Water Vapor Seen 'Raining Down' On Young Star System (Spitzer)

http://www.jpl.nasa.gov/news/news.cfm?release=2007-094

Water Vapor Seen 'Raining Down' On Young Star System
Jet Propulsion Laboratory
August 29, 2007

NASA's Spitzer Space Telescope has detected enough water vapor to fill
the oceans on Earth five times inside the collapsing nest of a forming
star system. Astronomers say the water vapor is pouring down from the
system's natal cloud and smacking into a dusty disk where planets are
thought to form.

The observations provide the first direct look at how water, an
essential ingredient for life as we know it, begins to make its way
into
planets, possibly even rocky ones like our own.

"For the first time, we are seeing water being delivered to the region
where planets will most likely form," said Dan Watson of the
University
of Rochester, N.Y. Watson is the lead author of a paper about this
"steamy" young star system, appearing in the Aug. 30 issue of Nature.

The star system, called NGC 1333-IRAS 4B, is still growing inside a
cool
cocoon of gas and dust. Within this cocoon, circling around the
embryonic star, is a burgeoning, warm disk of planet-forming
materials.
The new Spitzer data indicate that ice from the stellar embryo's outer
cocoon is falling toward the forming star and vaporizing as it hits
the
disk.

"On Earth, water arrived in the form of icy asteroids and comets.
Water
also exists mostly as ice in the dense clouds that form stars," said
Watson. "Now we've seen that water, falling as ice from a young star
system's envelope to its disk, actually vaporizes on arrival. This
water
vapor will later freeze again into asteroids and comets."

Water is abundant throughout our universe. It has been detected in the
form of ice or gas around various types of stars, in the space between
stars, and recently Spitzer picked up the first clear signature of
water
vapor on a hot, gas planet outside our solar system, named HD 189733b.

In the new Spitzer study, water also serves as an important tool for
studying long-sought details of the planet formation process. By
analyzing what's happening to the water in NGC 1333-IRAS 4B, the
astronomers are learning about its disk. For example, they calculated
the disk's density (at least 10 billion hydrogen molecules per cubic
centimeter or 160 billion hydrogen molecules per cubic inch); its
dimensions (a radius bigger than the average distance between Earth
and
Pluto); and its temperature (170 Kelvin, or minus 154 degrees
Fahrenheit).

"Water is easier to detect than other molecules, so we can use it as a
probe to look at more brand-new disks and study their physics and
chemistry," said Watson. "This will teach us a lot about how planets
form."

Watson and his colleagues studied 30 of the youngest known stellar
embryos using Spitzer's infrared spectrograph, an instrument that
splits
infrared light open into a rainbow of wavelengths, revealing
"fingerprints" of molecules. Of the 30 stellar embryos, they found
only
one, NGC 1333-IRAS 4B, with a whopping signature of water vapor. This
vapor is readily detectable by Spitzer, because as ice hits the
stellar
embryo's planet-forming disk, it heats up very rapidly and glows with
infrared light.

Why did only one stellar embryo of 30 show signs of water? The
astronomers say this is most likely because NGC 1333-IRAS 4B is in
just
the right orientation for Spitzer to view its dense core. Also, this
particular watery phase of a star's life is short-lived and hard to
catch.

"We have captured a unique phase of a young star's evolution, when the
stuff of life is moving dynamically into an environment where planets
could form," said Michael Werner, project scientist for the Spitzer
mission at NASA's Jet Propulsion Laboratory, Pasadena, Calif.

NGC 1333-IRAS 4B is located in a pretty star-forming region
approximately 1,000 light-years away in the constellation Perseus. Its
central stellar embryo is still "feeding" off the material collapsing
around it and growing in size. At this early stage, astronomers cannot
tell how large the star will ultimately become.

Other authors of the Nature paper include: Chris Bohac, Chat Hull,
Bill
Forrest, Ben Sargent, Joel Green and Kyoung Hee Kim of the University
of
Rochester; Elise Furlan of the University of California at Los
Angeles;
Joan Najita of the National Optical Astronomy Observatory; Nuria
Calvet
and Lee Hartmann of the University of Michigan, Ann Arbor; Paola
d'Alessio of the National Autonomous University of Mexico; and Jim
Houck
of Cornell University, Ithaca, N.Y.

JPL 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 in
Pasadena. Caltech manages JPL for NASA. Spitzer's infrared
spectrograph
was built by Cornell University. Its development was led by co-author
Houck. Watson and Forrest are also members of the team that built the
spectrograph.

For graphics and more information about Spitzer, visit
http://www.spitzer.caltech.edu/spitzer and http://www.nasa.gov/spitzer.

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Media contact: Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.

2007-094

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