[Spitzer News] Spitzer Finds Organics and Water Where New Planets May Grow

spitzer-news at lists.ipac.caltech.edu spitzer-news at lists.ipac.caltech.edu
Thu Mar 13 11:59:49 PDT 2008

In this issue:

1) Spitzer Finds Organics and Water Where New Planets May Grow
2) Spitzer's Eyes Perfect for Spotting Diamonds in the Sky


Researchers using NASA's Spitzer Space Telescope have discovered large  
amounts of simple organic gases and water vapor in a possible planet- 
forming region around an infant star, along with evidence that these  
molecules were created there. They've also found water in the same  
zone around two other young stars.

By pushing the telescope's capabilities to a new level, astronomers  
now have a better view of the earliest stages of planetary formation,  
which may help shed light on the origins of our own solar system and  
the potential for life to develop in others.

John Carr of the Naval Research Laboratory, Washington, and Joan  
Najita of the National Optical Astronomy Observatory, Tucson, Ariz.,  
developed a new technique using Spitzer's infrared spectrograph to  
measure and analyze the chemical composition of the gases within  
protoplanetary disks. These are flattened disks of gas and dust that  
encircle young stars. Scientists believe they provide the building  
materials for planets and moons and eventually, over millions of  
years, evolve into orbiting planetary systems like our own.

"Most of the material within the disks is gas," said Carr, "but until  
now it has been difficult to study the gas composition in the regions  
where planets should form. Much more attention has been given to the  
solid dust particles, which are easier to observe."

In their project, Carr and Najita took an in-depth look at the gases  
in the planet-forming region in the disk around the star AA Tauri.  
Less than a million years old, AA Tauri is a typical example of a  
young star with a protoplanetary disk.

With their new procedures, they were able to detect the minute  
spectral signatures for three simple organic molecules--hydrogen  
cyanide, acetylene and carbon dioxide--plus water vapor. In addition,  
they found more of these substances in the disk than are found in the  
dense interstellar gas called molecular clouds from which the disk  
originated. "Molecular clouds provide the raw material from which the  
protoplanetary disks are created," said Carr. "So this is evidence for  
an active organic chemistry going on within the disk, forming and  
enhancing these molecules."

Spitzer's infrared spectrograph detected these same organic gases in a  
protoplanetary disk once before. But the observation was dependent on  
the star's disk being oriented in just the right way. Now researchers  
have a new method for studying the primordial mix of gases in the  
disks of hundreds of young star systems.

Astronomers will be able to fill an important gap--they know that  
water and organics are abundant in the interstellar medium but not  
what happens to them after they are incorporated into a disk. "Are  
these molecules destroyed, preserved or enhanced in the disk?" said  
Carr. "Now that we can identify these molecules and inventory them, we  
will have a better understanding of the origins and evolution of the  
basic building blocks of life--where they come from and how they  
evolve." Carr and Najita's research results appear in the March 14  
issue of Science.

Taking advantage of Spitzer's spectroscopic capabilities, another  
group of scientists looked for water molecules in the disks around  
young stars and found them--twice. "This is one of the very few times  
that water vapor has been directly shown to exist in the inner part of  
a protoplanetary disk--the most likely place for terrestrial planets  
to form," said Colette Salyk, a graduate student in geological and  
planetary sciences at the California Institute of Technology in  
Pasadena. She is the lead author on a paper about the results in the  
March 20 issue of Astrophysical Journal Letters.

Salyk and her colleagues used Spitzer to look at dozens of young stars  
with protoplanetary disks and found water in many. They honed in on  
two stars and followed up the initial detection of water with  
complementary high-resolution measurements from the Keck II Telescope  
in Hawaii. "While we don't detect nearly as much water as exists in  
the oceans on Earth, we see essentially only the disk's surface, so  
the implication is that the water is quite abundant," said Geoffrey  
Blake, professor of cosmochemistry and planetary sciences at Caltech  
and one of the paper's co-authors.

"This is a much larger story than just one or two disks," said Blake.  
"Spitzer can efficiently measure these water signatures in many  
objects, so this is just the beginning of what we will learn."

"With upcoming Spitzer observations and data in hand," Carr added, "we  
will develop a good understanding of the distribution and abundance of  
water and organics in planet-forming disks."

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 Caltech, also in Pasadena. Caltech manages  



Diamonds may be rare on Earth, but surprisingly common in space -- and  
the super-sensitive infrared eyes of NASA's Spitzer Space Telescope  
are perfect for scouting them, say scientists at the NASA Ames  
Research Center in Moffett Field, Calif.

Using computer simulations, researchers have developed a strategy for  
finding diamonds in space that are only a nanometer (a billionth of a  
meter) in size. These gems are about 25,000 times smaller than a grain  
of sand, much too small for an engagement ring. But astronomers  
believe that these tiny particles could provide valuable insights into  
how carbon-rich molecules, the basis of life on Earth, develop in the  

Scientists began to seriously ponder the presence of diamonds in space  
in the l980s, when studies of meteorites that crashed into Earth  
revealed lots of tiny nanometer-sized diamonds. Astronomers determined  
that 3 percent of all carbon found in meteorites came in the form of  
nanodiamonds. If meteorites are a reflection of the dust content in  
outer space, calculations show that just a gram of dust and gas in a  
cosmic cloud could contain as many as 10,000 trillion nanodiamonds.

"The question that we always get asked is, if nanodiamonds are  
abundant in space, why haven't we seen them more often?" says Charles  
Bauschlicher of Ames Research Center. They have only been spotted  
twice. "The truth is, we just didn't know enough about their infrared  
and electronic properties to detect their fingerprint."

To solve this dilemma, Bauschlicher and his research team used  
computer software to simulate conditions of the interstellar medium-- 
the space between stars--filled with nanodiamonds. They found that  
these space diamonds shine brightly at infrared light ranges of 3.4 to  
3.5 microns and 6 to 10 microns, where Spitzer is especially sensitive.

Astronomers should be able to see celestial diamonds by looking for  
their unique "infrared fingerprints." When light from a nearby star  
zaps a molecule, its bonds stretch, twist and flex, giving off a  
distinctive color of infrared light. Like a prism breaking white light  
into a rainbow, Spitzer's infrared spectrometer instrument breaks up  
infrared light into its component parts, allowing scientists to see  
the light signature of each individual molecule.

Team members suspect that more diamonds haven't been spotted in space  
yet because astronomers have not been looking in the right places with  
the right instruments. Diamonds are made of tightly bound carbon  
atoms, so it takes a lot of high-energy ultraviolet light to cause the  
diamond bonds to bend and move, producing an infrared fingerprint.  
Thus, the scientists concluded that the best place to see a space  
diamond's signature shine is right next to a hot star.

Once astronomers figure out where to look for nanodiamonds, another  
mystery is figuring out how they form in the environment of  
interstellar space.

"Space diamonds are formed under very different conditions than  
diamonds are formed on Earth," says Louis Allamandola, also of Ames.

He notes that diamonds on Earth form under immense pressure, deep  
inside the planet, where temperatures are also very high. However,  
space diamonds are found in cold molecular clouds where pressures are  
billions of times lower and temperatures are below minus 240 degrees  
Celsius (minus 400 degrees Fahrenheit).

"Now that we know where to look for glowing nanodiamonds, infrared  
telescopes like Spitzer can help us learn more about their life in  
space," says Allamandola.

Bauschlicher's paper on this topic has been accepted for publication  
in Astrophysical Journal. Allamandola was a co-author on the paper,  
along with Yufei Liu, Alessandra Ricca, and Andrew L. Mattioda, also  
of Ames.

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.



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