Neptune, Uranus colors—green, blue? New images suggest a huge error

Newly released images challenge the long standing perception of Neptune's deep azure hue and Uranus's pale cyan appearance. The research, led by Professor Patrick Irwin from the University of Oxford, has unveiled that these two ice giants share a more similar shade of greenish blue than previously believed.

Historical Misconceptions: Voyager 2's impact on color Perception The misconception regarding Neptune's and Uranus's colors originated from images captured during the 20th century, primarily by NASA's Voyager 2 mission. These images, recorded in separate colors and later recombined to form composite color images, were not always accurately balanced.

Professor Irwin explained, “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.” In the recent study, researchers utilized data from the Hubble Space Telescope's Space Telescope Imaging Spectrograph ( ) and the Multi Unit Spectroscopic Explorer ( ) on the European Southern Observatory's Very Large Telescope.

By processing each pixel as a continuous spectrum of colors, the team achieved an unambiguous determination of the true apparent color of Uranus and Neptune. Rebalancing the composite color images from Voyager 2 and the Hubble Space Telescope's Wide Field Camera 3 revealed that both planets exhibit a similar shade of greenish blue.

, however, displays a slight hint of additional blue, attributed to a thinner haze layer. The study not only corrected misconceptions but also provided insights into the color changes observed in Uranus during its 84 year orbit of the Sun. By comparing images to brightness measurements recorded from 1950 to 2016, the researchers discovered that Uranus appears greener at its solstices and bluer during its equinoxes.

Understanding Uranus's Unique Spin: A Model Unveils the Mystery Uranus's unusual spin, almost on its side during orbit, plays a crucial role in its color changes. The researchers developed a model comparing the spectra of the polar and equatorial regions, revealing that the polar regions are more reflective at green and red wavelengths.

A 'hood' of gradually thickening icy haze, likely composed of methane ice particles, further explains Uranus' greener appearance at the solstice. Dr. Heidi Hammel, from the Association of Universities for Research in Astronomy ( ), commended the study, stating, "This comprehensive study should finally put both issues to rest." Professor Leigh Fletcher emphasized the importance of Earth based studies in understanding Uranus and Neptune, laying the groundwork for future missions.

Future exploration: The legacy of Voyager and beyond The study highlights the ice giants' potential as destinations for future robotic explorers. "A mission to explore the Uranian system – from its bizarre seasonal atmosphere to its diverse collection of rings and moons is a high priority for the space agencies in the decades to come." "Earth based studies like this, showing how Uranus' appearance and color has changed over the decades in response to the weirdest seasons in the Solar System, will be vital in placing the discoveries of this future mission into their broader context." In conclusion, the collaboration between the and the may have corrected misconceptions — but of course, only time will tell.

At the very least, it has provided valuable insights into the dynamic features of these distant ice giants..