Toward new frontiers : Encounter and synergy of state-of-the-art astronomical detectors and exotic quantum beams

Program D01-1	Synthesis and accumulation of space-weathered icy moon's surface materials uncovered by planetary quantum beam experiment and muon analysis
Principal Investigator	KIMURA, Tomoki (Tohoku University)

Our final goal is to universally understand creation and evolution of habitable environments in the space and atmosphere surrounding planets.

Our current scope is the icy bodies in our solar system, at which liquid water “subsurface ocean” is confirmed underneath solid icy surface. The extra-terrestrial life like deep sea creatures at Earth potentially exists in the subsurface ocean. In 2030s, we are going to explore space and surface environments at Jupiter’s icy moons “Ganymede” and “Europa” based on highly precise “in-situ” measurement with spacecraft developed in international collaboration with JAXA and ESA. Creation and evolution of the subsurface ocean will be uncovered by our laboratory experiment for the icy body's space environment in comparison with the in-situ spacecraft observation.

The key for our goal is the space plasma surrounding the icy body. The space plasma is accelerated by electromagnetic energy deposited in intrinsic magnetic field and rotation of planet. The energetic plasma irradiates materials of the icy body's surface. Chemical and physical alterations on the surface materials
Figure: Grand design of this study. Jupiter's high energy plasmas, which are energized by electromagnetic acceleration and circulation in the magnetosphere, are irradiated to surfaces of the icy moons Europa and Ganymede. The irradiated plasmas drive synthesis and dissociation of icy surface materials, as known as the space weathering. In this study, we try to quantify the surface materials newly produced via the space weathering. The quantified materials constrain age when the subsurface ocean materials surfaced and duration of icy moon's intrinsic magnetic field. are driven by the irradiation, which is referred to as the “space weathering”. The space weathering slowly progresses on timescales up to 100s Mega years.

The icy body also has the intrinsic magnetic field that is generate by fluid dynamics in the interior. The icy body magnetic field reflects the space plasma, leading to dependence of the space weathering on magnetic field strength on the surface. Based on laboratory experiment for the space weathering in comparison with the spacecraft exploration, we estimate the age of magnetic field that constrains differentiation of the icy body interior including development and evolution of the subsurface ocean.

In this study, we try to quantify the color agent that represents degree of surface space weathering based on the muon beam analysis of irradiated salty and icy samples, which constrain age when the subsurface ocean materials surfaced and duration of icy moon’s intrinsic magnetic field.

Members

Reference Materials

• T. Kimura et al., “Transient internally driven aurora at Jupiter discovered by Hisaki and the Hubble Space Telescope,” Geophys. Res. Lett. 42, 1662–1668 (2015), DOI:10.1002/2015GL063272
• T. Kimura et al., “Jupiter's X-ray and EUV auroras monitored by Chandra, XMM-Newton, and Hisaki satellite,” J. Geophys. Res. Space Physics 121, 2308–2320 (2016), DOI:10.1002/2015JA021893
• T. A. Nordheim, K. P. Hand, C. Paranicas, “Preservation of potential biosignatures in the shallow subsurface of Europa,” Nature Astronomy 2, 673–679 (2018)
• K. P. Hand, R. W. Carlson, “Europa's surface color suggests an ocean rich with sodium chloride,” Geophys. Res. Lett. 42, 3174–3178 (2015), DOI:10.1002/2015GL063559.
• K. K. Khurana, R. T. Pappalardo, N. Murphy, T. Denk, “The origin of Ganymede's polar caps,” Icarus 191, 193–202 (2007)