Study upending theories on auroral formation –

By Lin Chia-nan / Staff reporter

A Taiwan-made space instrument installed on Japans scientific satellite Arase has helped researchers observe aurora formation at unexpectedly high altitudes, helping to advance understanding about space weather and communications systems on Earth, scientists said on Tuesday.

The Taiwanese-Japanese team detailed their findings in a paper titled Active auroral arc powered by accelerated electrons from very high altitudes, which was published in the journal Scientific Reports on Monday.

Scientists from National Cheng Kung University (NCKU) and Academia Sinica were in charge of the Low-Energy Particle Experiments-Electron Analyzer, one of the nine instruments on the satellite, enabling it to observe energy distribution and density of low-energy electrons surrounding the Earth.

This is the first time that Taiwan has manufactured such fine and high-resolution instrument for space measuring, the university said in a news release.

Auroras are generated by electrons accelerated by a static electric field hitting the atmosphere, producing bright and elongated arcs in the nightside polar regions, Academia Sinica said.

Over the past 50 years, scientists had assumed that the electron acceleration takes places at altitudes of no more than 20,000km, but observations made through the Taiwan-made instrument found that it could occur at altitudes of up to 30,000km, it said.

The breakthrough not only overturns previous conception about the region of auroral formation, but generates new questions about how electrons work at higher altitudes, and might affect space weather, as well as communications and electrical systems on Earth, NCKU Institute of Space and Plasma Sciences professor Sunny Tam () said.

While domestic studies on space weather mainly revolve around the ionosphere, Tam said that more attention should be paid to the magnetosphere.

Tam said that his team was in 2010 invited by Japan Aerospace Exploration Agency (JAXA) to join the satellites development.

Due to budgetary concerns, they later invited Academia Sinica to join the team, Tam said.

From 2010 until the satellite was launched in 2016, the university and Academia Sinica devoted nearly NT$30 million (US$1.06 million) to the instruments development, he added.

The funding was modest when compared with that of a major satellite project, but the outcome is precious, Tam said, describing the case as an example of optimal international cooperation of space technology that would usually need astronomical funds.

While Taiwan aspires to launch more satellites into space, it should overlook developing advanced scientific instruments in partnership with other countries, he added.

The satellite is operating at an orbit of 200km to 32,000km above ground, meaning their instrument has flown farther than any other Taiwanese instrument has done before, said Wang Shiang-yu (), acting director of Academia Sinicas Institute of Astronomy and Astrophysics.

That also means it has proved resistant to strong radiation and temperature differences of up to 200oC in space, he said.

The satellite, designed to serve for only one year, has operated for more than four years, he added.

As auroras can also be observed in other celestial bodies, the teams findings would assist other efforts in space exploration, Wang said.

The Arase satellite, formerly known as the Exploration of Energization and Radiation in Geospace, is headed by JAXA, with NCKU and Academia Sinica being the only instrument team from outside of Japan.

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Study upending theories on auroral formation -