Jimmy's blog
The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2010-076&cid=release_2010-076
PASADENA, Calif. -- New studies of ripples and dunes shaped by the winds on Mars testify to variability on that planet, identifying at least one place where ripples are actively migrating and another where the ripples have been stationary for 100,000 years or more.
Patterns of dunes and the smaller ripples present some of the more visually striking landforms photographed by cameras orbiting Mars. Investigations of whether they are moving go back more than a decade.
Two reports presented at the 41st Lunar and Planetary Sciences Conference near Houston this week make it clear that the answer depends on where you look. Both reports used images from the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter, which allows examination of features as small as about a meter, or yard, across.
One report is by Simone Silvestro of the International Research School of Planetary Sciences at Italy's G. d'Annunzio University, and his collaborators. They investigated migration of ripples and other features on dark dunes within the Nili Patera area of Mars' northern hemisphere. They compared an image taken on Oct. 13, 2007, with another of the same dunes taken on June 30, 2007. Most of the dunes in the study area are hundreds of meters long. Ripples form patterns on the surfaces of the dunes, with crests of roughly parallel ripples spaced a few meters apart.
Careful comparison of the images revealed places where ripples on the surface of the dunes had migrated about 2 meters (7 feet) -- the largest movement ever measured in a ripple or dune on Mars. The researchers also saw changes in the shape of dune edges and in streaks on the downwind faces of dunes.
"The dark dunes in this part of Mars are active in present-day atmospheric conditions," Silvestro said. "It is exciting to have such high-resolution images available for comparisons that show Mars as an active world."
The other report is by Matthew Golombek of NASA's Jet Propulsion Laboratory, Pasadena, Calif., and collaborators. They checked whether ripples have been moving in the southern-hemisphere area of Mars' Meridiani Planum where the Mars Exploration Rover Opportunity has been working since 2004. They used observations by Opportunity as well as by HiRISE, surveying an area of about 23 square kilometers (9 square miles). Examination of ripples at the edges of craters can show whether the ripples were in place before the crater was excavated or moved after the crater formed.
"HiRISE images are so good, you can tell if a crater is younger than the ripple migration," Golombek said. "There's enough of a range of crater ages that we can bracket the age of the most recent migration of the ripples in this area to more than 100,000 years and probably less than 300,000 years ago."
Winds are still blowing sand and dust at Meridiani. Opportunity has seen resulting changes in its own wheel tracks revisited several months after the tracks were first cut.
Golombek has a hypothesis for why the ripples at Meridiani are static, despite winds, while those elsewhere on Mars may be actively moving. Opportunity has seen that the long ripples in the region are covered with erosion-resistant pebbles, nicknamed "blueberries," which the rover first observed weathering out of softer matrix rocks beside the landing site. These spherules -- mostly about 1 to 3 millimeters (0.04 to 0.12 inches) in diameter -- may be too large for the wind to budge.
"The blueberries appear to form a armoring layer that shields the smaller sand grains beneath them from the wind," he said.
HiRISE Principal Investigator Alfred McEwen, of the University of Arizona, Tucson, said, "The more we look at Mars at the level of detail we can now see, the more we appreciate how much the planet differs from one place to another."
The Mars Reconnaissance Orbiter and the Mars Exploration Rover missions are managed by JPL for NASA's Science Mission Directorate in Washington. Lockheed Martin Space Systems in Denver was the prime contractor for the orbiter and supports its operations. The University of Arizona operates the HiRISE camera, which was built by Ball Aerospace & Technologies Corp., Boulder, Colo.
Little Galaxy With a Tail This infrared portrait of the Small Magellanic Cloud, taken by NASA's Spitzer Space Telescope, reveals stars and dust in this galaxy as never seen before. T The image shows the main body of the Small Magellanic Cloud, which is comprised of the "bar" and "wing" on the left and the "tail" extending to the right. The bar contains both old stars (in blue) and young stars lighting up their natal dust (green/red). The wing mainly contains young stars. The tail contains only gas, dust and newly formed stars. Spitzer data has confirmed that the tail region was recently torn off the main body of the galaxy. Two of the tail clusters, which are still embedded in their birth clouds, can be seen as red dots. The data in this image are being used by astronomers to study the lifecycle of dust in the entire galaxy: from the formation in stellar atmospheres, to the reservoir containing the present day interstellar medium, and the dust consumed in forming new stars. The dust being formed in old, evolved stars (blue stars with a red tinge) is measured using mid-infrared wavelengths. The present day interstellar dust is weighed by measuring the intensity and color of emission at longer infrared wavelengths. The rate at which the raw material is being consumed is determined by studying ionized gas regions and the younger stars (yellow/red extended regions). The Small Magellanic Cloud, and its companion galaxy the Large Magellanic Cloud, are the two galaxies where this type of study is possible. Image Credit: NASA/JPL-Caltech/STScI
Wed, 03 Feb 2010 23:00:00 -0600
What's Up for February?
Jupiter’s moons.
Jupiter’s largest moons were first seen 400 years ago in early 1610.
Hello, and welcome. I’m Jane Houston Jones at NASA’s Jet Propulsion Laboratory in Pasadena, California.
On the seventh of January, 1610 in Padua, Italy, Galileo looked up above the constellation Orion. He aimed his telescope at the well-known starry wanderer, the planet Jupiter, which was near Orion that night.
What he saw through his telescope startled him and marked the beginning of modern astronomy.Jupiter was not just one object, as he wrote and drew in his journal. “There are three stars in the heavens moving about Jupiter, as Venus and Mercury around the sun,” he wrote.
Galileo’s January 7 observation showed three stars. The one star to the west was Ganymede. And to the east there were two objects.One was the moon Callisto. And the other was a tight pairing of Io and Europa.
Io and Europa appeared so close together they looked like one object in Galileo’s modest telescopic view.
On January 8 he saw a different lineup altogether. There were three stars on one side of the planet.Io was the moon closest to the planet, followed by Europa and Ganymede.
Two cloudy nights and two additional observations later, on January 13 Galileo identified a fourth object orbiting Jupiter. The arrangement this night turned out to be Europa on the east and Ganymede, Io and Callisto on the west.
On January 15 all four stars were seen on one side of the planet.
Everyone who aims a modest telescope, or even binoculars, at Jupiter will see the same view that Galileo did.
The views of tiny moons orbiting the king of the planets will surprise and delight all who look up.
[ Jupiter is hard to see in the evening sky this month. But northern hemisphere observers may see Jupiter and Venus close together, low on the southwestern horizon, on Valentine’s Day.
Then it will be a few months’ wait until Jupiter becomes visible in the morning sky.
By August you can once again view Jupiter and the four Galilean moons after dinner or as soon as the sun sets and the stars come out.
NASA’s Galileo Mission, which ended in 2003, changed the way we look at our solar system. It found evidence of subsurface saltwater on Europa, Ganymede and Callisto and intense volcanic activity on Io.
NASA’s JUNO Mission will launch in 2011 on a mission to study Jupiter. And the Europa-Jupiter System Mission, a joint mission of the European Space Agency and NASA, is slated to launch in 2020. It will primarily study Jupiter’s moons Europa and Ganymede and Jupiter’s magnetosphere.
You can learn all about NASA’s missions at www.nasa.gov.
That’s all for this month. I’m Jane Houston Jones.
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Pluto's White, Dark-Orange and Charcoal-Black Terrain Captured by NASA's Hubble
http://www.nasa.gov/mission_pages/hubble/main/index.html
WASHINGTON -- NASA has released the most detailed and dramatic images ever taken of the distant dwarf planet Pluto. The images from NASA's Hubble Space Telescope show an icy, mottled, dark molasses-colored world undergoing seasonal surface color and brightness changes. - end -
Pluto has become significantly redder, while its illuminated northern hemisphere is getting brighter. These changes are most likely consequences of surface ice melting on the sunlit pole and then refreezing on the other pole, as the dwarf planet heads into the next phase of its 248-year-long seasonal cycle. Analysis shows the dramatic change in color took place from 2000 to 2002.
The Hubble pictures confirm Pluto is a dynamic world that undergoes dramatic atmospheric changes not simply a ball of ice and rock. These dynamic seasonal changes are as much propelled by the planet's 248-year elliptical orbit as by its axial tilt. Pluto is unlike Earth, where the planet's tilt alone drives seasons. Pluto's seasons are asymmetric because of its elliptical orbit. Spring transitions to polar summer quickly in the northern hemisphere, because Pluto is moving faster along its orbit when it is closer to the sun.
Ground-based observations, taken in 1988 and 2002 show the mass of the atmosphere doubled during that time. This may be because of warming and melting nitrogen ice. The new Hubble images are giving astronomers essential clues about the seasons on Pluto and the fate of its atmosphere.
When the Hubble pictures taken in 1994 are compared to those of 2002 and 2003, astronomers see evidence that the northern polar region has gotten brighter, while the southern hemisphere darkened. These changes hint at very complex processes affecting the visible surface.
The images will help planetary astronomers interpret more than three decades of Pluto observations from other telescopes.
"The Hubble observations are the key to tying together these other diverse constraints on Pluto and showing how it all makes sense by providing a context based on weather and seasonal changes, which opens other new lines of investigation," says principal investigator Marc Buie of the Southwest Research Institute in Boulder, Colo.
These Hubble images, taken by the Advanced Camera for Surveys, will remain the sharpest view of Pluto until NASA's New Horizons probe is within six months of its flyby during 2015. The Hubble images are invaluable for picking the planet's most interesting hemisphere for imaging by the New Horizons probe.
New Horizons will pass by Pluto so quickly that only one hemisphere will be photographed in detail. Particularly noticeable in the Hubble images is a bright spot that has been independently noted to be unusually rich in carbon monoxide frost. It is a prime target for New Horizons. "Everybody is puzzled by this feature," Buie said. New Horizons will get an excellent look at the boundary between this bright feature and a nearby region covered in pitch-black surface material.
"The Hubble images also will help New Horizons scientists better calculate the exposure time for each Pluto snapshot which is important for taking the most detailed pictures possible," Buie said. With no chance for re-exposures, accurate models for the surface of Pluto are essential for properly exposed images.
The Hubble images surface variations a few hundred miles across that are too coarse for understanding surface geology. But in terms of surface color and brightness, Hubble reveals a complex-looking world with white, dark-orange and charcoal-black terrain. The overall color is believed to be a result of ultraviolet radiation from the distant sun breaking up methane present on Pluto's surface, leaving behind a dark and red-carbon-rich residue.
The Hubble images are a few pixels wide. Through a technique called dithering, multiple, slightly offset pictures are combined through computer-image processing to synthesize a higher-resolution view than can be seen in a single exposure.
"This has taken four years and 20 computers operating continuously and simultaneously to accomplish," Buie said. Buie developed the special algorithms to sharpen the Hubble data. He plans to use Hubble's new Wide Field Camera 3 to make additional observations prior to the arrival of New Horizons.
For Hubble information and images, visit:
Suspected Asteroid Collision Leaves Trailing Debris
Suspected Asteroid Collision Leaves Trailing Debris
Asteroid collisions are energetic, with an average impact speed of more than 11,000 miles per hour, or five times faster than a rifle bullet. The comet-like object imaged by Hubble, called P/2010 A2, was first discovered by the Lincoln Near-Earth Asteroid Research, or LINEAR, program sky survey on Jan. 6. New Hubble images taken on Jan. 25 and 29 show a complex X-pattern of filamentary structures near the nucleus.
"This is quite different from the smooth dust envelopes of normal comets," said principal investigator David Jewitt of the University of California at Los Angeles. "The filaments are made of dust and gravel, presumably recently thrown out of the nucleus. Some are swept back by radiation pressure from sunlight to create straight dust streaks. Embedded in the filaments are co-moving blobs of dust that likely originated from tiny unseen parent bodies."
Hubble shows the main nucleus of P/2010 A2 lies outside its own halo of dust. This has never been seen before in a comet-like object. The nucleus is estimated to be 460 feet in diameter.
Normal comets fall into the inner regions of the solar system from icy reservoirs in the Kuiper belt and Oort cloud. As comets near the sun and warm up, ice near the surface vaporizes and ejects material from the solid comet nucleus via jets. But P/2010 A2 may have a different origin. It orbits in the warm, inner regions of the asteroid belt where its nearest neighbors are dry rocky bodies lacking volatile materials.
This leaves open the possibility that the complex debris tail is the result of an impact between two bodies, rather than ice simply melting from a parent body.
"If this interpretation is correct, two small and previously unknown asteroids recently collided, creating a shower of debris that is being swept back into a tail from the collision site by the pressure of sunlight," Jewitt said.
The main nucleus of P/2010 A2 would be the surviving remnant of this so-called hypervelocity collision.
"The filamentary appearance of P/2010 A2 is different from anything seen in Hubble images of normal comets, consistent with the action of a different process," Jewitt said. An impact origin also would be consistent with the absence of gas in spectra recorded using ground-based telescopes.
The asteroid belt contains abundant evidence of ancient collisions that have shattered precursor bodies into fragments. The orbit of P/2010 A2 is consistent with membership in the Flora asteroid family, produced by collisional shattering more than 100 million years ago. One fragment of that ancient smashup may have struck Earth 65 million years ago, triggering a mass extinction that wiped out the dinosaurs. But, until now, no such asteroid-asteroid collision has been caught "in the act."
At the time of the Hubble observations, the object was approximately 180 million miles from the sun and 90 million miles from Earth. The Hubble images were recorded with the new Wide Field Camera 3 (WFC3), which is capable of detecting house-sized fragments at the distance of the asteroid belt.
For Hubble images and more information, visit:
Mystery of the Fading Star Using NASA's Spitzer Space Telescope, astronomers have found a likely solution to a centuries-old riddle of the night sky. Every 27 years, a bright star called Epsilon Aurigae fades over period of two years, then brightens. Although amateur and professional astronomers have observed the system extensively, the nature of both the bright star and the companion object that periodically eclipses it have remained unclear. The companion is known to be surrounded by a dusty disk, as illustrated in this artist's concept. Data from Spitzer finally seems to have solved the riddle. Spitzer's infrared vision revealed the size of the dusty disk that swirls around the companion object. When astronomers plugged this data into a model of the system, they were able to rule out the theory that the main bright star is a supergiant. Instead, it is a bright star with a lot less mass. The new model also holds that the companion object is a so-called "B star" circled by a dusty disk. Image credit: NASA/JPL-Caltech
Tue, 02 Feb 2010 23:00:00 -0600
Trio of Galaxies Mixes It Up Though they are the largest and most widely scattered objects in the universe, galaxies do go bump in the night. The Hubble Space Telescope has photographed many pairs of galaxies colliding. Like snowflakes, no two examples look exactly alike. This is one of the most arresting galaxy smash-up images to date. At first glance, it looks as if a smaller galaxy has been caught in a tug-of-war between a Sumo-wrestler pair of elliptical galaxies. The hapless, mangled galaxy may have once looked more like our Milky Way, a pinwheel-shaped galaxy. Now that it's caught in a cosmic blender, its dust lanes are being stretched and warped by the tug of gravity. Unlike the elliptical galaxies, the spiral is rich in dust and gas for the formation of new stars. It is the fate of the spiral galaxy to be pulled like taffy and then swallowed by the pair of elliptical galaxies, which will trigger a firestorm of new stellar creation. If there are astronomers on any planets in this galaxy group, they will have a ringside seat to seeing a flurry of star birth unfolding over many millions of years to come. Eventually, the elliptical galaxies should merge, creating one single super-galaxy many times larger than our Milky Way. This trio is part of a tight cluster of 16 galaxies, many of them being dwarf galaxies. This particular galaxy cluster is called the Hickson Compact Group 90 and lies about 100 million light-years away in the direction of the constellation Piscis Austrinus, the Southern Fish. Image Credit: NASA, ESA and R. Sharples (University of Durham)
Thu, 28 Jan 2010 23:00:00 -0600
Newborn Black Holes May Add Power to Many Exploding Stars
Previously, the only catastrophic events known to produce such high-speed jets were gamma-ray bursts, the universe's most luminous explosions. Supernovae and the most common type of gamma-ray bursts occur when massive stars run out of nuclear fuel and collapse. A neutron star or black hole forms at the star's core, triggering a massive explosion that destroys the rest of the star.
"The explosion dynamics in typical supernovae limit the speed of the expanding matter to about three percent the speed of light," explained Chryssa Kouveliotou, an astrophysicst at NASA's Marshall Space Flight Center in Huntsville, Ala., co-author of one of the new studies. "Yet, in these new objects, we're tracking gas moving some 20 times faster than this."
The new results, published in this week's edition of the journal Nature, used observations from several space and ground-based observatories, including NASA's SWIFT satellite.
The astronomers discovered the ultrafast debris by studying two supernovae at radio wavelengths using numerous facilities, including the National Science Foundation's Very Large Array in Socorro, N.M., and the Robert C. Byrd Green Bank Telescope in West Virginia. One team used the real-time operating mode of the European Very Long Baseline Interferometry Network, an international collaboration of radio telescopes, to rapidly analyze data.
"In every respect, these objects look like gamma-ray bursts -- except that they produced no gamma rays," said Alicia Soderberg at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.
Soderberg led a team that studied SN 2009bb, a supernova discovered in March 2009. It exploded in the spiral galaxy NGC 3278, located about 130 million light-years away.
The other object is SN 2007gr, which was first detected in August 2007 in the spiral galaxy NGC 1058, some 35 million light-years away. The study team, which included Kouveliotou and Alexander van der Horst, a NASA Postdoctoral Program Fellow in Huntsville, was led by Zsolt Paragi at the Netherlands-based Joint Institute for Very Long Baseline Interferometry in Europe.
The researchers searched for gamma-ray signals associated with the supernovae using archived records in the Gamma-Ray Burst Coordination Network located at NASA's Goddard Space Flight Center in Greenbelt, Md. The project distributes and archives observations of gamma-ray bursts by NASA's SWIFT spacecraft, the Fermi Gamma-ray Space Telescope and many others. However, no bursts coincided with the supernovae.
Unlike typical core-collapse supernovae, the stars that produce gamma-ray bursts possess what astronomers call a "central engine" -- likely a nascent black hole -- that drives particle jets clocked at more than 99 percent the speed of light.
By contrast, the fastest outflows detected from SN 2009bb reached 85 percent of the speed of light and SN 2007gr reached more than 60 percent of light speed.
"These observations are the first to show some supernovae are powered by a central engine," Soderberg said. "These new radio techniques now give us a way to find explosions that resemble gamma-ray bursts without relying on detections from gamma-ray satellites."
Perhaps as few as one out of every 10,000 supernovae produce gamma rays that we detect as a gamma-ray burst. In some cases, the star's jets may not be angled in a way to produce a detectable burst. In others, the energy of the jets may not be enough to allow them to overcome the overlying bulk of the star.
"We've now found evidence for the unsung crowd of supernovae -- those with relatively dim and mildly relativistic jets that only can be detected nearby," Kouveliotou said. "These likely represent most of the population."
For more information, images and animation about this discovery, visit:
Newborn Black Holes May Add Power to Many Exploding Stars
Previously, the only catastrophic events known to produce such high-speed jets were gamma-ray bursts, the universe's most luminous explosions. Supernovae and the most common type of gamma-ray bursts occur when massive stars run out of nuclear fuel and collapse. A neutron star or black hole forms at the star's core, triggering a massive explosion that destroys the rest of the star.
"The explosion dynamics in typical supernovae limit the speed of the expanding matter to about three percent the speed of light," explained Chryssa Kouveliotou, an astrophysicst at NASA's Marshall Space Flight Center in Huntsville, Ala., co-author of one of the new studies. "Yet, in these new objects, we're tracking gas moving some 20 times faster than this."
The new results, published in this week's edition of the journal Nature, used observations from several space and ground-based observatories, including NASA's SWIFT satellite.
The astronomers discovered the ultrafast debris by studying two supernovae at radio wavelengths using numerous facilities, including the National Science Foundation's Very Large Array in Socorro, N.M., and the Robert C. Byrd Green Bank Telescope in West Virginia. One team used the real-time operating mode of the European Very Long Baseline Interferometry Network, an international collaboration of radio telescopes, to rapidly analyze data.
"In every respect, these objects look like gamma-ray bursts -- except that they produced no gamma rays," said Alicia Soderberg at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.
Soderberg led a team that studied SN 2009bb, a supernova discovered in March 2009. It exploded in the spiral galaxy NGC 3278, located about 130 million light-years away.
The other object is SN 2007gr, which was first detected in August 2007 in the spiral galaxy NGC 1058, some 35 million light-years away. The study team, which included Kouveliotou and Alexander van der Horst, a NASA Postdoctoral Program Fellow in Huntsville, was led by Zsolt Paragi at the Netherlands-based Joint Institute for Very Long Baseline Interferometry in Europe.
The researchers searched for gamma-ray signals associated with the supernovae using archived records in the Gamma-Ray Burst Coordination Network located at NASA's Goddard Space Flight Center in Greenbelt, Md. The project distributes and archives observations of gamma-ray bursts by NASA's SWIFT spacecraft, the Fermi Gamma-ray Space Telescope and many others. However, no bursts coincided with the supernovae.
Unlike typical core-collapse supernovae, the stars that produce gamma-ray bursts possess what astronomers call a "central engine" -- likely a nascent black hole -- that drives particle jets clocked at more than 99 percent the speed of light.
By contrast, the fastest outflows detected from SN 2009bb reached 85 percent of the speed of light and SN 2007gr reached more than 60 percent of light speed.
"These observations are the first to show some supernovae are powered by a central engine," Soderberg said. "These new radio techniques now give us a way to find explosions that resemble gamma-ray bursts without relying on detections from gamma-ray satellites."
Perhaps as few as one out of every 10,000 supernovae produce gamma rays that we detect as a gamma-ray burst. In some cases, the star's jets may not be angled in a way to produce a detectable burst. In others, the energy of the jets may not be enough to allow them to overcome the overlying bulk of the star.
"We've now found evidence for the unsung crowd of supernovae -- those with relatively dim and mildly relativistic jets that only can be detected nearby," Kouveliotou said. "These likely represent most of the population."
For more information, images and animation about this discovery, visit:
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