Wednesday, July 22, 2005
1 PM Eastern Standard Time
Introductory Remarks by Dr. Paul Kalas, Priniciple Investigator
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Thanks Jennifer and good morning from UC Berkeley in California.  

I'm very pleased to have a chance to talk about our new findings 
using the Hubble Space Telescope.  

The star we are talking about today is called Fomalhaut, and because 
it is very bright it is actually a very well-known star since antiquity.  
Modern astronomy has been studying Fomalhaut for over a century because, 
at a distance of only 25 light years, it is one of the closest stars to the 
Sun.   But I think the biggest surprise occured back in 1984, when Fomalhaut 
was found to be surrounded by solid material in the form of dust grains.  
Remember that 1984 was a decade before solid material in the form of planets 
had been discovered around other stars such as 51 Peg, and seven years 
before the first Kuiper Belt object was discovered.  

It is important to note that dust around a star like Fomalhaut has a very 
short lifetime, and therefore we infer that comets and asteroids must 
have formed in its vicinity because collisions between asteroids and 
the activity of comets continuously launches new dust into orbit around the star. 

However, a stars radiation and gravity will cause dust to spread inward 
toward the star as well as outward away from the star.  Thus what we 
should see is a flattened disk of dust with virtually no interesting 
features.  But if you insert a planet into a dust disk, then the planet 
will sweep up material in its vicinity and block the dust from spreading 
inward.  And hence what you would see is a narrow belt, or a ring, of 
dusty material, and this is what we see in these new Hubble images of Fomalhaut.

Many of you may have be aware that images of dust belts around nearby stars have 
been shown several times over the past seven or eight years, very often from 
Hubble programs, and in most cases what is found is a donut-like structure 
that can be attributed to a planetary system.

What makes Fomalhaut system unique among all the other disk discoveries is 
that the star is not located at the center of the belt  in fact the belt 
center is displaced from the star by 15 astronomical units, which is like 
saying that our Kuiper Belt is not centered on the Sun, but on a point 
between Saturn and Uranus.  The leading theory to explain this phenomenon 
is that Fomalhaut has an outer planet that shepherds the material in the 
ring to match its own orbit, and the planets orbit happens to be very 
eccentric.   By eccentric we mean that the orbit is not a perfect circle, 
but elliptical (as shown by Kepler 400 years ago, Keplers First Law:  
Planets move in ellipses with the Sun at one focus).  This theoretical 
result is a difficult calculation, but the end result is best seen in 
the movies that we have posted on the press release web site.  These are 
computer simulations created independently by our Australian colleagues 
Sarah Maddison and Adam Deller, and they show what happens to a dust disk 
when an interior planet has an eccentric orbit.  In these particular 
simulations the planet is assumed to have a mass 1.8 times the mass of 
Jupiter and a distance of 76 AU from the star.   (eccentricity 0.3, the 
dust was released from parent bodies with semi-major axes in the range 
160-210 AU; 1 AU = 150 million kilometers = 93 million miles).

Fomalhaut is also unique among other systems that you may have seen before 
because it is the closest dust belt that has been imaged at optical 
wavelengths with a CCD.  Therefore we have exquisite spatial resolution 
and therefore we can measure the properties of the belt such as how sharp 
the inner and outer edges are. What we found is that the inner edge of 
the belt is consistent with a knife edge drop-off in dust density, 
implying that somewhere within the boundary of the belt we have a planet 
that is very persistent in keeping the dusty material seen in the image 
from spreading inward toward the star.  In fact you may be familiar with 
the recent images from the Cassini mission that show how the rings of 
Saturn are shepherded by small moons also in orbit around Saturn.  

So, in summary, what we now have is a direct image of a Kuiper Belt 
surrounding our neighbor Fomalhaut, and its Kuiper Belt is off-center 
and has a very sharp inner edge, and taken together the offset and 
inner edge point to a planetary system contained within the belt.

Our observations were challenging, because Fomalhaut the star is so 
bright, and the belt is so faint, and in fact I've been trying to get 
this image for the past 12 years, and it was only the new camera 
installed on Hubble that could have produced this image.  So from here 
I'll let you listen my co-author, Dr. Mark Clampin, who can tell you more 
about how we obtained these observations.