New research from The Ohio State University provides a groundbreaking update on the formation of exoplanets, specifically those with masses similar to Jupiter. The study reveals that these massive planets may have formed much earlier than previously believed, offering fresh insights into the process of accretion—the accumulation of gas and solid materials such as carbon and oxygen that are essential for the creation of large gas giants.
Published in The Astrophysical Journal, this study challenges existing theories about the timing of planetary formation. Traditionally, scientists thought that Jupiter-like planets took several million years to fully form, with estimates suggesting that the process took anywhere from 3 to 5 million years. However, new observations suggest that gas giants like Jupiter may have taken only 1 to 2 million years to develop, far quicker than earlier assumptions.
The research also presents a shift in our understanding of how these planets come to be. Planets, including exoplanets, are generally thought to form from protoplanetary disks, which are spinning clouds of dust and gas around young stars. These disks contain all the raw materials needed to create planets. According to the findings, the key to the formation of Jupiter-like exoplanets lies in the early stages of the disk’s life when it is still dense and young. The study’s results suggest that accretion—the critical process of gathering enough mass to form a planet—happens earlier than previously thought, when the disk is still massive.
One of the most intriguing aspects of the research is the study’s focus on exoplanets, which are planets that orbit stars outside of our solar system. Though scientists have discovered a growing number of these distant worlds, the exact processes that govern their formation remain a puzzle. The Ohio State University study contributes to this puzzle by providing new data that could lead to a re-evaluation of existing planet formation models, both for exoplanets and for planets within our own solar system.
Ji Wang, the assistant professor of astronomy at Ohio State and lead author of the study, explained that the study’s results could dramatically alter how scientists view planet formation. Traditional theories of planet formation often relied on a “bottom-up” approach, which suggests that planets grow gradually over time by accumulating smaller objects. This model assumes that the process is slow, taking millions of years for gas giants like Jupiter to form. However, the new research suggests that accretion, particularly for Jupiter-like planets, takes place much sooner and on a much shorter timescale than previously believed.
While the core accretion theory—the idea that planets form through the gradual accumulation of smaller bodies—has been widely accepted, an alternative theory, known as gravitational instability, also explains planetary formation. Gravitational instability occurs when parts of the protoplanetary disk become so massive that they collapse under their own gravity, forming planets in a much more sudden manner. Understanding which of these two mechanisms is more dominant in exoplanet formation is an essential part of the ongoing debate. Wang and his team analyzed seven exoplanets, all gas giants, whose chemical and stellar properties had already been measured. They compared these planets to the gas giants in our own solar system, particularly Jupiter and Saturn, to draw conclusions about their early formation.
The findings show that Jupiter-like exoplanets accreted a significant amount of solids very early in their formation. This observation is key because a planet’s metallicity—the amount of heavier elements, such as carbon, oxygen, and metals, in its atmosphere—can provide insight into how much solid material was present during the planet’s formation. The higher the metallicity, the more solid material a planet has accumulated, which is indicative of an earlier and faster formation process.
Wang’s research revealed that the exoplanets studied had accreted the equivalent of 50 Earth masses of solid material. This quantity of material would only be available in a protoplanetary disk that is less than 2 million years old. In contrast, our own solar system’s disk likely provided no more than 30 to 50 Earth masses of solids. This discrepancy suggests that the building blocks needed for planet formation in distant systems were available much earlier than expected. The availability of these materials decreased significantly as the protoplanetary disk aged, which adds further evidence to the idea that the process of accretion for Jupiter-like exoplanets was rapid.
The implications of this discovery are profound, as it forces scientists to rethink their models of how planets form. The idea that massive exoplanets could form in the early stages of a protoplanetary disk, when solid materials are abundant, challenges previous assumptions about the timing and nature of accretion. According to Wang, this finding is unexpected, and it suggests that current theories about the timeline of planetary formation may need to be revised.
Beyond simply revising theories, these findings have broader implications for understanding the evolution of planetary systems. Gas giants like Jupiter play an essential role in the development of the rest of the solar system. Their immense gravitational influence can affect the orbits of nearby planets, potentially preventing rocky planets from forming in certain regions or altering the size and structure of existing planets. In our own solar system, for instance, Jupiter and Saturn are thought to have influenced the orbits of Mercury and Mars, with Jupiter pushing Mercury out of its original orbit and contributing to the smaller size of Mars relative to Earth.
The new data also provides a framework for future studies of exoplanets. Wang’s statistical model for determining the mass of solid accretion in exoplanets can help researchers estimate the amount of solid material in planets that haven’t been directly observed. This model could become a valuable tool for analyzing a wide range of exoplanets and planetary systems, potentially unlocking further secrets about the early stages of planet formation.
While this study is based on archival data, Wang anticipates that new observations with more advanced instruments, such as the James Webb Space Telescope and next-generation ground-based telescopes, will expand upon this research. These improved tools will offer higher-resolution data, which could help refine the study’s conclusions and provide even more detailed insights into the early formation of exoplanets.
Wang’s research is part of a broader effort to understand not only how exoplanets form but also how the process compares to the formation of our own solar system. By understanding the formation of distant planets, scientists can learn more about the conditions that led to the creation of our own planet and its complex history. The findings also emphasize the importance of studying exoplanets, as they offer a unique window into the processes that shape planetary systems.
More information: Ji 吉 Wang 王, Early Accretion of Large Amounts of Solids for Directly Imaged Exoplanets, The Astrophysical Journal (2025). DOI: 10.3847/1538-4357/adb42c