According to a study published in Astronomy and Astrophysics, astronomers have identified a chemical signature in binary stars that reveals when a star has swallowed a rocky planet. Researchers measured precise differential abundances in the Sun-like binary system HD 129171 and HD 129209, located roughly 180 light-years away, discovering that an excess of beryllium in HD 129171 indicates it absorbed approximately 11 Earth masses of rocky material over its lifetime.
Detecting Planet Engulfment Through Beryllium Abundances
Binary stars form from the same molecular gas cloud and typically share an identical chemical composition. However, according to research led by Anne Rathsman, a doctoral student at the Institute of Astronomy, Geophysics, and Atmospheric Sciences in Brazil, the binary pair HD 129171 and HD 129209 exhibit distinct metallicity abundances despite sharing similar physical attributes, magnetic activity, and chemistry. To investigate these anomalies, the team utilized spectra obtained with the Very Large Telescope and its Ultraviolet and Visual Echelle Spectrograph.
The analysis showed that HD 129171 is enriched in refractory elements—such as iron, magnesium, silicon, calcium, and titanium—that condense into solid rocky planets. According to the study, the star also contains higher levels of lithium and beryllium. Because stellar nucleosynthesis does not produce stable beryllium isotopes, its presence in cool stellar photospheres cannot easily be explained by standard stellar evolution. Researchers concluded that the abundance pattern matches a model involving the engulfment of 11.2 Earth masses of rocky material.
Did you know? Beryllium is rarer in the universe than in the Earth’s crust, where it makes up only about 0.0004% of the material. Unlike lithium, which is easily destroyed during a star’s main sequence phase, beryllium is more resistant and preserves a lasting chemical signature of past planet consumption.
Implications for Planetary System Habitability
The discovery that Sun-like stars consume rocky worlds carries significant consequences for the search for habitable exoplanets. According to co-author Jorge Luis Melendez Moreno, systems similar to our own Solar System—characterized by stable, low-eccentricity orbits for inner rocky planets and outer gas giants—may be much rarer than previously assumed. If planetary engulfment is a common occurrence, it implies that many star systems undergo violent dynamical phases where inner planets are driven out of stable orbits and directly into their host stars.
Rathsman noted that for life to emerge and evolve, a planet requires billions of years in a sufficiently stable orbit to survive heavy gravitational perturbations. The research indicates that many planetary systems fail to provide this long-term stability, frequently losing their rocky worlds to stellar consumption.
Frequently Asked Questions
What is planet engulfment in binary star systems?
Planet engulfment occurs when a star gravitational pulls and absorbs a nearby rocky planet or planetary fragments into its outer layers, altering the star’s chemical composition.
Why is beryllium used instead of lithium to detect swallowed planets?
While lithium has historically been used as an indicator, it is easily destroyed during a Sun-like star’s main sequence and pre-main sequence phases. Beryllium is more resistant and retains its chemical signature much longer.
How much rocky material did HD 129171 absorb?
According to the study published in Astronomy and Astrophysics, chemical models indicate that HD 129171 absorbed approximately 11.2 Earth masses of rocky material.
Explore More Space Science
Want to stay updated on the latest exoplanet discoveries and stellar evolution research? Share your thoughts in the comments below or check out our related articles on astronomy and planetary systems.
Worth a look