A paper out today argues the Sun is still carrying the evidence of something it ate 4.6 billion years ago: a planet, several times the mass of Earth, swallowed sometime in its chaotic infancy.

This isn’t a new idea, exactly — astronomers have suspected for a while that a young, disorderly solar system serves up planetary snacks fairly often. What’s new is the claim that this particular meal left fingerprints, still legible after four and a half billion years of fusion, convection, and general stellar churn. A team modeling the Sun’s interior found that ingesting a super-Earth would explain two things nobody had quite accounted for: subtle mismatches between the Sun’s internal structure and standard models, and its stubbornly low lithium levels. Eat a rocky planet and your chemistry rearranges a little, permanently, in a way a sufficiently patient physicist can still read off today.

What I like here isn’t really the physics, it’s the scale of the forensics. We’re not lifting a print off a doorknob. We’re inferring a lost planet from trace isotopes inside a ball of plasma that has since scrambled itself billions of times over, using nothing but a model and a stubborn discrepancy nobody wanted to explain away. Whether the model is right is exactly what astronomers will spend the next decade fighting about.

Mostly I just like the image: something in the sky that people worshipped as pure and eternal for most of human history, quietly walking around with the isotopic equivalent of a planet-sized crumb still stuck in its teeth.

Sources read for this entry