Recent research led by Professor Patrick Irwin shows that: Neptune and Uranus Both have similar greenish-blue hues that defy previous perceptions of color. The study used modern telescope data to correct for historical color inaccuracies and account for Uranus’ slight color changes during its orbit.
Neptune is known for its rich blue color and Uranus for its green color, but a new study reveals that these two ice giants are actually much closer in color than commonly thought. became.
The correct hue of the planet was confirmed with the help of research led by Professor Patrick Irwin. oxford universitypublished today in Monthly Notices of the Royal Astronomical Society.
He and his team discovered that despite the common belief that Neptune is a deep azure blue and Uranus has a pale cyan appearance, both worlds are actually a similar greenish-blue color. I discovered that it was a shade of .
Misunderstanding of planet colors
Astronomers have long known that most modern images of the two planets do not accurately reflect their true colors.
This misunderstanding arose because the images of both planets were taken in the 20th century. NASAThe Voyager 2 mission was the only spacecraft to fly past these worlds, recording images in different colors.
The monochromatic images were later recombined to create a composite color image, but they were not always balanced exactly to achieve a “true” color image, and in the case of Neptune in particular, they were “too blue”. ” often happened.
Additionally, early images of Neptune from Voyager 2 were heavily contrast-enhanced to better reveal the clouds, bands, and winds that shape the modern Neptune perspective.
Professor Irwin said: “While the well-known Voyager 2 image of Uranus was released in close to ‘true’ color, the image of Neptune has actually been stretched and enhanced, making it appear artificially blue. It became too much,” he said.
“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.”
“By applying our model to the original data, we were able to reconstruct the most accurate representation to date of the colors of both Neptune and Uranus.”
Modern research reveals true color
In the new study, researchers used the following data: hubble space telescopeSpace Telescope Imaging Spectrograph (STIS) and Multi-Unit Spectroscopic Explorer (muse) European Southern Observatory very large telescope. In both devices, each pixel is a continuous spectrum of colors.
This means that the STIS and MUSE observations can be processed unambiguously to determine the actual apparent colors of Uranus and Neptune.
The researchers used these data to rebalance the composite color images recorded by the Voyager 2 camera and the Hubble Space Telescope’s Wide Field Camera 3 (WFC3).
This revealed that Uranus and Neptune are actually quite similar shades of greenish-blue. The main difference is that Neptune has a slight hint of additional blue. Models revealed that this is due to Neptune’s thin haze layer.
Animation of the seasonal changes in the colors of Uranus during the two Uranian years from 1900 to 2068 (one Uranian year is 84.02 Earth years). It begins just before the summer solstice, when Uranus’ south pole points almost directly at the sun.
The disk on the left shows what Uranus looks like to the naked eye, while the disk on the right has its colors stretched and enhanced to make atmospheric features more apparent. In this animation, Uranus’s rotation has been slowed by more than 3000 times than hers so that the planet’s rotation is visible, and discrete storm clouds can be seen passing through the planet’s disk.
As the planet moves towards the summer solstice, cloud opacity increases and a pale polar “hood” with decreasing methane content is seen filling more of the planet’s disk, leading to seasonal changes in color across the planet. It leads to
The size of Uranus’ disk changes because Uranus’ distance from the sun changes during its orbit.
Credit: Patrick Irwin, University of Oxford
Explaining the color variations of Uranus
The study also provides an answer to the long-standing mystery of why Uranus’ color changes slightly during the Sun’s 84-year revolution.
The authors reached their conclusion after first comparing images of the ice giant with brightness measurements recorded from 1950 to 2016 in blue and green wavelengths by the Lowell Observatory in Arizona.
These measurements showed that Uranus appears slightly greener during the summer and winter solstices, when one of the planet’s poles points toward our star. However, at the vernal equinox, when the sun is above the equator, the sun takes on a slightly bluish tinge.
Part of the reason for this is known to be because Uranus has a very unusual rotation.
During its orbit, it effectively rotates almost sideways. This means that during the planet’s summer solstice, either the north or south pole points almost directly in the direction of the sun and Earth.
This is important, the authors say, because any change in reflectance in the polar regions can have a large effect on Uranus’ overall brightness as seen from Earth.
Astronomers have not been very clear about how or why this reflectance differs.
This led the researchers to develop a model that compares the spectra of Uranus’ polar and equatorial regions.
They found that in polar regions, green and red wavelengths are more reflective than blue wavelengths. Part of the reason is that red-absorbing methane is about half as abundant near the poles as it is at the equator.
But this wasn’t enough to fully explain the color change, so the researchers looked at the gradually thickening icy surface of the planet’s sunlit poles, which they had previously observed during the summer. We added a new variable to the model in the form of a haze “hood”. We move from the vernal equinox to the summer solstice.
Astronomers believe it is likely made up of particles of methane ice.
When simulated in the model, the ice particles further increased reflection in green and red wavelengths at the poles, providing an explanation for why Uranus is green at the summer solstice.
Professor Irwin said: “This is the first study to match quantitative models with image data to explain why Uranus’s color changes during its orbit.”
“Thus, we prove that Uranus at the summer solstice is greener, not only because methane abundance is reduced in the polar regions, but also because the thickness of brightly scattering methane ice particles is increased. it was done.”
Dr Heidi Hummel of the Association of Universities for Research in Astronomy (AURA), who has spent decades studying Neptune and Uranus but was not involved in the study, said: Uranus has been bothering us for decades. This comprehensive study should ultimately resolve both issues. ”
Future exploration and continued research
The icy giants Uranus and Neptune continue to be attractive destinations for future robotic explorers, building on the legacy of Voyager in the 1980s.
Professor Lee Fletcher, a planetary scientist at the University of Leicester and co-author of the new study, said: It is a priority for space agencies for decades to come. ”
But even the long-lived planet explorers orbiting Uranus can only capture brief snapshots of Uranus over the course of a year.
“Earth-based studies like this, which show how Uranus’s appearance and color have changed over decades in response to the solar system’s strangest seasons, help place the findings of this future mission in a broader context. is essential,” Professor Fletcher said. Added.
Reference: “Modeling the seasonal cycle of color and size on Uranus and comparing it to Neptune” Patrick G.J. Irwin, Jack Dobinson, Arjuna James, Nicholas A. Teenby, Amy A. Simon, Lee N. Fletcher, Michael T. Roman, Glenn S. Orton, Michael H. Wong, Daniel Toledo, Santiago Perez-Hoyos, Julie Beck, September 12, 2023. Royal Astronomical Society Monthly Notices.
DOI: 10.1093/mnras/stad3761