The distant planet of Fomalhaut b located 25 light-years away from Earth was first caught insight in 2004 and 2006 as a bright, cool dot moving briskly across the sky. Ten years later, that dot suddenly disappeared.

Fomalhaut b, one of the first exoplanets discovered in visible light by NASA's Hubble Telescope disappeared from the night sky in 2014, what could have happened to this planet and where did it go?

A giant dust cloud, but not a planet

Daily Mail has reported that one of the first planet discovered outside of our solar system is found to be not a planet at all but a giant dust cloud that was formed from the aftermath of two 125-mile icy comets colliding into each other, according to a study.

More than a decade past when the Fomalhaut b, a Saturn-like planet found in the Fomalhaut star system 25 light-years from Earth, was discovered through NASA's Hubble Space Telescope. However, the University of Arizona claims that this was actually not a planet at all.

The image that the Hubble Space Telescope captured was an expanding cloud of fine dust particles shortly after the collision. The team said that an event like this happens once every 200,000 years, and sheds light on how the planets evolve.

Dr. Andras Gaspar of the Steward Observatory of the University of Arizona, and the study lead author said that it is exceedingly rare to witness such major discovery. He believes that the observation was made at the right place and at the right time to have witnessed such an unlikely event.

The collision is thought to have happened in the constellation of Pisces Austrinus, about 11 billion miles from the Fomalhaut star which is hotter and 15 times brighter than our star. The solar system of Fomalhaut is said to be the ultimate lab test for how planets destroy each other, said George Rieke of the Steward Observatory.

Cannot be seen anymore

Both Gaspar and Rieke believe that the collision occurred not too long before it was first discovered in 2004 given all the available data. Now, the Hubble cannot detect the debris anymore. The dust cloud is made up of very small particles that is a 5^th of the diameter of a human hair.

When Fomalhaut b was first announced in 2008, it was seen clearly and seemed to have a massive ring around it. The characteristics of Fomalhaut b seemed unusual for an exoplanet that should be too small to be seen from Earth.

Moreover, it also does not have any detectable infrared signatures that are expected from a young and bright planet that should be warm enough to shine. Gaspar said that upon analyzing all available archives on Fomalhaut, it reveals that the planet-sized object may never have existed at all.

When finally in 2014, scientists discovered that the planet discovered by the Hubble had vanished. There are some evidences also showing that the object continuously fades over time, something unlikely to happen for a planet.

"Fomalhaut b was doing things a bona fide planet should not be doing," Gaspar said.

The researchers published their findings in the Proceedings of the National Academy of Sciences.