October 26, 2012
Astronomers Revive Zombie Planet In New Study
[ Watch the Video: Studying Hubble Data Revives a Zombie Exoplanet ]
Lee Rannals for redOrbit.com - Your Universe Online
A new study suggests that the nearby star Fomalhaut hosts a massive "zombie" exoplanet that was previously thought to not exist, but is back from the dead.
Fomalhaut is the brightest star in the constellation Piscis Austrinus, and lies 25 light years away from us.
Hubble astronomers discovered the exoplanet back in November 2008, and it was one of the first directly imaged in visible light around another star.
The object sat just inside a vast ring of debris surrounding the host star. Its location and mass seemed just right for its gravity to explain the ring's appearance.
However, studies after this find claimed that this planetary interpretation is not accurate, and that Fomalhaut b was actually just a short-lived dust cloud unrelated to any planet.
Now, a new analysis has brought this zombie planet back to life, with claims that it is indeed an exoplanet.
"Although our results seriously challenge the original discovery paper, they do so in a way that actually makes the object's interpretation much cleaner and leaves intact the core conclusion, that Fomalhaut b is indeed a massive planet," said Thayne Currie, an astronomer at the University of Toronto.
The astronomers originally reported in 2008 that the exoplanet's brightness varied by a factor of about two, and cited this as evidence that the planet was accreting gas.
Follow-up studies interpreted this variability as evidence that the object was a transient dust cloud instead.
During the latest study, the team reanalyzed Hubble observations of the star from 2004 and 2006, and was able to recover the planet in observations taken at visible wavelengths near 600 and 800 nanometers.
The team attempted to detect Fomalhaut b in the infrared using the Subaru Telescope in Hawaii, but was unable to do so. This result implies that the mass of Fomalhaut b is less than two Jupiter masses.
Previous research trying to kill off the zombie planet said that it follows a tilted orbit that passes through the ring plane.
Currie and colleagues were able to establish that Fomalhaut b is moving with a speed and direction consistent with the original idea that the planet's gravity is modifying the ring.
"What we've seen from our analysis is that the object's minimum distance from the disk has hardly changed at all in two years, which is a good sign that it's in a nice ring-sculpting orbit," said Timothy Rodigas, a graduate student in the University of Arizona and a member of the team.
The team addressed studies that interpret the exoplanet as a compact dust cloud not gravitationally bound to a planet. Orbital dynamics would spread out or completely dissipate a cloud near Fomalhaut's ring in as little as 60,000 years. The dust grains experience additional forces as they interact with the star's light.
"Given what we know about the behavior of dust and the environment where the planet is located, we think that we're seeing a planetary object that is completely embedded in dust rather than a free-floating dust cloud," added team member John Debes, an astronomer at the Space Telescope Science Institute in Baltimore, Md.
The astronomers wrote about their zombie planet discovery in The Astrophysical Journal Letters.
Read redOrbit's exclusive interview with Dr. Thayne Currie.
Image 2 (below): This visible-light image from the Hubble Space Telescope shows the vicinity of the star Fomalhaut, including the location of its dust ring and disputed planet, Fomalhaut b. A coronagraphic mask helped dim the star's brightness. This view combines two 2006 observations that were taken with masks of different sizes (1.8 and 3 arcseconds). (Credit: NASA/ESA/T. Currie, U. Toronto)