The Jupiter Magnetospheric Orbiter (木星磁気圏オービター,JMO) is an orbiter probe proposed by the Japanese Aerospace Exploration Agency (JAXA), as the Japanese contribution to the Europa Jupiter System Mission (EJSM). JMO will be carried to Jupiter by the Jupiter and Trojan asteroid exploration (Trojan Asteroid Explorer), and once the mother spacecraft arrives in the Jovian system, the JMO probe will be separated and insert itself into Jupiter orbit. The mother space craft will continue its orbit toward the Jupiter Trojan asteroids. The JMO will cooperate with European Space Agency (ESA)'s JUICE (JUpiter ICey moon Explorer) probe, which will be launched during the same launch window with JMO.
 Mission overview
JMO is currently planned to be launched in 2019 or 2020, attached to its mother spacecraft, the Jupiter and Trojan asteroid explorer. It will be inserted into Jupiter orbit in 2026 following its separation from the Jupiter and Trojan asteroids exploration.
 Former plans
As of 2007, the spacecraft was slated for a lift-off in 2020 together with ESA's Jupiter Ganymede Orbiter (JGO) from which it will undock upon its arrival at Jupiter in 2025/2026. JMO was planned to undertake detailed in-situ studies of the magnetosphere of Jupiter as a template for an astrophysical magnetised disk and affording the opportunity for “3-point” investigations of the Jupiter system via synergistic observations with JGO and NASA's Jupiter Europa Orbiter (JEO).
The size and weight of the JMO is extremely limited since it has to fit inside its carrier spacecraft. Due to this, the JMO can only carry up to 10 kg of payloads, allowing it to have only 2 to 3 scientific instruments. No matter what kind of innovative technology is available, it is impossible to conduct in situ observations with such a limited number of instruments. In order to solve the mysteries of the Jovian magnetosphere effectively with limited instruments, and to conduct observations never made before, the space craft will have a X-ray imaging spectroscope, featuring different wavelengths from instruments onboard NASA's Juno probe.
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