All Hail Kronos, the Star That Eats Planets for Breakfast

Rocky planets, like those Kronos must have swallowed, come in a range of sizes and flavors. NASA/JPL-Caltech/R. Hurt (SSC-Caltech)

Everyone knows that if you eat 15 garlic cloves, you'll have terrible garlic breath.

But apparently a star known as HD 240430 did not get that memo—it has eaten about 15 Earths's worth of rocky planets, as astrophysicists concluded from the planetary equivalent of the stench of garlic in its chemical signature.

They explain their argument in a paper recently posted to the physics pre-print site arxiv. The scientists had been looking at HD 240430 and a similar star, HD 240429, to try to decide whether they were a binary pair, which would mean they orbit each other.

With two light-years of empty space between them, they're awfully far apart for a pair—the cut-off for what astronomers call a "wide binary" is stars with a distance of just 500 times our distance to the Sun, less than one percent of a light-year.

But they do look eerily similar: They're both yellowish G-type stars like our own Sun, and about 4 billion years old. A little extra nosing around from the researchers confirmed they orbit each other—but also showed that they aren't quite so similar in terms of their chemical makeup.

HD 240430 turns out to contain much more of certain elements—including iron, silicon, calcium, aluminum and nickel—than its partner star. Those are all elements that are solids at temperatures of up to 1,700 degrees Fahrenheit. When it came to elements that can be gases at cooler temperatures, like carbon, nitrogen and oxygen, the two stars have about the same amount.

The research team thinks there's only one way to get that kind of discrepancy: HD 240430 has gobbled up a bunch of Earth-like planets.

Think about our own solar system: The four planets closest to our Sun are rocky, and full of those elements that stay solid at warmer temperatures, like those you find closer to the Sun. The four planets farther away from the Sun are gas giants that formed under cooler temperatures. They still have some of those rocky elements buried deep in their cores, but in much smaller quantities than gases.

That means HD 240430 couldn't have binged on planets indiscriminately: Absorbing gas giants would have meant absorbing their gases as well as their solid cores, changing the star's chemical fingerprint in a different way.

And given how very much of those rocky elements HD 240430 contains, it has apparently snatched up the equivalent of about 15 Earths. There's no way to tell precisely how many planets those elements would have come from, but scientists say it's plausible for one solar system to include that much rocky material.

The star's greediness inspired its nickname, Kronos—the Greek name for the mythological Titan who devoured his children after a prophecy predicted one would be his downfall. (Unfortunately for Kronos, his wife didn't like this setup and eventually arranged for a son named Zeus to be spirited away to safety; he later returned and made the prophecy come true.)

Stars can't get indigestion, but gluttony still comes with a price: Astrophysicists will learn your secrets sooner or later.