A distant exoplanet located 140 light-years from Earth is rapidly disintegrating, according to MIT astronomers who observed the planet using NASA’s Transiting Exoplanet Survey Satellite (TESS).
With an ultra-tight orbit around its host star—just 30.5 hours—the planet is experiencing intense solar radiation that is melting its surface into magma. This molten material is evaporating into space, steadily reducing the planet’s size. Once roughly the size of Mercury, the planet is estimated to have a mass between Mercury and Earth’s moon.
Transiting Exoplanet Survey Satellite
TESS is an MIT-led NASA mission designed to discover exoplanets by monitoring nearby stars for periodic dips in brightness—called transits—that indicate orbiting bodies. MIT researchers took special notice when one star’s transit depth changed with each pass. After further investigation, the team determined the signal came from a rocky planet on a tight orbit, trailing a debris tail. The planet, located in the constellation Pegasus, was designated BD+05 4868 Ab.
“The extent of the tail is gargantuan, stretching up to 9 million kilometers long, or roughly half of the planet’s entire orbit,” says Marc Hon, a postdoc at MIT’s Kavli Institute for Astrophysics and Space Research.
Due to the planet’s rapid mass loss, astronomers estimate it may completely disintegrate within one to two million years. With each swift orbit, it sheds a mass roughly equivalent to Mount Everest’s.
“We got lucky with catching it exactly when it’s really going away,” says Avi Shporer, a collaborator on the discovery who is also at the TESS Science Office. “It’s like on its last breath.”
Unusual Transit Behavior
“We weren’t looking for this kind of planet,” Hon says. “We were doing the typical planet vetting, and I happened to spot this signal that appeared very unusual.”
Unlike typical exoplanets, the dimming signal lasted longer and varied in depth with each transit, suggesting the object was surrounded by a shifting, extended cloud of material.
“The shape of the transit is typical of a comet with a long tail,” Hon explains. “Except that it’s unlikely that this tail contains volatile gases and ice as expected from a real comet — these would not survive long at such close proximity to the host star. Mineral grains evaporated from the planetary surface, however, can linger long enough to present such a distinctive tail.”
A Planet in a Death Spiral
The planet’s extremely tight orbit heats its surface to an estimated 3,000 °F, causing minerals to evaporate and stream into space. Compounding the issue, the planet’s low mass results in weak gravity, making it difficult to retain an atmosphere or hold onto its surface materials.
“This is a very tiny object, with very weak gravity, so it easily loses a lot of mass, which then further weakens its gravity, so it loses even more mass,” Shporer explains. “It’s a runaway process, and it’s only getting worse and worse for the planet.”
To date, astronomers have identified only three other disintegrating exoplanets among the nearly 6,000 known planets. While those also sport comet-like tails, BD+05 4868 Ab has both the longest and most prominent tail observed.
“That implies that its evaporation is the most catastrophic, and it will disappear much faster than the other planets,” Hon explains.
A Window to Planetary Interiors
Not only is BD+05 4868 Ab the most extreme example of a disintegrating planet, but it’s also conveniently close by. Its proximity makes it an ideal candidate for future observation. NASA’s James Webb Space Telescope (JWST) will soon analyze the tail’s infrared spectrum to determine its mineral composition. Hon and Penn State University graduate student Nicholas Tusay will lead that effort.
“This will be a unique opportunity to directly measure the interior composition of a rocky planet, which may tell us a lot about the diversity and potential habitability of terrestrial planets outside our solar system,” Hon says.
Encouraged by their unique find, the team continues combing the TESS data for other interesting examples.
“Sometimes with the food comes the appetite, and we are now trying to initiate the search for exactly these kinds of objects,” Shporer says. “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 paper “A Disintegrating Rocky Planet with Prominent Comet-like Tails Around a Bright Star” appeared on April 22, 2025, in The Astrophysical Journal Letters.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.