IT House News on January 16, according to the website of the Shanghai Astronomical Observatory of the Chinese Academy of Sciences, during the Mars solar transit in 2021 (late September to mid-October), with the support of the National Space Administration, Chinese Academy of Sciences Shanghai Astronomical Observatory, Chinese Academy of Sciences National Space Science Center, Peking University School of Earth and Space Sciences, Chinese Academy of Sciences National Astronomical Observatory, University of Tasmania Australia and European Very Long Baseline Interferometry Institute and other Chinese and foreign scientific research institutions used the "Tianwen-1" orbiter and the "Mars Express" The orbiter's measurement and control communication signals have jointly carried out solar transit occultation observations of the sun and achieved important research results. The research papers have been published in The Astrophysical Journal Letters, an international professional journal.
The Mars solar transit refers to the natural phenomenon of the Earth and Mars moving to both sides of the Sun and the three are in a nearly straight line. During the transit of Mars, the radio signal transmitted by the probe to the Earth Measurement and Control Station passes through the adjacent solar space (hereinafter referred to as "solar space"), and its signal intensity and frequency change due to solar electromagnetic radiation interference.
▲ During the solar transit, the position relationship between the Earth, Mars and the Sun is | The picture is from the website of the Shanghai Astronomical Observatory of the Chinese Academy of Sciences, the same below
During the 2021 Mars solar transit, the "Tianwen-1" orbiter and the ESA "Mars Express" orbiter mission team controlled two probes to regularly transmit radio signals to the earth, and scientists from many countries used more than a dozen radio telescopes at home and abroad to observe the influence of the signals of the two probes by the sun.
During the transit of Mars, multiple VLBI stations observed Tianwen-1 and Mars Express
On October 9, 2021, when the Mars projection point (the projection of Mars near the Sun) was 2.6 Rs (solar radius) from the heliocentricity, the researchers found that 6 observatories received the strongest disturbance of 20Hz and ±10 minutes at the frequency of the radio signals of Tianwen-1 and Mars Express.
By analyzing the disturbance signal, the researchers found that when the radio signal traveled through the perisolar space, the total electron content in this region changed by thousands of TECUs (total electron number unit, 1TECU=1016 electrons / square meter). After comparing with optical remote sensing observations obtained by the Large Angle Spectrocoronagraph (LASCO) during the same period, it was found that the change in total electron content was caused by the phenomenon of coronal mass ejection (CME). As one of the most violent bursts on the sun, CME rapidly ejects a large number of plasmas carrying magnetic fields, and the refraction and scattering effects of these plasmas on the signal cause disturbances in the signal frequency.
Since the same frequency disturbance signal arrives at different location stations at different times, the plasma ejection velocity of CME can be calculated through the propagation distance and propagation time between the frequency disturbance signal and each station, so the multi-station joint test can be used to study the spatial propagation of solar activity in solar space.
At the same time, coronal flow waves caused by the interaction of CME and coronal streams were observed at a smaller spatial scale near the Mars projection point. Coronal wave is a large-scale coronal fluctuation phenomenon, also known as the "ribbon floating over the sun", reflecting the constraints of the magnetic field on the motion of the solar wind plasma.
IT House learned that this observation also detected the nascent high-speed solar wind flow when the CME left. The nascent solar wind refers to the solar wind that has just been ejected from the sun.
According to reports, this work benefits from the high sensitivity of the detector radio remote sensing observation method, as well as the advantages of high temporal resolution and high spatial resolution of multi-station joint observation. This method can observe the small-scale rapid change phenomenon of adjacent space that cannot be accessed by in-situ detectors and the small scale rapid change phenomenon of space that cannot be recognized by optical means, which is helpful for researchers to study the adjacent space environment and its impact on deep space communication in more detail.