Uranus’ 20-year Hubble study produces new atmospheric insights

Uranus is a weird and mysterious world around the sun. Now, in an unprecedented study spanning twenty years, researchers using NASA’s Hubble Space Telescope have discovered new insights into the composition and dynamics of Earth’s atmosphere. This is probably just because of Hubble’s sharp resolution, spectral capability and lifetime.

The team’s results will help astronomers better understand how Uranus’ atmosphere works and respond to changing sunlight. These long-term observations provide valuable data to understand the atmospheric dynamics of this distant ice giant, which can serve as a proxy for studying exoplanets of similar size and composition.

When Voyager 2 flew over Uranus in 1986, it provided a close-up snapshot of the lateral planet. I saw similar to the plain blue-green billiards. By comparison, Hubble chronicled a 20-year story of seasonal changes from 2002 to 2022. Over that period, a team led by Erich Karkoschka of the University of Arizona, and Larry Sromovsky and Pat Fry from the University of Wisconsin used the same Hubble instrument, STIS (the Space Telescope Imaging Spectrograph), to paint an accurate picture of the atmosphere structure of Uranus.

Uranus’ atmosphere is mainly hydrogen and helium, which contains a small amount of methane and traces of water and ammonia. Methane gives Uranus its cyan color through the red wavelength that absorbs sunlight.

The Hubble team observed Uranus four times over a 20-year period: in 2002, 2012, 2015 and 2022. They found that unlike the conditions of natural gas giants Saturn and Jupiter, methane is unevenly distributed throughout Uranus. Instead, it is greatly exhausted near the poles. This depletion has remained relatively constant over the past two decades. However, as the planet approaches its Arctic summer solstice in 2030, the aerosol and haze structures have changed dramatically in the Arctic, with significant changes in the Arctic.

It took Uranus more than 84 years to complete a single orbit of a sun. So, over the past two decades, the Hubble team has seen only the Northern Spring, as the sun shines from Uranus’ equator in 2030, almost directly on its Arctic. Hubble observations show that during this period, the atmospheric circulation patterns on Uranus were complex. Data that are most sensitive to methane distribution suggest that at upstreams in polar regions and other regions.

The team analyzed their results in a variety of ways. The image column shows the changes in Uranus over the four years when Uranus was observed in 20 years. During that time, researchers watched Uranus season as the Antarctic (left) darkened the winter shadows, while the Arctic (right) began to have a more direct view as the Arctic began, as the northern summer approached.

In visible light, the top row shows how the color of Uranus is seen through an amateur telescope in the human eye.

In the second row, the false color images of the planet are assembled based on visible and near-infrared light observations. Color and brightness correspond to the amount of methane and aerosol. These two quantities cannot be distinguished before they were first targeted at Uranus in 2002. Generally, the green area indicates less methane than the blue area and no methane in the red area. The red region is in the limbs, and the stratosphere of Uranus is almost completely free of methane.

The two bottom rows show the latitude structure of aerosols and methane from 1,000 different wavelengths (colors) visible to the near infrared. In the third row, bright areas represent cloudier conditions, while dark areas represent clearer conditions. In the fourth row, the bright area indicates the methane depletion, while the dark area shows the full methane.

In the middle and low latitudes, aerosols and methane depletion have their own latitude structures, which mostly have not changed much in the twenty years of observation. However, in polar regions, aerosols and methane depletion behave very differently.

In the third row, aerosols near the Arctic showed a sharp rise, showing very dark performance in the north early spring and became very bright in recent years. As solar radiation disappears, the aerosol seems to disappear on the left limb as well. This proves that solar radiation changes the aerosol mist in Uranus’ atmosphere. On the other hand, methane depletion in both polar regions seemed to remain high throughout the observation period.

As the Earth approaches Northern Summer, astronomers will continue to observe Uranus.

The Hubble Space Telescope has been in operation for more than three decades and continues to make groundbreaking discoveries to shape our basic understanding of the universe. Hubble is an international cooperation project between NASA and ESA (European Space Agency). NASA Goddard Space Flight Center in Greenbelt, Maryland manages telescopes and mission operations. Denver-based Lockheed Martin Space also supports Goddard’s mission operations. The Space Telescope Science Institute in Baltimore is run by the University’s Astronomy Research Association and conducts Hubble Science operations for NASA.