2024-04-12 15:28:33
Much is still unknown about Uranus and Neptune. Only one spacecraft has visited these ice giants, Voyager 2, which flew by in the 1980s. As a result, scientists have only a vague idea of the composition of the ice giants – for example, that they are rich in oxygen, carbon and hydrogen.
To learn more about the composition of Uranus and Neptune, astronomers created models that match the physical properties measured by Voyager 2 and Earth-based telescopes. Many models assume that the planets have a thin shell of hydrogen and helium, a layer of compressed superionic water and ammonia, and a central rocky core. By some estimates, Uranus and Neptune can contain 50,000 times more water each than in Earth’s oceans.
However, the authors of the new study say that these models do not take into account how the ice giants formed. When Uranus and Neptune formed from the dust cloud surrounding the young Sun, they swallowed objects called planetoids. According to the team, the planetoids resemble present-day comets such as 67P/Churyumov-Gerasimenko, which originated in the Kuiper Belt, a region of icy bodies beyond Neptune’s orbit.
However, unlike the supposed water-rich ice giants, a large fraction of these planet-like objects are rich in carbon. So, “how is it possible to form an ice giant from ice-free building blocks?” asks the study’s lead author, Uri Malamud, a planetary scientist at the Israel Institute of Technology.
To solve this apparent paradox, U. Malamud and his co-authors created hundreds of thousands of models of the interior of Uranus and Neptune. The algorithm they used “started to match the correct composition of the planet’s surface and gradually deepens toward the center point of the planet.” They looked at several chemicals, including iron, water and methane, a major component of natural gas. They then tried to determine which model most resembled the real ice giants based on features such as radius and mass.
Of the various models they created, the astronomers found that models with methane, in which the methane—either as solid lumps or as bubbles under pressure—forms a thick layer between a shell of hydrogen and helium and a layer of water, met their criteria. In some models, methane accounted for 10 percent. mass of the planet.
In March, the team presented its results, which have not yet been peer-reviewed, published on the arXiv pre-publication server.
This methane is the key to solving the ice paradox. Researchers say the ice may have formed when hydrogen in the forming planets chemically reacted with carbon. Such reactions take place at high temperatures and extremely high pressures – millions of times greater than the pressure of the air on Earth. These are the conditions, according to scientists, in the developing planets.
The results of the study could lead to a better understanding of these little-known planets – although verifying whether they are actually rich in methane would be difficult, Malamud says. That would be the goal of one of several proposed missions by NASA and other space agencies to explore Uranus, according to Live Science.
2024-04-12 15:28:33