Uranus and Neptune, the so-called ice giants, are the most distant giant planets in our Solar System. Our knowledge of these worlds was revolutionized by the flybys of NASA’s Voyager 2 spacecraft on January 24, 1986 and August 25, 1989, respectively. Since these Voyager encounters, our perception of the visible appearance of these worlds comes primarily from images reconstructed from observations from Voyager 2’s Imaging Science System (ISS), which recorded images in several separate filters, running from ultraviolet to orange. In those images, Uranus appears pale green, while Neptune appears darker blue, and this perception of the relative colors of these planets has become commonly accepted. But a new study has revealed that the two ice giants are actually far closer in color.
“Although the familiar Voyager 2 images of Uranus were published in a form closer to ‘true’ color, those of Neptune were, in fact, stretched and enhanced, and therefore made artificially too blue,” said University of Oxford’s Professor Patrick Irwin.
“Even though the artificially-saturated color was known at the time amongst planetary scientists — and the images were released with captions explaining it — that distinction had become lost over time.”
“Applying our model to the original data, we have been able to reconstitute the most accurate representation yet of the color of both Neptune and Uranus.”
In the study, Professor Irwin and his colleagues used data from the Space Telescope Imaging Spectrograph (STIS) on board the NASA/ESA Hubble Space Telescope and the Multi Unit Spectroscopic Explorer (MUSE) on ESO’s Very Large Telescope.
This means that STIS and MUSE observations can be unambiguously processed to determine the true apparent color of Uranus and Neptune.
The astronomers used these data to re-balance the composite color images recorded by the Voyager 2 camera, and also by Hubble’s Wide Field Camera 3 (WFC3).
This revealed that Uranus and…
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