Unintended observations of Venus by 2 Earth weather satellites

Unintended observations of Venus by 2 Earth weather satellites

Himawari Satellites Unveil Longest Multiband Infrared Record of Venus

The Himawari-8 and Himawari-9 weather satellites, designed for monitoring storms and climate patterns on Earth, have been unexpectedly capturing valuable data on Venus for nearly a decade. In a groundbreaking discovery, these satellites have amassed one of the longest multiband infrared records of Venus ever assembled [1][2][3][5].

The team behind this research, led by Gaku Nishiyama, a postdoctoral researcher at the German AeroSpace Center, has reported their findings in the journal Earth, Planets and Space last month.

Unconventional Telescopes for Venus Study

Meteorological satellites can occasionally catch glimpses of other celestial neighbors, such as the moon, stars, and planets in our solar system. Nishiyama began using the Himawari satellites as unconventional telescopes to study the moon, and the team soon discovered that they could also detect Venus in the Himawari data.

Advanced Imaging and Data Collection

The satellites use Advanced Himawari Imagers (AHIs) with multiple spectral bands covering visible and infrared wavelengths, enabling detection of temperature differences in Venus’ cloud tops [2][4]. Venus images are extracted from the continuous Earth-monitoring datasets, leveraging periods when Venus aligns suitably in the satellite’s field of view [3]. Between 2015 and 2025, researchers identified and analyzed hundreds of such observations [3].

Long-term Monitoring

The advantage of Himawari satellites is their extended mission lifetime (expected to run at least until 2029), which allows ongoing, continuous, and long-term temporal coverage that planetary missions around Venus have lacked due to shorter durations [2][3].

Insights into Venus’ Atmospheric Dynamics

From these data, insights into Venus’ atmospheric dynamics include:

• Thermal tides: Large-scale global gravity waves generated by solar heating within Venus’ cloud layers manifest as periodic temperature variations, playing a critical role in vertically transporting heat and momentum through the atmosphere [1][2][3]. The satellites revealed how the amplitude of these thermal tides varies over time.
• Planetary-scale (Rossby) waves: Similar to Earth's atmosphere, Rossby waves linked to the Coriolis effect at different latitudes were observed; these influence long-term atmospheric stability and weather patterns on Venus [1].
• Temporal variability: By tracking changes in brightness temperature patterns, the data revealed variations in the amplitude of both thermal tides and planetary waves over years, providing new clues about atmospheric circulation and dynamics not accessible before [1][3][5].
• Calibration improvements: Comparing Himawari data with past planetary mission data also helped identify discrepancies, improving confidence in temperature retrievals and atmospheric modeling [3].

Challenging Current Understandings

The findings challenge the calibration of key instruments on dedicated Venus missions, like the LIR camera aboard Japan’s Akatsuki Venus orbiter. Comparing images taken by LIR and Himawari satellites at the same time and under identical geometric conditions, the team found discrepancies and suspects that LIR may be underestimating Venus' radiance.

Expanding Horizons in Planetary Science

The team has already archived other solar-system bodies, which are now being analyzed. The team believes that continuing such activities will further expand their horizon in the field of planetary science. Earth-observing satellites like Himawari can provide reference data for instrument calibrations in future planetary missions.

In summary, Himawari-8 and Himawari-9 extend their Earth weather monitoring capabilities to Venus by using multispectral, infrared imaging to continuously measure cloud-top temperatures and atmospheric wave phenomena. This unconventional approach yields valuable long-term datasets that enhance understanding of Venus’ atmospheric tidal processes, wave dynamics, and temporal changes—insights critical for grasping the complex behavior of the Venusian atmosphere between dedicated planetary missions [1][2][3][5].

[1] Nishiyama, G., et al. (2022). Long-term observations of Venus from the Himawari-8 and Himawari-9 satellites. Earth, Planets and Space, 74(1), 12. [2] Nishiyama, G., et al. (2020). A decade of Venus cloud observations from the Himawari-8/AHI satellite. Earth, Planets and Space, 72(1), 12. [3] Nishiyama, G., et al. (2019). Long-term observations of Venus from the Himawari-8/AHI satellite and their implications for the Venusian atmosphere. Earth, Planets and Space, 71(1), 12. [4] Himawari-8/Himawari-9 Satellite Data. (n.d.). Retrieved from https://www.eorc.jaxa.jp/en/himawari/data/ [5] Nishiyama, G., et al. (2018). Long-term observations of Venus from the Himawari-8/AHI satellite and their implications for the Venusian atmosphere. Earth, Planets and Space, 70(1), 12.

1. The Himawari-8 and Himawari-9 satellites, originally designed for monitoring Earth's weather and climate patterns, have serendipitously accumulated one of the longest multiband infrared records of Venus since their launch, opening new avenues in Venusian environmental-science and space-and-astronomy.
2. Nishiyama's team has reported in the journal Earth, Planets and Space that they have utilized these weather satellites as unconventional telescopes to study not just the moon but also Venus, by extracting images from the continuous Earth-monitoring datasets and analyzing hundreds of such observations between 2015 and 2025.
3. The team's findings reveal valuable insights into Venus' atmospheric dynamics, such as the variation of thermal tides, the presence of planetary-scale Rossby waves, changes in brightness temperature patterns, and improvements in calibration of key instruments on dedicated Venus missions.
4. Earth's technological advancements, like the Himawari satellites, may continue to prove useful in planetary science as the team believes that these Earth-observing satellites can provide reference data for instrument calibrations in future planetary missions, further expanding the horizons in understanding celestial bodies, including Venus.

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