[meteorite-list] Dusty Shock Waves Generate Planet Ingredients (Spitzer)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed, 12 Nov 2008 10:51:02 -0800 (PST)
Message-ID: <200811121851.KAA23037_at_zagami.jpl.nasa.gov>

http://www.jpl.nasa.gov/news/news.cfm?release=2008-207

Dusty Shock Waves Generate Planet Ingredients
Jet Propulsion Laboratory
November 11, 2008

Shock waves around dusty, young stars might be creating the raw
materials for planets, according to new observations from NASA's Spitzer
Space Telescope.

The evidence comes in the form of tiny crystals. Spitzer detected
crystals similar in make-up to quartz around young stars just beginning
to form planets. The crystals, called cristobalite and tridymite, are
known to reside in comets, in volcanic lava flows on Earth, and in some
meteorites that land on Earth.

Astronomers already knew that crystallized dust grains stick together to
form larger particles, which later lump together to form planets. But
they were surprised to find cristobalite and tridymite. What's so
special about these particular crystals? They require flash heating
events, such as shock waves, to form.

The findings suggest that the same kinds of shock waves that cause sonic
booms from speeding jets are responsible for creating the stuff of
planets throughout the universe.

"By studying these other star systems, we can learn about the very
beginnings of our own planets 4.6 billion years ago," said William
Forrest of the University of Rochester, N.Y. "Spitzer has given us a
better idea of how the raw materials of planets are produced very early
on." Forrest and University of Rochester graduate student Ben Sargent
led the research, to appear in the Astrophysical Journal.

Planets are born out of swirling pancake-like disks of dust and gas that
surround young stars. They start out as mere grains of dust swimming
around in a disk of gas and dust, before lumping together to form
full-fledged planets. During the early stages of planet development, the
dust grains crystallize and adhere together, while the disk itself
starts to settle and flatten. This occurs in the first millions of years
of a star's life.

When Forrest and his colleagues used Spitzer to examine five young
planet-forming disks about 400 light-years away, they detected the
signature of silica crystals. Silica is made of only silicon and oxygen
and is the main ingredient in glass. When melted and crystallized, it
can make the large hexagonal quartz crystals often sold as mystical
tokens. When heated to even higher temperatures, it can also form small
crystals like those commonly found around volcanoes.

It is this high-temperature form of silica crystals, specifically
cristobalite and tridymite, that Forrest's team found in planet-forming
disks around other stars for the first time. "Cristobalite and tridymite
are essentially high-temperature forms of quartz," said Sargent. "If you
heat quartz crystals, you'll get these compounds."

In fact, the crystals require temperatures as high as 1,220 Kelvin
(about 1,740 degrees Fahrenheit) to form. But young planet-forming disks
are only about 100 to 1,000 Kelvin (about minus 280 degrees Fahrenheit
to 1,340 Fahrenheit) -- too cold to make the crystals. Because the
crystals require heating followed by rapid cooling to form, astronomers
theorized that shock waves could be the cause.

Shock waves, or supersonic waves of pressure, are thought to be created
in planet-forming disks when clouds of gas swirling around at high
speeds collide. Some theorists think that shock waves might also
accompany the formation of giant planets.

The findings are in agreement with local evidence from our own solar
system. Spherical pebbles, called chondrules, found in ancient
meteorites that fell to Earth are also thought to have been crystallized
by shock waves in our solar system's young planet-forming disk. In
addition, NASA's Stardust mission found tridymite minerals in comet Wild 2.

Other authors of the paper include C. Tayrien, M.K. McClure, A.R. Basu,
P. Mano, Dan Watson, C.J. Bohac, K.H. Kim and J.D. Green of the
University of Rochester; A Li of the University of Missouri, Columbia;
E. Furlan of NASA's Jet Propulsion Laboratory, Pasadena, Calif., and
G.C. Sloan 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, also
in Pasadena. Caltech manages JPL for NASA. Spitzer's infrared
spectrograph, which made the observations, was built by Cornell
University, Ithaca, N.Y. Its development was led by Jim Houck of Cornell.

More information about Spitzer is at
http://www.spitzer.caltech.edu/spitzer and http://www.nasa.gov/spitzer .
More information about exoplanets and NASA's planet-finding program is
at http://planetquest.jpl.nasa.gov .

Media contact: Whitney Clavin 818-354-4673
Jet Propulsion Laboratory
whitney.clavin at jpl.nasa.gov

2008-207
Received on Wed 12 Nov 2008 01:51:02 PM PST