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LI Hao, TIAN Hui, ZHANG Weihang, QIN Jianqi, YUE Xinan, HE Maosheng, YU Xizheng. Prospects for Scientific Research Based on Transit Observations of Earth by the Solar Polar-orbit Observatory (in Chinese). Chinese Journal of Space Science, 2026, 46(5): 1-14 doi: 10.11728/cjss2026.05.2025-0237
Citation: LI Hao, TIAN Hui, ZHANG Weihang, QIN Jianqi, YUE Xinan, HE Maosheng, YU Xizheng. Prospects for Scientific Research Based on Transit Observations of Earth by the Solar Polar-orbit Observatory (in Chinese). Chinese Journal of Space Science, 2026, 46(5): 1-14 doi: 10.11728/cjss2026.05.2025-0237
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Prospects for Scientific Research Based on Transit Observations of Earth by the Solar Polar-orbit Observatory

doi: 10.11728/cjss2026.05.2025-0237 cstr: 32142.14.cjss.2025-0237
  • 1.

    State Key Laboratory of Solar Activity and Space Weather, National Space Science Center, Chinese Academy of Sciences, Beijing 100190

  • 2.

    School of Earth and Space Sciences, Peking University, Beijing 100871

  • 3.

    Key Laboratory of Planetary Science and Frontier Technology, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029

  • 4.

    College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing 100049

  • Received Date: 2025-12-27
  • Rev Recd Date: 2026-03-23
    • Available Online: 2026-06-23
    Abstract
  • The Solar Polar-orbit Observatory (SPO) mission will employ a gravity assist of Jupiter to change its orbital inclination, enabling the spacecraft to leave the ecliptic plane and conduct direct imaging observations of the Sun’s poles. Before performing the gravity assist maneuver at Jupiter, SPO will orbit the Sun near the ecliptic plane, during which it will have the opportunity to observe the transit of the Earth across the solar disk in visible and Extreme-ultraviolet (EUV) bands. This paper focuses on the prospective Earth’s transit observations by SPO in the future and presents a preliminary assessment of the potential scientific investigations that could be carried out. First, the absorption of EUV radiation by the Earth’s atmosphere during transit can be used to retrieve the atomic oxygen number density in the thermosphere and its variation with altitude, thereby obtaining the vertical distribution of oxygen atoms. Using an empirical atmospheric model of Earth, we perform forward modeling of the absorption of EUV radiation by the Earth’s atmosphere. Inversion tests demonstrate that the absorption in these EUV wavelengths can be used to infer the distribution of atomic oxygen number density in the thermosphere within an altitude range of 250-600 km. Second, based on the characteristics of light curves in both the EUV and visible bands, obtained during the Earth’s transit, we can investigate the typical transit photometric signatures that may arise in future exoplanet transit detections in EUV bands. We simulate the light-curve characteristics during planetary transits in the EUV band. Due to the significant absorption of EUV radiation by planetary atmospheres, the resulting light curves exhibit characteristics that differ from those observed in the visible band. These results will provide important guidance and theoretical support for future EUV-based exoplanet detection missions.

     

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