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Deep learning-enabled size estimation of comets indicates a more dynamic early solar system.

Shunjing Zhao1,2,3, Xian Shi4, Hanlun Lei5,6

  • 1School of Astronomy and Space Science, Nanjing University, Nanjing, China.

Nature Communications
|May 5, 2026
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Comet nucleus sizes were estimated using AI, revealing the Oort Cloud is far more populated than the Scattered Disk. This suggests external forces like stellar flybys shaped the outer Solar System.

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Area of Science:

  • Astronomy and Astrophysics
  • Planetary Science
  • Computational Science

Background:

  • The formation and evolution of the Oort Cloud and Scattered Disk, major comet reservoirs, are not well understood.
  • Comet population ratios derived from flux observations significantly differ from giant planet instability models.
  • Accurately determining comet nucleus sizes is challenging due to obscuring comas.

Purpose of the Study:

  • To derive independent nucleus sizes for 28 comets using AI-driven activity modeling.
  • To investigate the population ratio between the Oort Cloud and Scattered Disk.
  • To explore the implications of these findings for the evolution of the outer Solar System.

Main Methods:

  • Nucleus sizes were inferred from variations in water emission using artificial intelligence (AI) based activity modeling.
  • Data from 28 comets were analyzed to derive independent nucleus size estimates.
  • Comet sizes were compared between long-period and short-period comets.

Main Results:

  • Long-period comets were found to have significantly larger nuclei than short-period comets of comparable absolute brightness.
  • The Oort Cloud is estimated to be nearly three orders of magnitude more populated than the Scattered Disk.
  • The derived population ratio exceeds predictions from giant planet instability models by over two orders of magnitude.

Conclusions:

  • The Oort Cloud's high population suggests processes beyond giant planet instability, such as stellar flybys, were crucial in shaping the outer Solar System.
  • AI-based activity modeling provides a novel method for estimating comet nucleus sizes.
  • The findings refine our understanding of comet reservoir dynamics and Solar System evolution.