NASA News - NASA Scientists Find History of Asteroid Impacts in Earth Rocks
WASHINGTON -- Research by NASA and international scientists concludesgiant asteroids, similar or larger than the one believed to have
killed the dinosaurs, hit Earth billions of years ago with more
frequency than previously thought.
To cause the dinosaur extinction, the killer asteroid that impacted
Earth 65 million years ago would have been almost 6 miles (10
kilometers) in diameter. By studying ancient rocks in Australia and
using computer models, researchers estimate that approximately 70
asteroids the same size or larger impacted Earth 1.8 to 3.8 billion
years ago. During the same period, approximately four similarly-sized
objects hit the moon.
"This work demonstrates the power of combining sophisticated computer
models with physical evidence from the past, further opening an
important window to Earth's history," said Yvonne Pendleton, director
of NASA's Lunar Science Institute (NLSI) at NASA's Ames Research
Center at Moffett Field, Calif.
Evidence for these impacts on Earth comes from thin rock layers that
contain debris of nearly spherical, sand-sized droplets called
spherules. These millimeter-scale clues were formerly molten droplets
ejected into space within the huge plumes created by mega-impacts on
Earth. The hardened droplets then fell back to Earth, creating thin
but widespread sedimentary layers known as spherule beds.
The new findings are published today in the journal Nature.
"The beds speak to an intense period of bombardment of Earth," said
William Bottke principal investigator of the impact study team at the
Southwest Research Institute (SwRI) in Boulder, Colo. "Their source
long has been a mystery."
The team's findings support the theory Jupiter, Saturn, Uranus and
Neptune formed in different orbits nearly 4.5 billion years ago,
migrating to their current orbits about 4 billion years ago from the
interplay of gravitational forces in the young solar system. This
event triggered a solar system-wide bombardment of comets and
asteroids called the "Late Heavy Bombardment." In the paper, the team
created a model of the ancient main asteroid belt and tracked what
would have happened when the orbits of the giant planets changed.
They discovered the innermost portion of the belt became destabilized
and could have delivered numerous big impacts to Earth and the moon
over long time periods.
At least 12 mega-impacts produced spherule beds during the so-called
Archean period 2.5 to 3.7 billion years ago, a formative time for
life on Earth. Ancient spherule beds are rare finds, rarer than rocks
of any other age. Most of the beds have been preserved amid mud
deposited on the sea floor below the reach of waves.
The impact believed to have killed the dinosaurs was the only known
collision over the past half-billion years that made a spherule layer
as deep as those of the Archean period. The relative abundance of the
beds supports the hypothesis for many giant asteroid impacts during
Earth's early history.
The frequency of the impacts indicated in the computer models matches
the number of spherule beds found in terrains with ages that are well
understood. The data also hint at the possibility that the last
impacts of the Late Heavy Bombardment on Earth made South Africa's
Vredefort crater and Canada's Sudbury crater, both of which formed
about 2 billion years ago.
"The Archean beds contain enough extraterrestrial material to rule out
alternative sources for the spherules, such as volcanoes," said Bruce
Simonson, a geologist from Oberlin College in Oberlin, Ohio.
The research was funded by NLSI and conducted by members or associates
of NLSI's Center of Lunar Origin and Evolution, based at SwRI.
The impact study team also includes scientists from Purdue University
in West Lafayette, Ind.; Charles University in Prague, Czech
Republic; Observatorie de la Cote d'Azur in Nice, France; and
Academia Sinica in Taipei, Taiwan.
To learn about the NLSI, visit:
http://lunarscience.arc.nasa.
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NASA Releases Call For Phase II Visionary Advanced Concepts
WASHINGTON -- The NASA Innovative Advanced Concepts (NIAC) Program isseeking proposals to continue promising studies for which it has
supported the first phase. These cutting-edge concepts have the
potential to transform future exploration missions, enable new
capabilities, or significantly alter current approaches to launching,
building, and operating aerospace systems.
"These transformative concepts have the potential to mature into the
new capabilities NASA needs for the challenging space missions in its
future," said Michael Gazarik, director of NASA's Space Technology
Program at NASA Headquarters in Washington.
NIAC projects are chosen based on their character as innovative and
visionary, technically substantiated, and very early in development
-- 10 years or more from use in a mission. NIAC's current diverse
portfolio represents multiple technology areas, including power,
propulsion, structures, and avionics.
"We are thrilled to be launching Phase II, so the 2012 NIAC portfolio
can feature the most exciting combination of new ideas and continued
development," said Jay Falker, NIAC program executive at NASA Headquarters.
The call for proposals follows last summer's inaugural selection of
Phase I concepts, which are now under study. NIAC will be accepting
proposals of no more than 20 pages until June 6.
NASA expects to fund between five and nine Phase II studies this year.
The number of awards will depend on the strength of proposals and
availability of appropriated funds. Awardees will receive up to
$500,000 over two years to further analyze and develop their
innovative concepts and help create new avenues for future NASA missions.
Selection announcements are expected in August. This limited
solicitation is only for continuing NIAC Phase I concepts. Phase II
proposals are eligible based on any current Phase I studies, or any
prior Phase I studies from the original NASA Institute for Advanced
Concepts that did not complete Phase II.
NASA's early investment and partnership with creative scientists,
engineers and citizen inventors from across the nation will pay huge
technological dividends and help maintain America's leadership in the
global technology economy. NIAC is part of NASA's Space Technology
Program, managed by the Office of the Chief Technologist. To view
this research announcement and for more information about NIAC and
NASA's Space Technology Program, visit:
http://go.usa.gov/R1N
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Warm Ocean Currents Cause Majority of Ice Loss from Antarctica
WASHINGTON -- Warm ocean currents attacking the underside of iceshelves are the dominant cause of recent ice loss from Antarctica, a
new study using measurements from NASA's Ice, Cloud, and land
Elevation Satellite (ICESat) revealed.
An international team of scientists used a combination of satellite
measurements and models to differentiate between the two known causes
of melting ice shelves: warm ocean currents thawing the underbelly of
the floating extensions of ice sheets and warm air melting them from
above. The finding, published today in the journal Nature, brings
scientists a step closer to providing reliable projections of future
sea level rise.
The researchers concluded 20 of the 54 ice shelves studied are being
melted by warm ocean currents. Most of these are in West Antarctica,
where inland glaciers flowing down to the coast and feeding into
these thinning ice shelves have accelerated, draining more ice into
the sea and contributing to sea-level rise. This ocean-driven
thinning is responsible for the most widespread and rapid ice losses
in West Antarctica and the majority of Antarctic ice sheet loss
during the period studied.
"We can lose an awful lot of ice to the sea without ever having
summers warm enough to make the snow on top of the glaciers melt,"
said the study's lead author Hamish Pritchard of the British
Antarctic Survey in Cambridge, United Kingdom. "The oceans can do all
the work from below."
To map the changing thickness of almost all the floating ice shelves
around Antarctica, the team used a time series of 4.5 million surface
height measurements taken by a laser instrument mounted on ICESat
from October 2003 to October 2008. They measured how the ice shelf
height changed over time and ran computer models to discard changes
in ice thickness because of natural snow accumulation and compaction.
The researchers also used a tide model that eliminated height changes
caused by tides raising and lowering the ice shelves.
"This study demonstrates the power of space-based, laser altimetry for
understanding Earth processes," said Tom Wagner, cryosphere program
scientist at NASA Headquarters in Washington." Coupled with NASA's
portfolio of other ice sheet research using data from our GRACE
mission, satellite radars and aircraft, we get a comprehensive view
of ice sheet change that improves estimates of sea level rise."
Previous studies used satellite radar data to measure the evolution of
ice shelves and glaciers, but laser measurements are more precise in
detecting changes in ice shelf thickness through time. This is
especially true in coastal areas. Steeper slopes at the grounding
line, where floating ice shelves connect with the landmass, cause
problems for lower-resolution radar altimeters.
ICESat was the first satellite specifically designed to use laser
altimetry to study the Earth's polar regions. It operated from 2003
to 2009. Its successor, ICESat-2, is scheduled for launch in 2016.
"This study demonstrates the urgent need for ICESat-2 to get into
space," said Jay Zwally, ICESat project scientist at NASA's Goddard
Space Flight Center in Greenbelt, Md. "We have limited information on
the changes in polar regions caused by climate change. Nothing can
look at these changes like satellite measurements do."
The new research also links the observed increase in melting that
occurs on the underside of a glacier or ice shelf, called basal melt,
and glacier acceleration with changes in wind patterns.
"Studies have shown Antarctic winds have changed because of changes in
climate," Pritchard said. "This has affected the strength and
direction of ocean currents. As a result warm water is funnelled
beneath the floating ice. These studies and our new results suggest
Antarctica's glaciers are responding rapidly to a changing climate."
A different picture is seen on the Antarctic Peninsula, the long
stretch of land pointing towards South America. The study found
thinning of the largest ice shelf on the peninsula can be explained
by warm summer winds directly melting the snow on the ice shelf
surfaces. The patterns of widespread ocean-driven melting and summer
melting on the Antarctic Peninsula can be attributed to changing wind patterns.
The study was carried out by an international team from the British
Antarctic Survey, Utrecht University in Utrecht, Netherlands, the
University of California in San Diego and the non-profit research
institute Earth and Space Research in Corvallis, Ore.
For more information, a visualization and related imagery, visit:
http://www.nasa.gov/topics/
For more information about ICESat and ICESat-2, visit:
http://icesat.gsfc.nasa.gov
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NASA Dawn Spacecraft Reveals Secrets of Giant Asteroid Vesta
WASHINGTON -- Findings from NASA's Dawn spacecraft reveal new detailsabout the giant asteroid Vesta, including its varied surface
composition, sharp temperature changes and clues to its internal
structure. The findings were presented today at the European
Geosciences Union meeting in Vienna, Austria and will help scientists
better understand the early solar system and processes that dominated
its formation.
Spacecraft images, taken 420 miles (680 kilometers) and 130 miles (210
kilometers) above the surface of the asteroid, show a variety of
surface mineral and rock patterns. Coded false-color images help
scientists better understand Vesta's composition and enable them to
identify material that was once molten below the asteroid's surface.
Researchers also see breccias, which are rocks fused during impacts
from space debris. Many of the materials seen by Dawn are composed of
iron- and magnesium-rich minerals, which often are found in Earth's
volcanic rocks. Images also reveal smooth pond-like deposits, which
might have formed as fine dust created during impacts settled into
low regions.
"Dawn now enables us to study the variety of rock mixtures making up
Vesta's surface in great detail," said Harald Hiesinger, a Dawn
participating scientist at Münster University in Germany. "The images
suggest an amazing variety of processes that paint Vesta's surface."
At the Tarpeia crater near the south pole of the asteroid, Dawn
revealed bands of minerals that appear as brilliant layers on the
crater's steep slopes. The exposed layering allows scientists to see
farther back into the geological history of the giant asteroid.
The layers closer to the surface bear evidence of contamination from
space rocks bombarding Vesta's surface. Layers below preserve more of
their original characteristics. Frequent landslides on the slopes of
the craters also have revealed other hidden mineral patterns.
"These results from Dawn suggest Vesta's 'skin' is constantly
renewing," said Maria Cristina De Sanctis, lead of the visible and
infrared mapping spectrometer team based at Italy's National
Institute for Astrophysics in Rome.
Dawn has given scientists a near 3-D view into Vesta's internal
structure. By making ultrasensitive measurements of the asteroid's
gravitational tug on the spacecraft, Dawn can detect unusual
densities within its outer layers. Data now show an anomalous area
near Vesta's south pole, suggesting denser material from a lower
layer of Vesta has been exposed by the impact that created a feature
called the Rheasilvia basin. The lighter, younger layers coating
other parts of Vesta's surface have been blasted away in the basin.
Dawn obtained the highest-resolution surface temperature maps of any
asteroid visited by a spacecraft. Data reveal temperatures can vary
from as warm as -10 degrees Fahrenheit (-23 degrees Celsius) in the
sunniest spots to as cold as -150 degrees Fahrenheit (-100 degrees
Celsius) in the shadows. This is the lowest temperature measurable by
Dawn. These findings show the surface responds quickly to
illumination with no mitigating effect of an atmosphere.
"After more than nine months at Vesta, Dawn's suite of instruments has
enabled us to peel back the layers of mystery that have surrounded
this giant asteroid since humankind first saw it as just a bright
spot in the night sky," said Carol Raymond, Dawn deputy principal
investigator at NASA's Jet Propulsion Laboratory (JPL) in Pasadena,
Calif. "We are closing in on the giant asteroid's secrets."
Launched in 2007, Dawn began its exploration of the approximately
330-mile- (530-kilometer-) wide asteroid in mid-2011. The
spacecraft's next assignment will be to study the dwarf planet Ceres
in 2015. These two icons of the asteroid belt have been witness to
much of our solar system's history.
Dawn's mission is managed by JPL for NASA's Science Mission
Directorate in Washington. Dawn is a project of the directorate's
Discovery Program, managed by NASA's Marshall Space Flight Center in
Huntsville, Ala. UCLA is responsible for overall Dawn mission
science. Orbital Sciences Corp. in Dulles, Va., designed and built
the spacecraft. The German Aerospace Center, the Max Planck Institute
for Solar System Research, the Italian Space Agency and the Italian
National Astrophysical Institute are international partners on the
mission team.
To view the new images and for more information about Dawn, visit:
http://www.nasa.gov/dawn
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