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“Even though these views were taken at different wavelengths, researchers would expect at least a hint of the clouds to show up in the upper image,” NASA officials said in a statement. “Thus, they have been trying to understand what’s behind the difference.”
[ads-post][right-side] “The answer to what could be causing the discrepancy [between the ISS and VIMS images] appears to lie with Titan’s hazy atmosphere, which is much easier to see through at the longer infrared wavelengths that VIMS is sensitive to (up to 5 microns) than at the shorter, near-infrared wavelength used by ISS to image Titan’s surface and lower atmosphere (0.94 microns),” NASA officials said in the statement .
Differences in illumination geometry or changes in the clouds themselves were ruled out, as the images taken by ISS and CIMS were made over the same 24-hour period.
“High, thin cirrus clouds that are optically thicker than the atmospheric haze at longer wavelengths, but optically thinner than the haze at the shorter wavelength of the ISS observations, could be detected by VIMS and simultaneously lost in the haze to ISS — similar to trying to see a thin cloud layer on a hazy day on Earth,” NASA officials said. “This phenomenon has not been seen again since July 2016, but Cassini has several more opportunities to observe Titan over the last months of the mission in 2017 , and scientists will be watching to see if and how the weather changes.”