Andrew Yee
September 21st 05, 02:05 PM
Bill Steigerwald
Goddard Space Flight Center, Greenbelt, Md. September 19, 2005
(Phone: 301/286 5017)
Deep Impact Comet May Have Formed in Giant Planets Region
Comet Tempel-1 may have been born in the region of the solar system
occupied by Uranus and Neptune today, according to one possibility from an
analysis of the comet's debris blasted into space by NASA's Deep Impact
mission. If correct, the observation supports a wild scenario for the
solar system's youth, where the planets Uranus and Neptune may have traded
places and scattered comets to deep space.
"Our observation is a definitive investigation revealing the composition
of comet Tempel-1," said Dr. Michael Mumma of NASA's Goddard Space Flight
Center, Greenbelt, Md. Mumma and his team used the powerful Keck telescope
on top of Mauna Kea, Hawaii, to analyze in great detail light emitted by
Tempel-1 gas ejected by the impact. Because each type of atom and molecule
emits light at unique colors (frequencies), the team was able to determine
the comet's chemical composition by separating its light into its
component colors with an instrument called a spectrometer. Mumma is lead
author of a paper on this research that appeared in Science Express on
Sept.15, 2005.
Comets are chunks of ice and dust that zoom around the solar system in
elongated orbits. This "dirty snowball" is the nucleus of the comet. Comet
nuclei are thought to be cosmic leftovers, condensed remains of the gas
and dust cloud that formed the solar system. As a comet gets close to the
sun, solar heat liberates gas and dust from the nucleus, forming the coma,
which is an extensive, bright cloud around the nucleus, and one or more
tails.
Repeated solar heating can remove materials that have low freezing
temperatures from the surface, giving the comet a crust that's different
chemically from its interior. This makes it hard to discover a comet's
true composition by simply looking at gas that's evaporating from the
surface. NASA's Deep Impact mission crashed into comet Tempel-1 July 4,
2005, allowing scientists to test whether material ejected from its
protected interior was closer to pristine.
By observing Tempel-1 before, during, and after impact, the team was able
to distinguish surface gas from the impact debris, and they discovered
that the interior does indeed have a different chemistry. "The amount of
ethane (C2H6) in the cloud around the comet was significantly higher after
impact than before," said Mumma.
There are two possible explanations for this. In the first, the surface
crust is different from the interior due to solar heating. The interior,
however, is all the same. In the second, the interior is a mix of regions
with different compositions because the nucleus is actually composed of
smaller "mini-comets" (cometesimals), each with a different chemistry.
Deep Impact could have just so happened to hit one of these cometesimals,
while the gas seen before impact might have came from a different region
on the comet with different chemistry. Multiple impacts in different
regions of the comet would be necessary to determine which scenario is
correct, according to the team.
If the first scenario is correct, the comet could have formed in the
region now bounded by the orbits of Uranus and Neptune, based on its
interior chemistry. Different chemicals get frozen into a comet depending
on its location. A comet that forms farther from the sun will have greater
amounts of ices with low freezing temperatures, like ethane, than a comet
that forms closer to the sun. By measuring the relative amounts of each
chemical, astronomers can estimate where a comet formed.
Formation in this location supports a theory that the gas giant planets
Uranus and Neptune formed closer to the sun than their current locations.
The theory, proposed by Dr. Alessandro Morbidelli of the Observatoire de
la Cote d'Azur, Nice, France, and his team, says that gravitational
interaction between the gas giant planets and numerous small planets left
over from the solar system's formation (planetesimals) brought the giant
planets into an unstable orbital configuration. Neptune and Uranus were
tossed outward and could have exchanged orbits. As they migrated outward,
their gravity disrupted a large disk of comets that had formed in the
region where Uranus and Neptune currently reside. Some were scattered into
deep space, to a roughly spherical region called the "Oort cloud" that
surrounds our solar system at about 10,000 times the earth-sun distance.
Others were directed to the Kuiper belt, a region beyond Neptune that
extends to several hundred times the Earth-sun distance.
If some Kuiper belt comets have similar chemistry to some Oort cloud
comets, it would support this model of the solar system's rowdy early days
by showing that certain comets had a common origin despite very different
final destinations. Tempel-1 shares certain orbital characteristics with
the "ecliptic" comets, a group that likely comes from the "scattered"
Kuiper belt. "The amount of ethane in Tempel-1, however, is similar to the
amount in the dominant group of comets that come from the Oort cloud
region," said Mumma. Its chemical similarity to Oort cloud comets supports
the idea that some Kuiper belt and Oort cloud comets formed in the same
place.
This research was funded by NASA, the National Science Foundation, and the
National Research Council. The team includes scientists from NASA Goddard,
Rowan University, Glassboro, N.J., University of Toledo, Toledo, Ohio,
Kyoto Sangyo University, Kyoto, Japan, Johns Hopkins University Applied
Physics Laboratory, Laurel, Md., University of Missouri-Saint Louis, and
the W. M. Keck Observatory, Kamuela, Hawaii.
[NOTE: Images supporting this release are available at
http://www.nasa.gov/centers/goddard/news/topstory/2005/deepimpact-090905.html]
Goddard Space Flight Center, Greenbelt, Md. September 19, 2005
(Phone: 301/286 5017)
Deep Impact Comet May Have Formed in Giant Planets Region
Comet Tempel-1 may have been born in the region of the solar system
occupied by Uranus and Neptune today, according to one possibility from an
analysis of the comet's debris blasted into space by NASA's Deep Impact
mission. If correct, the observation supports a wild scenario for the
solar system's youth, where the planets Uranus and Neptune may have traded
places and scattered comets to deep space.
"Our observation is a definitive investigation revealing the composition
of comet Tempel-1," said Dr. Michael Mumma of NASA's Goddard Space Flight
Center, Greenbelt, Md. Mumma and his team used the powerful Keck telescope
on top of Mauna Kea, Hawaii, to analyze in great detail light emitted by
Tempel-1 gas ejected by the impact. Because each type of atom and molecule
emits light at unique colors (frequencies), the team was able to determine
the comet's chemical composition by separating its light into its
component colors with an instrument called a spectrometer. Mumma is lead
author of a paper on this research that appeared in Science Express on
Sept.15, 2005.
Comets are chunks of ice and dust that zoom around the solar system in
elongated orbits. This "dirty snowball" is the nucleus of the comet. Comet
nuclei are thought to be cosmic leftovers, condensed remains of the gas
and dust cloud that formed the solar system. As a comet gets close to the
sun, solar heat liberates gas and dust from the nucleus, forming the coma,
which is an extensive, bright cloud around the nucleus, and one or more
tails.
Repeated solar heating can remove materials that have low freezing
temperatures from the surface, giving the comet a crust that's different
chemically from its interior. This makes it hard to discover a comet's
true composition by simply looking at gas that's evaporating from the
surface. NASA's Deep Impact mission crashed into comet Tempel-1 July 4,
2005, allowing scientists to test whether material ejected from its
protected interior was closer to pristine.
By observing Tempel-1 before, during, and after impact, the team was able
to distinguish surface gas from the impact debris, and they discovered
that the interior does indeed have a different chemistry. "The amount of
ethane (C2H6) in the cloud around the comet was significantly higher after
impact than before," said Mumma.
There are two possible explanations for this. In the first, the surface
crust is different from the interior due to solar heating. The interior,
however, is all the same. In the second, the interior is a mix of regions
with different compositions because the nucleus is actually composed of
smaller "mini-comets" (cometesimals), each with a different chemistry.
Deep Impact could have just so happened to hit one of these cometesimals,
while the gas seen before impact might have came from a different region
on the comet with different chemistry. Multiple impacts in different
regions of the comet would be necessary to determine which scenario is
correct, according to the team.
If the first scenario is correct, the comet could have formed in the
region now bounded by the orbits of Uranus and Neptune, based on its
interior chemistry. Different chemicals get frozen into a comet depending
on its location. A comet that forms farther from the sun will have greater
amounts of ices with low freezing temperatures, like ethane, than a comet
that forms closer to the sun. By measuring the relative amounts of each
chemical, astronomers can estimate where a comet formed.
Formation in this location supports a theory that the gas giant planets
Uranus and Neptune formed closer to the sun than their current locations.
The theory, proposed by Dr. Alessandro Morbidelli of the Observatoire de
la Cote d'Azur, Nice, France, and his team, says that gravitational
interaction between the gas giant planets and numerous small planets left
over from the solar system's formation (planetesimals) brought the giant
planets into an unstable orbital configuration. Neptune and Uranus were
tossed outward and could have exchanged orbits. As they migrated outward,
their gravity disrupted a large disk of comets that had formed in the
region where Uranus and Neptune currently reside. Some were scattered into
deep space, to a roughly spherical region called the "Oort cloud" that
surrounds our solar system at about 10,000 times the earth-sun distance.
Others were directed to the Kuiper belt, a region beyond Neptune that
extends to several hundred times the Earth-sun distance.
If some Kuiper belt comets have similar chemistry to some Oort cloud
comets, it would support this model of the solar system's rowdy early days
by showing that certain comets had a common origin despite very different
final destinations. Tempel-1 shares certain orbital characteristics with
the "ecliptic" comets, a group that likely comes from the "scattered"
Kuiper belt. "The amount of ethane in Tempel-1, however, is similar to the
amount in the dominant group of comets that come from the Oort cloud
region," said Mumma. Its chemical similarity to Oort cloud comets supports
the idea that some Kuiper belt and Oort cloud comets formed in the same
place.
This research was funded by NASA, the National Science Foundation, and the
National Research Council. The team includes scientists from NASA Goddard,
Rowan University, Glassboro, N.J., University of Toledo, Toledo, Ohio,
Kyoto Sangyo University, Kyoto, Japan, Johns Hopkins University Applied
Physics Laboratory, Laurel, Md., University of Missouri-Saint Louis, and
the W. M. Keck Observatory, Kamuela, Hawaii.
[NOTE: Images supporting this release are available at
http://www.nasa.gov/centers/goddard/news/topstory/2005/deepimpact-090905.html]