Tasked to watch Earth, Japanese satellite makes big discovery on Venus

India Today

01-07-2025

Tasked to look at Earth, Japan's Himawari-8 and -9 meteorological satellites have been successfully repurposed to observe changes in Venus' cloud-top temperatures, revealing unseen patterns in atmospheric waves.Led by the University of Tokyo, researchers used data from 2015 to 2025 to estimate brightness temperatures on daily and yearly scales. This study highlights how meteorological satellites can complement future planetary missions and ground-based telescopes.advertisementThe Himawari-8 and -9 satellites, launched in 2014 and 2016, respectively, were originally designed to monitor Earth's atmospheric phenomena through their multispectral Advanced Himawari Imagers (AHIs).
The University of Tokyo team, led by visiting researcher Gaku Nishiyama, identified an opportunity to utilise this sensor data for spaceborne observations of Venus. Nishiyama noted, "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."Monitoring the temperature variations in Venus' cloud tops is crucial for understanding its atmospheric dynamics, which include thermal tides and planetary-scale waves. Ground-based observations have limitations due to Earth's atmosphere and sunlight during the daytime.
Observing temporal temperature variations in the cloud tops of Venus is essential to understand its atmospheric dynamics. (Photo: Nasa)
advertisementThe Himawari satellites appear well-suited to bridge this gap with their extended mission lifetimes, scheduled to operate until 2029. They offer multiband infrared coverage essential for retrieving temperature information from different altitudes. "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," said Nishiyama.The research team established a data archive by extracting all Venus images from the AHI datasets, identifying 437 occurrences.By considering background noise and the apparent size of Venus in the images, they were able to track temporal variations in cloud-top temperature during specific alignment periods of the satellite, Venus, and Earth.Upon analysing the data, the team confirmed variations in thermal tide amplitude and changes in the amplitude of planetary waves over time. These findings, although limited by the resolution of the AHI data, suggested possible links to variations in Venus' atmospheric structure.
Surface oif Venus as seen by spacecraft from Earth.
The study also revealed calibration discrepancies in data from previous planetary missions.advertisementNishiyama sees broader implications for this novel approach, stating, "I think that our novel approach in this study successfully opened a new avenue for long-term and multiband monitoring of solar system bodies. This includes the moon and Mercury, which I also study at present."He expressed hopes that the study will enable assessments of physical and compositional properties, along with atmospheric dynamics, contributing to a greater understanding of planetary evolution.- Ends