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Rare chemical signal found in twin stars may reveal ancient episodes of planetary ingestion and broaden the debate on the stability of solar systems, the formation of rocky planets, and the necessary conditions for worlds capable of preserving life for long periods.
Astronomers led by Anne Rathsam, from IAG/USP, identified a chemical signal capable of aiding in the search for stars that have swallowed rocky material from planets.
Published in 2026 in the journal Astronomy & Astrophysics, the study analyzed the binary pair HD 129171 and HD 129209, formed by two stars considered “twins”.
As they were born from the same cloud of gas and dust, they should present very similar chemical compositions, but the comparison revealed significant differences.
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This variation reinforces the hypothesis that one of the stars incorporated planetary material throughout its history, leaving detectable marks in its composition.
The main evidence observed by the researchers is in beryllium, an element difficult to measure and considered a more lasting signature of the ingestion of rocky planets.
In addition, the team also evaluated lithium, iron, and other chemical elements, in search of patterns capable of differentiating a natural origin from contamination by external material.
Beryllium helps track swallowed planets
In the comparison between the two stars, HD 129171 appears richer in refractory materials than HD 129209.
These elements usually form solids and are among the main components of rocky planets, like Earth, as well as being part of the cores of giant planets.
The chemical pattern follows the condensation temperature of the elements, which makes the difference between the stars more expressive precisely in the materials associated with rocks.
In practical terms, the more refractory the element analyzed, the greater the chemical distance between the two stars tends to be, a behavior compatible with the addition of rocky material.
Among the elements evaluated, lithium and beryllium drew attention because they are not produced in the interior of these stars.
When they appear in excess, they may indicate that external material was incorporated after stellar formation.
The difference between the two lies in the resistance to internal heat.
While lithium is destroyed at lower temperatures, beryllium lasts longer and can preserve the chemical signature of the event.
According to the study, the difference in beryllium between the two stars can serve as a diagnostic of episodes of rocky material ingestion.
The research also indicates that the observed pattern is compatible with the absorption of about 11.2 Earth masses of rocky material.
Telescope in Chile measured the composition of the stars
To achieve the result, the researchers analyzed spectra obtained with the UVES instrument, connected to the Very Large Telescope, of the European Southern Observatory, in Chile.
Composed of 8.2-meter telescopes, the VLT allows observing distant objects with high precision and separating the light of stars into different frequencies.
From this decomposition, scientists can identify marks left by chemical elements and compare, with a high level of detail, the composition of very similar stars.
In the pair HD 129171 and HD 129209, the abundances of volatile elements remain similar, as expected in stars formed in the same environment.
The difference appears more strongly in refractory elements, precisely those most associated with rocky material and the formation of solid planets.
Signed by Anne Rathsam, Jorge Meléndez, Rodolfo Smiljanic, Fan Liu, and Lorenzo Spina, the work brings together researchers linked to institutions from Brazil, Germany, Italy, Poland, China, and Australia.
Twin stars and the search for life beyond Earth
The discovery helps clarify an old question about chemically different binary stars.
One possible explanation was that the original formation cloud was not as homogeneous as imagined.
Another possibility involved the ingestion of planets or rocky bodies by one of the stars after its formation.
With the detection of beryllium, the second hypothesis gains strength in the case of the pair HD 129171/HD 129209.
Even so, the study does not allow us to state whether the material came from a large planet or several smaller bodies, as everything mixes in the outer layers of the star.
There is also no exact date for the ingestion event.
The presence of lithium and beryllium indicates that the chemical signature has not yet been completely erased by the star’s internal processes, but the temporal estimate depends on theoretical models with uncertainties.
The relevance of the research goes beyond stellar chemistry.
If many planetary systems are unstable to the point of losing planets to their stars, organized systems like the Solar may be less common than they seem.
This hypothesis still depends on new measurements in other binary pairs.
In the Solar System, the eight planets maintain almost circular and stable orbits, an important characteristic for preserving planetary environments for long periods.
The comparison matters because planets with stable orbits offer more favorable conditions for slow processes, such as the evolution of complex life.
By transforming beryllium into an observational clue, the study paves the way to investigate events that, until now, were difficult to prove.
With similar measurements, astronomers can assess whether other chemically anomalous stars also carry signs of ancient rocky planets.
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