Mercury Plasma Particle Experiment (MPPE)

The Mercury Plasma Particle Experiment (MPPE) is a set of particle sensors on board the Japanese Mercury Magnetospheric Orbiter (MMO). The MPPE consortium is led by the Principal Investigator Y. Saito from ISAS, Tokio, Japan.

Scientific objectives

The scientific objectives of the experiment are:

Structure, dynamics, and physical processes of the Hermean magnetosphere
The magnetosphere will be surveyed in detail to investigate the dynamics of planetary magnetospheres in close proximity to the Sun.

  • Structure, variation, and origin of Hermean exosphere
    The large-scale structure and variation of the thin planetary neutral cloud will tell us more about the history of Mercury's atmosphere.
  • Space environment in the inner solar system
    The variations of solar wind, solar radiation and fields close to the Sun will tell us more about the structure and evolution of the heliosphere.

The MPPE experiment consists of the following sensors:

(Energetic Neutral Atom)
Detector for energetic neutral atoms with a mass resolution at 10 eV of 3,3 keV and an angular resolution of  9x30 °

(High Energy Particles - electron)
Electron-Spectrometer for energies 30-700 keV and a field-of-view of 20x130 °

(High Energy Particles - ion)
Ion- spectrometer for energies 30 keV-1,5 MeV, field-of-view of 11x110 °; mass resolution for
H, He, CNO, Na-Mg, K-Ca, Fe

(Mercury Electron Analyzer)
Electronen-Spectrometer for energies 3 eV-30 keV

(Mercury Ion Analyzer)
Ion-Spectrometer for energies 5 eV / q to 30 keV / q without mass resolution

(Mass Spectrum Analyzer)
Time-of-flight ion spectrometer for ions with energies of 5 eV / q to 40 keV / q, mass range
1 bis 60 amu  and angular resolution 10-15 °

Further information about the MPPE Experiment can be found in:
Saito, Y, et al., Scientific objectives and instrumentation of Mercury Plasma Particle Experiment (MPPE) onboard MMO, Plan.Space Sci, 58, 1-2, 182-200, 2010.

Saito, Y, et al., Pre-flight Calibration and Near-Earth Commissioning Results of Mercury Plasma Particle Experiment MPPE onboard MMO (Mio), Space Science Reviews, 2020, submitted

Sensors on MMO

The MPPE Mass spectrometer (MSA)

The sensor design is similar to the CAPS-IMS sensor flying on the Cassini spacecraft. The scientific objective of the MSA sensor is the measurement of 3-D distribution functions for low-energy ions with both solar wind and planetary origins as well as interstellar pick-up ions with a high mass resolution.

MSA Collaboration

The MSA-Sensor is a tophat ion spectrometer, developed by :

  * LPP, France (Sensor)
  * MPS, Deutschland (High voltage)
  * IDA-TU Braunschweig, Deutschland (CPU)
  * ISAS, Japan (Electronics and Sensor)

Technical Data

Energy Range

5 eV/q ~ 40 keV/q

Energy Steps

64 steps (nominal step duration : 16 ms)

Energy Resolution ΔE/E

~ 10 % (FWHM)

Mass Resolution m/Δm

40 for ion energies < 15 keV/q

15 for ion energies > 15 keV/q

Field of View

8 deg. x 360 deg. (nominal)

Angular Resolution

8 deg. x 11.25 deg

Time Resolution

2 seconds (half a spin period) for 3-D distribution function

geometry factor

10-4 cm2 sr /keV (nominal)

10-5 cm2 sr /keV (for solar wind ions)


Measurement principle

Ions enter the sensor at the top side through a planar disc with an opening angle of 8deg. An electric field applied to two toroidal shells then selects ions of a specific energy. After energy selection ions enter a time-of-flight (TOF) unit by exciting a start signal when passing through a thin carbon foil and a stop signal when hitting a solid state detector. Between carbon foil and solid state detector a high voltage electric field is applied. Depending on their charge after passing the carbon foil will hit two different detector planes. The principle of the sensor is further explained in D.T. Young et al, Cassini Plasma Spectrometer Investigation, SpaceSciRev, 114, 1-112, 2004.

Äußere Sensor-Struktur

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