Mysteries of Uranus; Need for further exploration

[Astronuc]

I was watching a video on Uranus and some recent developments. There is consideration of a new mission to Uranus to get up close.

What NASA Found Inside Uranus​

Planetary Society - Uranus' biggest unsolved mysteries
https://www.planetary.org/articles/uranus-biggest-unsolved-mysteries

Voyager 2 became the first and only spacecraft to visit Uranus in 1986, revolutionizing our understanding of the planet. Since then, scientists have continued to study Uranus with ground and space-based telescopes. But there are still many riddles to be addressed, as NASA makes preliminary plans for a new Uranus mission that could reveal the planet’s unsolved mysteries.

A Uranus mission has been one of the planetary science community’s top priorities for the past decade.

Every 10 years, scientists create a report for NASA called the Decadal Survey that sets priorities for the next decade of exploration. The 2013 Decadal Survey listed three top priorities: Europa Clipper, Mars Sample Return, and a Uranus mission.

Europa Clipper is set to launch this year. Mars Sample Return plans are in progress, even as it faces ongoing reviews and budgetary uncertainties. That leaves a Uranus mission as the new top priority, according to the 2023 Decadal Survey.

Rather than flying past Uranus like Voyager 2, the spacecraft would enter orbit and make a comprehensive tour of Uranus, its rings, and its moons. It would also drop a probe into the planet’s atmosphere. The mission would produce a feast of data for a wide range of space scientists.

A Uranus mission could, in theory, launch in 2031 and arrive in 2043. With NASA facing budgetary challenges and Mars Sample Return still struggling to gain momentum, that timeframe may be optimistic. Nevertheless, at some point a new mission will arrive at Uranus, becoming the first spacecraft to visit in over a half-century. The mission will usher in a new era of discovery and help reveal the planet’s unsolved mysteries.

Unsolved Mysteries of the Uranian System
https://science.nasa.gov/uranus/facts/


Related PF post

Post in thread 'The James Webb Space Telescope'

Aug 21, 2025

Webb discovers a new moon orbiting Uranus.

Article

https://phys.org/news/2025-08-webb-moon-orbiting-uranus.html

Time lapse of the orbits

• pinball1970

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[loop quantum gravity]

I didn't understand what is that "hot slush".
I also don't understand what is "normal" day for any object in chaotic dynamical systems; isn't it an oxymoron to have a "normal" day in the solar system or any other star system?

 

[Astronuc]

I didn't understand what is that "hot slush".

REf: https://science.nasa.gov/uranus/facts/

Uranus is one of two ice giants in the outer solar system (the other is Neptune). Most (80% or more) of the planet's mass is made up of a hot dense fluid of "icy" materials – water, methane, and ammonia – above a small rocky core. Near the core, it heats up to 9,000 degrees Fahrenheit (4,982 degrees Celsius).

Uranus' atmosphere is mostly hydrogen and helium, with a small amount of methane and traces of water and ammonia. The methane gives Uranus its signature blue color.

While Voyager 2 saw only a few discrete clouds, a Great Dark Spot, and a small dark spot during its flyby in 1986 – more recent observations reveal that Uranus exhibits dynamic clouds as it approaches equinox, including rapidly changing bright features.

Uranus' planetary atmosphere, with a minimum temperature of 49K (-224.2 degrees Celsius) makes it even colder than Neptune in some places.

Wind speeds can reach up to 560 miles per hour (900 kilometers per hour) on Uranus. Winds are retrograde at the equator, blowing in the reverse direction of the planet’s rotation. But closer to the poles, winds shift to a prograde direction, flowing with Uranus' rotation.

Somewhere in between the core and upper atmosphere, between temperatures of 5255 K and 49 K is the spot where temperature and pressure allow 'ice' to form within a fluid of water, methane and ammonia, which have different melting points depending on pressure. Most qualitative articles do not discuss inhomogeneities and phases in the interior structure.

A James Webb related site on Facebook mentions

The interior of Uranus is thought to consist of several layers. At its core, there’s likely a dense mixture of rock (silicates) and metals, possibly surrounded by a layer of high-pressure water, ammonia, and methane ices.

Above this, a thick mantle of icy materials, primarily water, ammonia, and methane in a fluid or semi-fluid state, exists under extreme pressure and temperature.

The outermost layer is a gaseous atmosphere composed mostly of hydrogen (about 83%) and helium (15%), with traces of methane (2%) and other gases, giving Uranus its pale blue-green color due to methane absorbing red light.

UC Berkeley News
https://news.berkeley.edu/2024/11/2...ath-the-bland-surfaces-of-uranus-and-neptune/

A planetary scientist [Burkhard Militzer] at the University of California, Berkeley, now proposes an alternative theory — that the interiors of both these planets are layered, and that the two layers, like oil and water, don’t mix. That configuration neatly explains the planets’ unusual magnetic fields and implies that earlier theories of the interiors are unlikely to be true.

The publications shows illustrations of the interior structures of Uranus and Neptune.

Burkhard Militzer, Phase separation of planetary ices explains nondipolar magnetic fields of Uranus and Neptune
https://www.pnas.org/doi/10.1073/pnas.2403981121

Abstract
The Voyager spacecraft discovered that the ice giants Uranus and Neptune have nondipolar magnetic fields, defying expectations that a thick interior layer of planetary ices would generate strong dipolar fields. Stanley and Bloxham showed that nondipolar fields emerge if the magnetic field is only generated in a thin outer layer. However, the origin and composition of this dynamo active layer has so far remained elusive. Here, we show with ab initio computer simulations that a mixture of H₂O, CH₄, and NH₃ will phase separate under the pressure–temperature condition in the interiors of Uranus and Neptune, forming a H₂O-dominated fluid in the upper mantle and a CH₄-NH₃ mixture below. We further demonstrate that with increasing pressure, the CH₄-NH₃ mixture becomes increasingly hydrogen depleted as it assumes the state of a polymeric C-N-H fluid. Since the amount of hydrogen loss increases with pressure, we propose that the C-N-H fluid forms a stably stratified layer. The magnetic fields are primarily generated in an upper layer that is H₂O-rich, homogeneous, convective, and electrically conducting. Under these assumptions, we construct ensembles of models for the interiors of Uranus and Neptune with the Concentric MacLaurin Spheroid method. We demonstrate that the phase separation of the solar-type H₂O-CH₄-NH₃ mixture leads to models that match the observed gravity field and to layer thicknesses that are compatible with magnetic field measurements.

The paper is probably at an upper class or graduate level.

As for a 'normal' day, that seems somewhat subjective, but I presume it means 'normal' for Uranus, which may be different from 'normal' on other planets. I take 'normal' to mean 'about average', i.e., somewhere between extremes, or perhaps 'expected conditions. 'About average' or 'about the mean' could be based on time-weighted observations.

I look at monthly precipitation and daily temperatures locally, and the meteorological site indicates 'normal' precipitation, which is an average over 3 or 5. years of observation (it mentions 3, but it seems more like 5, since the 'normal' value has not changed.)

I would expect 'normal' to vary seasonally.

 

[Astronuc]

I was not familiar with the Concentric MacLaurin Spheroid method, so I looked it up. The method has been applied to modeling structures of Jupiter, Saturn, Uranus and Neptune.

W. B. Hubbard, CONCENTRIC MACLAURIN SPHEROID MODELS OF ROTATING LIQUID PLANETS
https://iopscience.iop.org/article/10.1088/0004-637X/768/1/43

Sean M Wahl, William B Hubbard, Burkhard Militzer, The Concentric Maclaurin Spheroid method with tides and a rotational enhancement of Saturn's tidal response
https://arxiv.org/abs/1602.07350 , https://seanwahl.com/assets/docs/Wahl_Saturn_submitted_to_Icarus.pdf

J. Wisdom, W.B. Hubbard, Differential rotation in Jupiter: A comparison of methods
https://web.mit.edu/wisdom/www/wisdom-hubbard.pdf

F Debras, G Chabrier, A complete study of the precision of the concentric MacLaurin spheroid method to calculate Jupiter's gravitational moments
https://ui.adsabs.harvard.edu/abs/2018A&A...609A..97D/abstract

Saburo Howard et al., Robustness of Jupiter Interior Models Solutions: Importance of the Hydrogen-Helium Equation of State
https://app.cospar-assembly.org/2022/browser/presentation/30563

The articles are probably at the senior undergraduate or graduate level, but the provide a good background from the literature.