NASA/JPL-Caltech
A sun-like star seems to have devoured some of its own planetary offspring, prompting researchers to nickname it after the titan Kronos from Greek mythology.
The star HD 240430 is part of a binary system with HD 240429, and the two have now been nicknamed Kronos and Krios. The pair travel through the galaxy side by side some 320 light years from Earth.
They both seem to be about 4 billion years old, suggesting they were born from the same interstellar cloud, and initially shared the same chemical make-up.
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But an analysis by Semyeong Oh at Princeton University and her team suggests the twins have led very different lives. Krios has noticeably smaller concentrations of elements like lithium, magnesium and iron floating in its atmosphere than its companion Kronos does.
In fact, the stars are more chemically different than any pair yet discovered. “I initially thought these two stars must not be in a binary,” says Oh.
Separated after birth
Perhaps they weren’t born together and hooked up later in life. Maybe the cloud they came from endowed them with different concentrations of elements.
But Oh and her team argue that Kronos has devoured several orbiting rocky planets throughout its life. Hence why they are calling the star Kronos, after the titan of Greek mythology who devoured his own children, fearing they would overthrow him.
By contrast, the team refer to HD 240429 as Krios, a rather more anonymous titan who was Kronos’s brother.
Oh’s team calculate that it would take the chemical elements from 15 Earth masses crushed up and scattered throughout Kronos’s roiling atmosphere to explain the star’s blend of excess elements.
“I was really excited when I saw this,” says Johanna Teske at the Carnegie Observatories in Pasadena, California, who has looked at similar pairs to see if stars known to host planets have different chemical compositions to those without the hangers-on. “A lot of those signatures were very small,” she said. “This is a huge signature.”
Chowing down
How the star would eat its planets isn’t clear, though. Perhaps another star flew past, disrupting the orbits of outer planets around Kronos, which then distorted the paths of inner worlds and sent them careening into their star.
The Krios system, two light years away, might have escaped unscathed, however.
If this did happen to Kronos, any remaining outer giant planets around it might have stretched-out orbits, suggesting they participated in the same cataclysm that led to the demise of their siblings. To test this, the team has begun looking for giant planets around both Kronos and Krios.
The group hasn’t found any such worlds yet – but the ongoing European Space Agency’s Gaia mission should have good chance of turning them up as it releases more data.
Reference: arxiv.org/abs/1709.05344
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