Fomalhaut B - Early Follow-up Observations and Doubts About Fomalhaut B

Early Follow-up Observations and Doubts About Fomalhaut B

In the discovery paper, Kalas and Graham suggested that Fomalhaut b's emission originates from two sources: from circumplanetary dust scattering starlight and from planet thermal emission. Here, the former explains most of the 0.6 µm brightness and planet thermal emission contributes to much of the 0.8 µm brightness. Their non detections with ground-based infrared data suggested that Fomalhaut b had to be less massive than about 3 Jupiter masses.

However, Fomalhaut b should be detectable in the space-based infrared data in this scenario. But sensitive infrared Spitzer Space Telescope observations failed to detect Fomalhaut b, implying that Fomalhaut b does identify emission from a planet atmosphere. Furthermore, although the planet was thought to be a plausible explanation for Fomalhaut's eccentric debris ring, the measurements in Kalas and Graham's paper implied it was moving too fast (i.e. not apsidally aligned) for this explanation to work. Finally, researchers analyzing September–October 2011 Atacama Large Millimeter Array (ALMA) data for Fomalhaut's debris ring suggested an alternate hypothesis: that the ring is shaped by much smaller, shepherding planets neither of which needed to be Fomalhaut b. These results lead to serious doubts about Fomalhaut b's claimed properties, its status as a planet and even its existence.