かぐやによる月起源イオンの観測Observation of ions from the Moon by

MAP‐PACE IMA onboard SELENE(KAGUYA)

Shoichiro Yokota 02-Jun-2010 STPseminor

Observation results of MAP/PACE on KAGUYA

SW

2.2. SW penetration into the WAKESW penetration into the WAKE

1. SW ion reflection/scattering on the surface1. SW ion reflection/scattering on the surface

3. He, C, O, Na, (Al), K, Al desorbed from the surface3. He, C, O, Na, (Al), K, Al desorbed from the surface

4. Magnetic anomaly (Mini4. Magnetic anomaly (Mini--magnetosphere)magnetosphere)

Lunar exosphere

Ground-based observations found:

Na (30/cc) and K(15/cc)

Dependence on the SZA

Source mech.

-UV-SW sputtering

-Thermal desorption

Potter and Morgan 1998

Na exosphere

-Thermal desorption

-Micro-meteoroid

Loss mech.

-UV

-Solar wind

Gardening effect

Lunar exosphere

Photon-stimulated desorption

Electron-stimulated desorption Thermal desorption

Yakshinskiy & Madey, 1999

Madey & Yakshinskiy, 1998

Outline of KAGUYA(SELENE)SELENE: SELENE: SelSelenological and enological and EnEngineering gineering EExplorer :xplorer :

●●●●●●●●Launch : by HLaunch : by H--IIA launch vehicle on 14 September IIA launch vehicle on 14 September

20072007

Impact : 10 June Impact : 10 June 2009 (65.5S2009 (65.5S 80.4E)80.4E)

●●●●●●●●14 mission instruments; for global mapping 14 mission instruments; for global mapping

to elucidate the lunar origin and evolution.to elucidate the lunar origin and evolution.

chemical

elements

X-ray Spectrometer

Gamma-ray Spectrometerelements Gamma-ray Spectrometer

mineralogy Spectral Profiler, Multi-band Imager

surface

structure

Terrain Camera

Rader Sounder

Laser Altimeter

surface

environment

Magnetometer, Plasma Analyzer

Plasma Imager

Charged Particle Spectrometer

Radio Science Observation

gravity fieldDifferential VLBI Radio Sources

Relay Satellite Transponder

imaging High Definition Television Camera

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Angular scanning

deflectors

Sensitivity

control

electrodes

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IMA-EA

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Ion mass analyzer(IMA) of MAP/PACE

Linear-electric-field time-of-

flight (LEF TOF) method

m/dm ~10 for neutrals

m/dm~20 for reflected ions

*). Neutral, negative ion

or highly energetic ion

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-15 kV

+15 kV

3 cm

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deflectors

Inner: - V

Outer: GND

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MCP

Carbon foil Post acceleration

ie

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Center anode 1-D resistive anode

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resistors

Reflection

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MgO plate

Yokota et al. 2005, RSI

First direct detection of ions originating from the Moon (in the SW) [Yokota et al. 2009, GRL]

• Identified He+, C+, O+, Na+, K+ (H2O group, Al+, Ar+)

• Enables long-term and continuous monitoring of the lunar exospheres

First in-situ observation of the Moon-originating ions in the Earth’s Magnetosphere [Tanaka et al. 2009, GRL]

• Identified Ar+.• Moon holds its exospheres even in the Earth’s magnetosphere.

Observation results of MAP-PACE IMA on KAGUYA

• Moon holds its exospheres even in the Earth’s magnetosphere.

• The SW is not dominant source mechanism.

Solar zenith angle dependence [Tanaka 2010, Doctor thesis]

• UV maintains the lunar exospheres

Dawn-dusk asymmetry [Tanaka 2010 , Doctor thesis]

• Exospheric particles dry up in the daytime and are refilled in the nighttime.

SW gardening effect [in preparation]

MAPMAP--PACE IMA Observation PACE IMA Observation in the SW in the SW H+ He++

Detected He+, C+, O+, Na+ and K+.

E ~ a few 100s eV

In the northern hemisphere

Other species?Ar+ (near K+)

H2O group

Detection points of ions

in the white rectangle

H2O group

Al+

Yokota et al., GRL, 2009

Comparison between the potential difference (satellite-

surface) and the ion energy

E = -V(MAP-PACE IEA) x B(MAP-LMAG)

V

B

L

MAPMAP--PACE IMA Observation PACE IMA Observation in the SW in the SW

Yokota et al., GRL, 2009

MAPMAP--PACEPACE--IMA Observation IMA Observation in the Earth’s lobe regionin the Earth’s lobe region

Tanaka et al. GRL, 2009In the absence of plasma effects on the source process, ion

species of H+, He++, He+, C+, O+, Na+, K+ and Ar+ are

definitively identified. The ion fluxes were higher when the

solar zenith angle was smaller, which is consistent with the

idea that the solar photon driven processes dominates in

supplying exospheric components.

MAPMAP--PACE IMA ObservationPACE IMA Observation

SZA dependence of the pickSZA dependence of the pick--up ions up ions Tanaka, 2010

Na+ K+

Bar: Observation

Box: Simulation based on the ground-based observations(Yokota and Saito 2005)

The SZA dependence of Na+ flux is well matched between the simulation and observation.

The observed K+ flux is much higher than the simulation. One of our ideas is the in-situ

observation is able to detect ions from very low altitude (near surface) while the lunar

exosphere detected by the ground-based telescopes is located at more than ~10 km. There is

the possibility that the Moon maintains high-density potassium exosphere near the surface.

MAPMAP--PACE IMA ObservationPACE IMA Observation

Daily variation of the picked-up K+ flux from 1 June 2008 to 31 May 2009

Tanaka, 2010

Dawn-dust asymmetryMAPMAP--PACE IMA ObservationPACE IMA Observation

SSE longitude dependence of the K+ flux

Tanaka, 2010

The observed dawn-dusk asymmetry is caused mainly by the abundance of the

surface source. One of the conceivable replenishing sources is micrometeoroids.

SW gardening SW gardening (Killen et al., 1991)

SW ions

UV

UV takes out exospheric particles from the very shallow area (~A) of the lunar soil.

�The exospheric particles at the shallow area might dry up!

SW ions reach the deep area (100 A) and transport the exospheric particles to the

surface.

MAPMAP--PACEPACE--IMA ObservationIMA Observation

<Count/Sample>(1 day) of Na+ from 01-Jun-2008 to 30-Dec-2008

Count/Sample of Na+ slowly decreases in the Earth’s MS..⇒SW garden the lunar surface and supply Na to the very surface.

The results are consistent with Sarantos et al., 2009

Earth’s MS

Summary

UV

太陽風粒子太陽風粒子太陽風粒子太陽風粒子太陽風粒子太陽風粒子太陽風粒子太陽風粒子

DuskDusk：：：：：：：： Depletion of the exospheric Depletion of the exospheric particlesparticles

Standard model of the interaction between the SW and planetary surface⇒Mercury (BepiColombo)

He, C, O, Na, K, Ar, (Al)

太陽風粒子太陽風粒子太陽風粒子太陽風粒子太陽風粒子太陽風粒子太陽風粒子太陽風粒子のののの侵入侵入侵入侵入のののの侵入侵入侵入侵入

UV(photon)UV(photon)--desorptiondesorption

Dependence on the SZADependence on the SZA