A world on its last breath: Astronomers spot dying planet producing comet-like tail

MIT astronomers have found a planet about 140 light-years away that's quickly falling apart. (Image: MIT)

Someplace in the wide night sky, a small, doomed planet is disintegrating before our very eyes. Researchers at MIT have found a rocky planet about 140 light-years from our world that is being gradually dismantled as it orbits perilously close to its star. The planet, recently renamed BD+05 4868 Ab, is losing its outer layer piece by piece, with a comet-like trail of dust left behind in space. It's like the world is taking its last gasps as it speeds through space.

Too Close for Comfort

Scientists, using NASA's Transiting Exoplanet Survey Satellite (TESS), identified an unusual signal—one that didn't resemble the standard, periodic drop in brightness from exoplanets. Rather, the dips changed in depth and persisted longer, indicating a long tail behind the planet. That formation proved to be a gigantic tail of mineral dust up to 9 million kilometres long—close to half the orbital distance of the planet. Scientists verified that the signal was from a rocky planet breaking apart fast, its molten surface being evaporated into space with intense heat.

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The world is tiny compared with Earth, roughly the same mass as Mercury, and orbits its star about 20 times nearer than Mercury does to the Sun. It takes only 30.5 hours to make one full orbit, and it is thus one of the fastest-orbiting terrestrial worlds discovered. The surface temperature is so hot at this distance, reaching about 1,600 degrees Celsius. The heat vaporizes surface minerals, and they are released into space as vapour by the planet's weak gravity, leaving behind a huge dusty wake.

Losing Mass Like Mount Everest Every Orbit

What is more impressive about BD+05 4868 Ab is how quickly it's disintegrating. Scientists estimate that with every orbit, the planet loses a mass equivalent to one Mount Everest. Due to its tiny size and weak gravity, this loss perpetuates a cycle of destruction—the more mass it loses, the weaker its gravity, and the quicker it decays. MIT astrophysicist Avi Shporer labeled the planet "on its last breath," with total breakup likely in a span of one to two million years.

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Just three other planets that are disintegrating have been discovered, and they were all detected more than a decade ago based on observations from NASA's Kepler Space Telescope. BD+05 4868 Ab is distinguished by the longest tail and deepest brightness dips, indicating that its destruction is more violent compared to the past cases. The fact that the planet is close and its host star is bright makes it a good target for follow-up observations.

A Glimpse Inside a Rocky World

Later this year, NASA's James Webb Space Telescope will look at the planet to study the minerals in its dust tail. MIT's Marc Hon and Penn State University graduate student Nicholas Tusay will conduct this research, seeking to learn about the internal structure of the planet. The results may provide new information about rocky planets outside our solar system and how their structures differ from Earth-like worlds.

With this rare discovery, the MIT team is now turning its attention to hunting for more such doomed planets. They believe that similar strange signals might be hiding in TESS data, waiting to be uncovered. As Shporer put it, “These are weird objects, and the shape of the signal changes over time, which is something that’s difficult for us to find. But it’s something we’re actively working on.”

The study has been made available in Astrophysical Journal Letters and was funded in part by NASA.