The ice giants Neptune and Uranus may not be as wet as originally believed, according to a study. Enormous volumes of frozen methane might possibly be present in them, which could help explain how they formed.

The frozen water reserves of Uranus and Neptune have long been thought to exist by astronomers. They might, however, also hold a ton of methane ice, according to a recent research.

What is known about the formation of these cold worlds may be clarified by the discoveries.

There is still plenty to learn about Neptune and Uranus. Only one spacecraft, Voyager 2, has visited these ice giant worlds; it passed by them in the 1980s. Because of this, scientists only have a vague understanding of the composition of the ice giants, such as the fact that they are largely composed of carbon, hydrogen, and oxygen.

Astronomers have created models of Uranus and Neptune that correspond to the physical characteristics observed by Voyager 2 and Earth-based telescopes in order to get further insight into their composition. A thin envelope of hydrogen and helium, an underlying layer of compressed superionic water and ammonia, and a central rocky core are the assumptions made by several models for the planets. According to some estimations, the oceans of Uranus and Neptune may contain fifty times as much water as those on Earth.

Nevertheless, these models, according to the authors of the new study, disregard how the ice giants arose. Planetesimals were ingested by Uranus and Neptune during their merger from the dust cloud encircling the newborn sun. This process is known as accretion. 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, a significant portion of these planetesimal-like objects are rich in carbon, in contrast to the ice giants that are thought to be rich in water. Uri Malamud, the study’s principal author and a planetary scientist at the Technion-Israel Institute of Technology, questioned, “How is it possible to form an icy giant from ice-poor building blocks?”

Malamud and his coauthors constructed hundreds of thousands of models of the innards of Uranus and Neptune in an attempt to explain this seeming paradox. The method 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.” They took into account a number of substances, such as water, iron, and methane, which is the primary ingredient in natural gas. 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 a number of models, but only one containing methane that suited their requirements. The methane formed a thick layer between the water layer and the hydrogen-helium envelope, either in the form of solid chunks or, due to pressure, in a mushy state. Methane was 10% of the planet’s mass in certain models.

The group uploaded its findings to the preprint server arXiv in March; they have not yet undergone peer review.

The solution to the ice paradox lies in this methane. According to the researchers, the ice may have developed as a result of 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.

The results might shed further light on these poorly understood planets, but it would be difficult to confirm whether they are genuinely rich in methane, according to Malamud. That would be the objective of one of the numerous missions that NASA and other space agencies have planned to investigate Uranus.