[meteorite-list] APL Astronomer Spies Conditions 'Just Right' For Building an Earth

[Ron Baalke]

Johns Hopkins University Applied Physics Laboratory
Office of Communications and Public Affairs
Laurel, Maryland
Media Contact: Michael Buckley
(240) 228-7536 or (443) 778-7536
Michael.Buckley at jhuapl.edu
October 3, 2007

FOR IMMEDIATE RELEASE

APL ASTRONOMER SPIES CONDITIONS 'JUST RIGHT' FOR BUILDING AN EARTH

An Earth-like planet is likely forming 424 light-years away in a star 
system called HD 113766, say astronomers using NASA's Spitzer Space Telescope.

Scientists have discovered a huge belt of warm dust - enough to build 
a Mars-size planet or larger - swirling around a distant star that is 
just slightly more massive than our sun. The dust belt, which they 
suspect is clumping together into planets, is located in the middle 
of the system's terrestrial habitable zone. This is the region around 
a star where liquid water could exist on any rocky planets that might 
form. Earth is located in the middle of our sun's terrestrial habitable zone.

At approximately 10 million years old, the star is also at just the 
right age for forming rocky planets.

"The timing for this system to be building an Earth is very good," 
says Dr. Carey Lisse, of the Johns Hopkins University Applied Physics 
Laboratory, Laurel, Md. "If the system was too young, its 
planet-forming disk would be full of gas, and it would be making 
gas-giant planets like Jupiter instead. If the system was too old, 
then dust aggregation or clumping would have already occurred and all 
the system's rocky planets would have already formed."

According to Lisse, the conditions for forming an Earth-like planet 
are more than just being in the right place at the right time and 
around the right star - it's also about the right mix of dusty materials.

Using Spitzer's infrared spectrometer instrument, he determined that 
the material in HD 113866 is more processed than the snowball-like 
stuff that makes up infant solar systems and comets, which are 
considered cosmic "refrigerators" because they contain pristine 
ingredients from the early solar system. However, it is also not as 
processed as the stuff found in mature planets and the largest 
asteroids. This means the dust belt must be in a transitional phase, 
when rocky planets are just beginning to form.

How do scientists know the material is more processed than that of 
comets? From missions like NASA's Deep Impact - in which an 820-pound 
impactor spacecraft collided with comet Tempel 1 - scientists know 
that early star systems contain a lot of fragile organic material. 
That material includes polycyclic aromatic hydrocarbons (carbon-based 
molecules found on charred barbeque grills and in automobile exhaust 
on Earth), water ice, and carbonates (chalk). Lisse says that HD 
113766 does not contain any water ice, carbonates or fragile organic 
materials.

>From meteorite studies on Earth, scientists also have a good idea of 
what makes up asteroids, the more processed rocky leftovers of planet 
formation. These studies tell us that metals began separating from 
rocks in Earth's early days, when the planet's body was completely 
molten. During this time, almost all the heavy metals fell to Earth's 
center in a process called "differentiation." Lisse says that, unlike 
planets and asteroids, the metals in HD 113766 have not totally 
separated from the rocky material, suggesting that rocky planets have 
not yet formed.

"The material mix in this belt is most reminiscent of the stuff found 
in lava flows on Earth. I thought of Mauna Kea material when I first 
saw the dust composition in this system; it contains raw rock and is 
abundant in iron sulfides, which are similar to fool's gold," says 
Lisse, referring to a well-known Hawaiian volcano.

"It is fantastic to think we are able to detect the process of 
terrestrial planet formation. Stay tuned; I expect lots more 
fireworks as the planet in HD 113766 grows," he adds.

Lisse has written a paper on his research that will be published in 
an upcoming issue of Astrophysical Journal; he will also present his 
findings next week at the American Astronomical Society Division for 
Planetary Sciences meeting in Orlando, Fla. Lisse's research was 
funded through a Johns Hopkins Applied Physics Laboratory Stuart S. 
Janney Fellowship and a Spitzer Space Telescope guest observer grant.

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the 
Spitzer Space Telescope mission for NASA's Science Mission 
Directorate, Washington. Science operations are conducted at the 
Spitzer Science Center at the California Institute of Technology, 
also in Pasadena. Caltech manages JPL for NASA. The University of 
Maryland is responsible for overall Deep Impact mission science, and 
project management is handled by JPL.

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Note to editors: an image to accompany this release is available at: 
http://www.jhuapl.edu/newscenter/pressreleases/2007/071003.asp

Science Contact: Dr. Carey Lisse
(240) 228-0535 or (443) 778-0535
Carey.Lisse at jhuapl.edu


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