Water Hit With Young Star's Best Shot

Feature

September 18, 2008

Water Hit With Young Star's Best Shot

Water is being blasted to pieces by a young star's laser-like jets, according to new
observations from NASA's Spitzer Space Telescope.

The discovery provides a better understanding of how water -- an essential ingredient for
life as we know it -- is processed in emerging solar systems.

"This is a truly unique observation that will provide important information about the
chemistry occurring in planet-forming regions, and may give us insights into the
chemical reactions that made water and even life possible in our own solar system," said
Achim Tappe, of the Harvard-Smithsonian Center for Astrophysics, Cambridge, Mass.

A young star forms out of a thick, rotating cloud of gas and dust. Like the two ends of a
spinning top, powerful jets of gas emerge from the top and bottom of the dusty cloud. As
the cloud shrinks more and more under its own gravity, its star eventually ignites and the
remaining dust and gas flatten into a pancake-like disk, from which planets will later
form. By the time the star ignites and stops accumulating material from its cloud, the jets
will have died out.

Tappe and his colleagues used Spitzer's infrared eyes to cut through the dust surrounding
a nascent star, called HH 211-mm, and get a better look at its jets. These particular jets
are exceptionally young at 1,000 years old, and they are some of the most collimated, or
focused, known. An instrument on Spitzer called a spectrometer analyzed light from one
of the jets, revealing information about its molecules.

To the astronomers' surprise, Spitzer picked up the signature of rapidly spinning
fragments of water molecules, called hydroxyl, or OH. In fact, the hydroxyl molecules
have absorbed so much energy (through a process called excitation) that they are rotating
around with energies equivalent to 28,000 Kelvin (27,700 degrees Celsius). This far
exceeds normal expectations for gas streaming out of a stellar jet. Water, which is
abbreviated H2O, is made up of two oxygen atoms and one hydrogen; hydroxyl, or OH,
contains one oxygen and one hydrogen atom.

The results reveal that the jet is ramming its head into a wall of material, vaporizing ice
right off the dust grains it normally coats. The jet is hitting the material so fast and hard
that a shock wave is also being produced.

"The shock from colliding atoms and molecules generates ultraviolet radiation, which
will break up water molecules, leaving extremely hot hydroxyl molecules," said Tappe.

Tappe said this same process of ice being vaporized off dust occurs in our own solar
system, when the sun vaporizes ice in approaching comets. In addition, the water that
now coats our world is thought to have come from icy comets that vaporized as they
rained down on a young Earth.

Tappe is the lead author of a paper on this topic, which was published in a recent issue of
the Astrophysical Journal. Co-authors on the paper include Charlie Lada, and August
Muench, also of the Harvard-Smithsonian Center for Astrophysics; and J. H. Black, of
the Chalmers University of Technology, in Onsala, Sweden.

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