MIMI LEMMS at SOICompared to Voyager LECP

Thomas P ArmstrongFundamental Technologies, LLC

Report to MIMI TeamApril 21-22 2005

Scott Wadley, Presenter

Search for Microsignatures

• SOI was not designed to search, but we may have gotten lucky.

• Microsignatures can reveal a lot about instrument performance—especially electron background.

Note the apparent absorption signature at 2.54 Rs for G1, E1,E2, and E3 inbound

1.0E+02

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G1 E3 E2 E11980 S1 and S3

Take a closer look and include subsectors. The feature minimum occurs in subsectors 2 and 3. There are 2 peaks

(7,15)and minima (3,11) per revolution elsewhere.

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2.50 2.51 2.52 2.53 2.54 2.55 2.56 2.57 2.58 2.59 2.60

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G1 E3 E2 E1 Subsector

Further interpretative remarks

• Two peaks and two minima per revolution are expected for radiation axisymmetric around B, i.e. trapped radiation.

• The feature appears to have resulted from a deepening of a routinely occurring minimum.

• If the orbiter approached a flux tube depleted of electrons by absorption at latitude different from the spacecraft, then it would be reasonable to expect the absorption to be most evident for electrons not mirroring near the spacecraft which LEMMS would observe as a peak,

• The may be the most likely geometry to explain the nature of the absorption.

E4, E5, and E6 show the inbound microsignature less distinctly than do the lower energy channels.

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G1 E4 E5 E6

Note the lack of apparent absorption signature at 2.54 Rs for G1, E1,E2, and E3 outbound

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G1 E3 E2 E1

Inbound absorption feature is also present in BE, C0, and C1 channel (other electron channels also show it—omitted

for clarity)

1.0E+01

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G1 BE C0 C1

Ion Channels do not show the microsignature but show substantial drift shell absorption! The microsignature occurs at the outer edge of the drift shell absorption.

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G1 A5 A6 A7

Drift Shell

Is there a candidate object at 2.54 Rs?

• Answer—not in the identified lists from Pioneer 11 and Voyager investigations.

• Have the Cassini SSI folks shown anything at 2.54 Rs?

Designation Semi Major (Rs) Size (km) Reference 1980 S28 2.282 ~31 Thomas, JGR 88, 1983 1980 S 27 2.31 102 Thomas, JGR 88, 1983 1980 S26 2.349 85 Thomas, JGR 88, 1983 1980 S1 2.52 Marsden, JGR 85,1980 1980 S1 (S10) 2.511 188 Thomas, JGR 88, 1983 1980 S3 2.52 Marsden, JGR 85,1980 1980 S3 (S11) 2.510 117 Thomas, JGR 88, 1983 Mimas 3.09 Marsden, JGR 85,1980 Enceladus 3.97 Marsden, JGR 85,1980 Tethys 4.91 Marsden, JGR 85,1980 1980 S25 4.884 24 Thomas, JGR 88, 1983 1980 S13 4.884 22 Thomas, JGR 88, 1983 Dione 6.29 Marsden, JGR 85,1980 1980 S6 6.29 Marsden, JGR 85,1980 1980 S6 6.267 32 Thomas, JGR 88, 1983 Rhea 8.79 Marsden, JGR 85,1980 Titan 20.4 Marsden, JGR 85,1980 Hyperion 24.7 Marsden, JGR 85,1980 Hyperion 260 Thomas, JGR 88, 1983 Iapetus 59.3 Marsden, JGR 85,1980 Phoebe 216 Marsden, JGR 85,1980 Phoebe 200 Thomas, JGR 88, 1983

Another Interesting effect—inbound/outbound flux assymmetries. Note the clear difference for C2 (43 to 57

keV electrons)

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C2 Inbound C2 Outbound

Note that A5 (0.49 to .78 MeV) protons are nicely symmetric—but a suspicious plateau exists in the 2.3-2.35

range inbound.

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A5 Inbound A5 Outbound