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A radio signal travels from Mars to Earth, but on the way it has to push through the invisible "wind" of charged particles blowing from the Sun. This wind, like ripples on water, slightly distorts radio waves. In October 2021, China's Tianwen-1 probe found itself behind the Sun, and its signal passed just 4.5 solar radii from our star — where the wind is especially dense. A ground antenna in Wuchin (70 meters across) caught these distortions, and scientists were able to "feel out" the solar corona with them.

It turned out that the radio signal's flicker, like the shimmer of air over hot asphalt, intensifies when the beam passes closer to the Sun. On October 5, 13, and 15, instruments recorded particularly strong spikes. Comparing these with images from the SOHO and SDO spacecraft, researchers saw that each spike coincided with the birth of bright structures in the corona: giant streamers, fast wind flows, or mass ejections.

Now astronomers can use any probe passing near the Sun as a free space weather sensor. No need to launch dedicated spacecraft, just "listen" to the radio signal distortions and use them to pinpoint where on the Sun a storm was born. It's like knowing from the flicker of a shadow on the wall that the wind has picked up outside.

Original abstract

as written by the authors arXiv:2604.13670

During the first superior conjunction of the Tianwen-1 Mars probe in October 2021, its downlink signal received by the Wuqing 70-m radio telescope passed within 4.53 solar radii of the Sun. The signal was significantly perturbed by the solar wind, providing a mechanism to probe coronal activity. We analyze the Doppler frequency scintillation spectrum of the solar wind within 10 solar radii to derive a characteristic frequency scintillation parameter. Statistical analysis indicates this parameter increases as the signal path approaches the Sun, with notable anomalies observed on October 5, 13, and 15. Comparisons with SOHO and SDO data reveal strong spatio-temporal correlations between these scintillation anomalies and coronal activity. We demonstrate that this parameter effectively identifies solar phenomena, including coronal streamers, high-speed solar wind, and coronal mass ejections (CMEs). Quantitative analysis confirms a distinct temporal correlation and delay between frequency scintillation and solar wind speed changes, validating the feasibility of spatially localizing solar activity.