[Concatenation of three related NASA press releases from Thursday]
== 1 ==
http://amesnews.arc.nasa.gov/releases/2002/02_126AR.html
Dec. 5, 2002
Kathleen Burton
NASA Ames Research Center, Moffett Field, Calif.
Phone: 650/604-1731 or 604-9000
E-mail: [EMAIL PROTECTED]
RELEASE: 02-126AR
NOTE TO EDITORS AND NEWS DIRECTORS:
You are invited to a special
session at the American Geophysical Union (AGU) meeting titled
"Mysteries of the Martian Rivers," to be held on Dec. 6 from 2 p.m.
to 4 p.m. PST in the Moscone Convention Center (MCC) Theatre, Exhibit
Hall C, San Francisco. The session is an oral debate and discussion
about the formation of rivers and valleys on Mars. After the session,
researchers will be available for follow-up questions from the media
in the MCC Press Room between 4 p.m. and 5 p.m. PST. In addition,
there will be a poster session on the topic beginning at 8:30 a.m.
PST on Dec. 6 in MCC Hall D (P51B).
SCIENTISTS SAY ANCIENT ASTEROIDS, COMETS MAY HAVE CAUSED MARS RAIN
Scientists from NASA and the University of Colorado suggest the
bombardment of comets and asteroids on early Mars caused cycles of
rain that led to global flooding and the formation of Mars' river
valleys and other water-sculpted landscapes.
The researchers emphasize that the period when large comets and
asteroids struck Mars appears to correlate with the formation of
ancient rivers when water once flowed on Mars, and that both 'events'
seem to have ended about the same time, between 3.5 billion and 3.8
billion years ago. The research will be published on Dec. 6 in
Science magazine in an article entitled "Environmental Effects of
Large Impacts on Mars."
"The river valleys and large craters on Mars may both be about the
same age geologically," said Teresa Segura, the paper's lead author.
"We think that the two must be related, and our paper describes one
possible connection." Segura, a graduate student in atmospheric and
oceanic sciences at the University of Colorado, is based at NASA Ames
Research Center, in California's Silicon Valley.
The researchers modeled the impacts of asteroids and comets between
60 miles and 150 miles in diameter that bombarded Mars billions of
years ago. Such impact events packed a huge energy wallop, equal to
about 10,000 million megatons of TNT depending on collision
velocities, which were lower back then.
The impacts released water on Mars in four ways, the scientists say -
from the vaporized asteroid or comet itself, from Mars' icy polar
caps, from the ground where the crater formed and from the heat from
hot 'ejecta' (a mixture of soil, rocks and water) that gradually
baked water out of the martian soil.
When Mars eventually cooled down after an impact episode, scientists
theorize, water that had evaporated into the atmosphere condensed
into rain. During Mars' rainy periods, precipitation rates probably
averaged between 1 meter and 2 meters a year, similar to Earth's
average annual rainfall today.
"This happened dozens of times, maybe more, but after it rained, Mars
would go dry," said Dr. Kevin Zahnle, a co-author from NASA Ames. "In
the times between impacts, the water sank back into the soil, where
it lay dormant until the next time an impact occurred."
Scientists think the martian rains lasted for episodes ranging from
months to decades and that, between bombardments, Mars returned to
its typical cold, dry state. Besides bringing moisture, the impacts
also caused Mars to warm up, they say. During bombardment episodes,
hot 'ejecta' from impacts kept Mars' surface warm for hundreds of
years at a time.
The martian cratering record shows that there are at least 30 craters
carved by impactors that are 100 kilometers or more in diameter.
These were created during the planet's period of heavy bombardment by
comets and asteroids more than 3.5 billion years ago.
Scientists do not know why a late heavy bombardment stopped about 3.5
billion years ago, according to Segura. "Our research provides some
insight into what early Mars might have been like, but we've fit only
a couple of pieces into the puzzle of Mars' past," Segura said.
Team members include Dr. Owen B. Toon, University of Colorado, and
Dr. Anthony Colaprete, NASA Ames.
The project is funded by the University of Colorado Center for
Astrobiology in Boulder, and the NASA Astrobiology Institute (NAI)
through NASA Ames Research Center. The NAI is an international
research consortium with its central offices located at NASA Ames.
-end-
== 2 ==
http://www.usgs.gov/public/press/public_affairs/press_releases/pr1693m.html
----------------------------------------------------------------------------
News Release Address
Office of Communication
U.S. Department of the Interior 119 National Center
U.S. Geological Survey Reston, VA 20192
Release Contact Phone Fax
December 5, 2002 Stephannie Hanna 415-905-1007 (until 12/10)
Timothy Titus 928-555-7201
Catherine Puckett 797-442-1329
----------------------------------------------------------------------------
Exposed Water Ice Discovered Near the South Pole of Mars
Surface water in the form of ice exposed near the edge of Mars's southern
perennial polar cap has been discovered for the first time, according to
U.S. Geological Survey (USGS) research released today in the journal
Science. There is evidence that the surface water ice in this region may be
widespread - from a half-mile to six miles around the entire southern polar
ice cap.
USGS space scientist Timothy Titus and his colleagues Hugh Kieffer of USGS
and Philip Christensen of Arizona State University noted that although it
has long been known that water ice should be present in the southern polar
region of Mars, until recently little evidence for water ice had been found.
Previously, surface water ice had been documented on the northern polar cap
of Mars, but this is the first time exposed water ice has been documented on
the southern polar cap of the solar system's fourth planet.
Titus and his colleagues used images from the Mars Odyssey Thermal Emission
Imaging System (THEMIS) and temperature data from the Mars Global Surveyor
Thermal Emission Spectrometer (TES) to confirm the presence of water ice at
the surface of the southern polar cap.
In addition, the Mars Odyssey Gamma Ray Spectrometer (GRS) observations
showed that there is quite a bit of water ice buried beneath the surface in
the southern polar region, but because GRS could not "identify" exposed
water ice at the surface when the ice is only a few miles wide, scientists
were not sure if exposed water ice existed at the surface of the southern
polar regions of Mars.
Enter THEMIS and TES - with their high-resolution images and sensitive
temperature-monitoring data, THEMIS was "able" to tell the scientists where
to look for possible water areas. "When we first saw the images from THEMIS,
we noticed that areas that were dark were not all the same temperature,
which suggested that the areas were composed of different stuff, perhaps
even water ice," Titus said.
The scientists then looked at TES data that overlapped the THEMIS images and
found that in one area, called Unit I, the water ice warmed up slowly in the
summer after the dry ice covering had sublimated away. (Under martian
conditions water ice does not melt, it goes directly from solid to a gaseous
state, a process called sublimation.) The temperature remained under about
-90 degrees Fahrenheit, the hottest martian ice gets and about the
temperature of the northern summer ice cap on Mars, which is composed of
dirty water ice (ice mixed with dirt and dust).
"On the southern polar ice caps, the differences between daytime and
nighttime temperatures were small, which also suggested to us that the
"stuff" might be water ice," Titus said.
Titus and his colleagues also examined unit S, located adjacent to unit I.
It showed a different trend in temperatures than unit I. In unit S, as
temperatures warmed early in the Mars summer, the dry ice covering changed
from solid ice to gas much earlier than in unit I, and in a matter of a few
days or so. Suddenly, said Titus, daytime temperatures jumped and the
nighttime temperature stayed the same, which told us that as the dry ice
sublimated, probably what was left behind was a 2-7 mm layer of dust over
ice.
"This suggests that the top layer changed from dirty water ice to dry dust,"
Titus said. "The cool nighttime temperatures are what one would expect from
having a layer of water ice underneath the thin layer of dust."
Titus and his colleagues are excited about the implications of these
findings. "In some ways, this water ice may just be the 'tip' of the
iceberg," Titus said. "The speculation is that there may be a whole mass of
water ice underneath the southern polar cap."
Determining the abundance and distribution of surface and near-surface water
ice is fundamental for both understanding the water cycle of Mars and for
the future exploration of Mars, Titus noted in the paper. Water ice, at or
near the surface, is available for surface interactions and exchange with
the atmosphere, causing, for example, atmospheric changes such as water
vapor and water ice clouds.
In addition, water ice that is in the top few inches of soil will most
likely be accessible to future robotic probes and, ultimately, human
exploration.
For more information on this and other thermal observations of the Mars
polar region, please visit http://www.mars-ice.org (will be updated on Dec.
6).
The USGS serves the Nation by providing reliable scientific information to
describe and understand the Earth; minimize the loss of life and property
from natural disasters; manage water, biological, energy and mineral
resources; and enhance and protect our quality of life.
### USGS ###
== 3 ==
http://www.colorado.edu/NewsServices/NewsReleases/2002/2092.html
Contact:
University of Colorado at Boulder
Teresa Segura, (650) 604- 0321
[EMAIL PROTECTED]
Owen B. Toon, (303) 492-1534
[EMAIL PROTECTED]
Jim Scott, (303) 492-3114
Dec. 3, 2002
Note Editors: Contents embargoed for use until 2 p.m. EST on Thursday, Dec.
5. The phone number to contact Segura or Toon after Dec. 5 is (415) 905-1007
at AGU.
NEW CU-NASA RESEARCH BELIES PREVIOUS IDEA
THAT MARS WAS ONCE WARM, WET PLANET
A new study led by University of Colorado at Boulder researchers indicates
Mars has been primarily a cold, dry planet following its formation some 4
billion years ago, making the possibility of the evolution of life there
challenging at best.
Led by CU-Boulder doctoral candidate Teresa Segura and her adviser,
Professor Owen B. Toon, the team used Mars photos and computer models to
show that large asteroids or comets hit the planet some 3.5 billion years
ago. These impacts apparently occurred about the time major river channels
were formed on the Red Planet, said Segura.
According to the available evidence, roughly 25 huge impactors, each about
60 miles to 150 miles in diameter, slammed into Mars roughly every 10
million to 20 million years during the period, blowing a volume of debris
equivalent to a global blanket hundreds of yards thick into the atmosphere.
The material is believed to have melted portions of subsurface and polar
ice, creating steam and scalding water that rained back on Mars at some six
feet per year for decades or centuries, causing rivers to form and flow,
according to the study.
But the study belies the warm, wet, Mars theory of rivers and oceans
embraced by many planetary scientists, since such impactors were so
infrequent. "There apparently were some brief warm and wet periods on Mars,
but we believe that through most of its history, Mars has been a cold, dry
planet," said Segura, currently a visiting researcher at NASA-Ames in
California.
A paper by Segura, Toon, CU-Boulder graduate Anthony Colaprete -- now at
NASA-Ames -- and Kevin Zahnle of NASA-Ames, will appear in the Dec. 6 issue
of Science.
"When the river valleys on Mars were confirmed in the 1970s, many scientists
believed there once was an Earth-like period with warmth, rivers and
oceans," said Toon, director of CU-Boulder's Program in Oceanic and
Atmospheric Sciences and a professor at the University's Laboratory for
Astrophysics and Space Physics. "What sparked our interest was that the
large craters and river valleys appeared to be about the same age."
In between such catastrophic events, the planet was likely very cold, dry
and inhospitable to any life forms, said Toon. "We definitely see river
valleys but not tributaries, indicating the rivers were not as mature as
those on Earth."
The rare, hot rains pelting Mars that likely came from water in asteroids
and comets hitting the planets and the evaporation of some ice from polar
caps and ice beneath the impacts would have been spectacular, said Segura.
"We believe these events caused short periods of a warm and wet climate, but
overall, we think Mars has been cold and dry for the majority of its
history."
According to Toon, previous theories that carbon dioxide gas and clouds
warmed Mars during its early history "just have not worked out
quantitatively." There is no evidence on Mars of large limestone deposits
from the first billion years, which would be directly linked to large
amounts of C02, a greenhouse gas, he said.
There also is no evidence that another greenhouse gas, methane -- which can
be created naturally by volcanic eruptions or produced by primitive life --
was present in the Martian atmosphere. But even CO2 and methane combined
would not be enough to warm the planet as greenhouse gases did on Earth and
Venus in their early histories, Toon said.
"Hypotheses of a warm, wet Mars, based on the presumption that the valley
networks formed in a long-lasting greenhouse climate, imply that Mars may
once have been teeming with life," wrote the authors in Science. "In
contrast, we envision a cold and dry planet, an almost endless winter broken
by episodes of scalding rains followed by flash floods.
"Only during the brief years or decades after the impact events would Mars
have been temperate, and only then might it have bloomed with life as we
know it," they wrote. Although temperatures in the subsurface of Martian
soil may have exceeded the boiling point during the impact period and
provided a possible refuge for life underground, the short duration of warm
periods predicted by the researchers would have made it difficult for life
to ever establish itself on Mars, the team concluded.
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