This Disintegrating Planet Leaves a Destructive Trail Spanning Over 5 Million Miles

Astronomers have identified one of the most inhospitable exoplanets ever seen—a tiny world being scorched by its parent star and trailing a massive, comet-like plume of vaporized rock behind it.

A Molten Planet with a Vapor Tail

While much of exoplanet research focuses on potentially habitable worlds with the right conditions for liquid water, BD+05 4868 Ab is the polar opposite. On this extreme planet, searing temperatures have turned its surface into a molten ocean, which evaporates into space, forming a vast tail of mineral vapor.

“The tail’s size is astonishing—it stretches nearly 9 million kilometers [5.6 million miles], about half the length of the planet’s orbit,” said Marc Hon, an astrophysicist at MIT’s Kavli Institute.

Located around 140 light-years from Earth, BD+05 4868 Ab orbits its star once every 30.5 hours, keeping it roughly 20 times closer than Mercury is to the Sun. This close proximity subjects the planet to relentless heat, which has been gradually stripping it of its mass.

Scientists believe the planet once had over twice its current mass—now estimated to be less than half of Mercury’s—but it’s rapidly shrinking. According to researchers, with each orbit, the planet sheds material equivalent in mass to Mount Everest, suggesting it may disappear entirely within 1 to 2 million years.

“It’s a small planet with weak gravity, making it easy for it to lose material,” explained Avi Shporer, a member of the TESS (Transiting Exoplanet Survey Satellite) mission. “As it loses mass, its gravity weakens further, accelerating the process in a downward spiral.”

Only three other “melting Mercury” exoplanets have been found so far, but none appear to be deteriorating as quickly as this one. For comparison, a similar planet orbiting KIC 12557548 is expected to survive for another 200 million years. BD+05 4868 Ab, however, is disintegrating at a much faster pace.

Not All Planetary Tails Are Alike

Astronomers have observed other planets with tails, mostly large gas giants like HAT-P-32b, which releases helium through massive tails stretching 53 times the planet’s size—but these planets still have far more time before they vanish completely. WASP-69b, another hot Jupiter, loses its atmosphere much more slowly and likely won’t disappear before its star ends its life.

Astronomers discovered BD+05 4868 Ab using the transit method, a common technique in which they monitor dips in a star’s brightness as a planet crosses in front of it.But something unusual stood out: the dimming lasted longer than expected, and the brightness varied from orbit to orbit.

“The shape of the transit resembled a comet, with a long tail following the planet,” Hon said. “But unlike a comet’s icy tail, this one likely consists of mineral particles from the planet’s surface, vaporized by intense heat and lingering long enough to form this extended structure.”

Even more curious, researchers noticed a smaller tail leading the planet. This secondary tail may provide insight into how these dust structures form and behave.

A Rare Look Into a Rocky Planet’s Interior

Though clearly not a vacation destination, BD+05 4868 Ab could offer valuable clues about more Earth-like worlds. As the planet’s interior spills into space, astronomers gain a rare opportunity to study the composition of rocky planets.

Scientists hope that the James Webb Space Telescope (JWST) could soon observe the planet’s disintegration in more detail, analyzing the star’s light as it passes through the dust to determine its composition.

This is a rare opportunity to study the internal makeup of a rocky planet,” said Hon. “It could tell us a great deal about the variety and potential habitability of terrestrial planets beyond our own Solar System.

Read the original article on: Science Alert

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