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MMO: Mercury Magnetospheric Orbiter Japanese page>>
MMO (Mercury Magnetospheric Orbiter) : Objectives
The MMO spacecraft mainly aims the study of the magnetic field and magnetosphere of Mercury. JAXA/ISAS is responsible for its development and employment on the Mercury orbit.

Earth and Mercury have intrinsic magnetic field, but Mars and Venus do not. Why? Comparison of the Mercury's magnetic field with Earth's brings us the large step for the understanding of the terrestrial magnetic field and magnetosphere, and the magnetospheres in the various scales in the Universe.

The main objectives of the MMO spacecraft are as follows:
  • Structure and origin of Hermean magnetic field
    The magnetic field around Mercury in high accuracy will be surveyed for the study of the origin of planetary magnetic field.
  • Structure, dynamics, and physical processes of Hermean magnetosphere
    The magnetosphere will be surveyed in detail for the investigation of the universality and the singularity of planetary magnetospheres.
  • Structure, variation, and origin of Hermean exosphere
    The large-scale structure and variation of the thin 'atmosphere' tell us their generation / disappearance processes.
  • Environment of inner solar system
    The powerful environment near the sun is observed, and the energy process is solved.
MMO: Overview
MMO is the 'Spin-type' spacecraft with the spin rate of 4 seconds.
This is because of the "3-dimensional velocity distribution of particles" and "extension of four long wire antennas (15m) and two MASTs (5m) for electromagnetic field measurements with centrifugal force".
The spin axis is almost perpendicular to the Mercury equatorial plane.
This is 1) the rejection of solar reflection light into the upper / lower surface of the spacecraft and 2) the continuing aiming of the High-Gain antenna to the Earth with small efforts.
On the side panel, "SSM", a kind of mirror, is fully stuck in order to reflect the much intence sun light.
SSM reflects the optical light and emitts the infrared light, so that the temperature inside the spacecraft is kept near 'the room temperature'. (Normal operation of an electric device is not guaranteed at high temperature.)
The MMO spacecraft will enter to the polar orbit with "400km periheam and 12,000km apoherm", in order to make magnetic field mapping of all spheres and observation of the Mercury magnetosphere in whole regions.
Orbital period is 9.2 hours.
This orbit has the same plane and and 4 times cycle (MPO:2.3 hour) of the MPO orbit, and can perform cooperation observation with MPO easily.
In the cruise phase to Mercury, MMO is carried with Mecury Composite System (MCS) under the control of ESA, jointed with the MPO spacecraft and promotion modules.
After the arrival, the MMO will be separated by spin-ejection, and be operated by Sagamihara Space Operation Centre in ISAS/JAXA with UDSC 64m antenna in Nagano Japan.
MMO: Payload Selection
Payloads for MMO and MPO spacecraft was selected by the international payload review comittee in fall 2004. Now, several joint payload teams with Japanese and European scientists actively make design and development efforts. Moreover, the observation plan after the Mercury arrival will draw up and carry out by the "BepiColombo Science Working Team" which involved in not only the payload development members but also the theoretical researchers in both Europe and Japan.

((( MMO Science Working Sub-Group: Payload Teams )))
Target PI and Co-PIs Other Institutions
magnetic field W. Baumjohann (IWF, Austria)

A. Matsuoka (ISAS/JAXA)
Japan: Tokai Univ., Kyushu Univ., Tohoku Inst. Tech.,
Kumamoto Univ., Tokyo Inst. Tech., Univ. Tokyo, NiCT
Europe:Tech. Univ. Braunschweig (Germany)
Imperial College (UK)
low / high energy
electrons / ions,
energetic neutrals
Y. Saito (ISAS/JAXA)

J.-A. Sauvaud (CESR-CNRS, France)
M. Hirahara (Rikkyo Univ.)
S. Barabash (IRF, Sweden)
Japan: Kyoto Univ., STEL/Nagoya Univ.,
Tokyo Inst. Tech., Tohoku Univ., Univ. Tokyo,
Europe: CETP-IPSL, CNRS (France), MSSL/UCL (UK),
CNR-IFSI (Italy), Charles Univ., IAP (Czech),
BIRA-IASB (Belgium), MPS (Germany)
Univ. Bern (Switzerland)
Others: Boston Univ. (USA), National Central Univ. (Taiwan)
electric field,
plasma wave,
radio wave
Y. Kasaba (Tohoku Univ.)

J.-L. Bougeret (LESIA, France)
L. Blomberg (Alfven Lab., KTH, Sweden)
H. Kojima (RISH, Kyoto Univ.)
S. Yagitani (Kanazawa Univ.)
Japan: Toyama Pref. Univ., Ehime Univ.,
Kyoto Sangyo Univ., ISAS/JAXA
Europe: LPCE-CNRS, CETP-IPSL (France), IRF (Sweden),
Univ. Oslo (Norway), Finn. Meteo. Inst.,
Univ. Oulu (Finland), Eotvos Univ. (Hungary),
image (Na line)
I. Yoshikawa (Univ. Tokyo)
O. Korablev(IKI, Russia)
Japan: Rikkyo Univ., Tohoku Univ.,
Tokyo Polytech. Univ., NIPR, JAXA
dust count/moment H. Shibata (Kyoto Univ.) Japan: Tokyo Univ. Marine Sci. Tech., Waseda Univ., Osaka City Univ., NAO, ISAS/JAXA
Europe: MPI-NP (Germany)

<<< MMO model payloads: basis for the project start in 2004 >>>

MMO:Payload (2010/11)
Mercury Plasma Particle Experiment
Mercury Electron Analyzer (MEA) Low-energy electrons 3eV-30keV, dt=1sec
Mercury Ion Analyzer (MIA) Low-energy ions 5eV-30keV, dt=2sec
Mass Spectrum Analyzer (MSA) Ion Mass 5eV-40keV, dt=2sec
High-Energy Ions (HEP-ion) High energy Particle-Ions 30keV-1MeV,
High energy Particle-electrons 30keV-700keV,
Energetic Neutrals
Analyzer (ENA)
High-energy Neutral Atoms <25eV-3.3keV,
Magnetic Fierld Investigation (MGF) Magnetic field DC-64Hz
Plasma Wave Investigation (PWI) Electric Field, Plasma wave, Radio wave


Mercury Sodium Atomosphere Spectral Imager (MSASI) Na-atmosphere image FOV:-30deg
Mercury Dust Monitor (MDM) Interplanetary Dust PZT
BepiColombo : Spacecraft
Japan Aerospace Exploration Agency (JAXA) Institute of Space and Astronautical Science (ISAS) European Space Agency (ESA) BepiColombo Project (ESA)
BepiColombo, a cooperative mission by Japan Aerospace Exploration Agency (JAXA) / Institute of Space and Astronautical Science (ISAS) and European Space Agency (ESA), will explore Mercury, the planet closest to the Sun. ISAS/JAXA is building one of the main spacecraft, the Mercury Magnetospheric Orbiter (MMO), and ESA will contribute the other, the Mercury Planetary Orbiter (MPO).
[Mercury exploration] JAXA >> ISAS >> [Space Plasma Group, ISAS/JAXA]
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