Gemini North Telescope Helps Describe Why Uranus And Neptune Are Different Colors

“This is the first model to simultaneously fit observations of shown sunlight from uaviolet in order to near-infrared wavelengths. “

Astronomers may now understand why the similar planets Uranus plus Neptune are different colors. Using observations from the Gemini Northern telescope, the NASA Infrared Telescope Facility, and the Hubble Space Telescope, researchers allow us a single atmospheric model that will matches observations of each planets.

The model uncovers that excess haze upon Uranus builds up in the world’s stagnant, sluggish atmosphere and makes it appear a lighter in weight tone than Neptune.

Neptune and Uranus have much in common — they have similar masses, dimensions, and atmospheric compositions — yet their appearances are usually notably different. At visible wavelengths Neptune has a distinctly bluer color whereas Uranus is a pale shade associated with cyan. Astronomers now have evidence for why the two exoplanets are different colors.

New research suggests that a layer of concentrated haze that exists on both exoplanets is thicker on Uranus than a similar layer on Neptune and ‘ whitens’ Uranus’s appearance more than Neptune’s [1]. If there were no haze in the atmospheres of Neptune and Uranus, both would appear almost equally blue [2].

This conclusion comes from a model [3] that an international team directed by Patrick Irwin, Professor of Planetary Physics in Oxford University, developed to describe aerosol layers in the atmospheres of Neptune and Uranus [4]. Previous research of these planets’ upper atmospheres had focused on the appearance of the atmosphere at only specific wavelengths. However , this new design, consisting of multiple atmospheric layers, matches observations from each planets across a wide range of wavelengths. The new model also consists of haze particles within deeper layers that had formerly been thought to contain just clouds of methane plus hydrogen sulfide ices.

“ This is the initial model to simultaneously suit observations of reflected sunshine from uaviolet to near-infrared wavelengths, ” explained Irwin, who is the lead writer of a paper presenting this particular result in the  Log of Geophysical Research: Exoplanets . “ It’s also the first to explain the difference in visible color between Uranus and Neptune. ”

The team’s model includes three layers of aerosols at different heights [5]. The key layer that affects the colors could be the middle layer, which is a coating of haze particles (referred to in the paper because the Aerosol-2 layer) that is thicker on Uranus than on Neptune. The team suspects that, on both planets, methane ice condenses onto the particular particles in this layer, tugging the particles deeper into the atmosphere in a shower associated with methane snow. Because Neptune has a more active, violent atmosphere than Uranus really does, the team believes Neptune’s atmosphere is more efficient in churning up methane particles into the haze layer and producing this snow. This removes more of the haze and keeps Neptune’s haze layer thinner than it is upon Uranus, meaning the azure color of Neptune looks stronger.

“ We all hoped that developing this model would help us understand clouds and hazes in the ice giant atmospheres, ” commented Mike Wong, an astronomer at the University or college of California, Berkeley, plus a member of the team behind this result. “ Explaining the difference in color among Uranus and Neptune was an unexpected bonus! ”

To create this design, Irwin’s team analyzed a collection of observations of the planets covering uaviolet, visible, and near-infrared wavelengths (from 0. 3 to 2 . 5 micrometers) taken with the Near-Infrared Integral Field Spectrometer (NIFS) in the Gemini North telescope close to the summit of Maunakea in Hawai’i — which is area of the international Gemini Observatory, a course of NSF’s NOIRLab — as well as archival data from your NASA Infrared Telescope Facility, also located in Hawai’i, as well as the NASA/ESA Hubble Space Telescope.

The NIFS instrument on Gemini North was particularly important to this result as it is able to supply spectra — measurements of how bright an object is at different wavelengths — for every stage in its field of view. This provided the team with detailed measurements of how reflective both planets’ atmospheres are across both the full disk of the planet and throughout a range of near-infrared wavelengths.

“ The Gemini observatories continue to deliver brand new insights into the nature of our own planetary neighbors, ” stated Martin Still, Gemini System Officer at the National Science Foundation. “ In this experiment, Gemini North provided an element within a suite of ground- and space-based facilities important to the detection and portrayal of atmospheric hazes. ”

The model also helps explain the darkish spots that are occasionally noticeable on Neptune and less commonly detected on Uranus. While astronomers were already aware of the presence of dark areas in the atmospheres of each planets, they didn’t understand which aerosol layer had been causing these dark places or why the aerosols at those layers had been less reflective. The team’s research sheds light on these questions by showing that a darkening of the deepest layer of their model would certainly produce dark spots similar to those seen on Neptune and perhaps Uranus.


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