Scientists baffled by 'unique object of uncertain nature' orbiting a star

Data from NASA's TESS mission has revealed something mysterious and dusty.

This image of space around TIC 400799224 with the crosshairs marking the location of the mysterious dusty object. 
Powell et al., 2021

"What in the universe is that?" That question's driven many science inquiries. When it comes to a "mysterious dusty object" discovered in observations from NASA's Transiting Exoplanet Survey Satellite, the question remains open. 

Astronomers are investigating something unusual happening around a binary star system called TIC 400799224, part of the TESS Input Catalog that logs objects seen by the NASA exoplanet-hunting mission. While TESS has confirmed over 170 exoplanets, it's also caught sight of a lot of other objects, including TIC 400799224.

In a statement last week, the Harvard & Smithsonian Center for Astrophysics (CfA) said TIC 400799224 stood out during a computer analysis of TESS data due to "its rapid drop in brightness, by nearly 25% in just a few four hours, followed by several sharp brightness variations that could each be interpreted as an eclipse."

TESS seeks out exoplanets by looking for telltale drops in brightness when a planet moves in front of a star. It takes follow-up work to confirm an exoplanet, and sometimes these dips in brightness indicate other things are going on.

The astronomers dug into previous observations of TIC 400799224 and found it's likely a binary star system, like Tatooine in Star Wars. One of the stars is pulsating regularly, which could be caused by an orbiting object emitting dust that appears to dim the star. The dust clouds are irregular in size, shape and duration.

"The nature of the orbiting body itself is puzzling because the quantity of dust emitted is large; if it were produced by the disintegration of an object like the asteroid Ceres in our solar system, it would survive only about 8,000 years before disappearing," CfA said. An analysis of six years of data on TIC 400799224 indicate the object is intact despite its odd outbursts. 

The team published a paper on the dust-emitting object in The Astrophysical Journal in December, describing it as "a unique object of uncertain nature -- but quite possibly a disintegrating asteroid or minor planet -- orbiting one star of the widely separated binary TIC 400799224."

There are still plenty of unknowns left to investigate, including which star in the system the object is orbiting and what kind of object is able to give off so much dust without falling apart. Said CfA, "The team plans to continue monitoring the object and to incorporate historical observations of the sky to try to determine its variations over many decades."

While TESS may be focused on finding exoplanets, it has delivered plenty of bonus material, like this nifty look at a comet, a glorious view of the starry southern sky and, now, the intriguing mystery of TIC 400799224.