オーロラの科学と測定
Hello everyone, SCIENSPOT is the podcast that shines the spotlight on the latest
scientific technology from Japan. Your host is REN from SCIEN-TALK.
Today I'm gonna talk about the magnificent natural phenomenon, the aurora. We know that
aurora is caused when electrons streaming from space collide with gases in the Earth's atmosphere,
primarily oxygen and nitrogen, causing them to light up in various colors.
The color of the light, whether it's red, green, purple, or blue we're focusing on today,
holds vital information about the incoming particles and the state of our atmosphere.
For scientists, a long-standing challenge has been accurately determining the altitude
at which the aurora light is emitted. Traditionally, this required complex
setups using multiple cameras placed far apart to take a stereo image,
making precise height estimation difficult with just one camera. Furthermore,
understanding the altitude distribution of these emissions is key to solving the mystery
of how ions, charged particles, are created in the ionosphere and how they escape into space.
青いオーロラの観測技術
This is a crucial unresolved issue in space science.
A breakthrough has been achieved by a Japanese international research team
led by Project Professor Katsumi Iida and Assistant Professor Yoshinuma of the National
Institute of Fusion Science, along with Professor Ebihara of Kyoto University and
Shiokawa of Nagoya University. The team achieved the world's first precise observation of the
altitude distribution of the blue aurora, which is generated by nitrogen ions,
observed during astronomical twilight. The core instrument used was the hyperspectral camera.
for auroral imaging, installed in Sweden in 2023.
A hyperspectral camera is far more advanced than a standard camera, which only captures
red, green, and blue. A hyperspectral camera can divide light into hundreds of colors,
allowing scientists to analyze the light components with incredible details.
The innovative methodology involved observing during astronomical twilight.
This is a period right before sunrise or after sunset when the sun is just below the horizon
and sunlight is scattered by the atmosphere, causing a faint brightness.
新技術によるオーロラの測定
The key innovation is the sunrise during twilight, the height at which
the aurora is illuminated by the sunlight changes, sweeping from high altitude downwards.
The researchers utilized the resonant scattering of light, the light emitted by the aurora when
excited by the sun's rays, to calculate the altitude using principles borrowed from
laboratory plasma research. By tracking the interaction of the camera's sight line and the
illuminated section, they could determine the height using a single camera.
Using this new technique on the blue aurora, the research team found a remarkable result.
While the emissions are typically strongest at 130 km during the night, the twilight
observations showed the emission intensity had its maximum increase rate at 200 km.
This directly indicates that the blue aurora is extremely bright and strong at this high
altitude during twilight. This finding supports previous observations suggesting that the density
of nitrogen ions is higher than conventional models have assumed at these high altitudes.
The international team successfully demonstrated a new method using a hyperspectral camera during
オーロラの高度測定
astronomical twilight to precisely map the altitude of the blue aurora, confirming very strong
emissions at 200 km. This high-precision observation provides strong scientific evidence
that validates theoretical models of aurora generation and is expected to open new pathways
for research into the long-unsolved mystery of ion production and outflow from the Earth's ionosphere.
The balance between the generation and outflow of ions can determine the very fate of a planet.
So Earth has a powerful magnetic field that acts as a shield protecting it from the sun wind
and preventing it from directly striking the atmosphere. However, ions still escape from the
polar regions, which are the gaps in this magnetic shield, and understanding this rate of outflow is
essential for predicting whether Earth can retain its atmosphere far into the future.
On the other hand, Mars currently lacks a significant magnetic field. As a result,
the solar wind directly collides with the Martian atmosphere,
violently and continuously stripping away atmospheric ions into space. It is believed
オーロラの科学的理解
that this severe ion outflow is why Mars became such a cold, dry planet,
it is today having lost the majority of its ancient atmosphere and water.
In summary, studying the problem of ionospheric generation and outflow is crucial for understanding
why Earth did not suffer the same fate as Mars. Furthermore, it directly contributes to the
research for the conditions that make a planet habitable. It's very interesting, isn't it?
Honestly, in this week, I have a plan to visit Finland to see the aurora. So I'm looking forward
to seeing the beautiful aurora and the point of aurora's height and some scientific issues
in my mind. So that's all for today's SciencePod. This podcast is broadcast in both Japanese and
English. I'd love for you to listen to the podcast and post your thoughts with the hashtag
SciencePod. Thank you for listening and see you next time.
