Table of Contents

1 Preliminary............................................................................................................................................................ 1

1.1 Objectives:.................................................................................................................................................. 1

1.2 Background Information............................................................................................................... 2

2 The New Data.......................................................................................................................................................... 4

2.1 Orientation............................................................................................................................................... 4

2.2 Science.......................................................................................................................................................... 6

3 The Outlook......................................................................................................................................................... 18

3.1 Conclusions:........................................................................................................................................... 18

4 References............................................................................................................................................................ 20

A Appendix: Contact information for the Authors................................................................. A-1

List of Figures

Figure 1.1 EPD Low Energy Magnetospheric measurements System (LEMMS) Detector Head 3

Figure 2.1 (Galileo’s Trajectory Over the Amalthea Orbit)......................................................... 4

Figure 2.2 (Galileo’s Trajectory Over Amalthean Centered Coordinates)........................ 5

Figure 2.3 Galileo EPD Orbit A34 Distribution of 32 Sector Rates............................................... 6

Figure 2.4 (16 Sector EPD Energy Ion Data Collected Over Amalthea Swingby) Part II 7

Figure 2.5 ( High Energy Electrons as Measured by the EPD Instrument Over the Amalthea Swingby) 8

Figure 2.6 (Galileo EPD Orbit A34 Deadtime Corrected Ion Flux Spectra).............................. 9

Figure 2.7 (Uncorrected Ion Fluxes for Particles with Pitch Angles Between 80 and 100 Degrees Over the Amalthea Swingby..................................................................................................................................... 11

Figure 2.8 (Uncorrected Ion Fluxes for Particles with Pitch Angles Between 80 and 100 Degrees Between 3.8 and 5.3 Rj)............................................................................................................................................................ 12

Figure 2.9 Galileo EPD Ion Pitch Angle Distributions in the Inner Jovian Magnetosphere Part I 13

Figure 2.10 Galileo EPD Ion Pitch Angle Distributions in the Inner Jovian Magnetosphere Part II 14

Figure 2.11 Galileo EPD Ion Pitch Angle Distributions in the Inner Jovian Magnetosphere Part III 15

Figure 2.12 (Galileo EPD Orbit A34 Time Series of 64 Sector Rates: Examination of Possible Amalthean Moonlets).......................................................................................................................................................... 16

List of Tables

Table 1.I Important Facts about Jupiter, Amalthea, Galileo, the EPD, and Charged Particles 2

Table 1.II Amalthea Encounter Velocity Summary.......................................................................... 3

1 Preliminary

The purpose of this document is to reformat the poster presentation given at the American Geophysical Union on December 9^th 2003, in San Francisco CA by Dr. Thomas Armstrong and Lucas Miller with contributions by the other authors

1.1 Objectives:

There are four main objectives sought in this research:

1. Evaluate the performance of the Galileo Orbiter Energetic Particle Detector in the intense radiation environment of the inner (< 6 Rj) Jovian magnetosphere

2. Search for signatures of interaction between trapped radiation and natural satellites—especially Amalthea.

3. Calculate and check parameters essential to the interpretation of trapped radiation observations—especially pitch and phase angles.

4. Begin the analysis of the sources, losses, and transport of trapped radiation.

1.2 Background Information

Table 1.I provides some of the necessary facts about the environment of study.

Table 1.I Important Facts about Jupiter, Amalthea, Galileo, the EPD, and Charged Particles

Description	Symbol	Value	Units
Jupiter
Mass	M_J	1.9*10²⁷	kg
Equatorial Radius	R_JEQ	71398	km
Roche Limit	R_JRoche	134211	km
Magnetospheric Angular Velocity	w_J	1.76*10^-4	Rad/s
Amalthea
Mass	M_A	7.17*10¹⁸	kg
Idealized Radius	R_A	86.2	km
Density	r_A	1800	kg/m³
Orbital Radius		181300	km
Orbital Period	P_A	11.96	hours
Orbital Eccentricity		0.003	~
Galileo
Mass	M_Gal	2223	kg
Velocity at Amalthea	V	17.05	km/s
Beginning of Mission		10/18/89
End of Mission- RIP		09/21/03
EPD
Ion Energy Range	DE_Z_³₁	0.022-100	MeV
Electron Energy Range	DE_e-	.015-11	MeV
Charged Particles (At Amalthea)
Gyro-Radius for 1 MeV Proton	R_{+1 MEV}	5.180	km
Gyro-Radius for 2 MeV Proton	R_{+2 MEV}	7.327	km
Gyro-Radius for 1 MeV Electron	R_{-1 MEV}	0.170	km
Gyro-Radius for 10 MeV Electron	R_{-10 MEV}	1.255	km

Table 1.II Provides calculated values for the velocities of various components in the Jovian centered system.

Table 1.II Amalthea Encounter Velocity Summary

Description	Velocity
	Magnitude
	km/s
Amalthea's Orbit	26.47

Jovian Magnetic Field Rotation at Amalthea	31.88

Galileo	34.11

1 MeV Protons ÑB	3.49
2 MeV Protons ÑB	4.94

1 MeV Proton Gyration	1.3830E+04
2 MeV Proton Gyration	1.9543E+04
1 MeV Electron Gyration	2.8213E+05
10 MeV Electron Gyration	2.9944E+05

Figure 1.1 EPD Low Energy Magnetospheric measurements System (LEMMS) Detector Head

2 The New Data

2.1 Orientation

Figure 2.1 (Galileo’s Trajectory Over the Amalthea Orbit)

Figure 2.2 (Galileo’s Trajectory Over Amalthean Centered Coordinates)

The Star Scanner

The star scanner (Fiesler at JPL) registered brief responses after Amalthea closest approach. These responses could be due to moonlets traveling with Amalthea in its orbit. Searching through the EPD high-resolution data, several micro-signature candidates for these moonlets where observed. There is a slight lag, however, between the time stamps of the EPD and star scanner events.

3 The Outlook

3.1 Conclusions:

1. Penetrating electrons (>1 MeV) are diminished by about a factor of 10 in intensity beginning at 6:18:27 and ending at 6:18:44 SCET. Closest approach of the Galileo orbiter to Amalthea occurred at 6:18:40 SCET. We believe that this feature is caused by the absorption of penetrating electrons by Amalthea.

2. Deadtime corrected EPD measured the energy spectra of 0.5 to 10 MeV protons to be:

a 1.42 x 10⁵ E^-1.1 at the center of the absorption feature and b 5.21 x 10⁵ E^-2.2outside the feature

3. Uncorrected EPD measurements of the ion fluxes between 3.8 and 5.3 Rj were found to be :

a Flux = (8*10⁷)*e^-1.175*Rj for 0.515-0.825 MeV ions.

b Flux = (2*10⁷)*e^-1.208*Rj for 0.828-1.680 MeV ions.

c Flux = (2*10⁷)*e^-1.498*Rj for 1.680-3.20 MeV ions.

4. The absorption of ions by Amalthea is energy dependent.

5. The absorption of ions by Amalthea is strongest at 90 degrees local pitch angle.

6. The theoretical dipole loss cone at 2.5 Rj is approximately 11 degrees. Observations of 0.5 to 10 MeV ions at 2.521 Rj cover the range from 6.5 to 125 degrees of pitch angle and show the lowest (possibly zero) flux in the loss cone. The instrument acceptance angle of +/- 7.5 degrees did not resolve the loss cone.

7. Pitch angle distributions (PAD’s) of energetic ions appear to be of two types: One type is broadly peaked at 90 degrees and the second has two peaks (approximately 60 and 120 degrees). Some PADs appear to have evidence of complicated gradient anisotropies. We have found no evidence of convection related anisotropy (nor did we expect to for 0.5 to 10 MeV protons at the modest convection speeds (30 km/sec) of the inner magnetosphere.