Argon on Uranus and Neptune may reveal more about their origins than their interiors

New measurements of argon in the atmospheres of Uranus and Neptune may provide insights into the origins of these ice giants, rather than revealing details about their interiors. Dr. Olivier Mousis, a planetary scientist from Southwest Research Institute, led a study published in The Planetary Science Journal that analyzed the amount of argon-40 in the planets' atmospheres.

This isotope could indicate the presence of rock beneath the surfaces of Uranus and Neptune, as well as shed light on their formation environments and histories. The argon-40 found in the planets' atmospheres likely originated from two sources: the protosolar nebula, which formed the solar system 4.6 billion years ago, and radioactive decay of potassium-40 deep inside the planets.

By comparing the ratios of these sources, researchers can estimate the amount of rock present within Uranus and Neptune. However, the team concluded that atmospheric argon-40 measurements are more likely to reveal information about the planets' formation environments than their rocky or icy interiors. The study's findings suggest that the materials for planets rich in argon may have formed near an argon frost line, a boundary in the protosolar nebula where low temperatures condense argon gas into solid ice.

This discovery could help guide future missions aimed at directly sampling noble gases and isotopic ratios from Uranus and Neptune, providing more accurate data on their formation processes.