When it comes to the size of its protoplanetary disk, our solar system is just an average Joe. That’s what researchers will report in an upcoming issue of The Astronomical Journal about the extent of dust and gas from which our planetary system first formed. Using observational data and computer models that rewound the solar system back to the time of Jupiter's formation some 4.56 billion years ago, the team argues that our protoplantary disk stretched no farther than 80 astronomical units, roughly double the distance of Pluto's orbit. If the disk had been any bigger, gravitational forces within it would have pushed some icy bodies smaller than Pluto outward into steeply tilted orbits—a situation astronomers have not observed in our solar system. While disks around other young stars can run the gamut from tens to thousands of astronomical units, the average is roughly 60 AU. So even though we might think we’re special, the galaxy would tend to disagree.
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