2021 Activity Report for Mission 3: Sustainable Space Environments for Humankind
Research 1: Study on dynamic variation of relativistic electron fluxes in the radiation belts
Principal Investigator (PI): Yoshiharu Omura (Kyoto University)
Research collaborator: Yikai Hsieh (RISH, Kyoto University)
Energetic electron acceleration and precipitation in the Earth’s outer radiation belt are highly associated with wave-particle interactions between whistler mode chorus waves and electrons. We perform test particle simulations to investigate electrons interacting with parallel and oblique chorus emissions with maximum amplitude 2.1 nT and 370 pT at L = 4.5. Oblique chorus emissions lead to more electron precipitation than parallel chorus emissions in the range 370 pT–2.1 nT. We propose a two-step precipitation process for oblique chorus emissions that contributes to more electron loss: (a) Through Landau resonance interaction with a chorus emission, electrons at high pitch angles are effectively accelerated in the parallel direction, and their pitch angles become lower. (b) The electrons bounce back toward the equator, and they are pushed into loss cone through nonlinear scattering due to cyclotron resonance with another chorus emission.
Fig. 1: Schematic pictures of the wave-particle interactions between chorus emissions and an electron showing the precipitation process by multiple resonances of different emissions. (a) Interaction along a field line. (b) Variation of kinetic energy and equatorial pitch angle.
Hsieh, Y.-K., Omura, Y., & Kubota, Y. (2022), Energetic electron precipitation induced by oblique whistler mode chorus emissions, Journal of Geophysical Research: Space Physics, 127, e2021JA029583. https://doi.org/10.1029/2021JA029583.
Research 2: Substorms (aurora substorms)
Principal Investigator (PI): Yusuke Ebihara (Kyoto University)
Research collaborator: Takashi Tanaka (Kyushu University)
Substantial disturbances in the near-Earth space, including substorms and magnetic storms, are sustained and driven by energy originating in the solar wind. The solar wind-originated energy is thought to reach the polar ionosphere by way of the magnetosphere in the form of the magnetic energy. By using the global magnetohydrodynamics simulation, we traced ‘packets’ of Alfvén waves (low-frequency magnetohydrodynamics waves) that carry magnetic energy toward the Earth. The ‘packet’ is assumed to propagate along the magnetic field line in the convecting motion of plasma. Fig. 2 shows the result. The Alfvén waves are found to be generated in the regions labeled by G1 and G2, corresponding to the (low latitude) flank of the magnetopause. In these regions, solar wind- and magnetosphere-originated plasma pulls newly reconnected magnetic field lines, resulting in the generation of the Alfvén waves and the large-scale field-aligned current.
Fig. 2：Packets of the Alfvén waves in the global magnetohydrodynamics simulation (short cylinders). The white lines indicate the magnetic field lines extending from the packets. Plasma pulls the magnetic field lines in the blue regions. The sun is to the lower left.
Ebihara, Y., & Tanaka, T. (2022). Where is Region 1 field-aligned current generated? Journal of Geophysical Research: Space Physics, 127, e2021JA029991. https://doi.org/10.1029/2021JA029991
Research 3: Microstructure of Wood-Based Carbon Coatings Durable in Low-Earth Orbit Space Environments
Principal Investigator (PI): Toshimitsu Hata (Kyoto University)
Research collaborators: Hirotsugu Kojima (Kyoto university)
The similarity between the degradation of material surfaces by atomic oxygen (AO) irradiation and material combustion in the space environment led us to investigate the structure of a hard-to-oxidize material made of wood-derived carbon material for use in the space environment. The resistance to AO irradiation was evaluated by examining the effect of AO irradiation on the flammability of wood-derived carbon (filter paper carbonized at 700°C) containing a Si compound (silsequioxane). It is noteworthy that the amount of surface abrasion by AO was lower for the carbonized filter paper only than for the material containing 33% silsequioxane.
Fig. 3: Surface of wood-derived carbon oxidized by AO
Research 4:Research on electromagnetic environments related to human activities on the moon and their measurement techniques
Principal Investigator (PI): Satoshi Kurita (Kyoto University)
Research collaborator(s): Hirotsugu Kojima (Kyoto University), Hideyuki Usui (Kobe University), Yohei Miyake (Kobe University)
Understanding of electromagnetic environments around the moon is important to assess human activities on the moon. Development of measurement techniques for the electromagnetic environments is also required. This research aims to develop an electric field sensor that can be equipped with devices and vehicles operated on the moon and to consider the measurement technique. The sensor is required to measure electric fields in the wide frequency range (DC to ~MHz), and the sensor element needs to be self-sustained. To satisfy these requirements, we have been developing a new type of electric field sensor.
In FY 2021, we developed a test model of the sensor. The frequency-dependent sensitivity of the sensor was quantified by comparing the level of broadcast radio waves measured by the developed sensor and the standard antenna. We found that the developed sensor has sufficient sensitivity to measure AC electric fields.
Fig. 4: Test model of the new sensor and the standard antenna during the sensitivity measurement.
Research 5: Research on new materials for space applications (Ultra-fine bubble for agricultural use)
Principal Investigator (PI): Yoshikatsu Ueda (RISH, Kyoto University)
Research collaborator(s): Kiyoshi Yoshikawa (Kyoto University), Morio Iijima (Kinai University), Yoshihiro Hirooka (Kindai University)
In FY2021, we are conducting field tests and field trials to investigate the differences in crop growth using UFB in oligotrophic conditions. In particular, crop growth was enhanced when UFB was present in water, indicating the potential of UFB as a new material.
Fig. 5: Differences in wheat growth. (nUFB:without UFB, UFB:with UFB)
- M. Iijima, K. Yamashita, Y. Hirooka, Y. Ueda, K. Yamane and C. Kamimura, Ultrafine bubbles alleviated osmotic stress in soybean seedlings, Plant Production Science, 2021/12, 10.1080/1343943X.2021.2021094
- M. Iijima, K. Yamashita, Y. Hirooka, Y. Ueda, K. Yamane and C. Kamimura, Promotive or suppressive effects of ultrafine bubbles on crop growth depended on bubble concentration and crop species,Plant Production Science 2021, 10.1080/1343943X.2021.1960175