themis and artemis david g. sibeck themis project scientist nasa/gsfc 2/17/2007 cape canaveral

THEMIS and ARTEMIS

David G. Sibeck

THEMIS Project Scientist

NASA/GSFC

2/17/2007Cape Canaveral

Outline

• Substorms

• NASA’s THEMIS mission • Recent results

• Status and Future plans

Earth’s Magnetosphere

SW

Earth’s dipole magnetic field carves out a cavity in the oncoming supersonic solar wind

.. . . . JB

B

Solar Wind Pressure Variations

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Variations in the solar wind dynamic pressure (nMV2) buffet the magnetosphere,

But the IMF Orientation Controls the Interaction…

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…which generally turns out to be unsteady….

Our own Dedicated Array of THEMIS Ground Observatories Shows Just how Unsteady!

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Themis Mission Objective:Distinguish Between Two Substorm Models …

Current Disruption Reconnection(a) Near Earth Initiation (b) Mid-Tail InitiationEIct.V. VPlasma process on auroral field line causescurrent disruption (CD) and substorm current wedgeAn X-type magneticneutral line formsat a CD siterarefaction wave causes CDto spread tailward

Multiple CD sites1 2

34 Substorm current wedge3 Braking & dawnward current

High-speed flow NENL124

Implosion near Earth

Equatorward arc brightens

Explosion far from Earth

Poleward arc brightens

Flows

?Rarefaction wave

?

P2P3

P4P5

GBOP1

THEMIS Mission Objective: Pinpoint When, Where, How

Energy Stored in Magnetotail is Released

First distant magnetotail and poleward arcOr

First near magnetotail and equatorward arc?

SPACECRAFT AND INSTRUMENTS

SST

ESAEF

IaEFIs

FGM

SCM

Tspin=3s

FIVE IDENTICALLY-INSTRUMENTEDSPACECRAFT (128 kg), EACH CARRYING:

ESA: Electrostatic analyzer measures0.003-30 keV ions/electrons (UCB)

SST: Solid state telescopes measures0.03-6 MeV ions and electrons (UCB)

FGM: Fluxgate magnetometer measures magnetic field to 128 Hz (Germany)

SCM: Search coil magnetometer measures 0.001 - 4 kHz magnetic field (France)

EFI: Electric field instrument on wires andaxial booms 0.0003 - 400 kHz (UCB)

5 THEMIS SpacecraftLine Up Once/4 Days in Tail

Sun

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Case study addressed our primary objective:

Argued that distant tail reconnection triggerssubstorm onset (not vice-versa)

•Vassilis Angelopoulos et al. [2008]

“I see flows consistent with reconnection in thedistant tail followed by auroral brightening,currents, and pulsations at the ground, and thendipolarization in the near-Earth tail. Thisindicates reconnection drives substorms“

…but see comment [Lui, 2009], reply [Angelopoulous, 2009]

Magnetic FieldB(nT)δ Z

Flow( / )V km s Z

AuroralIntensity

( )Relative Units

1P

2P

3P

Magnetic Field( )B nTδ Z

Flow( / )V km s Z

Magnetic Field( )B nTδ Z

Flow( / )V km s X

TRx

TAI

TCD3rd

1st

2nd

P2 P1P3P4

P5 T=0Rx

x

X [R]GSM E

Z

[R]

GSM

E

T=182sCD

T=96sAI

Magnetotail

Earth

ToSun

3rd

1st

2nd

Timing of ground and space:

Vz

Vz

123

TIMELINE

Time the wiggles and demonstratetheir sense is consistent withreconnection. What about arcs?

?

If the substorm begins far from Earth, why does the most equatorward arc (mapping to near Earth) often appear to brighten

first? Nishimura et al. [2009] argue that it doesn’t!

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1 Initial Brightening

2

3 Equatorward arc

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Nishimura et al. propose this model to resolve contradiction

Aurora Feature Magnetotail Feature1 Poleward boundary intensifies Reconnection begins in distant tail

2 N/S arc moves equatorward Earthward flow

3 Contact with existing arc Contact with near-Earth plasma sheet

4 Azimuthal drift along growth phase arc

Azimuthal drift in response to increasing pressure gradient

5 Breakup Instability in near-Earth tail

Out

In

Hi-Lat

Low-Lat

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[Runov et al., 2009]

Earthward-moving

Observations prompt SimulationsEarthward

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Match old MHD simulations [Hesse et al., 1998] and prompt new full particle simulations [Sitnov et al., 2009]

Pc1 Waves Propagate OutwardFrom Footprint on the Ground

Model Observations

Audience: Please HelpRemind Speaker To Show MovieNOW!

Magnetoseismology with Pc 1 (1 Hz) Waves [Rae et al., 2009 Spring AGU Press Release]

Direct Evidence for Magnetic Field Lines Resonating at Individual Frequencies

Multiple spacecraft validate themagnetic field line resonance model[Sarris et al. Feb 2009]:

Disturbances cause each field line to oscillate at its own natural frequency, determined by its length and the mass it carries

1-30 mHz

What Comes Next?THEMIS and ARTEMIS

P1=TH-BP2=TH-CP3=TH-DP4=TH-EP5=TH-A

Daily orbits,

new interspacecraft

separations in

meridional plane

Lissajous andLunar orbits

How ARTEMIS Reaches the Moon

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What ARTEMIS will do at the MoonFor Heliophysics

• When Moon is in the Magnetosphere:– Reconnection, particle acceleration, turbulence

• When Moon is in the Solar Wind:– Reconnection, particle acceleration, turbulence

• Near the Moon:– Lunar wake, electric fields, particle acceleration

If Planetary has funding, ARTEMIS will optimize orbits and operations to study….

• Dust Levitation in Electric Fields:– Monitor input and study lunar electric field – Use reflectometry to study surface electric field– Provide local electric field, particles to LADEE

• LADEE dust detector detects response to input

• Lunar Exosphere– Composition, distribution of:

• exospheric ions• sputtered ions• regolith

– Exospheric variations with solar activity, cycle

• Lunar Surface and Interior– Crustal magnetic fields– Conductivity depth profile– Surface charging

P1P1P2P2

LADEELADEE

Exospheric orSputtered ions

Secondary and photo-electronsreveal regolith properties

Core?

P2P1 Conductivity

ARTEMIS and Exploration

• First operational use of Lunar Lissajous orbits (LL1 & LL2), useful for:– Staging lunar landings– Positioning communications relay stations at the moon(Station-keeping requirements thus far unknown)

• ARTEMIS’s 6 month residence in LL1&LL2 provides:– Good estimate of station-keeping fuel requirements – Proof of operational requirements (frequency/magnitude of thrusts) needed– Rapid transition of knowledge to NASA centers for future planning

LL1 LL2

~12

0000

km

To Earth

Moon

TOP VIEW

SIDE VIEW

Moon

Summary• THEMIS

– A mission to determine the cause of geomagnetic substorms employing 5 S/C and a dedicated array of ground observatories…

– Case studies addressing primary objective completed, statistical studies underway!

• Recent results from the extended THEMIS mission– Working on reconciling conflicting substorm observations

• Future plans– Outer two THEMIS spacecraft go to the Moon: ARTEMIS– Inner three THEMIS S/C continue core mission

All data public: Need your help analyzing!