Meteor/Meteorite News- Tektites Sent Flying 11AUG09

Planet Smash-Up Sends Vaporized Rock, Hot Lava Flying
Jet Propulsion Laboratory
August 10, 2009
http://www.jpl.nasa.gov/news/news.cfm?release=2009-119

PASADENA, Calif. -- NASA's Spitzer Space Telescope has found evidence of
a high-speed collision between two burgeoning planets around a young star.

Astronomers say that two rocky bodies, one as least as big as our moon
and the other at least as big as Mercury, slammed into each other within
the last few thousand years or so -- not long ago by cosmic standards.
The impact destroyed the smaller body, vaporizing huge amounts of rock
and flinging massive plumes of hot lava into space. An artist's
animation of the event is at
http://www.nasa.gov/mission_pages/spitzer/multimedia/spitzer-20090810.html

.

Spitzer's infrared detectors were able to pick up the signatures of the
vaporized rock, along with pieces of refrozen lava, called tektites.

"This collision had to be huge and incredibly high-speed for rock to
have been vaporized and melted," said Carey M. Lisse of the Johns
Hopkins University Applied Physics Laboratory, Laurel, Md., lead author
of a new paper describing the findings in the Aug. 20 issue of the
Astrophysical Journal. "This is a really rare and short-lived event,
critical in the formation of Earth-like planets and moons. We're lucky
to have witnessed one not long after it happened."

Lisse and his colleagues say the cosmic crash is similar to the one that
formed our moon more than 4 billion years ago, when a body the size of
Mars rammed into Earth.

"The collision that formed our moon would have been tremendous, enough
to melt the surface of Earth," said co-author Geoff Bryden of NASA's Jet
Propulsion Laboratory, Pasadena, Calif. "Debris from the collision most
likely settled into a disk around Earth that eventually coalesced to
make the moon. This is about the same scale of impact we're seeing with
Spitzer -- we don't know if a moon will form or not, but we know a large
rocky body's surface was red hot, warped and melted."

Our solar system's early history is rich with similar tales of
destruction. Giant impacts are thought to have stripped Mercury of its
outer crust, tipped Uranus on its side and spun Venus backward, to name
a few examples. Such violence is a routine aspect of planet building.
Rocky planets form and grow in size by colliding and sticking together,
merging their cores and shedding some of their surfaces. Though things
have settled down in our solar system today, impacts still occur, as was
observed last month after a small space object crashed into Jupiter.

Lisse and his team observed a star called HD 172555, which is about 12
million years old and located about 100 light-years away in the far
southern constellation Pavo, or the Peacock (for comparison, our solar
system is 4.5 billion years old). The astronomers used an instrument on
Spitzer, called a spectrograph, to break apart the star's light and look
for fingerprints of chemicals, in what is called a spectrum. What they
found was very strange. "I had never seen anything like this before,"
said Lisse. "The spectrum was very unusual."

After careful analysis, the researchers identified lots of amorphous
silica, or essentially melted glass. Silica can be found on Earth in
obsidian rocks and tektites. Obsidian is black, shiny volcanic glass.
Tektites are hardened chunks of lava that are thought to form when
meteorites hit Earth.

Large quantities of orbiting silicon monoxide gas were also detected,
created when much of the rock was vaporized. In addition, the
astronomers found rocky rubble that was probably flung out from the
planetary wreck.

The mass of the dust and gas observed suggests the combined mass of the
two charging bodies was more than twice that of our moon.

Their speed must have been tremendous as well -- the two bodies would
have to have been traveling at a velocity relative to each other of at
least 10 kilometers per second (about 22,400 miles per hour) before the
collision.

Spitzer has witnessed the dusty aftermath of large asteroidal impacts
before, but did not find evidence for the same type of violence --
melted and vaporized rock sprayed everywhere. Instead, large amounts of
dust, gravel, and boulder-sized rubble were observed, indicating the
collisions might have been slower-paced. "Almost all large impacts are
like stately, slow-moving Titanic-versus-the-iceberg collisions, whereas
this one must have been a huge fiery blast, over in the blink of an eye
and full of fury," said Lisse.

Other authors include C.H. Chen of the Space Telescope Science
Institute, Baltimore, Md.; M.C. Wyatt of the University of Cambridge,
England; A. Morlok of the Open University, London, England; I. Song of
The University of Georgia, Athens, Ga.; and P. Sheehan of the University
of Rochester, N.Y.

JPL manages the Spitzer 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, which made the
observations in 2004 before the telescope began its "warm" mission, was
built by Cornell University, Ithaca, N.Y. Its development was led by Jim
Houck of Cornell.

For more information about Spitzer, visit
http://www.spitzer.caltech.edu/spitzer

and http://www.nasa.gov/spitzer

<http://www.spitzer.caltech.edu/spitzer

> . More information about NASA's
planet-finding program is at http://planetquest.jpl.nasa.gov

<http://planetquest.jpl.nasa.gov/

>

Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.
whitney.clavin@jpl.nasa.gov

2009-119