Astronomers Discover a Sun-Like Star That Has Gobbled up 15 Earth-Mass Planets

The study of the star Kronos has provided a fascinating body of research and discoveries for a Princeton University research team, who at the same time are hoping to disprove some popular theories about chemical abundances in the universe.
Mario L. Major

A team of Princeton University astronomers has uncovered evidence of a planet-devouring star. Named Kronos, it has been slowly carving its path of gastronomic destruction through the universe, absorbing 15 planetary objects during its lifetime of 4 billion years.

The astronomical name a reference to the mythological hero Titan, who devoured his own children, Poseidon, Heides, and his three daughters. The names of the first two, of course, are references to Neptune and Pluto, respectively. This is all to say that the name of Kronos seems well deserved.

Let’s start with the facts. The “solar-type stars” —Kronos and Krios—form a binary pair and are given the designations of HD 240430 and HD 240429. To put it all into perspective, they are roughly 350 light years away. The more the team delved into studying them, the more important questions emerged and discoveries occurred.

Astronomers Discover a Sun-Like Star That Has Gobbled up 15 Earth-Mass Planets
Source: NASA/JPL-Caltech/R. Hurt (SSC-Caltech)

The findings appeared last month in a paper draft form, titled “KRONOS & KRIOS: EVIDENCE FOR ACCRETION OF A MASSIVE, ROCKY PLANETARY SYSTEM IN A COMOVING PAIR OF SOLAR-TYPE STARS.” In the initial stages of the research, the team, led by study author Semyeong Oh, was simply interested in compiling data about the formation and movement of the star pair that had been collected from Gaia, the European Space Agency’s spacecraft. They were encouraged by a colleague to push their research a step further and study the chemical compositions.

At this point, the dual task of the researchers became not only explaining the composition of the pair but trying to account for the different behavior between the two stars. The most compelling point for the astronomers was that Krios, the lesser-known half of the binary pair, had not exhibited the same planet-engulfing behavior as Kronos.

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They found that both had the relatively same levels of volatile elements, but that Kronos has a significantly higher number of rock-forming minerals—aluminum, silicon, magnesium and iron, among them.

Astronomers Discover a Sun-Like Star That Has Gobbled up 15 Earth-Mass Planets
Source: NASA/CXC/M. Weiss

Oh explains how careful analysis of chemical abundance as it relates to condensation temperature—the temperature at which volatiles become solids—moved the research into a completely different direction:

“All of the elements that would make up a rocky planet are exactly the elements that are enhanced on Kronos, and the volatile elements are not enhanced,” Oh said, adding, “so that provides a strong argument for a planet engulfment scenario, instead of something else.” Oh and her team concluded, therefore, that the devoured planets had served as a kind of metal-rich “dietary supplement” for Krios.


The team was quick to come up with a theory behind the planetary engulfing that had occurred. They propose that Kronos and Krios at one point came into close contact with another star, which threw off the alignment of the outer planets of the inner solar system. This, in turn, altered their orbit and sent them on the trajectory that led to their tragic demise. The fact that the two stars orbit one another only about every 10,000 years could explain why Krios did not meet a fate similar to the other planets.

The researchers hope that their work in this area will help shed light on the inner workings of other solar systems in the galaxy. When we consider this fascinating reality, we are relatively lucky. The Sun may have its flaws, but planet Earth, along with the other planets in our neck of the woods, has been spared a cruel fate.

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