Scientists have discovered a new exoplanet, BD+05 4868 Ab, located around 140 light-years from Earth. The planet is rapidly disintegrating and shedding material into space at a mass loss rate of 10 M⊕ Gyr−1.
With a mass similar to Mercury, it orbits its bright K-dwarf star TIC 466376085 at a distance about 20 times closer than Mercury’s orbit around the Sun. The planet completes one orbit every 30.5 hours. The extreme heat at this proximity melts its surface, turning it into molten rock.
As it circles its star, the planet is losing vast amounts of mass, creating a tail of vaporized minerals that stretches millions of km into space. This rapid disintegration offers a chance to study the effects of extreme proximity to a star on rocky planets.
Astronomers initially noticed an unusual transit signal, marked by a fluctuating dip in brightness with each orbit. These observations were made possible by NASA’s Transiting Exoplanet Survey Satellite (TESS), which detected the planet’s unusual transit and light variations.
The story behind BD+05 4868 Ab’s slow disintegration
The discovery of BD+05 4868 Ab’s gradual yet fiery breakdown happened unexpectedly during a routine vetting of exoplanets.
While examining data, Marc Hon, a postdoc researcher at Massachusetts Institute of Technology’s Kavli Institute for Astrophysics and Space Research, noticed an unusual signal that didn’t match the typical patterns of planetary transits. This led the team to investigate further, eventually identifying the planet as one that was rapidly disintegrating.
The planet’s decay is marked by a massive tail extending up to 9 million km, roughly half the length of its orbit. Owing to its small mass, Hon and his team predict that BD+05 4868 Ab could completely vanish within the next 1 to 2 million years.
Normally, when a planet orbits its star, it causes a small, regular dip in the light curve. This happens because the planet passes in front of the star, blocking a bit of its light.
The signal Hon and his team observed from the host star BD+05 4868 A in the Pegasus constellation was very different from the usual patterns. While a transit occurred every 30.5 hours, the star’s brightness took much longer to return to normal. This hinted at something large trailing behind the planet and continuing to block light. What stood out even more was the changing depth of the light dip with each orbit. This suggested that the object passing in front of the star wasn’t a uniform shape and was blocking different amounts of light each time.
Hon further elucidated, saying, “The shape of the transit is typical of a comet with a long tail, 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.”
Because the planet orbits so close to its star, researchers estimate its surface reaches temperatures near 1 600°C (3 000°F). At that heat, minerals on the surface vaporize and escape into space. As the material cools, it forms the signature long, dusty tail trailing behind the planet.
This planet’s rapid breakdown is likely tied to its small size, which is said to be somewhere between the mass of Mercury and the Moon. Ergo, BD+05 4868 Ab doesn’t have the strength to hold itself together. Researchers think its weak gravity is the prime culprit, allowing material to escape into space very easily.
This offers a rare opportunity to investigate a planet’s rapid breakdown
Out of the thousands of exoplanets found so far (around 6 000 to be precise), only a handful have shown signs of falling apart. Before this discovery, just three such crumbling planets had been identified. Like BD+05 4868 Ab, they left comet-style tails in their wake.
But this newly found planet stands out. Its tail is the longest observed so far and it dims its star more than any of the others. According to Marc Hon, this points to a much more intense rate of evaporation. In other words, BD+05 4868 Ab is vanishing faster than any disintegrating planet seen to date.
Thanks to its brightness and relative proximity, the star hosting BD+05 4868 Ab offers a rare opportunity for deeper investigation. Unlike the dimmer stars linked to other known disintegrating planets before, this one is well-suited for close study. Scientists plan to use the James Webb Space Telescope to examine the dust the planet leaves behind. By studying which wavelengths of infrared light are absorbed, they hope to pinpoint the minerals being lost from the planet’s surface.
Upcoming on the agenda for the scientists is to figure out what this crumbling planet is made of on the inside. It’s a rare chance to get a direct look at the interior makeup of a rocky world outside our solar system and better understand how different these distant planets can be.
References:
1 A Disintegrating Rocky Planet with Prominent Comet-like Tails Around a Bright Star – Marc Hon et al. – American Astronomical Society – April 22, 2025 – DOI 10.3847/2041-8213/adbf21