Weather Satellites Become Accidental Venus Monitors

Japan’s weather satellites have been quietly conducting a decade-long study of Venus—completely by accident.

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

The unexpected findings, published in Earth, Planets and Space, reveal that these weather satellites can detect temperature variations in Venus’s atmosphere across multiple altitudes and time scales. More importantly, they’ve uncovered previously unseen patterns in atmospheric waves and thermal tides that could reshape our understanding of Venus’s mysterious climate system.

“We believe this method will provide precious data for Venus science because there might not be any other spacecraft orbiting around Venus until the next planetary missions around 2030,” explained visiting researcher Gaku Nishiyama, who led the study.

Finding Venus in the Margins

The discovery began when researchers realized that Venus occasionally appears near Earth’s rim in Himawari satellite images. Despite Venus appearing incredibly small—just a few pixels in the vast satellite imagery—the team found they could extract meaningful scientific data.

Between 2015 and 2025, the researchers identified 437 instances where Venus appeared in the satellite data. Using advanced image analysis techniques, they tracked temperature changes in Venus’s cloud tops across nine different infrared wavelengths, creating an unprecedented long-term dataset.

The satellites’ frequent calibration and low noise levels proved crucial. With measurement errors below 1 Kelvin, the instruments could detect even subtle temperature variations in Venus’s atmosphere—variations that reveal the planet’s complex atmospheric dynamics.

Unexpected Atmospheric Discoveries

The analysis revealed several surprising findings about Venus’s atmosphere:

• Thermal tide patterns showed significant variations between 2015 and 2024, particularly around sunrise
• Five-day atmospheric waves (Rossby waves) weakened with increasing altitude above 68 kilometers
• Temperature structures varied differently at different altitudes, suggesting complex vertical atmospheric dynamics
• Diurnal thermal tide amplitude appeared to correlate with changes in atmospheric stability

Calibrating Space Missions

Beyond discovering new atmospheric phenomena, the research revealed an important technical finding not highlighted in the press release: Japan’s dedicated Venus probe, Akatsuki, appears to have been underestimating Venus temperatures by 15-17% due to calibration issues.

By comparing data from the weather satellites with measurements from both Akatsuki and the European BepiColombo mission during its Venus flyby, the team identified systematic discrepancies. The weather satellites’ frequent calibration against known temperature standards made them reliable reference points for validating planetary mission data.

“The atmosphere of Venus has been known to exhibit year-scale variations in reflectance and wind speed; however, no planetary mission has succeeded in continuous observation for longer than 10 years due to their mission lifetimes,” Nishiyama noted. Ground-based observations face their own limitations from Earth’s atmosphere and daylight interference.

Filling Critical Gaps

The timing of this discovery proves particularly valuable. With Akatsuki experiencing communication problems and no dedicated Venus orbiters planned until around 2030, weather satellites offer a unique bridge for continuous atmospheric monitoring.

The Himawari satellites operate until 2029, and their successors are expected to have similar infrared capabilities. Other weather satellite systems, including America’s GOES satellites, could potentially provide similar Venus monitoring capabilities.

A New Era of Accidental Science

This research demonstrates how existing infrastructure can serve multiple scientific purposes. Weather satellites weren’t designed for planetary science, yet their consistent operation and sophisticated sensors make them powerful tools for studying other worlds.

The approach could extend beyond Venus. The researchers suggest similar techniques might work for monitoring the Moon, Mercury, and other solar system bodies that occasionally drift through weather satellite imagery.

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