In situ dust monitoring on the Moon an experimental approach

Transcription

1 In situ dust monitoring on the Moon an experimental approach Luigi Colangeli 1, Pasquale Palumbo 2, Alessandro Aronica 1,3, Francesca Esposito 1, Elena Mazzotta Epifani 1, Vito Mennella 1, Alessandra Rotundi 2, Giampaolo Preti 4, Massimo Cosi 4, Roberto Destefanis 5, Marco Giuliani 5 1 INAF Osservatorio Astronomico di Capodimonte, Via Moiariello Napoli (Italy) 2 University Parthenope, Via A: De Gasperi Napoli (Italy) 3 University Federico II, Piazzale Tecchio 80, Napoli, Italy 4 Galileo Avionica, Via Albert Einstein 3, Campi Bisenzio (Fi), Italy 5 ThalesAlenia Space Functional Systems and Operations, Strada Antica di Collegno Torino (Italy) colangeli@na.astro.it

2 Content Dust on the Moon Dust types on the Moon Experimental approach for in situ analysis Every Apollo astronaut did it. They couldn't touch their noses to the lunar surface. But, after every moonwalk (or "EVA"), they would tramp the stuff back inside the lander. Moondust was incredibly clingy, sticking to boots, gloves and other exposed surfaces. No matter how hard they tried to brush their suits before re-entering the cabin, some dust (and sometimes a lot of dust) made its way inside. Once their helmets and gloves were off, the astronauts could feel, smell and even taste the Moon (The Smell of Moondust ).

3 Dust on the Moon Despite the fact that the Moon is an airless body, the space close to its surface is populated by different kinds of particles. Two main classes of particles can be identified: o meteoroids coming from interplanetary space and impinging onto the lunar surface o grains lifted from the regolithic surface, due to several local phenomena, Physical, chemical and dynamic properties of these particles are quite different.

4 Micro-meteorite impacts An impactor body of 10 cm at 20 km s -1 produces a plume 2.5 s has a conical shape; the density of the vapor core is gcm -3. After the plume expansion begins (Nemtchinov et al., 2000). During the expansion of the vapor plume, the process of condensation occurs condensation of grains (r» 3 μm) - speed ~ 3-5 km s -1 => escape from the moon surface (lunar escape velocity 2.38 km s -1 lunar dust grains (30 μm) lifted from the crater and the surrounding regolith layer - speed: km s -1. Mass ejected: times the impactor mass. Dust falls back in ~ 400 s / Max altitude ~ 130 km. L. Taylor

5 Meteoroid impacts on the Moon Meteoroid expected velocity: km s -1 (more recently 20 km s -1 ) Maximum reported velocity: 100 km s μm Cumulative meteoroid flux at Lunar surface Lunar secondary ejecta distribution West, Wright, and Euler, 1977

6 Meteoroid impacts on the Moon Laboratory simulations to calibrate microcrater size with impacting particle size, mass and energy. Cumulative meteoroid flux on the Moon of 4 (±3) x 10-5 particles m -2 s -1, fairly consistent with in situ satellite measurements Fechtig et al. 1977

7 Dust on the Moon L. Taylor

8 Dust on the Moon: regolith Size distribution for lunar regolith samples from Apollo 11,12, 14, and 15 all fall within this band (Smith and West, 1983)

9 Dust on the Moon: soil Mean grain sizes : μm Mean grain mass : 1 μg 1 g Mission Number of Analyses Medians * Means References Apollo μm Carrier (1973) Apollo μm Carrier (1973) Apollo μm McKay et al. (1972) Apollo μm Carrier (1973) Apollo μm Heiken et al. (1973) Apollo μm McKay et al. (1974) Luna μm Vinogradov (1971) Luna μm Vinogradov (1973)

10 Mc Coy Criswell 1974 Electrostatic lifting of dust Micron-sized dust can be transported by the interactions between charged dust particles and electric fields near the lunar surface (Borisov and Mall, 2006 and references within) Evidence: LEAM (Lunar Ejecta and Meteorite Experiment) sensor data from the Apollo 17, during its terminator passages It was argued that dust grains from the surface of the Moon acquire electric charges that allow them to levitate

11 Stubbs et al The dynamic fountain model Once the dust grain has attained sufficient charge to leave the lunar surface, it is accelerated upward through a sheath region with a height of order the plasma Debye length, λ D. The dust grains in question are so small that initially Fq >> Fg, such that the dust grains leave the sheath region with a large upward velocity (V exit ) and follow a near-parabolic trajectory back toward the lunar surface since the main force acting on them now is gravity. Surface charging in the model is driven by photoelectron currents on the dayside and plasma electron currents on the nightside. This reveals that dust can be lofted by the fountain effect at most locations on the lunar surface. At the terminator dust grains < 0.1 μm can be lofted to ~1 100 km.

12 Analysis of Dust Transport Rate of transport: ~ 6 x 10 7 times larger than the rate of primary meteoroids, and ~ 2 x 10 5 times larger than the rate of secondary micrometeoroids (Rennilson and Criswell, 1974). Better strategy to study lunar transient events: analysis instrumentation onboard lander and rover => lander would act as a control, while the rover investigated dust plasma-surface variations due to, for example, changes in topography and surface composition. The rover could reach not shaded regions of lunar surface to better investigate the phenomenon in case the landing site illumination should be compromised by darkened areas (e.g. caused by crater s edges). The mobility of the rover could place the experiment over regions characterized by finest regolith. Stubbs et al. 2005

13 Technologies from comet exploration 1P/Halley vista da Giotto (1986)

14 High speed dust capture in aerogel

15 DARLING Experiment (Direct Analysis and Retrieval in Low earth orbit of INterplanetary Grains) PI: P. Palumbo Approved by ESA (Life and Physical Sciences and Applied Research Projects) In situ active measurement + passive collection for return to Earth

16 GIADA Grain Impact Analyser and Dust Accumulator Quartz micro-balances for dust collection (MBS) Optical device for grain detection (GDS) Impact sensor (IS) Grain 5 Micro-balances (MBS) GDS lasers GDS receivers Electronics Impact sensor (IS)

17 Conclusion Scientific and operational importance of Moon dust characterisation is evident Technologies are already available for a thorough characterisation in situ of Moon dust families

18 Gerf Kern Particle hunters