# Sentence-Level Insights from the Martian Literature: A Natural Language Processing Approach
## 2 Data and Method  
### Corpus  
This study compiled 10,655 academic papers related to Martian research, drawn from leading journals in Earth and space sciences, including _Journal of Geophysical Research: Planets (JGR: Planets), Journal of Geophysical Research: Space Physics (JGR: Space Physics), Journal of Geophysical Research: Earth Surface (JGR: Earth Surface), Geophysical Research Letters (GRL), Earth and Planetary Science Letters (EPSL), Geochimica et Cosmochimica Acta (GCA), Environmental Science & Technology (EST), Nature, Nature Geoscience, Science, among others. The publication years span from 2001 to 2024. All selected papers are peer-reviewed journal articles, retrieved in full-text from major publishers such as American Geophysical Union, European Geosciences Union, American Meteorological Society, Elsevier, Springer, Wiley, and Nature Publishing Group. The selection focused on journals with high relevance and impact in the fields of Earth and space sciences. All selected papers must include keywords such as \"Mars,\" \"MARS,\" and \"Martian\" (case-insensitive). The corpus does not cover all Mars-related publications. After completing the full-text download, all PDF files were systematically converted into text format, following conventions aligned with human reading habits. Specifically, multi-column layouts (dual or triple columns) were reformatted into a single-column structure. Figures, captions, and publisher-related information were excluded, retaining only the core content, such as abstracts and main body text. The resulting text was then segmented into sentences, each constrained to a minimum of 10 words and a maximum of 256 words. Sentences containing the keywords \"Mars,\" \"MARS,\" and \"Martian\" (case-insensitive) were further screened, yielding a corpus of 151,196 sentences directly relevant to Mars research. Figure 1 illustrates the trends in the annual number of publications, the total number of sentences per year, and the distribution of sentences across different journals within the corpus. Overall, both the number of annual publications and the number of sentences show an upward trend with time. Among the top five journals by total sentence count (Figure 1b), _JGR: Planets_ primarily focuses on the Martian surface and environment, _JGR: Space Physics_ emphasizes the Martian magnetic field and ionosphere, and _GCA_ concentrates on geochemistry. These findings suggest that the Martian space environment, surface processes, and chemical composition have been important areas of research interest. Figure 1: Annual trends of Mars-related publications and sentence counts from 2001 to 2024. (**a**) The green curve illustrates the number of Mars-related papers published from 2001 to 2024. (**b**) Changes in the number of Mars-related statements across different journals are shown, with the green curve representing the total number of statements and the colored curves representing individual journals, including _Journal of Geophysical Research: Planets, Journal of Geophysical Research: Space Physics, Geophysical Research Letters, Earth and Planetary Science Letters, and Geochimica et Cosmochimica Acta. The Mars-related corpus is primarily sourced from journals published by the American Geophysical Union (AGU), although the database includes journals from multiple publishers. Notably, while the annual number of publications in journals such as \(GRL\) remained relatively stable, the volume of Mars-related sentences increased significantly since 2020. This trend may align with the timeline of several major Mars exploration missions. For example, in February 2021, China's Tianwen-1 spacecraft entered Mars orbit, initiating a comprehensive investigation of the planet's morphology, geology, subsurface water ice, material composition, climate, and physical fields to better understand its evolutionary history and potential habitability [11; 12].