Progress of radio occultation exploration of Mars

Mars is the sister star of Earth. Studying Mars is important to understand its evolution as well as that of Earth and even the solar system. Since the launch of American Mariner 4 in 1964 and the first successful use of radio occultation technology to explore the environmental characteristics of Mars, many international missions to Mars have conducted occultation experiments and made important progress. This article investigates Mars probes based on their launch time sequence, which utilized radio occultation techniques for exploration, focusing on groundbreaking missions such as the Mariner series, Mars Global Surveyor, Mars Express, Mars Atmosphere and Volatile Evolution, and Tianwen-1. We review, analyze, and summarize the product information, including the number and distribution of profile measurements, and the methods of acquisition obtained from each mission's radio occultation. Additionally, this article analyzes the limitations of the current Mars radio occultation approaches and explores possible countermeasures. Mars radio occultation can be further improved by considering the mode of star-star occultation combined with star-ground occultation to form occultation constellation, choosing an appropriate signal detection frequency, and improving the inversion algorithm. It can also be combined with the Mars top detection radar and direct detection means to develop multi-source data fusion. With the continuous improvement of detection modes, radio occultation detection will be an important tool for Mars exploration in the future. Detections will grow in number and become increasingly more comprehensive in time and space coverage, and more accurate occultation data for the entire space environment of Mars will be obtained, including large, mesoscale, and even small-scale structure characteristics and evolution laws.