Scientists Discover How Uranus and Neptune First Formed in Our Solar System

Scientists have taken a closer look at Uranus and Neptune and may have found an answer when it comes to their problematic chemical composition. The new findings provide new clues when it comes to understanding their formation.

Uranus and Neptune are two of the outermost planets in the solar system. Each has a mass of about 15 times that of Earth, which consists of up to 90 percent ice. Both are also highly enriched in carbon. Because of these characteristics, though, the origins of these planets remains unsolved; earlier models could not explain exactly how the planets managed to form in the area that they are today since it's likely the region didn't contain enough materials to create the planets.

In order to learn a bit more about these two planets, the Herschel Space Observatory focused on the isotopic composition of the planets, including the deuterium-to-hydrogen ratio (D/H). This ratio can be used to examine the origin of the elements that formed the solar system.

Dynamic models suggest that Uranus and Neptune formed in the same distant region as comets, and therefore should have a high D/H ratio. Yet Herschel found that the D/H ratio in the two planets was much lower than that found in comets. This suggests that there should be a new model to explain the planets' formation.

The newly proposed model is based on detailed simulations of the distribution and transport of the most abundant volatile elements in the solar system's protostar nebula. These simulations revealed that there were density "peaks" of solids in regions where nebular gas was low enough for gas condensation. It's likely that Uranus and Neptune formed on the carbon monoxide ice line; this, in particular, explains why they consist of carbon-rich solids but nitrogen-depleted gas.

The findings reveal a bit more about planet formation and show how these two planets in particular managed to form in our solar system.

The findings are published in The Astrophysical Journal.