Zombie Planet Interview With Dr Thayne Currie
November 2, 2012

RedOrbit Exclusive Interview: Dr. Thayne Currie, University of Toronto’s Department of Astronomy and Astrophysics

Dr. John Millis and Jedidiah Becker for redOrbit.com — Your Universe Online

In 2008, astronomers announced that the Hubble Space Telescope had captured images of an alien planet orbiting the nearby star Fomalhaut, located a mere 25 light years away in the constellation Piscis Austrinus. Dubbed Fomalhaut b and claimed as the first exoplanet to be confirmed through direct imaging in visible light, the planet appeared to orbit its star immersed in a massive ring of dust and debris.

In the years that followed, however, a number of astronomers began to dispute Fomalhaut b´s status as a planet, noting among other things its conspicuous absence of an infrared signature and concluding that it was more likely a large cloud of dust.

In a new study, however, researchers have taken another look at Hubble images from 2004 and 2006, and are now reaffirming that Fomalhaut b is indeed a “massive planet” — albeit a somewhat smaller one than originally suspected. The University of Toronto astronomer and lead author of the new study Dr. Thayne Currie recently talked with redOrbit about bringing Fomalhaut b back from the dead.

Read the Original Article “Astronomers Revive Zombie Planet

RO: Dr. Currie, the media has certainly grabbed ahold of the "Zombie Planet" title given to Fomalhaut b. Where exactly did this come from?

Currie: The web video accompanying our paper release uses the phrase ''zombie planet'' once. The phrase never appears in our paper. What the video means by ''zombie'' is simply a colorful description of how the scientific community has viewed Fomalhaut b.  It was announced to be a directly imaged planet in 2008, but several papers appearing later based on new data expressed serious doubts about whether it exists. In the minds of many, it was discredited. Our paper ℠revives´ or ℠brings back to life´ the claim that Fomalhaut b identifies a directly imaged planet, although the exact form in which it has been ℠reanimated´ differs from what the original discoverers of Fomalhaut b thought it was. We do not literally mean that a planet was alive, then dead, and now alive again.

RO: In what ways does your analysis differ from that performed in the original Fomalhaut b discovery paper?

Currie: First, we used different image processing techniques to extract the signal of Fomalhaut b from the noisy stellar halo. Although these methods are far more complex, they have been critical in yielding detections of some other directly imaged planets and have been recently and successfully applied to detect planets in other Hubble Space Telescope data. Because of these successes, we decided to try them on the Fomalhaut data.

Second, we tried to investigate Fomalhaut b's orbit not just by measuring its absolute position but also [its] position relative to the debris ring. Third, we compared Fomalhaut b's emission to a wider range of planet atmosphere models, including new data that was unavailable to the original discovery paper.

RO: It seems that much of the controversy surrounding the status of Fomalhaut b comes from the lack of an infrared counterpart. What are the implications of this, and how does this new interpretation of the Hubble data compensate for this?

Currie: The original discovery paper posited that some of the HST [Hubble Space Telescope] observed emission originates from a planet atmosphere. If this were true, then Fomalhaut b should have been detected in the infrared. The non-detection means that Fomalhaut b must be less massive than thought in the original paper (less than 2-3 Jupiter masses).

Our study simply points out that Fomalhaut b can still be planet-mass yet be undetectable in the infrared. This would happen if its mass is less than 2 Jupiter masses. Analyses trying to derive Fomalhaut b's mass from its effect on the surrounding debris ring appear to favor these smaller masses.

The other components of our study focus on and (in our opinion) resolve issues specific to the original discovery paper: claimed evidence for variability, the fact that it was moving faster than it should if it were a planet responsible for sculpting the ring, etc.

RO: Are there alternative interpretations that could explain the Hubble data — for instance, that the observed optical data is simply scattered light from another source inside the dust cloud?

Currie: Yes, the primary alternate interpretation is that Fomalhaut b is a dust cloud that was produced from collisions between two exo-Kuiper belt-like objects (about 50-100 kilometers in size, or 31-62 miles). While this scenario is certainly possible, we consider it to be unlikely for reasons explained in the paper. The primary reasons are: 1.) that such a cloud would be exceptionally short lived compared to the age of the system and that 2.) the most likely place for such a collision to occur is within the debris ring, not interior to it, yet we do not see any other Fomalhaut b-like objects located within the ring even though we had the capability to do so.

RO: Early estimates put the age of the planet at roughly 100 million years — quite young in galactic terms. Is there anything that we could hope to gain by studying such a young planet so near to Earth?

Currie: Yes, because the system is young (450 million years), it can in principle provide a window into understanding the physical properties of planets in earlier stages of their evolution, especially their atmospheres. Because we do not yet detect light from the atmosphere of any planet identified from Fomalhaut b, we can't really use it to study the atmospheric evolution of planets.

However, the Fomalhaut system as a whole may provide a useful contrast to what we think the early solar system may have looked like. Our solar system has its own disk of icy dust and planetesimals (the Kuiper belt) that is sculpted by a planet (Neptune). Earlier in its history (at an age more comparable to Fomalhaut's age), the Kuiper belt may have been greatly perturbed by the solar system's gas giant planets. Studying the Fomalhaut debris disk and candidate planet then provides a detailed look at planet formation outcome different from our own.

RO: Are their plans for follow-up observations of this system? What do we hope to learn?

Currie: Yes, the team that discovered Fomalhaut b 4 years ago has their own paper in preparation using new Hubble data to better determine Fomalhaut b's orbit. I am certainly interested in doing more studies of this system. While Fomalhaut b has so far eluded detection in the infrared, I am not ready to give up. If we do one day get a detection of Fomalhaut b in the infrared, it might tell us about what kind of atmosphere any planet at Fomalhaut b's location might have. Although I believe getting this infrared detection is out of reach from even the largest ground-based telescopes and might also be very tough with Hubble, the James Webb Space Telescope will have a far better chance at detection.

RO: Finally, despite the fact that the exoplanet catalog has been building at a rapid rate in recent years, we have yet to find an Earth-like planet orbiting in the habitable zone of its parent star. Do you think it is only a matter of time before we find such a system?

Currie: I think so. It might be possible to soon detect an Earth-mass planet in the habitable zone around a nearby M-dwarf using the transit method. For Sun-like stars and more massive stars we will probably need direct imaging. Although a terrestrial planet finding mission is likely decades off, we have made substantial progress in laboratory tests of instruments that might help us separate out the light of a true Earth-twin around a Sun-like star.

RO: Dr. Currie, thanks very much for taking the time have a chat with us. On behalf of the redOrbit team and our readership, we wish you the best of luck on your future research and look forward to reading about your future work.


Dr. Thayne Currie is currently a postdoctoral fellow in the Department of Astronomy and Astrophysics at the University of Toronto. His research focuses on detecting and characterizing massive planets via direct imaging. The main goals of his research are to understand the formation and evolution of planetary systems, to determine how the solar system fits within the range of planet formation outcomes and how the properties of planets around other stars compare to those in our solar system.