ARTEMIS TAIL SCIENCE Two THEMIS probes at lunar

ARTEMIS TAIL SCIENCE Two THEMIS probes at lunar distances The magnetotail at lunar distances is an ideal region to study particle acceleration, reconnection, magnetotail structure and dynamics Moon

Detection probability of Earthward & Tailward flows In Geotail data (from H. Hasegawa) The probabilities of earthward & tailward flows are roughly equal at –x = 50 to 80 Re. Dominant X-line at –x = 50 to 80 Re? Distant X-line?

ARTEMIS TAIL SCIENCE Two THEMIS probes orbiting the moon The magnetotail at lunar distances is an ideal region to study particle acceleration, reconnection, magnetotail structure and dynamics jet Moon

Why is the distant tail at XGSE = 50 -70 RE an ideal region to study particle acceleration and reconnection? More likely to encounter X-line than in the near-Earth tail Reconnection quasi-steady (unlike near-Earth) → we can study the basic structure of reconnection without the complication of time variability No obstacle for reconnection outflow (unlike near-Earth) Ion heating in reconnection can be studied since the inflow region (mantle) is better measured than in the near-Earth region (where the inflow region is the lobe) Slow shock studies can be performed since both upstream (mantle) and downstream conditions can be measured

Why is ARTEMIS better than previous spacecraft in this region? For the first time we will have two spacecraft in the XGSE = -50 -70 RE region ARTEMIS will have better time resolution than previous spacecraft. ARTEMIS will have electric field measurements, something that was missing in previous observations of this region Previous spacecraft have spent very limited time in this region while ARTEMIS will provide unprecedented coverage of this region. MMS will not be in this region

ARTEMIS tail science topics 1. Magnetic reconnection/acceleration and plasmoid (flux rope) studies 2. Formation of the cold dense plasma sheet and the length and topology of the magnetotail during northward IMF 3. Turbulence 4. Minimum ARTEMIS tail science (can be done using one spacecraft): Mass, momentum, and energy coupling between distant and near-Earth tail + some of the above

1. Magnetic reconnection/acceleration and plasmoid (flux rope) studies a) How and to what energies are particles accelerated in X-lines and O-lines? With two spacecraft one can easily distinguish between X-lines and O-lines b) What is the cross-tail extent of X-lines in this region? Is reconnection patchy or spatially extended in this region? Use ARTEMIS two-spacecraft measurements c) How are ions heated in reconnection? Need simultaneous measurements in the inflow region and the outflow region. Inflow region parameters can be easily measured in the distant tail (mantle, not lobe) d) How do plasmoids and flux ropes evolve as they travel downstream? What is their dimension, shape, and internal structure? ARTEMIS two spacecraft observations will be able to resolve this question.

2. Formation of the cold dense plasma sheet and the length and topology of the magnetotail during northward IMF a) Does the tail close and become short when the IMF is northward? We can determine whether the tail really closes near XGSE = -65 RE as some simulations suggest. b) Does the cold dense plasma sheet (CDPS) extend to these downtail distances? Where and when is the CDPS observed and what are the properties of the CDPS at this distance? ARTEMIS will investigate the CDPS occurrence as a function of the IMF direction. Two-spacecraft studies will shed light on the entry mechanism.

3. Turbulence a) When and where does Kelvin-Helmholtz instabilities develop on the flanks? Two-spacecraft measurements can be used to identify non-linear KH vortices which have been suggested to provide significant solar wind entry into the tail during northward IMF conditions. b) What are the characteristics and role of plasma sheet turbulence? - At what spatial separation is the end of the correlation scale? - Do turbulence characteristics vary with the radial distance down the plasma sheet? - What is the mechanism(s) that generate turbulent fluctuations in the magnetic field? Two point spacecraft measurements can be used to answer these questions as well as to calculate energy transfer rates within the plasma sheet.

Minimum ARTEMIS tail science (can be done using one spacecraft): a) Conjunctions with Geotail Mass, momentum, and energy coupling in the tail b) Statistical studies: Fill the gap, Geotail/Wind did not cover well –XGSE = 50 ~ 100 RE This region is crucial for mass, momentum, and energy coupling c) Some aspects of previously discussed questions (reconnection, turbulence, CDPS) can still be addressed

ARTEMIS tail science topics 1. Magnetic reconnection/acceleration and plasmoid (flux rope) studies 2. Formation of the cold dense plasma sheet and the length and topology of the magnetotail during northward IMF 3. Turbulence 4. Minimum ARTEMIS tail science (can be done using one spacecraft): Mass, momentum, and energy coupling between distant and near-Earth tail + some of the above