits

47 Cloud Anisotropy Sremcevic et al., PSS 53, 2006

48 Cloud Anisotropy Moon magnifies weak impactor streams Sremcevic et al., PSS 53, 2006

49 Cloud Anisotropy Moon magnifies weak impactor streams Acts as an large area dust detector Sremcevic et al., PSS 53, 2006

50 Cloud Anisotropy Moon magnifies weak impactor streams Acts as an large area dust detector Galactic dust streams should appear in LDEX data Sremcevic et al., PSS 53, 2006

51 Ejecta Production Map (Erosion Map) Ejecta detected by LDEX at 100 km altitude Distance from most probable ejection point (km) Postberg et al., Plan. Space Sci., subm.

52 Ejecta Production Map (Erosion Map) Ejecta detected by LDEX (with trajectory sensor) at 100 km altitude Distance from most probable ejection point (km) Postberg et al., Plan. Space Sci., subm.

53 Weakness: Ejecta Production Ejecta mass production: M + = F imp YS sat Ejecta Yield: Y = G sil 1 Gsil G sil m 0.23 impvimp 2.46 Koschny & Grün, 2001

54 Ejecta Production Production Rate of Ejecta > s: Energy Transfer: K e /K i = Y v min e v imp 2 8 >< 3 1 >: 2 ln apple v min e ve max v min e v max e 3 1 < 3, =3

55 Lunar Dust Cloud Grains > 0.5µm 0.1m 2 detector 100 km orbit: / 3 month

56 CCLDAS Accelerator at CU Boulder 3 MV Pelletron