MIT astronomers have identified a planet approximately 140 light-years away from Earth that is swiftly disintegrating.
This collapsing world has a mass comparable to that of Mercury, yet it orbits roughly 20 times closer to its star than Mercury does to the sun, completing an orbit every 30.5 hours. Due to its close distance to the star, the planet is probably enveloped in molten rock that is vaporizing into space. As the searing planet speeds around its star, it is losing a significant amount of surface minerals and effectively evaporating.
The astronomers detected the planet utilizing NASA’s Transiting Exoplanet Survey Satellite (TESS), an MIT-led endeavor that tracks nearby stars for transits, or periodic reductions in starlight that may indicate orbiting exoplanets. The signal that alerted the astronomers was an unusual transit, featuring a dip that varied in depth with each orbit.
The scientists verified that the signal signifies a closely orbiting rocky planet that is trailing a lengthy, comet-like tail of debris.
“The length of the tail is enormous, extending up to 9 million kilometers, or about half of the planet’s entire orbit,” states Marc Hon, a postdoctoral researcher at MIT’s Kavli Institute for Astrophysics and Space Research.
This planet appears to be disintegrating at an extraordinary rate, losing material equivalent to one Mount Everest with every orbit around its star. At this rate, considering its small mass, the researchers anticipate that the planet could completely fall apart in approximately 1 million to 2 million years.
“We got fortunate in observing it precisely at this moment of rapid disintegration,” remarks Avi Shporer, a partner in the discovery who is also affiliated with the TESS Science Office. “It’s akin to witnessing its final moments.”
Hon and Shporer, alongside their associates, have shared their findings today in the Astrophysical Journal Letters. Their MIT co-authors include Saul Rappaport, Andrew Vanderburg, Jeroen Audenaert, William Fong, Jack Haviland, Katharine Hesse, Daniel Muthukrishna, Glen Petitpas, Ellie Schmelzer, Sara Seager, and George Ricker, together with collaborators from various other institutions.
Burning away
The newly discovered planet, designated as BD+05 4868 Ab, was found almost by chance.
“We weren’t searching for this type of planet,” Hon explains. “We were engaged in the standard planet verification process, and I happened to notice this signal that seemed quite peculiar.”
The usual signal of an orbiting exoplanet resembles a short dip in a light curve that repeats at regular intervals, indicating that a compact body, such as a planet, intermittently passes in front of and briefly obstructs the light from its host star.
This typical pattern was unlike what Hon and his colleagues observed from the host star BD+05 4868 A, situated in the Pegasus constellation. Although a transit occurred every 30.5 hours, the brightness took significantly longer to return to normal, implying a long trailing structure still obstructing starlight. More intriguingly, the depth of the dip varied with each orbit, suggesting that whatever was passing in front of the star wasn’t consistently the same shape or obstructing the same amount of light.
“The shape of the transit resembles that of a comet with an extended tail,” Hon elaborates. “However, it’s improbable that this tail contains volatile gases and ice as one would expect from a genuine comet — these substances wouldn’t endure long at such a close distance to the host star. Mineral particles evaporating from the planetary surface can, however, persist long enough to create such a distinctive tail.”
Considering its close proximity to its star, the team theorizes that the planet is roasting at approximately 1,600 degrees Celsius, or nearly 3,000 degrees Fahrenheit. As the star heats the planet, any minerals on its surface are likely boiling away and escaping into space, where they cool into an extensive and dusty tail.
The dramatic fate of this planet is a result of its low mass, which lies between that of Mercury and the moon. Larger terrestrial planets like Earth possess a more powerful gravitational force and can thus retain their atmospheres. For BD+05 4868 Ab, the researchers believe there is insufficient gravity to keep the planet intact.
“This is a minuscule object with exceedingly weak gravity, which causes it to easily lose a significant amount of mass, further diminishing its gravity, leading to even greater mass loss,” Shporer clarifies. “It’s a runaway process, and it keeps worsening for the planet.”
Mineral trail
Of the nearly 6,000 planets that astronomers have identified so far, scientists are aware of only three other disintegrating planets beyond our solar system. Each of these deteriorating worlds was observed over a decade ago using data from NASA’s Kepler Space Telescope. All three planets exhibited similar comet-like tails. BD+05 4868 Ab boasts the longest tail and the deepest transits among the four known disintegrating planets thus far.
“That suggests that its evaporation is the most severe, and it will vanish significantly quicker than the other planets,” Hon states.
The planet’s host star is relatively nearby, and therefore brighter than the stars hosting the other three disintegrating planets, making this system ideal for further observations using NASA’s James Webb Space Telescope (JWST), which can assist in determining the mineral composition of the dust tail by identifying the colors of infrared light it absorbs.
This summer, Hon and graduate student Nicholas Tusay from Penn State University will spearhead observations of BD+05 4868 Ab using JWST. “This presents a unique opportunity to directly assess the internal composition of a rocky planet, which may provide significant insights into the diversity and potential habitability of terrestrial planets beyond our solar system,” Hon remarks.
The researchers will also scrutinize TESS data for indications of other disintegrating worlds.
“Sometimes when food is presented, an appetite develops, and we are now attempting to embark on the search for precisely these types of objects,” Shporer shares. “These are unusual objects, and the signal’s shape alters over time, which makes it challenging for us to detect. However, it is something we are actively pursuing.”