MessageToEagle.com - Direct imaging of exoplanets has been a field in rapid development over the past few years, with detections
of several planets and low-mass brown-dwarfs.
Among these discoveries, one claimed planet detection that stands out as peculiar in many ways is that of Fomalhaut b.
Is Fomalhaut b a planet? New observations suggest this question will probably be debated for a while from now on.
Some years ago Hubble took an image of a planet circling another star. The planet is called Fomalhaut b and it orbits the
bright southern star Fomalhaut, located 25 light-years away in the constellation Piscis Austrinus (the Southern Fish).
Astronomers have long suspected there might be a planet in the region.
In 2004, it became clear that a large dust belt is surrounding Fomalhaut.
Soon it became obvious that this structure is in fact a ring of protoplanetary debris approximately 34.5 billion kilometres across with a sharp inner edge.
This large debris disk is similar to the Kuiper Belt.
Some years later, in 2008, Hubble managed to take the first visible image of Fomalhaut b, a point source of light lying 3 billion
kilometres inside the ring's inner edge.
"Our Hubble observations were incredibly demanding. Fomalhaut b is 1 billion times fainter than the star. We began this
program in 2001, and our persistence finally paid off", said astronomer Paul Kalas of the University of California, Berkeley
"Fomalhaut is the gift that keeps on giving. Following the unexpected discovery of its dust ring, we have now found an exoplanet
at a location suggested by analysis of the dust ring's shape.
The lesson for exoplanet hunters is 'follow the dust'", says team member Mark Clampin of NASA's Goddard Space Flight Center.
This visible-light image from the Hubble shows the newly discovered planet, Fomalhaut b, orbiting its parent star.
Credit: NASA, ESA, P. Kalas, J. Graham, E. Chiang, and E. Kite (University of California, Berkeley), M. Clampin (NASA
Goddard Space Flight Center, Greenbelt, Md.), M. Fitzgerald (Lawrence Livermore National Laboratory, Livermore, Calif.),
and K. Stapelfeldt and J. Krist (NASA Jet Propulsion Laboratory, Pasadena, Calif.)
New research and observations made by astronomers from the
University of Princeton and University of Montreal suggest Fomalhaut b is not a planet but a dust cloud!
The team led by Princeton's Markus Janson has used NASA's Spitzer Telescope to obtain ten times better resolution of the star.
"No signature is found at the position where Fomalhaut b would be expected.
There is almost certainly no direct flux from a planet contributing to the visible-light signature.
Final reduced image for the real data (left) and for the data with an artificial companion introduced at the
expected position of Fomalhaut b (right). Arrow 1 points out the expected position of the companion based on earlier
detections in the visible-light images. There is no corresponding point source seen in the real data. The artificial
companion in the right-hand image passes through the data reduction without any flux loss, verifying that the nondetection
is real, such that a stringent upper flux limit can be set. Arrow 2 points toward the brightest possible point
source in the field. Its position is consistent with a ring-nested orbit, but the significance is too low to make any
assessment of whether or not it is a real object. North is up and East is to the left in the images.
This, in combination with the existing body of data for the Fomalhaut system, strongly implies that the dynamically
inferred giant planet companion and the visible-light point source are physically unrelated," says the new study.
According to the Princeton team, the "real" Fomalhaut b still hides in the system waiting to be discovered.
The Hubble team is interested in the news data but questions its interpretation. Hubble astronomers have ruled out the possibility
Fomalhaut b could be a dust cloud.
According to Professor Kalas, Spitzer is capable of taking very sharp images but, it lacks the light sensitivity to detect a Saturn-sized
planet and Fomalhaut b is assumed to be only 10 times heavier than Earth, smaller than Neptune in other words.
This illustration shows the discovered planet, Fomalhaut b, orbiting its sun, Fomalhaut.
This structure is a Saturn-like ring that astronomers say may encircle the planet. Fomalhaut also is surrounded by a ring of material.
The edge of this vast disk is shown in the background as the curving cloud-like feature that appears to intersect the 200-million year-old star.
Fomalhaut b lies three billion kilometres inside the disk's inner edge. The planet completes an orbit around Fomalhaut every 872 years.
Credit: ESA, NASA and L. Calçada (ESO)
Additionally, scientists say that "giant planet companion and the visible-light point source are physically unrelated.
This in turn implies that the real Fomalhaut b still hides in the system."
"Although we do find a tentative point source in our images that could in principle correspond to this object, its significance
is too low to distinguish whether it is real or not at this point.
Concerning the visible-light point source, its underlying physics is unclear, but the only hypothesis that can be shown to reasonably
fit all existing data is an optically thin dust cloud, which is transient or has a transient component.
If this interpretation is valid, the cloud may or may not be physically bound to a central object in the super-Earth mass regime.
While astronomers keep debating this issue, we hope that NASA's infrared
James Webb Space Telescope scheduled for launch in 2018 will later be able to shed some light on this controversy.
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