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After Pluto's demotion to dwarf planet in 2006, our solar system went from having nine planets to eight. But about a decade later, some astronomers proposed there was another planet, larger than Earth, hiding in the Kuiper Belt. And in 2023, another team calculated there's a chance there's a gas giant orbiting the Sun in the outermost boonies of the solar system: the Oort cloud.

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Sources:
https://solarsystem.nasa.gov/solar-system/kuiper-belt/in-depth/
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Image Sources:
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