Fastest disintegrating world ever seen 'spills its guts' for NASA's exoplanet hunter

Using NASA's exoplanet-hunter TESS (Transiting Exoplanet Survey Satellite), astronomers have discovered the fastest disintegrating planet ever seen. The planet is crumbling so fast due to bombardment from its star that it is losing a "moon's worth" of matter every million years. Soon, it is doomed to vanish entirely.

The extrasolar planet, or "exoplanet," is named BD+05 4868 Ab and, aptly, orbits a star designated BD+05 4868 A. That star is located around 141 light-years away, which also makes this particular exoplanet the closest disintegrating world ever seen. The misfortune of this planet, BD+05 4868 Ab — and other disintegrating exoplanets, for that matter — is a boon for astronomers. These situations allows scientists to investigate the usually hidden interiors of terrestrial worlds.

Both teams presented their work at the 245th meeting of the American Astronomical Society in National Harbor, Maryland, on Thursday (Jan. 17).

“It's remarkable that directly measuring the interior of planets in the solar system is so challenging — we have only limited sampling of the Earth's mantle, and no access to that of Mercury, Venus, or Mars — but here we have found planets hundreds of light-years away that are sending their interiors into space and backlighting them for us to study with our spectrographs," Penn State team member Jason Wright said in the statement. “It's a remarkable and fortuitous opportunity to understand terrestrial planet interiors."

Despite using different space telescopes to obtain their results, both the MIT and Penn State teams hunted and studied exoplanets as they crossed or "transited" the face of their stars. This transiting causes a tiny dip in light from a star that signals the passage of a planet.

Not only has this transit method been used to discover thousands of worlds in NASA's exoplanet catalog, but when starlight shines through a transiting planet's atmosphere or even debris around it, the characteristic absorption of light by the elements can also leave a fingerprint. Astronomers can read these fingerprints to reveal the composition of said material. That technique is called "spectroscopy." So, when the planet's insides are on the outside, spectroscopy offers a clever way to see within terrestrial worlds.

The planets these two teams are interested in are so close to their planets that they orbit them in just a matter of hours. These planets are known as "ultra-short period planets," or "USPs."

Just a tiny fraction of USPs are hot enough and have small enough surface gravities to disintegrate such that they can be distinguished by telescopes around Earth. Prior to the discovery of BD+05 4868 Ab, there were only three disintegrating planets among the over 6,000 entries in NASA's exoplanet catalog.

The tail of BD+05 4868 Ab is so significant in density and size that when it crosses the face of its star, it blocks 1% of the star's light, and the transit signal it creates lasts 15 hours.

The dust trail of BD+05 4868 Ab is divided into two distinct sections: one that leads the planet in its orbit around its star and one that follows it. The MIT team thinks this is a result of dust grains with different sizes. The trail leading the planet consists of larger grains, comparable to desert sand, while the following trail has finer grains resembling soot particles.

The planet only has around the equivalent of the moon's mass left intact, and at the rate it is losing matter, that means it will soon be gone entirely.

"The rate at which the planet is evaporating is utterly cataclysmic, and we are incredibly lucky to be witnessing the final hours of this dying planet," Hon said.

The two teams have jointly submitted a JWST proposal to study BD+05 4868 Ab in the same manner as K2-22b, meaning the future of this doomed exoplanet is bright.

“What's also highly exciting about BD+05 4868 Ab is that it has the brightest host star out of the other disintegrating planets — about 100 times brighter than K2-22 —establishing it as a benchmark for future disintegrating studies of such systems," MIT team member Avi Shporer said in the statement. "Prior to our study, the three other known disintegrating planets were around faint stars, making them challenging to study.

"The data quality we should get from BD+05 4868 A will be exquisite. These studies have proven the validity of this approach to understanding exoplanetary interiors and opened the door to a whole new line of research with JWST."

The BD+05 4868 Ab research is available on the paper repository site arXiv, as is a paper discussing the K2-22b findings.

Robert Lea is a science journalist in the U.K. whose articles have been published in Physics World, New Scientist, Astronomy Magazine, All About Space, Newsweek and ZME Science. He also writes about science communication for Elsevier and the European Journal of Physics. Rob holds a bachelor of science degree in physics and astronomy from the U.K.’s Open University. Follow him on Twitter @sciencef1rst.