6:15 PM - 7:30 PM
[PCG32-P11] The Terrestrial Exosphere observed by Space Satellites
Keywords:exosphere, plasmasphere, magnetosphere, magnetic storm, geocorona, lyman alpha
In 1972, Apollo 16 obtained the first image of the geocorona from the lunar orbit with approximately field-of-view of 10 RE. In 1988, furthermore, the Ultraviolet Imaging Spectrometer (UVS) onboad the Nozomi satellite gave us the geocorona expanding down to 20 RE. Therefore the observation of Apollo-16 was not enough to image whole geocorona. No observations of the geocorona had been done so far.
The observations of the geocorona have also been conducted by the Earth-orbiting satellites. Recently, hydrogen atoms in the geocorona sur-rounding from 3 RE to 8 RE are reported to increase by approximately 10% during magnetic storms. However, the responsible mechanism has not been proposed.
In September 2013, HISAKI/EXCEED was launched by the Epsilon rocket. It is now observing the geocorona in the orbit. During the strong geomagnetic storms in February 2014, the brightness at the Lyman-alpha emission was identified. I found the responsible mechanism to increase the brightness during the magnetic storms and compared it with observations. As a result, I have made a conclusion that thermospheric expansion and charge exchange with plasmaspheric ions should be responsible for the increases of hydrogen atoms.
In December 2014, the ultra-small deep space satellite (PROCYON) launched together with HAYABUSA-2. Lyman Alpha Imaging Camera (LAICA) is boarded on PROCYON. The LAICA instrument observes the so-lar resonant scattering lights from hydrogen atoms. It takes pictures of whole geocorona with a wide FOV (corresponding to more than 25 RE from Earth). I have calibrated the performance of the LAICA before the launch. As a result, the LAICA has a total sensitivity of 1.1×10-3 cps/Rayleigh/pix at H I (121.6nm). Then, on 5th January 2015, I succeeded in imaging the geocorona from the deep space (13,000,000 km away from Earth). Not only it was 42 years after the Apollo-16 observation, but also this geocoronal imagery has the widest perspective in the world.