The iconic images of Uranus and Neptune captured by NASA's Voyager 2 probe do not faithfully represent the colors of these two gaseous planets. Over time, NASA's explanations of these colors gradually became forgotten, giving rise to misconceptions about the true reality of the hues. A team of scientists led by Professor Patrick Irwin from the University of Oxford has managed to put together the most accurate representation of the color of Neptune and Uranus to date. Surprised!
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While astronomers have long known that most modern images of Neptune, Neptune and Uranus, do not faithfully represent their actual colors, the spectacular and famous images of these two planets captured by Voyager 2Voyager 2 have led us incorrectly to believe that Neptune is a deep azure blue and Uranus has a pale blue-green appearance.
In a study published in the Monthly Notices of the Royal Astronomical Society, Professor Patrick Irwin of the University of Oxford and his team show that the two planets are actually much closer in color than generally thought. In reality, these two planets have a similar green-blue hue, with Neptune showing just a hint of additional blue due to a thin layer of haze.
The combined use of Hubble and VLT shows us the true face of these two planets
This misconception has its origins in the fact that images of the two planets in the 20th century – particularly from NASA's Voyager 2 mission, the only probe to fly over these worlds – recorded images in different colors. The monochrome images were then combined into composite color images, which were not always perfectly balanced to achieve an accurate representation of the actual colors. Particularly in the case of Neptune, these images were often artificially enhanced with a “too blue” hue. In addition, the first images of Neptune taken by Voyager 2 had greatly improved contrast to make clouds, bands and winds more visible, influencing our current perception of the planet. Professor Irwin points out: “Although the known images of Uranus from Voyager 2 were released with more accurate colors, those of Neptune were stretched and enhanced, rendering them artificially too blue.”
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To reconstruct the most accurate color of Neptune and Uranus to date, the researcher and his team used HubbleHubble's STIS imaging spectrograph and the Muse spectrograph at ESO's VLT. They also solved the mystery of Uranus' seasonal color change during its 84-year orbit around the Sun. They attribute this to the planet's unusual rotation, in which the poles point almost toward the sun during the solstice, causing fluctuations in the reflectivity of the polar regions. This is important, say the authors, because any change in the reflectivity of the polar regions would therefore have had a significant impact on the overall brightness of Uranus from our planet.
Professor Irwin emphasized that this study is the first to combine a quantitative model with image data to explain the color changes of Uranus as it orbits. Dr. Heidi Hammel of the Association of Universities for Astronomical Research (Aura), who studied Neptune and Uranus for decades but was not involved in the study, believes that “this comprehensive study will finally put an end to the misperception of the color of Uranus.” and the unusual color changes of Uranus that lasted for decades.