Educational Activities

Graduate school: Planetary atmosphere, Planetary exploration, Geophysical experiment, Seminar

Research Activities

Plasmaspheric imaging of the Earth in EUV (1, 2, 3)
In the late 1990s, I started developing a visualization technique for space plasma.
At the beginning of this century, I succeeded in terrestrial plasma imaging in EUV, a world first, by detecting solar resonantly scattered lights by terrestrial plasmas.
I then built an EUV telescope that was placed on board Japan's lunar orbiter (Kaguya). It took images of the Earth's polar wind from the lunar orbit.
In addition to plasmaspheric imaging, the Kaguya orbiter provided the following important findings for Earth and the Moon.


(1) Source mechanism of lunar sodium exosphere
It is commonly agreed upon that the lunar exosphere is build by the interaction between the lunar surface and the outer environment.
The main components of the lunar exosphere are Sodium, Potassium, and Calcium.
Sodium exosphere is the brightest among the elements seen from the Earth's ground -based telescopes.
There is a controversial and long-standing discussion regarding source mechanisms for the lunar exosphere.
We have identified the source mechanism responsible for maintaining the lunar exosphere on the basis of the fact that the lunar exospheric brightness has a correlation with solar wind density.
My leading team's results have stimulated the scientific community to study the atmospheres of small satellites and the interaction between solid planets and ambient plasmas.


(2) EUV stars
One of the key functions of astrophysical observation in the EUV spectral range is to identify the source of a diffuse EUV background in the universe.
That is to say, do we ascribe the source to the sum of dark EUV stars or to hot interstellar gas (100000 K)?
This also is a controversial and long-standing discussion.
Our newly developed EUV telescope has succeeded in identifying EUV stars outside the Earth's corona, where our instrument is free of contamination from Geocorona.
In the EUV spectral range, it is impossible to see deep inside the galaxy.
This means that the distribution of the EUV star should be uniform, but it seems not!
Is this really the answer for the source of the EUV star?!
For the identification of diffuse EUV stars, observation from interplanetary space is necessary.


(2) Planetary explorations (4, 5, 6)
I have been involved in BepiColombo Mercury exploration, which is a joint international program with JAXA and ESA.
As part of my work with this project, I have developed an ultraviolet spectrometer and a sodium imaging camera.
These will be launched in 2017, with data available by 2021.
EXCEED is an existing space telescope, still observing the planetary exosphere.
The Hisaki spacecraft was launched with EXCEED in September 2013 from Kagoshima in Japan.

Literature

1) Yoshikawa, I., M. Nakamura, M. Hirahara, Y. Takizawa, K. Yamashita, H. Kunieda, T. Yamazaki, K. Misaki, and A. Yamaguchi, Observation of He II emission from the plasmasphere by a newly developed EUV telescope on board sounding rocket S-520-19, Journal of Geophysical Research, Vol. 102, 19897-19902, 1997.
2) Nakamura, M., I. Yoshikawa, A. Yamazaki, K. Shiomi, Y. Takizawa, M. Hirahara, K. Yamashita, Y. Saito, and W. Miyake, Terrestrial plasmaspheric imaging by an extreme ultraviolet scanner on Planet-B, Geophysical Research Letters, Vol. 27, 141, 2000.
3) Yoshikawa, I., G. Murakami, G. Ogawa, K. Yoshioka, Y. Obana, M. Taguchi, A. Yamazaki, S. Kameda, M. Nakamura, M. Kikuchi, M. Kagitani, S. Okano, and W. Miyake, Plasmaspheric EUV image seen from the lunar orbit: Initial Result of Extreme Ultraviolet Telescope onboard KAGUYA spacecraft, Journal of Geophysical Research, 115, CiteID A04217, 2010.
4) Ichiro Yoshikawa, Kazuo Yoshioka, Go Murakami, Atsushi Yamazaki, Fuminori Tsuchiya, Masato Kagitani, Takeshi Sakanoi, Naoki Terada, Tomoki Kimura, Masaki Kuwabara, Kuto Fujiwara, Tomoya Hamaguchi, and Hiroyasu Tadokoro, Extreme Ultraviolet Radiation measurement for planetary atmospheres/magnetospheres from the Earth-orbiting spacecraft (Extreme Ultraviolet Spectroscope for Exospheric Dynamics: EXCEED), Space Science Reviews, Doi: 10.1007/s11214-014-0077-z, 2014.
5) K. Yoshioka, G. Murakami, A. Yamazaki, F. Tsuchiya, T. Kimura, M. Kagitani, T. Sakanoi, K. Uemizu, Y. Kasaba, I. Yoshikawa, and M. Fujimoto, Evidence for the Global Electron Transportation into the Jovian Inner Magnetosphere, Science, 345, 1581-1584, 2014.
6) Yoshikawa, I., O. Korablev, S. Kameda, D. Rees, H. Nozawa, S. Okano, V. Gnedykh, V. Kottsov, K. Yoshioka, G. Murakami, F. Ezawa, and G. Cremonese, The Mercury Sodium Atmospheric Spectral Imager for the MMO Spacecraft of Bepi-Colombo, Planetary and Space Science, Vol. 58, 224-237, 2010.
7) Yoshikawa, I., J. Ono, K. Yoshioka, G. Murakami, F. Ezawa, T. Toyota, S. Kameda, and S. Ueno, Observation of Mercury?fs sodium exosphere during the transit on November 9, 2006, Planetary and Space Science, Vol. 56, 1676-1680, 2008.
8) Kameda, S., I. Yoshikawa, M. Kagitani, and S. Okano, Interplanetary dust distribution and temporal variability of Mercury?fs atmospheric Na, Geophysical Research Letters, Vol. 36, Doi: 10.1029/2009GL039036, 2009.

Other Activities

Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS) steering committee member (2007-2015)

Future Plan

In my laboratory, we are studying electromagnetic phenomena occurring in the vicinity of Earth and solar planets (Plasma Physics) and trying to understand the resultant and long-term variations in the planets. Our ultimate objective is to understand the environments of extra-solar planets (Astrobiology).

Messages to Students

I hope you will join us in the space mission to witness what nobody has ever seen before. If you want to do something exciting, here is the perfect place to study.

URL

http://www.astrobio.k.u-tokyo.ac.jp/yoshikawa/