Water Vapor Seen 'Raining Down' on Young Star System
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.
Image right: Spitzer observed a fledgling solar system like the one depicted in this artist's concept, and discovered deep within it enough water vapor to fill the oceans on Earth five times. Image credit: NASA/JPL-Caltech
+ Full image and caption
Related images: + Diagram: Steamy solar system+ Plot of infrared data
"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.
Image left: This image from Spitzer shows the stellar nursery, called NGC 1333, that contains the "steamy" young solar system, called NGC 1333-IRAS 4B. Image credit: NASA/JPL-Caltech/Harvard-Smithsonian CfA + Full image and caption
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.nasa.gov/spitzer
. More information about extrasolar planets and NASA's planet-finding program is at http://planetquest.jpl.nasa.gov
Media contact: Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.