Scientists are discovering more exoplanets, but they’re still figuring out how these planets form. Jupiter-like exoplanets were thought to take 3 to 5 million years to form, but recent observations suggest they form much faster, in about 1 to 2 million years.
Research from Ohio State University challenges existing theories about the “age” of the disks from which planets form. This new information could lead scientists to re-think how planets in our solar system and beyond form.
Ji Wang, author of the study and an assistant professor in astronomy at Ohio State, said, _“Everything we know about exoplanets can be put in the context of the solar system and vice versa. Usually, planet formation is a bottom-up scheme, meaning it starts with small objects that build up to form a bigger planet, but that takes time.”_
The core accretion theory suggests that _planets form from the gradual buildup of smaller particles. Still, another theory, gravitational instability, proposes that planets form quickly from collapsing clumps in a star’s disk. Since a planet’s formation history could involve either or both of these processes, it’s essential to determine which one is more common._
The study looked at seven gas giant exoplanets and compared their chemical properties to those of Jupiter and Saturn. It found that these exoplanets, like Jupiter, likely formed much faster than previously thought due to the high amount of solids they gathered. This supports the idea that Jupiter formed earlier than scientists once believed.
When a planet forms, it gathers materials that increase its atmosphere’s metallicity (metal content). By studying these traces, researchers can measure the amount of solids the planet collected during its early formation.
The higher the metallicity, the more solids and metals—elements heavier than hydrogen and helium—scientists believe were gathered during the planet’s formation.
Wang explained that _each of the five planets studied collected an average of 50 Earth masses worth of solids. This amount can only be found in systems younger than 2 million years, while our solar system has about 30 to 50 Earth masses worth of solids._
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This new data suggests that the building blocks for these exoplanets were available earlier in the protoplanetary disk’s evolution than previously thought. The availability of these building blocks decreased over millions of years. Since scientists didn’t expect to find evidence of planets forming that early, this discovery challenges current theories.
Wang [explained](https://news.osu.edu/astronomer-finds-gas-giant-exoplanets-formed-earlier-than-previously-thought/) that _these exoplanets formed so early that there were still a lot of metals available, which surprised scientists. Now, researchers will have to develop new theories to explain it._
Like Jupiter and Saturn, gas giants pull in large amounts of matter as they form and move through space. This process affects the development of rocky planets in the same area. In our solar system, Jupiter and Saturn’s movements pushed Mercury out of its original orbit, making Mars smaller than Earth or Venus.
Additionally, this study offers a statistical method for determining the total mass of solid materials a planet has gathered. This tool will help astronomers with future planetary formation studies and analyze other types of complex elemental data.
Wang’s research used only existing data, but he expects that new high-resolution data from advanced tools like ground-based observatories and the James Webb Space Telescope will provide even more insights.
He hopes that studying more exoplanets will confirm the findings in this research.
**Journal Reference**