Ice Giants Neptune and Jupiter May Contain Frozen Methane That Explains Their Formation [Study]

Uranus and Neptune are not only watery, but they may also contain huge amounts of methane. The presence of methane is reportedly crucial in their
formation.

Uranus and Neptune May Contain Frozen Methane

Only little is known about the ice giants -- Neptune and Jupiter. However, previous studies suggest that the two planets contain oxygen, carbon and hydrogen.

In a new study, astronomers created different models of the two planets, matching the physical properties measured by Voyager 2 and Earth-based telescopes. Several models assumed they had a thin hydrogen and helium envelope, an underlying layer of compressed, superionic water and ammonia, and a central rocky core.

Nevertheless, according to the authors, these models disregard how the ice giants arose. Planetesimals were ingested by Uranus and Neptune during their merger from the dust cloud encircling the newborn sun. The group claims that these planetesimals are similar to modern comets like 67P/Churyumov-Gerasimenko, which are thought to have formed in the Kuiper Belt -- the doughnut-shaped region of frozen bodies located beyond Neptune's orbit.

However, many of these planetesimal-like objects are carbon-rich, unlike the purportedly water-rich ice giants. This led the researchers to question how the icy giants developed from ice-poor building blocks.

Uri Malamud, the study's lead author and a planetary scientist at Technion – Israel Institute of Technology, and his coauthors constructed hundreds of thousands of models of the innards of Uranus and Neptune in an attempt to explain this seeming paradox. They considered several substances, including iron, water, and methane, the primary component of natural gas. The algorithm they employed "starts matching a suitable composition for the surface of the planet, and it gradually works its way deeper into the central point of the planet." Next, they attempted to identify which model's characteristics, including mass and radius, most closely matched those of the real ice giants.

The astronomers constructed several models, but only one containing methane suited their requirements. The methane formed a thick layer between the water layer and the hydrogen-helium envelope, either in solid chunks or, due to pressure, in a mushy state. Methane was 10% of the planet's mass in certain models.

Methane resolves the ice giant paradox. According to the researchers, the ice may have developed due to a chemical reaction between the hydrogen in the developing planets and the carbon in the planetesimals that the planets accreted. These kinds of reactions take place at extreme pressures and temperatures, millions of times higher than those found on Earth. Scientists believe that the developing planets had precisely these conditions.

Why Uranus and Neptune Are Called Ice Giants?

Although the hydrogen and helium shells surrounding Uranus and Neptune appear to be made of fluids, astronomers believe that the water, ammonia, and methane found in their mantles are actually fluids under extreme pressure rather than ice. Since scientists believe that methane, ammonia, and water were all ice when the planets formed, Uranus and Neptune are truly referred to as ice giants. Methane freezes at -182 °C, which means that Uranus and Neptune evolved in incredibly frigid conditions!

Uranus and Neptune are very different from the gas giants -- Jupiter and Saturn -- as demonstrated by the fleeting Voyager flybys. Uranus and Neptune are referred to as "ice giants" because of how much colder they are in relation to the Sun and how much other ice-forming molecules and atmospheric water they have in their atmospheres.

The visible clouds are most likely made up of ice crystals with varying compositions. Ice giants are primarily composed of water, most likely in the form of a supercritical fluid. Despite their frigid temperature, they still support huge storms like Jupiter's Great Red Spot or Saturn's massive, cyclical eruptions.

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