Spitzer Finds
Organics And Water Where New Planets May Grow
(13 March 2008) Researchers using
NASA's Spitzer Space Telescope have discovered large amounts of simple organic
gases and water vapour 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 analyse 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 vapour 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 JPL for
NASA.
(source: NASA Jet Propulsion Laboratory)
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