The first scientific results of the Tianwen-1 Martian Energy Particle Analyzer were released

Recently, the Tianwen-1 Mars Energy Particle Analyzer obtained the first scientific result, which discussed a solar high-energy particle event observed in the earth-fire transfer orbit based on the payload. The results were published In The Astrophysical Journal Letters on July 26 and were selected as highlights by the American Astronomical Society (AAS) and featured.

The study was done in collaboration with a team of Macau University of Science and Technology, China University of Geosciences (Beijing), Institute of Modern Physics of the Chinese Academy of Sciences, Lanzhou Institute of Space Technology and Physics, University of Science and Technology of China, University of Alabama Huntsville and the National Space Science Center of the Chinese Academy of Sciences.

The Mars Energy Particle Analyzer is China’s first payload for the study of interplanetary and near-Martian space radiation environment, jointly developed by the Institute of Modern Physics of the Chinese Academy of Sciences and the Lanzhou Institute of Space Technology and Physics, and launched on the Tianwen-1 Mars rover in July 2020, officially opening the exploration mission.

On November 29, 2020, the Mars Energy Particle Analyzer observed the first large-scale solar high-energy particle event for the 25th solar cycle at a ground fire transfer orbit 1.39 astronomical units (AU) from the sun. At the time of the event, Tianwen-1 was approximately on the same magnetic field line as the Earth, which enabled Tianwen-1 and spacecraft near the Earth to observe solar high-energy particles from the same source region tens of millions of kilometers apart, providing a valuable opportunity for studying the propagation of solar high-energy particles along magnetic field lines in interplanetary space.

Understanding the acceleration and propagation mechanism of solar high-energy particles has always been one of the important topics in space physics and space weather research.

It is understood that once they leave the near-Earth environment and enter space and lose the protection of the earth’s magnetic field, astronauts and spacecraft will inevitably be exposed to intense high-energy particle radiation. Unlike galactic cosmic rays, which have long stable fluxes, the occurrence of solar high-energy particle events is sporadic and unpredictable. The energy particles produced during the outbreak of such events usually originate from the acceleration of shock waves driven by solar flare bursts and coronal mass ejections, and their fluxes can be up to several orders of magnitude higher than the background cosmic rays, which will not only have a huge impact on the interplanetary and near-Earth space radiation environments, but also pose a huge threat to space missions such as manned spaceflight and deep space exploration.

By comparing and analyzing proton flux observations from the Mars Energy Particle Analyzer and spacecraft near Earth during the November 29, 2020 event, the team found that the magnetic field lines associated with Tianwen-1 and the spacecraft near Earth were not connected to the burst source region and interplanetary shocks on the surface of the Sun, which meant that high-energy particles had to cross magnetic field lines to reach Tianwen-1 and spacecraft near Earth.

The team also found that the proton spectra observed at the two locations were very similar in shape, both appearing as power law spectra, and their proton intensity time curves also had a similar evolutionary trend during the decay stage of the solar high-energy particle event, showing a typical reservoir phenomenon.

The research team believes that the power law energy spectrum is likely to be generated in the source region of shock wave acceleration, and the vertical diffusion effect during propagation is a key factor in explaining the reservoir phenomenon in this event.

At the same time, the study also discussed the radial correlation of the peak intensity of solar high-energy particle events and the correlation of magnetic field line length.

Image 1.png

The relative positions of Tianwen-1 (gray dot), Mars (red dot), Earth (blue dot), and other satellites at the time of the event. (Source/Astrophysical Journal Letters)

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Comparison of proton time intensity curves were observed by soHO satellites and MEPA on similar energy channels. (Source/Astrophysical Journal Letters)

It is understood that in the solar high-energy particle event, the observation data of the Mars energy particle analyzer and the near-Earth spacecraft have a very good consistency, which shows that the functions and performance of the Mars energy particle analyzer instrument are in line with the design expectations, and the data measured by the instrument is reliable, which lays a good foundation for the follow-up research of the ring Mars exploration data, and is expected to help people better understand the Mars radiation environment and plan the deep space exploration mission. (Source: China Science Daily, Liu Ruinan, Gan Xiao)

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