Diversity of planetary origins and compositions traced by stellar abundance differences of co-natal star systems

Bertram Bitsch, Fan Liu, and Haiyang S. Wang investigate whether chemical abundance differences between stars born together can reveal the compositions and formation histories of planets those stars later consumed. Co-natal stars, including wide binary companions formed from the same molecular cloud, are expected to begin with nearly identical chemical compositions. Yet observations reveal abundance differences in a small fraction of these systems. One proposed explanation is planetary ingestion: a consumed planet can alter the chemical abundances measured in a star’s outer layers. The authors examine a previously studied sample of co-natal stars to determine which planetary compositions and formation locations could explain the observed chemical patterns. They compare differences in refractory elements, particularly iron, magnesium, and silicon, with those in more volatile elements, including oxygen, carbon, and sulfur. Their interpretation rests on the idea that planetary composition depends on where a planet acquires material relative to evaporation fronts in its natal disk. These fronts separate regions where particular compounds survive as solids from regions where they evaporate. The abstract focuses on the water, carbon-grain, and iron sulfide evaporation fronts. The principal finding is that different combinations of refractory and volatile abundance differences imply different ingestion histories. When one star is enriched in both refractory and volatile elements relative to its companion, ingestion of at least one planet by that star can explain the pattern. However, refractory enrichment accompanied by unchanged or lower oxygen or carbon abundances requires a more complex explanation in the authors’ interpretation. In such cases, both stars must have ingested planets that formed in different chemical environments, inside or outside the water and/or carbon-grain evaporation fronts. Thus, an abundance contrast need not result from planetary ingestion by only one member of a stellar pair. Sulfur offers an additional diagnostic. In some systems, the sulfur abundance difference is smaller by a factor of a few than the differences in iron, silicon, and magnesium. The authors attribute this pattern to planetary migration across the iron sulfide, or FeS, evaporation front. A planet may initially accumulate substantial sulfur before moving into a region where it stops acquiring sulfur but continues to accrete other refractory elements. Its eventual ingestion could then produce a relatively weak sulfur enhancement alongside stronger enhancements in iron, magnesium, and silicon. This mechanism links the stellar chemical signature to both the planet’s formation location and its subsequent movement through the disk. The authors conclude that detailed abundance comparisons between co-natal stars can help constrain the compositions of otherwise inaccessible, ingested exoplanets. Their interpretations suggest substantial diversity in planetary compositions resulting from different formation locations and migration histories, consistent with planet formation models. Only the title, authors, and abstract are available in the supplied record, which states that the paper’s license prevents access to the full text. The abstract does not report the sample size, individual abundance measurements, uncertainties, inferred planetary masses, or quantitative model comparisons. Its numerical details are limited to the minimum single-planet explanation for some abundance patterns and the factor-of-a-few sulfur discrepancy. Without the full analysis, the statistical strength, modeling assumptions, and uniqueness of the proposed explanations cannot be assessed.

When Stars Eat Planets, Their Chemistry May Tell the Story

A planet swallowed by its star might seem to leave little evidence behind. But its disappearance could change the star’s observable chemistry—and offer clues to where that planet formed and how it traveled through its planetary system. The key is finding another star that began with almost exactly the same chemical ingredients.

In “Diversity of planetary origins and compositions traced by stellar abundance differences of co-natal star systems,” Bertram Bitsch, Fan Liu, and Haiyang S. Wang investigate whether chemical contrasts between stars born together can reveal the compositions and histories of planets they later consumed. Their interpretation suggests that these stellar differences may preserve a surprisingly varied record of lost worlds.

Stars Born Together Provide a Chemical Baseline

Co-natal stars form from the same molecular cloud and are expected to begin with nearly identical chemical compositions. Widely separated binary companions can therefore serve as useful comparison partners: if their present-day abundances differ, something may have altered one or both stars after birth.

Observations reveal such differences in a small fraction of co-natal systems. One proposed explanation is planetary ingestion. When a star consumes a planet, the added material can modify the abundances measured in its outer layers. Comparing that star with its companion could help identify the chemical contribution of the swallowed planet.

The challenge is that an abundance contrast does not automatically tell us which star consumed a planet—or whether both did. The researchers examine a previously studied sample of co-natal stars to explore which planetary compositions and formation locations could produce the observed patterns.

Why a Planet’s Birthplace Matters

The study’s interpretation connects planetary composition to evaporation fronts in the planet-forming disk. These fronts separate regions where particular compounds can survive as solids from regions where they evaporate. A planet collecting material on opposite sides of a front can therefore acquire different chemical ingredients.

The abstract highlights three important boundaries: the water, carbon-grain, and iron sulfide evaporation fronts. Together, these provide a framework for interpreting differences between refractory elements, particularly iron, magnesium, and silicon, and more volatile elements, including oxygen, carbon, and sulfur.

Rather than treating all swallowed planets as chemically interchangeable, the researchers ask whether different mixtures of these elements point to different formation environments. In this picture, a star’s chemical alteration depends not simply on whether it ate a planet, but also on what that planet contained.

When One Swallowed Planet Is Not the Whole Explanation

Enrichment across both element groups

Some abundance patterns fit a relatively straightforward scenario. If one star is enriched in both refractory and volatile elements compared with its companion, ingestion of at least one planet by the enriched star can explain the contrast.

That does not identify every detail of the lost planet. It does, however, provide a plausible connection between the extra elements observed in the star and the material delivered by planetary ingestion.

More complicated chemical contrasts

Other patterns require a more involved explanation in the authors’ interpretation. A star may show enhanced refractory abundances while its oxygen or carbon abundance remains unchanged or is lower than its companion’s. Simply adding one planet to that star does not account for the full contrast within their framework.

Instead, the authors interpret these cases as requiring ingestion by both stars. The consumed planets would have formed in different chemical environments, inside or outside the water and/or carbon-grain evaporation fronts. The measured difference would then reflect two distinct histories of planetary consumption, rather than an altered star compared with an untouched companion.

Sulfur Offers a Clue to Planetary Migration

Sulfur adds another dimension to the investigation. In some systems, its abundance difference is smaller by a factor of a few than the differences in iron, silicon, and magnesium. The authors attribute this relatively weak sulfur signal to migration across the iron sulfide, or FeS, evaporation front.

In their proposed scenario, a planet first accumulates substantial sulfur. It then moves into a region where it stops acquiring sulfur while continuing to collect other refractory elements. If the star eventually consumes that planet, the resulting chemical signature can show stronger enhancements in iron, magnesium, and silicon than in sulfur.

This makes sulfur potentially useful for tracing movement as well as birthplace. A planet’s final composition may record multiple stages of growth across chemically different regions of its disk.

A Promising Method, with Important Limits

The findings suggest that detailed comparisons of co-natal stars could help constrain the compositions of otherwise inaccessible, ingested exoplanets. They also point toward substantial compositional diversity arising from different formation locations and migration histories, consistent with planet formation models.

However, only the title, authors, and abstract are available in the supplied record; a licensing restriction prevents access to the full text. The abstract gives no sample size, individual measurements, uncertainties, inferred planetary masses, or quantitative model comparisons. The statistical strength and uniqueness of the proposed explanations therefore cannot be assessed here.

The central insight remains compelling: chemical differences between stellar companions may reveal not just that planets disappeared, but something about the environments where those planets grew and the journeys they took before being consumed.