First results from NASA's Magnetospheric Multiscale (MMS) Mission

Space Sciences
1 March 2016
19 March 2018

Magnetic reconnection at the dayside magnetopause. Advances with MMS. Credit: Southwest Research Institute.

The Magnetospheric Multiscale (MMS) mission has been performing particle and electromagnetic field measurements in the near-Earth environment since its launch in March 2015. Thanks to data with unprecedented time resolution on four identical spacecraft in a close tetrahedron configuration (down to 10 km), MMS science goals are to probe and understand the electron-scale physics involved in the magnetic reconnection process. This collection provides a selection of key results obtained during the first phase of the mission at the dayside magnetopause. It includes new observations of the geometry and variability of the reconnection process, the detailed dynamics of particles, fields and waves in the vicinity of the reconnection region, the observation of small-scale signatures at current sheets formed in the magnetosheath, in Kevlin-Helmholtz vortices, or flux transfer events, as well as other small-scale features which are by-products of magnetic reconnection or not. These results open a new window for our understanding of magnetic reconnection in space, with direct and numerous implications for astrophysical and laboratory plasmas.
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Electron microphysics

Open Access

Magnetic reconnection at the dayside magnetopause: Advances with MMS

J. L. Burch,  T. D. Phan, 
Key Points

  • Electron-scale measurements of magnetic reconnection at the Earth's magnetopause with a moderate magnetic guide field were made by MMS
  • Confirmed simulation results of a mixture of low- and high-energy electrons at magnetic null and nongyrotropic electrons at stagnation point
  • Bifurcated out-of-plane current system was observed with peaks near the in-plane magnetic null and the flow stagnation point

Free Access

On the electron diffusion region in asymmetric reconnection with a guide magnetic field

Michael Hesse,  Yi-Hsin Liu,  Li-Jen Chen,  Naoki Bessho,  Masha Kuznetsova,  Joachim Birn,  James L. Burch, 
Key Points

  • Magnetic reconnection involves mixing of distributions from both inflow regions
  • The electric field at the flow stagnation point is always given by nongyrotropic pressure tensor effects
  • Even here, magnetic gradient scale lengths compared to Larmor radii are necessary to facilitate reconnection

Free Access

Electron energization and mixing observed by MMS in the vicinity of an electron diffusion region during magnetopause reconnection

Li-Jen Chen,  Michael Hesse,  Shan Wang,  Daniel Gershman,  Robert Ergun,  Craig Pollock,  Roy Torbert,  Naoki Bessho,  William Daughton,  John Dorelli,  Barbara Giles,  Robert Strangeway,  Christopher Russell,  Yuri Khotyaintsev,  Jim Burch,  Thomas Moore,  Benoit Lavraud,  Tai Phan,  Levon Avanov, 
Key Points

  • Distribution functions of accelerated meandering electrons in the diffusion region are observed
  • Effects of meandering electrons on the electric field normal to the reconnection layer are detected
  • Mixing of the inflowing and exhaust electrons shapes the exhaust flow pattern

Free Access

Estimates of terms in Ohm's law during an encounter with an electron diffusion region

R. B. Torbert,  J. L. Burch,  B. L. Giles,  D. Gershman,  C. J. Pollock,  J. Dorelli,  L. Avanov,  M. R. Argall,  J. Shuster,  R. J. Strangeway,  C. T. Russell,  R. E. Ergun,  Victoria Wilder,  K. Goodrich,  H. A. Faith,  C. J. Farrugia,  P.-A. Lindqvist,  T. Phan,  Y. Khotyaintsev,  T. E. Moore,  G. Marklund,  W. Daughton,  W. Magnes,  C. A. Kletzing,  S. Bounds, 
Key Points

  • Pressure Gradient and Inertial Terms in Ohm's law evaluated in an Electron Diffusion Region
  • Ion and electron Frozen-in Condition observed to be broken

Free Access

Electron distribution functions in the diffusion region of asymmetric magnetic reconnection

N. Bessho,  L.-J. Chen,  M. Hesse, 
Key Points

  • Meandering electrons accelerated by the normal electric field determine a crescent distribution
  • Crescent-shaped populations exist near the electron stagnation point and in the outflow region
  • The distance of penetration into the magnetosphere by magnetosheath electrons is derived

Free Access

Electron energization and structure of the diffusion region during asymmetric reconnection

Li-Jen Chen,  Michael Hesse,  Shan Wang,  Naoki Bessho,  William Daughton, 
Key Points

  • Accelerated unmagnetized electrons support the reconnection current in asymmetric reconnection
  • Cyclotron turning by the normal magnetic field limits the reconnection current
  • Accelerated sheath electrons form a prominent signature to identify the electron diffusion region

Free Access

Kinetic signatures of the region surrounding the X line in asymmetric (magnetopause) reconnection

M. A. Shay,  T. D. Phan,  C. C. Haggerty,  M. Fujimoto,  J. F. Drake,  K. Malakit,  P. A. Cassak,  M. Swisdak, 
Key Points

  • Where the sunward normal electric field overlaps the magnetic field reversal (the “shoulder”) is a signature of electron diffusion region
  • Signatures in the regions upstream of the X line establish context to find the diffusion region
  • Cusp-like motion of magnetosheath electrons associated with electron acceleration produce crescent-shaped particle distributions

Free Access

Currents and associated electron scattering and bouncing near the diffusion region at Earth's magnetopause

B. Lavraud,  Y. C. Zhang,  Y. Vernisse,  D. J. Gershman,  J. Dorelli,  P. A. Cassak,  J. Dargent,  C. Pollock,  B. Giles,  N. Aunai,  M. Argall,  L. Avanov,  A. Barrie,  J. Burch,  M. Chandler,  L.-J. Chen,  G. Clark,  I. Cohen,  V. Coffey,  J. P. Eastwood,  J. Egedal,  S. Eriksson,  R. Ergun,  C. J. Farrugia,  S. A. Fuselier,  V. Génot,  D. Graham,  E. Grigorenko,  H. Hasegawa,  C. Jacquey,  I. Kacem,  Y. Khotyaintsev,  E. MacDonald,  W. Magnes,  A. Marchaudon,  B. Mauk,  T. E. Moore,  T. Mukai,  R. Nakamura,  W. Paterson,  E. Penou,  T. D. Phan,  A. Rager,  A. Retino,  Z. J. Rong,  C. T. Russell,  Y. Saito,  J.-A. Sauvaud,  S. J. Schwartz,  C. Shen,  S. Smith,  R. Strangeway,  S. Toledo-Redondo,  R. Torbert,  D. L. Turner,  S. Wang,  S. Yokota, 
Key Points

  • Observation of Hall current-associated electron dynamics near the diffusion region
  • Confirmation of low-energy electron scattering by curved magnetic field lines
  • Simultaneous observation of inflowing and outflowing, bouncing populations

Free Access

Finite gyroradius effects in the electron outflow of asymmetric magnetic reconnection

C. Norgren,  D. B. Graham,  Yu. V. Khotyaintsev,  M. André,  A. Vaivads,  L.-J. Chen,  P.-A. Lindqvist,  G. T. Marklund,  R. E. Ergun,  W. Magnes,  R. J. Strangeway,  C. T. Russell,  R. B. Torbert,  W. R. Paterson,  D. J. Gershman,  J. C. Dorelli,  L. A. Avanov,  B. Lavraud,  Y. Saito,  B. L. Giles,  C. J. Pollock,  J. L. Burch, 
Key Points

  • An electron scale reconnecting current sheet is observed
  • Crescent-shaped electron distributions are observed in the electron outflow
  • The crescents are associated with finite electron gyroradius effects

Free Access

Electron currents and heating in the ion diffusion region of asymmetric reconnection

D. B. Graham,  Yu. V. Khotyaintsev,  C. Norgren,  A. Vaivads,  M. André,  P.-A. Lindqvist,  G. T. Marklund,  R. E. Ergun,  W. R. Paterson,  D. J. Gershman,  B. L. Giles,  C. J. Pollock,  J. C. Dorelli,  L. A. Avanov,  B. Lavraud,  Y. Saito,  W. Magnes,  C. T. Russell,  R. J. Strangeway,  R. B. Torbert,  J. L. Burch, 
Key Points

  • The ion diffusion region of asymmetric reconnection is investigated
  • Electron-scale currents develop in the ion diffusion region
  • Electron heating is consistent with electron trapping by DC electric fields

Free Access

Electron jet of asymmetric reconnection

Yu. V. Khotyaintsev,  D. B. Graham,  C. Norgren,  E. Eriksson,  W. Li,  A. Johlander,  A. Vaivads,  M. André,  P. L. Pritchett,  A. Retinò,  T. D. Phan,  R. E. Ergun,  K. Goodrich,  P.-A. Lindqvist,  G. T. Marklund,  O. Le Contel,  F. Plaschke,  W. Magnes,  R. J. Strangeway,  C. T. Russell,  H. Vaith,  M. R. Argall,  C. A. Kletzing,  R. Nakamura,  R. B. Torbert,  W. R. Paterson,  D. J. Gershman,  J. C. Dorelli,  L. A. Avanov,  B. Lavraud,  Y. Saito,  B. L. Giles,  C. J. Pollock,  D. L. Turner,  J. D. Blake,  J. F. Fennell,  A. Jaynes,  B. H. Mauk,  J. L. Burch, 
Key Points

  • Electron outflow jet of asymmetric magnetic reconnection is observed
  • Electron jet is unstable to Buneman-type instability generating intense electrostatic waves
  • The instability leads to thermalization and braking of the electron jet

Free Access

MMS observations of electron-scale filamentary currents in the reconnection exhaust and near the X line

T. D. Phan,  J. P. Eastwood,  P. A. Cassak,  M. Øieroset,  J. T. Gosling,  D. J. Gershman,  F. S. Mozer,  M. A. Shay,  M. Fujimoto,  W. Daughton,  J. F. Drake,  J. L. Burch,  R. B. Torbert,  R. E. Ergun,  L. J. Chen,  S. Wang,  C. Pollock,  J. C. Dorelli,  B. Lavraud,  B. L. Giles,  T. E. Moore,  Y. Saito,  L. A. Avanov,  W. Paterson,  R. J. Strangeway,  C. T. Russell,  Y. Khotyaintsev,  P. A. Lindqvist,  M. Oka,  F. D. Wilder, 
Key Points

  • Demonstrate unprecedented MMS measurements of current density at 30 ms, capable of resolving current layers on electron skin depth scales
  • Evidence for electron-scale filamentary Hall currents in exhaust and at its boundaries ~70 ion skin depths downstream of the X line
  • Nongyrotropic crescent shape electron distributions in electron current layer embedded in the ion diffusion region near the X line

Ion microphysics

Free Access

Ion demagnetization in the magnetopause current layer observed by MMS

Shan Wang,  Li-Jen Chen,  Michael Hesse,  Daniel J. Gershman,  John Dorelli,  Barbara Giles,  Roy B. Torbert,  Craig J. Pollock,  Benoit Lavraud,  Robert Strangeway,  Robert E. Ergun,  Jim Burch,  Levon Avanov,  Thomas E. Moore,  Yoshifumi Saito, 
Key Points

  • Magnetosheath ions are demagnetized near the magnetopause reconnection X line and tens of ion skin depths downstream
  • The distributions with demagnetized ions elongate in the out-of-plane direction and rotate toward the outflow direction
  • Signatures of acceleration by reconnection electric fields are more pronounced near the X line than downstream

Free Access

Cold ion demagnetization near the X-line of magnetic reconnection

Sergio Toledo-Redondo,  Mats André,  Yuri V. Khotyaintsev,  Andris Vaivads,  Andrew Walsh,  Wenya Li,  Daniel B. Graham,  Benoit Lavraud,  Arnaud Masson,  Nicolas Aunai,  Andrey Divin,  Jeremy Dargent,  Stephen Fuselier,  Daniel J. Gershman,  John Dorelli,  Barbara Giles,  Levon Avanov,  Craig Pollock,  Yoshifumi Saito,  Thomas E. Moore,  Victoria Coffey,  Michael O. Chandler,  Per-Arne Lindqvist,  Roy Torbert,  Christopher T. Russell, 
Key Points

  • High-resolution observations of cold ions near the X-line
  • Cold ions decouple from hot ions inside the separatrices and follow the electron motion
  • A layer at cold ion scales (cold IDR) is found near the X-line where cold ions are demagnetized and accelerated parallel to E

Free Access

Magnetic reconnection and modification of the Hall physics due to cold ions at the magnetopause

M. André,  W. Li,  S. Toledo-Redondo,  Yu. V. Khotyaintsev,  A. Vaivads,  D. B. Graham,  C. Norgren,  J. Burch,  P.-A. Lindqvist,  G. Marklund,  R. Ergun,  R. Torbert,  W. Magnes,  C. T. Russell,  B. Giles,  T. E. Moore,  M. O. Chandler,  C. Pollock,  D. T. Young,  L. A. Avanov,  J. C. Dorelli,  D. J. Gershman,  W. R. Paterson,  B. Lavraud,  Y. Saito, 
Key Points

  • Verification at high resolution that cold ions introduce a new length scale at the magnetopause
  • Verification at high resolution that cold ions modify the Hall physics of magnetic reconnection and reduce Hall currents
  • Separatrix normal electric field balanced by the Hall term, the cold ion term, and the divergence of the electron pressure tensor

Waves and turbulence

Free Access

Magnetospheric Multiscale observations of large-amplitude, parallel, electrostatic waves associated with magnetic reconnection at the magnetopause

R. E. Ergun,  J. C. Holmes,  K. A. Goodrich,  Victoria Wilder,  J. E Stawarz,  S. Eriksson,  D. L. Newman,  S. J. Schwartz,  M. V. Goldman,  A. P. Sturner,  D. M. Malaspina,  M. E. Usanova,  R. B. Torbert,  M. Argall,  P.-A. Lindqvist,  Y. Khotyaintsev,  J. L. Burch,  R. J. Strangeway,  C. T. Russell,  C. J. Pollock,  B. L. Giles,  J. J. C. Dorelli,  L. Avanov,  M. Hesse,  L. J. Chen,  B. Lavraud,  O. Le Contel,  A. Retino,  T. D. Phan,  J. P. Eastwood,  M. Oieroset,  J. Drake,  M. A. Shay,  P. A. Cassak,  R. Nakamura,  M. Zhou,  M. Ashour-Abdalla,  M. André, 
Key Points

  • Magnetospheric Multiscale observations of large-amplitude, parallel, electrostatic waves associated with magnetic reconnection
  • Simulations support that the strong electrostatic linear and nonlinear wave activities appear to be driven by a two-stream instability
  • The frequent observation of these waves suggests that cold plasma is often present near the magnetopause

Free Access

The effects of turbulence on three-dimensional magnetic reconnection at the magnetopause

L. Price,  M. Swisdak,  J. F. Drake,  P. A. Cassak,  J. T. Dahlin,  R. E. Ergun, 
Key Points

  • Three-dimensional simulations of an MMS observation demonstrate that turbulence should exist at the X line and separatrices
  • This turbulence plays a significant role in balancing Ohm's law at the X line
  • As turbulence does not disrupt crescents in distribution functions, crescent observations cannot be used to diagnose the role of turbulence

Free Access

Whistler mode waves and Hall fields detected by MMS during a dayside magnetopause crossing

O. Le Contel,  A. Retinò,  H. Breuillard,  L. Mirioni,  P. Robert,  A. Chasapis,  B. Lavraud,  T. Chust,  L. Rezeau,  F. D. Wilder,  D. B. Graham,  M. R. Argall,  D. J. Gershman,  P.-A. Lindqvist,  Y. V. Khotyaintsev,  G. Marklund,  R. E. Ergun,  K. A. Goodrich,  J. L. Burch,  R. B. Torbert,  J. Needell,  M. Chutter,  D. Rau,  I. Dors,  C. T. Russell,  W. Magnes,  R. J. Strangeway,  K. R. Bromund,  H. K. Leinweber,  F. Plaschke,  D. Fischer,  B. J. Anderson,  G. Le,  T. E. Moore,  C. J. Pollock,  B. L. Giles,  J. C. Dorelli,  L. Avanov,  Y. Saito, 
Key Points

  • A quasi-steady whistler mode wave emission is detected on the magnetospheric side, just before the opening of the magnetic field lines
  • Hall electric fields are calculated and found to be consistent with the decoupling of ions from the magnetic field
  • The source of the whistler mode waves is likely the perpendicular temperature anisotropy of the energetic part of the electron distribution

Free Access

Observation of high-frequency electrostatic waves in the vicinity of the reconnection ion diffusion region by the spacecraft of the Magnetospheric Multiscale (MMS) mission

M. Zhou,  M. Ashour-Abdalla,  J. Berchem,  R. J. Walker,  H. Liang,  M. El-Alaoui,  M. L. Goldstein,  P.-A. Lindqvist,  G. Marklund,  Y. V. Khotyaintsev,  R. E. Ergun,  Victoria Wilder,  C. T. Russell,  R. J. Strangeway,  C. Zhao,  W. R. Paterson,  B. L. Giles,  C. J. Pollock,  R. B. Torbert,  J. L. Burch,  J. C. Dorelli,  D. J. Gershman,  L. A. Avanov,  B. Lavraud,  M. O. Chandler, 
Key Points

  • Ion diffusion region was identified by MMS spacecraft in the Earth's dayside magnetopause
  • High-frequency electrostatic waves were observed in the vicinity of the ion diffusion region
  • Energy dissipated by these high-frequency waves is negligible compared to that by the lower-frequency process

Free Access

Observations of whistler mode waves with nonlinear parallel electric fields near the dayside magnetic reconnection separatrix by the Magnetospheric Multiscale mission

Victoria Wilder,  R. E. Ergun,  K. A. Goodrich,  M. V. Goldman,  D. L. Newman,  D. M. Malaspina,  A. N. Jaynes,  S. J. Schwartz,  K. J. Trattner,  J. L. Burch,  M. R. Argall,  R. B. Torbert,  P.-A. Lindqvist,  G. Marklund,  O. Le Contel,  L. Mirioni,  Yu. V. Khotyaintsev,  R. J. Strangeway,  C. T. Russell,  C. J. Pollock,  B. L. Giles,  F. Plaschke,  W. Magnes,  S. Eriksson,  J. E. Stawarz,  A. P. Sturner,  J. C. Holmes, 
Key Points

  • Whistler mode waves are observed on the magnetic reconnection separatrix
  • These waves are propagating toward the X line
  • Solitary bipolar parallel electric fields appear to be in phase with the wave and may correspond with electron enhancements