Scientists Measure How Deep 'Deep Impact' Was, With X-Rays

http://live.psu.edu/story/12671

Scientists measure how deep 'Deep Impact' was, with X-rays
Pennsylvania State University
July 8, 2005

University Park, Pa. -- Here come the X-rays, on cue. Scientists
studying the Deep Impact collision using NASA's Swift satellite report
that comet Tempel 1 is getting brighter and brighter in X-ray light
with
each passing day.

The X-rays provide a direct measurement of how much material was kicked
up in the impact. This is because the X-rays are created by the newly
liberated material lifted into the comet's thin atmosphere and
illuminated by the high-energy solar wind from the sun. The more
material liberated, the more X-rays are produced.

Swift data of the water evaporation on comet Tempel 1 also may provide
new insights into how solar wind can strip water from planets such as
Mars.

"Prior to its rendezvous with the Deep Impact probe, the comet was a
rather dim X-ray source," said Paul O'Brien of the Swift team at the
University of Leicester. "How things change when you ram a comet with a
copper probe traveling over 20,000 miles per hour. Most of the X-ray
light we detect now is generated by debris created by the collision. We
can get a solid measurement of the amount of material released."

"It takes several days after an impact for surface and sub-surface
material to reach the comet's upper atmosphere, or coma," said Dick
Willingale, also of the University of Leicester. "We expect the X-ray
production to peak this weekend. Then we will be able to assess how
much
comet material was released from the impact."

Based on preliminary X-ray analysis, O'Brien estimates that several
tens
of thousands of tons of material were released, enough to bury Penn
State's football field under 30 feet of comet dust. Observations and
analysis are ongoing at the Swift Mission Operations Center at Penn
State as well as in Italy and the United Kingdom.

Swift is providing the only simultaneous multi-wavelength observation
of
this rare event, with a suite of instruments capable of detecting
visible light, ultraviolet light, X-rays and gamma rays. Different
wavelengths reveal different secrets about the comet.

The Swift team hopes to compare the satellite's ultraviolet data,
collected hours after the collision, with the X-ray data. The
ultraviolet light was created by material entering into the lower
region
of the comet's atmosphere; the X-rays come from the upper regions.
Swift
is a nearly ideal observatory for making these comet studies, as it
combines both a rapidly responsive scheduling system with both X-ray
and
optical/UV instruments in the same satellite.

"For the first time, we can see how material liberated from a comet's
surface migrates to the upper reaches of its atmosphere," said John
Nousek, director of Mission Operations at Penn State. "This will
provide
fascinating information about a comet's atmosphere and how it interacts
with the solar wind. This is all virgin territory."

Nousek said Deep Impact's collision with comet Tempel 1 is like a
controlled laboratory experiment of the type of slow evaporation
process
from solar wind that took place on Mars. The Earth has a magnetic field
that shields us from solar wind, a particle wind composed mostly of
protons and electrons moving at nearly light speed. Mars lost its
magnetic field billions of years ago, and the solar wind stripped the
planet of water.

Comets, like Mars and Venus, have no magnetic fields. Comets become
visible largely because ice is evaporated from their surface with each
close passage around the Sun. Water is dissociated into its component
atoms by the bright sunlight and swept away by the fast-moving and
energetic solar wind. Scientists hope to learn about this evaporation
process on Tempel 1 now occurring quickly -- over the course of a few
weeks instead of a billion years -- as the result of a planned, human
intervention.

Swift's "day job" is detecting distant, natural explosions called
gamma-ray bursts and creating a map of X-ray sources in the universe.
Swift's extraordinary speed and agility enable scientists to follow
Tempel 1 day by day to see the full effect from the Deep Impact
collision.

For the latest news on Swift analysis of comet Tempel 1, refer to:
-- http://www.science.psu.edu/alert/Swift-Deep-Impact.htm
-- http://swift.gsfc.nasa.gov and
-- http://swift.sonoma.edu/

The Deep Impact mission is managed by NASA's Jet Propulsion Laboratory,
Pasadena, Calif. Swift is a medium-class NASA explorer mission in
partnership with the Italian Space Agency and the Particle Physics and
Astronomy Research Council in the United Kingdom, and is managed by
NASA
Goddard. Penn State controls science and flight operations from the
Mission Operations Center in University Park. The spacecraft was built
in collaboration with national laboratories, universities and
international partners, including Penn State University; Los Alamos
National Laboratory, N.M.; Sonoma State University, Rohnert Park,
Calif.; Mullard Space Science Laboratory in Dorking, Surrey, England;
the University of Leicester, England; Brera Observatory in Milan,
Italy;
and ASI Science Data Center in Frascati, Italy.

Contact
Barbara Kennedy

www.science.psu.edu
814-863-4682