For decades, images of Neptune have shown it to have a deep blue hue, while Uranus has appeared more green. But these two ice giants may actually be more similar to each other than astronomers previously believed.according to The study was published on January 5th. Royal Astronomical Society Monthly Noticesthe true color of our solar system’s most distant planets may be a similar pale shade of greenish-blue.
[Related: The secret to Voyagers’ spectacular space odyssey.]
image and reality
NASA’s Voyager 2 mission remains the only flyby of both ice giants conducted by a spacecraft. It gave us the first detailed images of these distant planets. Voyager 2 conducted his 1986 flyby of Uranus, and its images revealed a paler cyan or blue planet. The ship flew close to Neptune in her 1989 year, and images showed the rich blue planet.
However, astronomers have long understood that most modern images of both planets do not accurately reflect their true colors. Voyager 2 took images of each planet in a separate color, and then combined these monochromatic images to create a composite image. These composite images weren’t always exactly balanced, especially in the case of Neptune, which was thought to be too blue. The contrast of Voyager’s early images of Neptune was also significantly enhanced to better reveal the planet’s clouds and winds.
“While the well-known Voyager 2 image of Uranus was released in close to ‘true’ color, the image of Neptune was actually stretched and enhanced, making it artificially too blue. ” said study co-author Patrick Irwin, an astronomer at the University of Oxford. stated in a statement. “Although artificially saturated colors were known to planetary scientists at the time and images were published with descriptive captions, over time that distinction has been lost. I lost it.”
Creating more accurate views
new studythe team applied data obtained from the Hubble Space Telescope’s Space Telescope Imaging Spectrograph (STIS) and the European Southern Observatory’s Very Large Telescope’s Multi-Unit Spectroscopic Explorer (MUSE).
In both STIS and MUSE, each pixel is a continuous spectrum of color, so observations can be processed more clearly to determine a more accurate color of the planet, rather than what is seen with a filter.
The researchers used that data to rebalance the composite color images recorded by Voyager 2’s onboard camera and Hubble Space Telescope’s Wide-Field Camera 3. This rebalancing revealed that both Uranus and Neptune are actually a similar pale greenish-blue color. Neptune has a slight bluish tint, which models showed was a thin layer of haze on the planet.
Uranus color change
The study also provides a possible answer as to why Uranus changes color slightly during its 84-year orbit around the sun. The researchers first compared images of Uranus to brightness measurements taken in blue and green wavelengths from 1950 to 2016 by the Lowell Observatory in Arizona. These measurements showed that Uranus appears slightly greener during the summer and winter solstices, when it is at the poles. facing the direction of the sun. However, during the vernal equinox, when the sun is above the Earth’s equator, it appears more bluish.
One of the already established reasons for this change is due to the very unusual rotation of Uranus. The planet rotates almost sideways during its orbit, so during the summer solstice the north and south poles point almost directly at the sun and Earth. According to the authors, any changes in the reflectivity of Uranus’ poles would have a significant effect on the planet’s overall brightness as seen from Earth. How and why this reflectance differs has been less clear to astronomers. The research team developed a model that compares the color bands in Uranus’s polar and equatorial regions.
they discovered it Polar regions are more reflective in green and red wavelengths than the blue wavelength. Uranus is more reflective at these wavelengths because the gas methane absorbs red light, and because there is about half as much methane near Uranus’s poles as there is at the equator.
[Related: Neptune’s bumpy childhood could reveal our solar system’s missing planets.]
However, this was not enough to fully explain the color change, so the researchers Added new variable to model This is in the form of a “hood” of gradually thickening icy haze that was previously observed as Uranus moves from the equinox to the summer solstice. They think this haze is probably made up of methane ice particles.
After simulating this pole shift in the model, the ice particles further increased reflection in green and red wavelengths at the planet’s poles. This explained why Uranus appeared greener on the summer solstice, as there was less methane at the poles and the thickness of the methane ice particles increased.
“The misperceptions of Neptune’s colors and the unusual color changes of Uranus have puzzled us for decades,” says Heidi Hummel of the Association of Universities for Astronomical Research. stated in a statement. “This comprehensive study should finally settle both questions.” Hammel is not an author of the new study.
Bridging the gap between public perception of Neptune and its reality shows how data can be manipulated to show off specific features of the planet or enhance visualization.
“We were never trying to deceive,” said study co-author Lee Fletcher, a planetary scientist at the University of Leicester. Said new york times. “But there have been attempts to tell stories with these images by making them visually beautiful, so that people can see these beautiful scenes in a way that perhaps makes them look more like the world’s blurry grays.” can be enjoyed in a more meaningful way than an amorphous mass of ‘distance. “