18/12/2023
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The NASA/ESA/CSA James Webb Space Telescope recently trained its sights on weird and enigmatic Uranus, an ice giant that orbits on its side. What Webb found is a dynamic world with rings, moons, storms and other atmospheric features – including a seasonal polar cap. The image expands upon a two-colour version released earlier this year, adding additional wavelength coverage for a more detailed look.
With its exquisite sensitivity, Webb captured Uranus’s dim inner and outer rings, including the elusive Zeta ring – the extremely faint and diffuse ring closest to the planet. It also imaged many of the planet’s 27 known moons, even seeing some small moons within the rings.
In visible wavelengths, Uranus appeared as a placid, solid blue ball. In infrared wavelengths (as seen here), Webb is revealing a strange and dynamic ice world filled with exciting atmospheric features.
One of the most striking of these is the planet’s seasonal north polar cap. Compared to the image from earlier this year, some details of the cap are easier to see in these newer images. These include the bright, white, inner cap and the dark lane in the bottom of the polar cap, toward the lower latitudes.
Several bright storms can also be seen near and below the southern border of the polar cap. The number of these storms, and how frequently and where they appear in Uranus’s atmosphere, might be due to a combination of seasonal and meteorological effects.
The polar cap becomes prominent when the planet’s pole begins to point towards the Sun, as it approaches solstice and receives more sunlight. Uranus reaches its next solstice in 2028, and astronomers are eager to watch any possible changes in the structure of these features. Webb will help disentangle the seasonal and meteorological effects that influence Uranus’s storms, which is critical to help astronomers understand the planet’s complex atmosphere.
Because Uranus orbits on its side at a tilt of about 98 degrees, it has the most extreme seasons in the Solar System. For nearly a quarter of each Uranian year, the Sun shines over one pole, plunging the other half of the planet into a dark, 21-year-long winter.
With Webb’s unparalleled infrared resolution and sensitivity, astronomers now see Uranus and its unique features with groundbreaking clarity. These details, especially of the close-in Zeta ring, will be invaluable to planning any future missions to Uranus, particularly the proposed Uranus orbiter and probe.
Scientists want to bring any visiting spacecraft as close to the planet as possible to measure the gravitational field of Uranus and better analyse the atmosphere. However, such a close approach would need to be planned carefully to avoid collisions with any possible debris from icy and dusty rings.
Uranus can also serve as a proxy for studying the many far-off, similarly sized exoplanets that have been discovered in the last few decades. This ‘exoplanet in our backyard’ can help astronomers understand how planets of this size work, what their meteorology is like, and how they formed. This can in turn help us understand our own Solar System as a whole by placing it in a larger context.
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Webb is the largest, most powerful telescope ever launched into space. Under an international collaboration agreement, ESA provided the telescope’s launch service, using the Ariane 5 launch vehicle. Working with partners, ESA was responsible for the development and qualification of Ariane 5 adaptations for the Webb mission and for the procurement of the launch service by Arianespace. ESA also provided the workhorse spectrograph NIRSpec and 50% of the mid-infrared instrument MIRI, which was designed and built by a consortium of nationally funded European Institutes (The MIRI European Consortium) in partnership with JPL and the University of Arizona.
Webb is an international partnership between NASA, ESA and the Canadian Space Agency (CSA).
Release on esawebb.org
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