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Astronomers have long believed that the ice giants Uranus and Neptune are rich in frozen water. However, a new study suggests it may also contain tons of methane ice.
The findings could help solve the mystery of how these icy worlds formed.
a lot about Uranus And Neptune It is still unknown. These giant icy worlds have only had one visitor, the Voyager 2 spacecraft, which flew by in the 1980s. As a result, scientists have only a vague idea about the compositions of ice giants – for example, that they contain large amounts of oxygen, carbon and hydrogen.
To learn more about the composition of Uranus and Neptune, astronomers have created models that match the physical properties measured by Voyager 2 and ground-based telescopes. Many models assume that planets contain thin shells of hydrogen and helium; Base layer of super-ionized pressurized water ammonia; And a central rocky core. (Water is what gives them the “ice giant” mark.) Some estimates suggest that Uranus and Neptune may have 50,000 times the amount of water In the Earth's oceans.
But the authors of the new study say these models ignore the way the ice giants formed. When Uranus and Neptune coalesced from the dust cloud surrounding the young sun, they devoured or accreted objects called planetesimals. The team says these planetesimals resemble present-day comets such as 67P/Churyumov-Gerasimenko, which originate in the Kuiper Belt, a doughnut-shaped region of icy bodies outside the orbit of Neptune.
Related: Where does the solar system end?
Unlike ice giants that are supposed to be water-rich, a significant portion of these planetesimal-like bodies are water-rich carbon. So “how can an ice giant be formed from ice-poor building blocks?” He said Uri Malamudlead author of the study and a planetary scientist at the Technion-Israel Institute of Technology.
To resolve this apparent paradox, Malamud and his colleagues built hundreds of thousands of models of the interiors of Uranus and Neptune. The algorithm they used “begins by matching the appropriate composition to the planet's surface, and gradually works its way deeper into the planet's central point.” They considered several chemicals, including iron, water, and methane, the main components of natural gas. They then tried to determine which model was most similar to actual ice giants in features such as radius and mass.
Among the various models they built, the astronomers found that those containing methane fit their criteria, where methane — either in solid pieces or, under pressure, in a soft state — forms a thick layer between the hydrogen and helium shell and the water layer. In some models, methane makes up 10% of the planet's mass.
The team posted their results, which have not yet been peer-reviewed, on a preprint server arXiv in March.
This methane holds the key to solving the ice paradox. The researchers said the ice may have formed when hydrogen in growing planets reacted chemically with carbon in young planets that accumulated on the planets. Such reactions occur under extremely high temperatures and extremely high pressures, millions of times the air pressure we experience on Earth. These are the exact conditions that scientists believe existed on developing planets.
Malamud said the findings could provide greater insight into these poorly understood planets, although verifying whether they are actually rich in methane will be difficult. This will be the goal of one of several goals Proposed missions From NASA and other space agencies aiming to explore Uranus.
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