The Mystery of the Exoplanet That Wasn’t There - Astronomy News with The Cosmic Companion

The exoplanet that wasn’t there – A team of astronomers discovered that an exoplanet spotted in a distant star system never actually existed.

By Robert Lea

A team of astronomers from the University of Arizona have discovered that an exoplanet spotted in a distant star system by the Hubble Space Telescope, actually never existed. Fomalhaut b —located in the Fomalhaut system 25 light-years from Earth — is actually an expanding dust cloud leftover from a massive collision between two planetesimals — icy bodies that often act as the seed for planets.

Top: Composition of the 2010–2014 images of the Fomalhaut system The green circles with crosses highlight the then-current positions of Fomalhaut b, with 3σ astrometric error radii, while the smaller cyan colour circles show the previous positions, to highlight the spatial motion of the source. For the 2014 image, we show the two locations predicted by the two independent trajectory fits. The bright spot “near” the predicted locations is too far to be considered associated with Fomalhaut b. Image credit: Gáspár. A, Rieke. G. H

The team made their discovery whilst reexamining data collected by the Hubble Space Telescope (HST) between 2004–2012. In addition to these four data sets which had been thoroughly investigated in the past, the team had access to two data sets from 2013 and 2014 which had not previously been published.

It was in these two data sets that the astronomers found something fishy about Fomalhaut b which was announced as an exoplanet in 2008, based on data collected in 2004 and 2006. The planet had seemingly disappeared.

The astronomer’s results are published in the journal Proceedings of the National Academy of Sciences.

“One of the programs, that I am leading, will be observing the massive debris disk system around Fomalhaut using the Mid-Infrared Instrument (MIRI),” Explains Andras Gáspár, a member of James Webb Space Telescope NIRCam and MIRI Science Teams at the University of Arizona, and first author on the paper. “ While doing my preparations, I downloaded all archival HST data on the system and reduced them to see if there is anything interesting that someone may not have noticed before.

“I decided to check on Fomalhaut b, and to my surprise, it was not present on the latest images. So, I went through all the data and started to analyze it and noticed a pattern: it was fading.”

This stroke of pure luck inspired Gáspár and his colleague George Rieke, a Regents Professor of Astronomy at Steward Observatory, to look at the object in greater detail, an opportunity that the researcher could not pass up given his work primarily concerns modelling collisions and dust production.

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