Small, rocky planets orbiting their host stars too closely can vaporize. Subject to tidal locking and extreme stellar irradiation, the dayside surfaces of such planets are hot enough to melt and develop thin atmospheres of evaporated rocky material.
MIT astronomers have discovered a planet, designated BD+05 4868 Ab, located approximately 140 light-years away and undergoing a process of disintegration.
The planet, roughly the mass of Mercury, orbits its star extremely close, so close that its surface is likely covered in magma evaporating into space. As it orbits its star in just 30.5 hours, the planet loses a massive amount of material, forming a long, comet-like debris tail.
Scientists detected this crumbling world using NASA’s TESS mission, which monitors changes in starlight that signal the presence of orbiting planets. They noticed an unusual, fluctuating dip in the star’s light, leading to the discovery.
This planet is disappearing at an astonishing rate—shedding an amount of material equal to one Mount Everest per orbit. Based on its small size, researchers estimate that it may completely vanish within 1 to 2 million years.
It’s like catching a dying planet in its final moments! Cosmic drama at its finest.
Astronomers were not looking for this type of planet. They were conducting the typical planet vetting and spotted an unusual-looking signal.
Astronomers studying the star BD+05 4868 A in Pegasus noticed something unusual: instead of a regular dip in brightness that signals an orbiting planet, they saw a prolonged dimming with a fluctuating pattern. This suggested that something larger than a simple planet was blocking the star’s light.
Further analysis revealed that the planet BD+05 4868 Ab has a mass between that of Mercury and the Moon and orbits extremely close to its star. The extreme heat—around 1,600°C (3,000°F)—is vaporizing minerals from its surface, creating a long, dusty tail similar to a comet. However, unlike a typical comet, this tail does not contain ice or volatile gases, which would not survive at this temperature.
Due to its low mass and weak gravity, BD+05 4868 Ab is rapidly losing material. While larger planets like Earth have enough gravity to retain their atmospheres, this planet is disintegrating, shedding massive amounts of debris into space. Each orbit sees another chunk of its surface evaporate, signaling that it may completely break apart within 1 to 2 million years.
This is a very small object with weak gravity, so it easily loses a significant amount of mass, which further weakens its gravity, causing it to lose even more mass. It’s a runaway process that only worsens for the planet.
Astronomers have identified only four disintegrating planets beyond our solar system, making BD+05 4868 Ab a rare discovery in the cosmos. The first three were spotted over a decade ago using NASA’s Kepler Space Telescope, each showing comet-like tails of material streaming away. BD+05 4868 Ab is the most extreme case, with the most extended tail and deepest transits, indicating the fastest evaporation rate.
Since BD+05 4868 Ab’s host star is relatively close and bright, scientists see this as a prime candidate for further study using NASA’s James Webb Space Telescope (JWST). This powerful observatory will analyze the mineral composition of the planet’s dust tail, providing insights into what this rocky world was composed of before it began disintegrating.
MIT’s Marc Hon and Penn State’s Nicholas Tusay are leading these investigations. They plan to use JWST this summer to study the planet’s interior composition. This rare opportunity could enhance our understanding of how rocky planets form and what factors make some more stable and potentially habitable than others.
In addition, researchers are combining TESS data to search for other exoplanets that are disintegrating. Since these objects are rare and difficult to detect, spotting more could improve our understanding of planetary destruction and the forces shaping exoplanets across the galaxy.
Journal Reference:
- Marc Hon, Saul Rappaport, Avi Shporer, Andrew Vanderburg, Karen A. Collins, Cristilyn N. Watkins, Richard P. Schwarz, Khalid Barkaoui, et al. A Disintegrating Rocky Planet with Prominent Comet-like Tails around a Bright Star. The Astrophysical Journal Letters. DOI 10.3847/2041-8213/adbf21
