Space and Science

The planet that never existed

CNN  — 

Planets are hard to lose, unless you’re Obi-Wan Kenobi in “Star Wars: Episode II - Attack of the Clones.” But astronomers believe that what was once among the first observed exoplanet discoveries, actually never existed.

Instead, NASA’s Hubble Space Telescope likely observed the leftover bright cloud of an explosion after two icy objects collided, according to a new study. The telescope just happened to look in time to catch the aftermath, rather than the explosion itself, as the fine dust particles expanded.

“These collisions are exceedingly rare and so this is a big deal that we actually get to see evidence of one,” said Andras Gaspar, lead study author and an assistant astronomer at the University of Arizona’s Steward Observatory, in a statement. “We believe that we were at the right place at the right time to have witnessed such an unlikely event with NASA’s Hubble Space Telescope.”

The study published Monday in the Proceedings of the National Academy of Sciences.

Previously, the exoplanet was likely believed to be orbiting a star named Fomalhaut, which is 25 light-years from Earth. The planet was dubbed Fomalhaut b and announced in 2008 after data gathered in 2004 and 2006 suggested the presence of a planet around the star.

This was one of the first exoplanet discoveries found using direct imaging. Hubble showed the clearly observable moving dot.

But the astronomers did have questions about it. The planet showed up brightly in the visible light spectrum of Hubble’s observations – the light we can see. This isn’t normally the case for exoplanets, which are too small to reflect the light of their host star and be seen so clearly at such a distance from us.

A Hubble image, left, shows a vast ring of icy debris around the star Fomalhaut. On the right is an image showing how the object faded in observations over time.

And there was no heat signature. Exoplanets, especially young ones, usually radiate heat in the form of detectable infrared light.

But the researchers thought that perhaps a ring of dust orbited the planet.

And in images taken by Hubble in 2014, the planet simply isn’t there any longer. And images leading up to that one showed the object’s brightness fading.

Lost a planet these astronomers have, as Yoda would say.

“Our study, which analyzed all available archival Hubble data on Fomalhaut, revealed several characteristics that together paint a picture that the planet-sized object may never have existed in the first place,” Gaspar said. “Clearly, Fomalhaut b was doing things a bona fide planet should not be doing.”

So how did this bright dust cloud, which isn’t a planet, disappear?

As the dust cloud expanded over time, which was first observed in 2004, the dusty debris cloud is likely too faint to be seen by Hubble even though it’s likely larger than Earth’s orbit around the sun.