Dead Planets Sing Sad, Sad Songs

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Creatures of habit, planets cling to their host stars long after they've been stripped to the core. Monart/Shutterstock

Is there anything sadder than the song of long-dead planet at the other end of the galaxy?

Stripped to its core, betrayed and flayed by the sun it still orbits, it's a husk of its former self.

It's a good thing grown-up astronomers don't cry.

Indeed, research published in Monthly Notices of the Royal Astronomical Society suggests they're actually listening in on that soundtrack of despair, hoping these magnetic signatures can shed light on the lives of former planets.

Specifically, Dimitri Veras of the University of Warwick notes in a press release, a so-called zombie planet may "provide a glimpse into our own distant future, and how the solar system will eventually evolve."

To do that, researchers need a couple of things to happen. The dead planet would have to be orbiting a white dwarf — a compact star that has shed all its outer layers and burned through its fuel. But on its way to the retirement home, the star went through its red giant phase, expanding outward for a surprise annihilation of any orbiting planet.

The final configuration — a planetary carcass orbiting a white dwarf— would literally be music to the ears of astronomers.

Illustration of a star that's become a white dwarf.
After a star has spent its nuclear fuel, it may become a very compact body called a white dwarf. sciencepics/Shutterstock

That's because, according to the research paper, the magnetic field between the spent star and its clingy corpse creates a circuit that produces radio waves.

"There is a sweet spot for detecting these planetary cores: a core too close to the white dwarf would be destroyed by tidal forces, and a core too far away would not be detectable," Veras explains. "Also, if the magnetic field is too strong, it would push the core into the white dwarf, destroying it."

If they find that perfect scenario, scientists would only have to tune their radio telescopes into Zombie Planet Radio.

"Nobody has ever found just the bare core of a major planet before, nor a major planet only through monitoring magnetic signatures, nor a major planet around a white dwarf. Therefore, a discovery here would represent 'firsts' in three different senses for planetary systems," Veras adds.

Time is certainly on their side. Dead planets, they claim, can broadcast for up to a billion years.

"We think that our chances for exciting discoveries are quite good," notes study co-author Alexander Wolszczan of Pennsylvania State University.

And, at the very least, a zombie radio signal might serve as an eerie reminder of our own planet's mortality. Someday Earth's bones will be picked clean by the sun, and it will sing into the void of all things it used to be.

And maybe — just maybe — an alien astronomer will heed its call.