Although they are technically gas giants, Uranus and Neptune are referred to as "ice giants" due to their composition.
This refers to the fact that Uranus and Neptune have more methane, water, and other volatiles than their larger counterparts ( Jupiter and Saturn).
Given the pressure conditions in the planets' interiors, these elements become solid, essentially becoming 'ices.'
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However, new research from the University of Zurich (UZH) and the National Centre of Competence in Research (NCCR) PlanetS is challenging our understanding of these interior regions of these planets.
According to the research team's findings, which appeared this month in Astronomy & Astrophysics, Uranus and Neptune may be more rocky in their cores and less 'icy' than previously thought.
In addition, their research suggests that their interiors could experience convection, in which material is cycled (as on Earth through tectonic activity), rather than remaining stable. These possibilities, they indicate, could explain some of the more mysterious characteristics of the "ice giants."
Historically, scientists have divided the planets of the Solar System into three distinct categories based on their composition, which corresponds to their distance from the Sun.
This includes the terrestrial (rocky) planets of the inner Solar System – Mercury, Venus, Earth, and Mars, followed by the planets beyond the so-called 'Frost Line' (where volatile materials like water freeze). This includes the gas giants (Jupiter and Saturn) and the ice giants (Uranus and Neptune).
The new study, conducted by PhD Student Luca Morf and Professor Ravit Helled of UZH and the NCCR PlanetS, challenges this framework.
Of all the Solar planets, Uranus and Neptune are the least understood. This is due to the fact that only one mission, the Voyager 2 probe, has studied them up close (in 1986 and 1989, respectively).
Morf and Helled developed a unique process to simulate the interiors of Uranus and Neptune that considered compositions beyond the water-rich model. This consisted of random density profiles, followed by calculations of the resulting planetary gravitational field.
They then repeated the process to obtain results consistent with observational data of Uranus and Neptune.
"The ice giant classification is oversimplified, as Uranus and Neptune are still poorly understood," Morf explained in a UZH press release.
"Models based on physics were too assumption-heavy, while empirical models are too simplistic. We combined both approaches to get interior models that are both 'agnostic' or unbiased and yet are physically consistent."
Their results showed that the best fit for their internal composition is not limited to ice (predominantly water) and could instead be predominantly composed of rock.
These results are consistent with findings provided by the Hubble Space Telescope and the New Horizons mission, which indicate that Pluto's composition is about 70% rock and metals and 30% water by mass.
The study also provides possible explanations for why Uranus and Neptune have such mysterious magnetic fields, characterized by more than two poles.
"It is something that we first suggested nearly 15 years ago, and now we have the numerical framework to demonstrate it," said Helled.
"Our models have so-called 'ionic water' layers, which generate magnetic dynamos in locations that explain the observed non-dipolar magnetic fields. We also found that Uranus's magnetic field originates deeper than Neptune's."
Naturally, there are uncertainties in this model, which highlights the need for future missions to investigate the 'ice giants' further.
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In the meantime, the new results present new scenarios and challenge decades-old assumptions regarding the interior composition of giant planets. They could also guide future materials science studies on planetary conditions and how matter behaves under extreme conditions.
"Both Uranus and Neptune could be rock giants or ice giants, depending on the model assumptions," said Helled.
"Data are currently insufficient to distinguish the two, and we therefore need dedicated missions to Uranus and Neptune that can reveal their true nature."
This article was originally published by Universe Today. Read the original article.