地球近傍微小ダスト
Near Earth Small Meteoroids
阿部 新助 (avell@kobe-u.ac.jp)
神戸大学 大学院理学研究科 地球惑星科学専攻
惑星科学研究センター(CPS: Center for Planetary Science)

小研究会「流星とダスト計測（第１回）」＠国立天文台
2007/07/03

Source of Meteoroids• Stream Meteoroids “流星群”• Sporadic Meteoroids “散在”Source of Sporadic

Interplanetary dusts; 短周期彗星, エンケ彗星, 小惑星(衝突破砕dust)
Interstellar dust; 対地速度72km/s以上, dust直径40μm?, flux?
It is evident that sporadic meteors exhibit diurnal and seasonal variations in their activity.
Sporadic radiants were initially distributed isotropicly, but appear to be concentrated about the apexof the Earth because of the Earth’s orbital motion.
The seasonal variation of sporadic meteors in the strength of the apparent maxima of the helion
and antihelion sources shows asymmetric features during certain periods.

Stream Meteoroids
Source; planet-approaching comets
金星

地球

火星
: Halley Type Comets•high speed; > 25 km/s
•strong annual activity•outbursts: Jupiter Family Comets•low speed; > 25 km/s
•weak annual activity•outbursts

流星群発生の条件
Δ<0.1 AU
the contribution from JFCs is an increasing function of heliocentric
distance roughly similar numbers of HTCs at the three planets
two “hat trick” comets: 1P/Halley and 45P/Honda-Mrkos-Pajdusáková

Beech, MNRAS, 1998,Christou & Beurle, P&SS, 1999,
Treiman & Treiman 2000,Larson, AJ, 2001,
Christou, Icarus, 2004,
Selsis et al, A&A, 2004

Apex(地球向点) 15-28%
Halley-type comets
Long-period comets
Source: 南北15° Apex sources
V〜45-72km/s, Vmean=62km/s

Antihelion(反太陽方向)
Helion(太陽方向) 30-40%
Jupiter-family comets
Appolo-type asteroids
Source: ±70° from the Apex
V〜11-45km/s, Vmean=20km/s
daily motion〜1°/day
Ecliptic showers(黄道流星群, Zodiac)
北半球の場合: HR〜15/hr in fall,
HR〜5/hr in spring

N-S-Troidal

3-6%

N-S Source: ±67° latitude
a〜1.0AU, e〜0.3, 順行軌道
Variations of Sporadic Meteors and Radiant Distribution Vmean〜24-42km/s?, JFCの進化天体?
Contours of apparent density of meteor radiants from the combined Harvard (upper plot) andAdelaide (lower plot) radio surveys (Jones and Brown, 1994).
H denotes the position of the Sun, AP the Earth’s apex and AH the antihelion point.

Production rate of cometary meteoroids
Comet group% of total

Jupiter family91Halley family

5Long period

4

JF彗星の近日点/遠日点分布

彗星起源ダスト供給源はQ<7AUのJF彗星である。

Activity of short period cometary meteoroids

HRMP: Harvard Radio Meteor Project (Sekanina, 1967, Lindblad, 1987)
CMOR: Canadian Meteor Orbit Radar (Campbell-Brown&Jones, 2003)

短周期彗星起源meteoroidsの輻射点分布

Activity of long period cometary meteoroids

長周期彗星起源meteoroidsの輻射点分布

Toroidal source

V_mean = 42 km/s

V_mean = 24 km/s

Distribution of asteroid taxonomy

sin iCSVaC; carbonaceous chondrites, outer region
S ; ordinary chondrites, inner region
V; HED meteorites, around 2.3AU

小惑星起源のダスト

小惑星イトカワCircumsolar ring 検出可能性
20% of 12µm asteroidal dust particles(β=0.37) trapped in resonance(3:4-17:18).
Carbonaceous particles are dominant.
Asteroidal Dusts

S.F. Dermott et al., Nature, 1994

ダストに働く”Drag forces”✦Light Pressure✦Poynting-Robertson✦Solar Wind

Meteor observation from LEO
Distance of Horizon at each altitude1997 Leonids observed by MSX under full Moon.
40min composed image (Jenniskens, et al., 2000)

900 km
X〜3300km

150 km100 kmMSX image of 1997 Leonids

6,378 km

P. Jenniskens et al., 2000

Earthaltitude (km)distance (km)Leonid MAC

101100ISS4002000

MSX

9003300

13.1°× 10.5°

地球大気の分類

1/1000 s high speed camera image of a meteor

Hans Stenbaek-Nielsen, 2001

with ablation

Ablation
without ablation

The term ablation has the meaning of mass loss of ameteoroid in any form and phase: solid as fragments,
fluid as droplets and loss of hot gas, which forms
always the final stage and is responsible for theobserved meteor phenomenon.
Trains with duration up to 3 s are produced by the forbidden
auroral line of neutral oxygen at 557.7 nm.

temperature in meteor plasma
Ian Boyd, EMP 82/83, 2000

Fe I, Mg I, Ca I, Na I …. Main component (〜4,500 K)
Ca II, Mg II, Fe II …….. 2nd component (〜10,000 K)Jiří Borovička (1993)1999 Leonid Meteor Storm, Leonid MAC, 4,000 hr-1 at 02:02 UT on November 18, 1999.
Yano, Abe, NHK, NASA

1999 Leonid Meteor Spectrum (V=71 km/s)
Meteor light consists mostly of radiation of
discrete emission spectral lines belonging forthe most part to metals and mainly to iron.
More than 90% of the meteor light originatesfrom radiation of single low-excited atoms ofmeteoroid material (several eV;
temperatures 3000 to 5000 K).

S. Abe et al. Earth Moon & Planets, 82/83, 2000

Interplanetary Dust Models
地球回りの単純化した”Interplanetary Dust Model”, 軌道(方向)情報なし; Grün, Zook, Fechtig and Giese (1985)
軌道分布を考慮した“Interplanetary dust complex”, 黄道光, impact
dataや電波流星をコンパイル; Divine (1993)
Divine's modelの問題点(速度分布のバイアス除去)を改良; Taylor(1995)
Taylor(1995) modelを更に単純化; Garret, Drouilhet, Oliver andEvans (1999), Jehn (2000)

地球近傍巨大ダストの分布

P. Brown et al. (2002)

ISSから観測される１日当りのメテオロイド

Revised from Ceplecha et al., (1998)

石質流星体が突入速度40km/s, 突入角45度で石質の流星が高度100kmで発光すると仮定
The interplanetary dust component of the influx is 4 x10^6 kg per year per Earth,about 17% of the influx originates in the interplanetary dust.
about 83% in bodies mostly inside a mass range of 10^5 to 10^8 kg (10 to 100 m sizes).
Atmospheric penetration of meter and ten meter size bodies can be regularly and globally observed by satellites.

「きぼう」船外プラットフォームからの流星の観測
ISSメテオ・ウォッチャーJAXA「きぼう」船外実験プラットフォーム第2期利用候補ミッションの公募（不採択）

本研究チームが地中海上空よりHDTVにて撮影した米国の軍事衛星MSXから撮影された1999年しし座流星雨

1997年しし座流星群(1) ミッション名
メテオ・ウォッチャー（Meteor Watcher）(2) 組織名
神戸大学／国立天文台／理研／甲南大／JAXA／高知工科大／DLR／ESA(3) 代表研究者名・所属・職名
阿部新助・神戸大学理学研究科地球惑星科学専攻・助教(4) ポート利用形態
ポート共有利用

我々の提案によりロシアの宇宙飛行士がISSから撮影した流星群映像

2001しし群 by HDTV(旧NASDA提供)

日常的に発生する流星現象を、非日常的な宇宙から観察することで、地球が巨大な望遠鏡の役割を演じているということを多くの人々に認識してもらい、改めて地球という存在を意識してもらうという大きな意義が、我々が提案する「メテオ・ウォッチャー」に込められている。

JEM-EUSO
Extreme Universe Space Observatory-2005; EUSO was originally planed to be deployed by ESA
 2005 Oct@ESTEC; Original plan was canceled because ofchanging situation of ESA’s budget.
 2006; Phase-A (JEM-EUSO WG) collaborating with Italy,France, Switzerland, Germany, Portugal, Spain, Japan, USA,Brazil, I’m involved as a meteor analyst
 2007-2008; Phase-A, B ← We were selected as phase-A
 2009-2012; Phase-C,D 2013; Launch using Japanese transport plane (HTV)JEM-EUSO(Japanese Extreme Universe Space Observatory)
The purpose is to distinguish the source of extreme high energy particles more than 1.0E20 eV originated probably fromAGNs, which relates with cosmology.
The technics is to observe the extensive air-shower induced by energetic particle entered the atmosphere.
By using EUSO main telescope, 2.5 m in diameter, Evaporated N2 and N2+ by electron shower can be observed as
fluorescence, moreover Cerenkov light along the path of shower can also be detected.

Cerenkov light

Photon counts★FOV; ±30 deg from height of 430km★Time resolution; 2.5μsec★Spacial resolution; 9.75 x 0.75 km(0.1 deg.)★Wavelength region; 300-400 nm

fluorescenceTimeAdvantages from Space

Determination of mass distribution especially for bright-end.
✓Between meteoroids and asteroids.
Steady monitoring for sporadic meteors.
✓EUSO has 2 view angles, 90 deg for perpendicular- and 45 deg for tilt-mode.
Ultraviolet region without absorption.
✓Below 300nm region is absorbed by ozone layer.
High-altitude meteors.
✓Higher than 200 km would be detected.

Disadvantages from Space

CCD noises caused by cosmic ray.
Limited data down-link rate, 300 Kbps from ISS.
Disturbed by cloud, reflected moon-light and ionospheric emissions.

Search for organics through Iron free windows from the space
生命起源物質（有機物, 水）の地球到来のプロセスを調べる上で，宇宙からの紫外線領域の分光観測が有効である。

Iron windows

Oparin, 1924

Discovery of new UV Bands in Leonid Fireball(-5 mag.) from the ground.

Atoms + N2+ +OH

N2+ was strongest band in UV emission.

Atom;4500K
N2+;10000K

Bow shockrecompression shock

thermochemical non-equilibrium state

wake coreneck

Shock layer
N2+

backward flow

(1,0)
Mg I+OH N2+(2,0)

N2+(0,1)N2+(0,0)S. Abe et al., ApJ 618, L141-L144, 2005.

Moon Impact Flush

NASA-MSFS
The Video plays 7x slow motion.
7th magnitude corresponds diameter of 25 cm and velocityof 38 km/s rocky meteoroid.

Sodium Tail enhanced bymeteoroids impacts.

月のダスト(Na, K)の尾（ガスの中に塵も含まれると仮定）
新月の昼間に月起源のダストを検出できる可能性
流星群活動(Stream)による超過ダストを検出できる可能性

Lunar impact prospects
セレーネ月探査機と地上との同時観測可能性

Table 10c from Jenniskens (2006)

Japanese spacecraft heading for the Moon this year: