Weather satellites become accidental Venus monitors

It is by chance that Japan’s weather satellites have been quietly studying Venus for decades.

Scientists at the University of Tokyo have discovered that Himawari -8 and -9 meteorological satellites designed to track Earth’s storms have been capturing detailed temperature data from Venus’ clouds, as the planet drifts in its field of view.

Unexpected discoveries have been published in Earth, planets and space, indicating that these weather satellites can detect temperature changes in Venus’ atmosphere on multiple altitude and time scales. More importantly, they discovered previously invisible patterns in atmospheric waves and crazes that could reshape our understanding of the mysterious climate system of Venus.

“We believe this approach will provide valuable data for Venus science, because there may be no other spacecraft orbiting around Venus until the next planetary mission around 2030.”

Searching for Venus on the Edge

The discovery began when researchers realized that Venus occasionally appeared near the edge of the Earth in Himawari satellite images. Although Venus looks small—just a few pixels in a huge satellite image, the team found that they could extract meaningful scientific data.

Between 2015 and 2025, the researchers identified 437 instances, with Venus appearing in satellite data. They used advanced image analysis technology to track temperature changes at the top of Venus clouds in nine different infrared wavelengths, creating an unprecedented long-term dataset.

Frequent calibration and low noise levels of satellites have proven to be crucial. Since measurement errors are less than 1 Kelvin, these instruments can detect subtle temperature changes in Venus’ atmosphere – revealing changes in the complex atmospheric dynamics of the planet.

Unexpected atmospheric discovery

This analysis reveals several surprising findings about Venus’ atmosphere:

• Hot tide patterns show significant differences between 2015 and 2024, especially around sunrise
• Five-day Rossby Waves weakens the height above
• The temperature structure varies at different heights, indicating complex vertical atmospheric dynamics
• The amplitude of the day-night hot tide appears to be related to changes in atmospheric stability

Calibration space tasks

In addition to discovering new atmospheric phenomena, the study reveals important technical findings not highlighted in the press release: Japan’s Venus probe Akatsuki seems to have underestimated 15-17% of Venus’ temperature due to calibration issues.

By comparing the data from the weather satellite with measurements from the Akatsuki and Akatsuki and European Bepicolombo missions, the team identified differences in the system. Weather satellites are frequently calibrated to known temperature standards, making them a reliable reference point for verifying planetary mission data.

“It is well known that Venus’ atmosphere exhibits annual scale changes in reflectivity and wind speed; however, due to its mission lifespan, no planetary mission successfully observed for more than 10 years.” Ground observations face their own limitations, from the Earth’s atmosphere and sunlight interference.

Fill in key gaps

The timing of this discovery proved particularly valuable. Until around 2030, Akatsuki had communication problems and no planned Venus orbital machine, so Weather Satellites provided a unique bridge for continuous atmospheric monitoring.

The Himawari satellite is operating until 2029, and its successor is expected to have similar infrared capabilities. Other weather satellite systems, including satellites in the United States, may offer similar Venus monitoring capabilities.

A new era of accidental science

This study shows how existing infrastructure can achieve multiple scientific purposes. Weather satellites are not designed for planetary science, but their consistent operation and complex sensors make them a powerful tool for studying other worlds.

This method can go beyond Venus. Researchers believe similar techniques may be used to monitor the moon, mercury and other solar systems that occasionally drift in weather satellite images.

As space missions become increasingly expensive and complex, finding innovative ways to leverage existing satellites provides a cost-effective way to expand our understanding of the planetary atmosphere and climate systems across the solar system.

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