HD 81809B Shows Signs of Swallowing Up to 75 Earth-Like Planets
Updated
Updated · Interesting Engineering · Jun 6
HD 81809B Shows Signs of Swallowing Up to 75 Earth-Like Planets
3 articles · Updated · Interesting Engineering · Jun 6
Summary
HD 81809B, a main-sequence star 90 to 101 light-years away in Hydra, appears chemically enriched in a way astronomers say points to past planetary engulfment.
A comparison with its binary companion found far more lithium and an iron abundance difference of about 3.7 times, an unusual mismatch for stars thought to have formed together from the same gas cloud.
Researchers say the most likely scenario is that rocky planets spiraled inward, became orbitally unstable and were absorbed; a possible debris disk around the star supports that idea.
Models, however, create a puzzle: matching the metal enrichment would require roughly 25 to 75 Earth masses of material, while the observed lithium level fits accretion of less than 6 Earth masses.
That tension suggests the engulfment may have been recent or involved unusually composed planets, leaving HD 81809B as a potentially important test case for binary-star and planet-formation theories.