Uranus and Neptune are actually similar blues, 'true' color images reveal

In the summer of 1989, Voyager 2, a NASA spacecraft, transmitted the first images of Neptune from a remote part of our solar system where the sun provides only a faint light. The photos showed a stunning, deep blue planet, Neptune, quite different from the noticeably lighter Uranus, its planetary companion, which was the first to be discovered through a telescope. Despite being twins in many aspects, including mass, size, and possessing similar heavy atmospheres, their different hues of blue raised questions among the scientific community for many years. Researchers have now concluded, following a comprehensive analysis of Voyager 2's images, that both Neptune and Uranus are actually a similar shade of greenish-blue, providing an accurate portrayal of their true shades according to a recent study. In the late 20th century, the images of Uranus and Neptune, as revealed by Voyager 2, were singularly colored and merged to develop composite images, resulting in cyan and azure tones for the planets, respectively. Whilst photos of Uranus replicated its actual tone, initial images of Neptune were intensified and magnified to illustrate its clouds, bands, and winds, causing them to appear overly blue. This information has been confirmed by Patrick Irwin, the study's lead author and a planetary physicist at Oxford University in the U.K. To rectify this misunderstanding, fresh images from NASA's Hubble Space Telescope and the European Space Agency's Very Large Telescope were used by Irwin and his team. These tools register a wide range of colors in each pixel, providing the true hues of Uranus and Neptune after processing. They then compared the newly acquired data to Voyager 2's images, confirming both planets’ hues to be comparable shades of blue. The colors are created by the planets' red light-absorbing methane layers in their respective atmospheres. The new study discloses that Uranus appears whiter because its relatively stagnant atmosphere allows a methane fog to form, reflecting a larger proportion of sunlight's red segments than Neptune. This could also explain why Uranus changes colors during its 84-year solar orbit, appearing greener during solstices and bluer during equinoxes. In addition, the team deduced from brightness measurements on comparative pictures that near the poles, methane is abundant half as much as at the equator, which contributes to the color variation. According to Heidi Hammel from the Association of Universities for Research in Astronomy, unrelated to the new study, the bout over Neptune's misplaced shade, in tandem with Uranus's peculiar color shifts, have been longstanding disputes. She hopes that this study will conclusively address these issues. The research has been published in the Royal Astronomical Society's Monthly Notices journal on Thursday (Jan. 4).