Posted on by Fraser Cain

Predicting Titan’s Weather

False-colour images of Titan obtained by Cassini-Huygens Visual Infrared Mapping Spectrometer. Image credit: Click to enlarge
Using recent Cassini, Huygens and Earth-based observations, scientists have been able to create a computer model which explains the formation of several types of ethane and methane clouds on Titan.

Clouds have been observed recently on Titan, Saturn’s largest moon, through the thick haze, using near-infrared spectroscopy and images of the south pole and temperate regions near 40? South. Recent observations from Earth-based telescopes and the NASA/ESA/ASI Cassini spacecraft are now providing an insight into cloud climatology.

A European team, led by Pascal Rannou of the Service d?Aeronomie, IPSL Universite de Versailles-St-Quentin, France, has developed a general circulation model which couples dynamics, haze and cloud physics to study Titan climate and enables us to understand how the major cloud features which are observed, are produced.

This climate model also allows scientists to predict the cloud distribution for the complete Titan year (30 terrestrial years), and especially in the next years of Cassini observations.

The Voyager missions of the early 1980s gave the first indications of condensate clouds on Titan. Because of the cold temperatures in the moon?s atmosphere (tropopause), it was assumed that most of the organic chemicals formed in the upper atmosphere by photochemistry would condense into clouds while sinking. Methane would also condense at high altitudes, it was believed, having been transported from the surface.

Since then, several one-dimensional models of Titan’s atmosphere including sophisticated microphysics models were created to predict the formation of drops of ethane and methane. Similarly, the methane cycle had been studied separately in a circulation model, but without cloud microphysics.

These studies generally found that methane clouds could be triggered when air parcels cooled while moving upward or from equator to pole. However, these models hardly captured the fine details of the methane and ethane cloud cycles.

What Rannou’s team has done is to combine a cloud microphysical model into a general circulation model. The team can now identify and explain the formation of several types of ethane and methane clouds, including the south polar and sporadic clouds in the temperate regions, especially at 40? S in the summer hemisphere.

The scientists found that the predicted physical properties of the clouds in their model matched well with recent observations. Methane clouds that have been observed to date appear in locations where ascending air motions are predicted in their model.

The observed south polar cloud appears at the top of a particular ‘Hadley cell’, or mass of vertically circulating air, exactly where predicted at the south pole at an altitude of around 20-30 kilometres.

The recurrent large zonal (longitudinal direction) clouds at 40? S and the linear and discrete clouds that appear in the lower latitudes are also correlated with the ascending part of similar circulation cell in the troposphere, whereas smaller clouds at low latitudes, similar to the linear and discrete clouds already observed by Cassini are rather produced by mixing processes.

“Clouds in our circulation model are necessarily simplified relative to the real clouds, however the main cloud features predicted find a counterpart in reality.

“Consistently, our model produces clouds at places where clouds are actually observed, but it also predicts clouds that have not, or not yet, been observed,” said Pascal Rannou.

Titan’s cloud pattern appears to be similar to that of the main cloud patterns on Earth and Mars. The puzzling clouds at 40? S are produced by the ascending branch of a Hadley cell, exactly like tropical clouds are in the Intertropical Convergence Zone (ITCZ), as on Earth and Mars.

Polar clouds – produced by ‘polar cells’ – are similar to those produced at mid-latitudes on Earth. On other hand, clouds only appears at some longitudes. This is a specific feature of Titan clouds, and may be due to a Saturn tidal effect. The dynamical origin of cloud distribution on Titan is easy to test.

Cloudiness prediction for the coming years will be compared to observations made by Cassini and ground-based telescopes. Specific events will definitely prove the role of the circulation on the cloud distribution.

Original Source: ESA Portal

Posted on by Fraser Cain

NASA’s IMAGE Mission Ends

IMAGE launch on March, 2000. Image credit: NASA Click to enlarge
NASA’s Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) satellite recently ceased operations, bringing to a close a successful six-year mission. IMAGE was the premier producer of new discoveries on the structure and dynamics of the Earth’s external magnetic field (magnetosphere) and its contents.

“The IMAGE mission showed us space around the Earth is anything but empty, and that plasma clouds can be imaged and tracked just as we do from space for Earth’s surface weather,” said Barbara Giles, IMAGE Program Scientist at NASA headquarters.

Prior to the launch of IMAGE, the energetic particles and electrically charged gas (plasma) surrounding the Earth were completely invisible to human observers. IMAGE enabled researchers to study the global structure and dynamics of the Earth’s inner magnetosphere as it responded to energy from solar winds.

“Nearly six years of imagery by the pioneering cameras on IMAGE revolutionized our understanding of geospace and our knowledge of its space weather,” said James Burch, IMAGE principal investigator at the Southwest Research Institute, San Antonio.

IMAGE was launched on March 25, 2000. It successfully completed its two-year primary mission and continued providing data into December 2005, when it stopped responding to commands from ground controllers. Preliminary analysis indicated the craft’s power supply subsystems failed, rendering it lifeless. The satellite is in an extended elliptical orbit and poses no threat to the planet.

IMAGE discoveries have been reported in more than 400 peer-reviewed publications. More than 20 Ph.D. theses were based on data from the mission. Science highlights include:

– Confirmations: plasma plume creation, post-midnight peak in storm plasmas, the neutral solar wind, terrestrial origin of geospace storm plasmas and continuous nature of magnetic reconnection.

– Discoveries: plasmaspheric shoulders and notches, proton auroras in unexpected places, surprisingly slow plasmasphere rotation, a hot oxygen geocorona and a secondary interstellar neutral atom stream.

– Resolutions: the source of kilometric continuum radiation, solar- wind and auroral intensity effects on ionospheric out flow and the relationship between proton and electron auroras during geospace storms.

The IMAGE education and public outreach program received numerous awards for videos, books, primary and secondary school curricula, teacher training, museum exhibits, planetarium shows, student workbooks and web-based information.

The extensive archival database generated by IMAGE promises to yield new discoveries and will support investigations by other spacecraft and ground-based observatories for many years.

IMAGE was a Medium Explorer mission sponsored by NASA’s Sun-Earth Connections Program and managed by NASA’s Goddard Space Flight Center, Greenbelt, Md. The Southwest Research Institute conducts IMAGE science operations. James Burch is the mission principal Investigator, and Thomas Moore at Goddard is the Mission Scientist.

For information about the IMAGE mission on the Web, visit:

http://image.gsfc.nasa.gov/

Original Source: NASA News Release

Posted on by Fraser Cain

Icy Martian Glaciers

Perspective view of ‘hourglass’ shaped craters. Image credit: ESA Click to enlarge
The spectacular features visible today on the surface of the Red Planet indicate the past existence of Martian glaciers, but where did the ice come from?

An international team of scientists have produced sophisticated climate simulations suggesting that geologically recent glaciers at low latitudes (that is near the present-day equator) may have formed through atmospheric precipitation of water-ice particles.

Moreover, the results of the simulations show for the first time that the predicted locations for these glaciers match extensively with many of the glacier remnants observed today at these latitudes on Mars.

For several years, the presence, age and shape of these glacier remnants have raised numerous questions in the scientific community about their formation, and about the conditions on the planet when this happened.

To start narrowing down the rising number of hypotheses, a team led by Francois Forget, University of Paris 6 (France) and interdisciplinary scientist for ESA’s Mars Express mission, decided to ‘turn back the clock’ in their Martian global climate computer model, a tool usually applied to simulate the detail of present-day Mars meteorology.

As a starting point, Forget and colleagues had to make some assumptions – that the north polar cap was still the ice reservoir of the planet, and that the rotation axis was tilted by 45? with respect to the planet?s orbital plane.

“This makes the axis much more oblique than it is today (about 25?), but such an obliquity has probably been very common throughout Mars?s history. Actually, it last occurred only five and a half million years ago,” says Forget.

As expected with such a tilt, the greater solar illumination in the north polar summer increased the sublimation of the polar ice and led to a water cycle much more intense than today.

The simulations showed water ice being accumulated at a rate of 30 to 70 millimetres per year in a few localised areas on the flanks of the Elysium Mons, Olympus Mons and the three Tharsis Montes volcanoes.

After a few thousand years, the accumulated ice would form glaciers up to several hundreds of metres thick.

When the team compared the location and shape of the ‘simulated’ glaciers with the actual glacier-related deposits of Tharsis – one of the three main regions on the planet where signs of glaciers are seen – they found an excellent agreement.

In particular, the maximum deposition is predicted on the western flanks of the Arsia and Pavonis Montes of the Tharsis region, where the largest deposits in this area are actually observed.

In their simulations, the team could even ‘read’ why and how ice was accumulated on the flanks of these mountains in the Tharsis region millions of years ago.

Back then, constant year-long winds similar to monsoons on Earth would favour the upslope movement of water-rich air around Arsia and Pavonis Montes.

While being cooled down by tens of degrees, water would condense and form ice particles (larger than those we observe today in the Tharsis region’s clouds) that settled on the surface.

Other mountains like Olympus Mons show smaller-scale deposits because, according to the simulations, they were exposed to the monsoon-type strong winds and water-rich air only during the northern summer.

“The north polar cap may not have always been the only source of water during the planet’s high obliquity periods,” adds Forget.

“So we ran simulations assuming that ice was available in the south polar cap. We could still see ice accumulation in the Tharsis region, but this time also on the east of the Hellas Basin, a six-kilometre deep crater.”

This would explain the origins of another major area where ice-related landforms are observed today, the eastern Hellas Basin. indeed.

“The Hellas basin is in fact so deep as to induce the generation of a northward wind flow on its eastern side that would carry most of the water vapour sublimating from the south polar cap during summer. When the water-rich air meet colder air mass over eastern Hellas, water condense, precipitate, and form glaciers,” said Forget.

However, the team could not predict ice deposition in the Deuterolinus-Protonilus Mensae region, where glaciers could have been formed by other mechanisms. The scientists are considering several other hypotheses on the formation of recent glaciers.

For instance, observations of Olympus Mons by the High Resolution Stereo Camera on board Mars Express suggest that movement of water from the subsurface to the surface due to hydrothermal activity may have led to the development of glaciers on the cold surface.

Original Source: ESA Mars Express

Posted on by Fraser Cain

World’s Largest Telescope

An image of how one element of the SKA might look. Image credit: Chris Fluke. Click to enlarge
European funding has now been agreed to start designing the world’s biggest telescope. The “Square Kilometre Array” (SKA) will be an international radio telescope with a collecting area of one million square metres – equivalent to about 200 football pitches – making SKA 200 times bigger than the University of Manchester’s Lovell Telescope at Jodrell Bank and so the largest radio telescope ever constructed. Such a telescope would be so sensitive that it could detect TV Broadcasts coming from the nearest stars.

The four-year Square Kilometre Array Design Study (SKADS) will bring together European and international astronomers to formulate and agree the most effective design. The final design will enable the SKA to probe the cosmos in unprecedented detail, answering fundamental questions about the Universe, such as “what is dark energy?” and “how did the structure we see in galaxies today actually form?”.

The new telescope will test Einstein’s General Theory of Relativity to the limit – and perhaps prove it wrong. It is certain to add to the long list of fundamental discoveries already made by radio astronomers including quasars, pulsars and the radiation left over from the Big Bang. By the end of this decade the design will be complete and astronomers anticipate building SKA in stages, leading to completion and full operation in 2020.

The SKA concept was first proposed to observe the characteristic radio emission from hydrogen gas. Measurements of the hydrogen signature will enable astronomers to locate and weigh a billion galaxies.

As the University of Manchester’s Prof Peter Wilkinson points out, “Hydrogen is the most abundant element in the universe, but its signal is weak and so a huge collecting area is needed to be able to study it at the vast distances that take us back in time towards the Big Bang”. To which Prof Steve Rawlings, University of Oxford, adds,”The distribution of these galaxies in space tells us how the universe has evolved since the Big Bang and hence about the nature of the Dark Energy which is now making the universe expand faster with time”.

Another target for the SKA is pulsars – spinning remnants of stellar explosions which are the most accurate clocks in the universe. A million times the mass of the Earth but only the size of a large city, pulsars can spin around hundreds of times per second. Already these amazing objects have enabled astronomers to confirm Einstein’s prediction of gravitational waves, but University of Manchester’s Dr Michael Kramer is looking further ahead. “With the SKA we will find a pulsar orbiting a black hole and, by watching how the clock rate varies, we can tell if Einstein had the last word on gravity or not”, he says.

Prof Richard Schilizzi, the International SKA Project Director, stresses the scale of the instrument needed to fulfil these science goals. “Designing and then building, such an enormous technologically-advanced instrument is beyond the scope of individual nations. Only by harnessing the ideas and resources of countries around the world is such a project possible”. Astronomers in Australia, South Africa, Canada, India, China and the USA are collaborating closely with colleagues in Europe to develop the required technology which will include sophisticated electronics and powerful computers that will play a far bigger role than in the present generation of radio telescopes. The European effort is based on phased array receivers, similar to those in aircraft radar systems. When placed at the focus of conventional mass-produced radio ‘dishes’, these arrays operate like wide-angle radio cameras enabling huge areas of sky to be observed simultaneously. A separate, much larger, phased array at the centre of the SKA will act like a radio fish-eye lens, constantly scanning the sky.

Funding for this global design programme has been provided by the European Commission’s Framework 6 ‘Design Studies’ programme, which is contributing about 27% of the total ?38M funding over the next four years. Individual countries are contributing the remainder. The UK has invested ?5.6M (?8.3M) funding provided by PPARC.
When coupled with the UK’s share of the EC contribution, then the UK’s overall contribution to the SKA Design Study (SKADS) programme is about 30% of the total.

The ?38M European technology development programme is funded by the European Commission and governments in eight countries led by the Netherlands, the UK, France and Italy. The programme is being coordinated by Ir. Arnold van Ardenne, Head of Emerging Technologies at The Netherlands ASTRON Institute. In van Ardenne’s view “the critical task is to demonstrate that large numbers of electronic arrays can be built cost effectively – so that our dreams of radio cameras and radio fish-eye lenses can be turned into reality”.

In the UK, a group of universities currently including Manchester, Oxford, Cambridge, Leeds and Glasgow, funded by PPARC, is involved in all aspects of the design but is concentrating on sophisticated digital phased arrays and the distribution and analysis of the enormous volumes of data which the SKA will produce. University of Cambridge’s Dr Paul Alexander makes the point that “the electronics in the SKA makes it very flexible and allows for completely new ways of scanning the sky. But to make it work will require massive computing power”. Designers believe that by the time the SKA reaches full operation, 14 years from now, a new generation of computers will be up to the task.

The geographical location of SKA will be decided in the mid-term future and several nations have already expressed interest in hosting this state of the art astronomical facility.

Original Source: PPARC News Release

Posted on by Fraser Cain

New Horizons Blasts Off for Pluto

Liftoff of the Atlas V carrying NASA’s New Horizons spacecraft. Image credit: NASA/KSC Click to enlarge
The first mission to distant planet Pluto is under way after the successful launch today of NASA’s New Horizons spacecraft from Cape Canaveral Air Force Station, Fla.

New Horizons roared into the afternoon sky aboard a powerful Atlas V rocket at 2 p.m. EST. It separated from its solid-fuel kick motor 44 minutes, 53 seconds after launch, and mission controllers at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., where the spacecraft was designed and built, received the first radio signals from New Horizons a little more than five minutes later. The radio communications, sent through NASA’s Deep Space Network antennas in Canberra, Australia, confirmed to controllers that the spacecraft was healthy and ready to begin initial operations.

“Today, NASA began an unprecedented journey of exploration to the ninth planet in the solar system,” says Dr. Colleen Hartman, deputy associate administrator for NASA’s Science Mission Directorate, Washington, D.C. “Right now, what we know about Pluto could be written on the back of a postage stamp. After this mission, we’ll be able to fill textbooks with new information.”

The 1,054-pound, piano-sized spacecraft is the fastest ever launched, speeding away from Earth at approximately 36,000 miles per hour, on a trajectory that will take it more than 3 billion miles toward its primary science target. New Horizons will zip past Jupiter for a gravity assist and science studies in February 2007, and conduct the first close-up, in-depth study of Pluto and its moons in summer 2015. As part of a potential extended mission, the spacecraft would then examine one or more additional objects in the Kuiper Belt, the region of ancient, icy, rocky bodies (including Pluto) far beyond Neptune?s orbit.

“The United States of America has just made history by launching the first spacecraft to explore Pluto and the Kuiper Belt beyond,” says Dr. Alan Stern, New Horizons principal investigator, from Southwest Research Institute in Boulder, Colo. No other nation has this capability. This is the kind of exploration that forefathers like Lewis and Clark, 200 years ago this year, made a trademark of our nation.”

Over the next several weeks, mission operators at APL will place the spacecraft in flight mode, check out its critical operating systems and perform small propulsive maneuvers to refine its path toward Jupiter. Following that, among other operations, the team will begin checking and commissioning most of the seven science instruments.

“This is the gateway to a long, exciting journey,” says Glen Fountain, New Horizons project manager from APL. “The team has worked hard for the past four years to get the spacecraft ready for the voyage to Pluto and beyond, to places we’ve never seen up close. This is a once-in-a-lifetime opportunity, in the tradition of the Mariner, Pioneer, and Voyager missions to set out for first looks in our solar system.”

After the Jupiter encounter ? during which New Horizons will train its science instruments on the large planet and its moons ?? the spacecraft will “sleep” in electronic hibernation for much of the cruise to Pluto. Operators will turn off all but the most critical electronic systems and check in with the spacecraft once a year to check out the critical systems, calibrate the instruments and perform course corrections, if necessary.

Between the in-depth checkouts, New Horizons will send back a beacon signal each week to give operators an instant read on spacecraft health. The entire spacecraft, drawing electricity from a single radioisotope thermoelectric generator, operates on less power than a pair of 100-watt household light bulbs.

New Horizons is the first mission in NASA’s New Frontiers Program of medium-class spacecraft exploration projects. Stern leads the mission and science team as principal investigator. APL manages the mission for NASA’s Science Mission Directorate and is operating the spacecraft in flight. The mission team also includes Ball Aerospace Corporation, the Boeing Company, NASA Goddard Space Flight Center, NASA Jet Propulsion Laboratory, Stanford University, KinetX, Inc., Lockheed Martin Corporation, University of Colorado, the U.S. Department of Energy, and a number of other firms, NASA centers, and university partners.

Original Source: APL News Release

Posted on by Fraser Cain

Self-Repairing Spacecraft

A time lapse sequence of self-repair taking place. Image credit: ESA Click to enlarge
Building spacecraft is a tough job. They are precision pieces of engineering that have to survive in the airless environment of space, where temperatures can swing from hundreds of degrees Celsius to hundreds of degree below zero in moments. Once a spacecraft is in orbit, engineers have virtually no chance of repairing anything that breaks. But what if a spacecraft could fix itself?

Thanks to a new study funded by ESA’s General Studies Programme, and carried out by the Department of Aerospace Engineering, University of Bristol, UK, engineers have taken a step towards that amazing possibility. They took their inspiration from nature.

“When we cut ourselves we don’t have to glue ourselves back together, instead we have a self-healing mechanism. Our blood hardens to form a protective seal for new skin to form underneath,” says Dr Christopher Semprimoschnig, a materials scientist at ESA’s European Space Technology Research Centre (ESTEC) in the Netherlands, who oversaw the study.

He imagined such cuts as analogous to the ‘wear-and-tear’ suffered by spacecraft. Extremes of temperature can cause small cracks to open in the superstructure, as can impacts by micrometeroids – small dust grains travelling at remarkable speeds of several kilometres per second. Over the lifetime of a mission the cracks build up, weakening the spacecraft until a catastrophic failure becomes inevitable.

The challenge for Semprimoschnig was to replicate the human process of healing small cracks before they can open up into anything more serious. He and the team at Bristol did it by replacing a few percent of the fibres running through a resinous composite material, similar to that used to make spacecraft components, with hollow fibres containing adhesive materials. Ironically, to make the material self-repairable, the hollow fibres had to be made of an easily breakable substance: glass. “When damage occurs, the fibres must break easily otherwise they cannot release the liquids to fill the cracks and perform the repair,” says Semprimoschnig.

In humans, the air chemically reacts with the blood, hardening it. In the airless environment of space, alternate mechanical veins have to be filled with liquid resin and a special hardener that leak out and mix when the fibres are broken. Both must be runny enough to fill the cracks quickly and harden before it evaporates.

“We have taken the first step but there is at least a decade to go before this technology finds its way onto a spacecraft,” says Semprimoschnig, who believes that larger scale tests are now needed.

The promise of self-healing spacecraft opens up the possibility of longer duration missions. The benefits are two-fold. Firstly, doubling the lifetime of a spacecraft in orbit around Earth would roughly halve the cost of the mission. Secondly, doubling spacecraft lifetimes means that mission planners could contemplate missions to far-away destinations in the Solar System that are currently too risky.

In short, self-healing spacecraft promise a new era of more reliable spacecraft, meaning more data for scientists and more reliable telecommunication possibilities for us all.

Original Source: ESA Portal

Posted on by Fraser Cain

Saturnian Storms About to Merge

Saturnian storms swirling in the region “storm alley”. Image credit: NASA/JPL/SSI Click to enlarge
Two Saturnian storms swirl in the region informally dubbed “storm alley” by scientists. This mid-latitude region has been active with storms since Cassini scientists began monitoring Saturn in early 2004.

The large storm at left is at least 2,500 kilometers (1,600 miles) across from north to south. This is bigger than typical storms in the region, which are the size of large Earth hurricanes, or about 1,000 kilometers (600 miles) across. To the left, the smaller storm is about 700 kilometers (400 miles) across.

The two storms are interacting. Their threadlike arms are intertwined, and they might have merged a few days after this image was taken. See PIA06082 and PIA06083 for movies of storm activity in this region.

The image was taken with the Cassini spacecraft narrow-angle camera on Dec. 9, 2005, at a distance of approximately 3.2 million kilometers (2 million miles) from Saturn. The image was obtained using a filter sensitive to wavelengths of infrared light centered at 727 nanometers. The image scale is 38 kilometers (23 miles) per pixel.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org .

Original Source: NASA/JPL/SSI News Release

Posted on by Fraser Cain

Asteroid Broke Up 8.2 Million Years Ago

The Earth. Image credit: NASA Click to enlarge
In a new study that provides a novel way of looking at our solar system’s past, a group of planetary scientists and geochemists announce that they have found evidence on Earth of an asteroid breakup or collision that occurred 8.2 million years ago.

Reporting in the January 19 issue of the journal Nature, scientists from the California Institute of Technology, the Southwest Research Institute (SwRI), and Charles University in the Czech Republic show that core samples from oceanic sediment are consistent with computer simulations of the breakup of a 100-mile-wide body in the asteroid belt between Mars and Jupiter. The larger fragments of this asteroid are still orbiting the asteroid belt, and their hypothetical source has been known for years as the asteroid “Veritas.”

Ken Farley of Caltech discovered a spike in a rare isotope known as helium 3 that began 8.2 million years ago and gradually decreased over the next 1.5 million years. This information suggests that Earth must have been dusted with an extraterrestrial source.

“The helium 3 spike found in these sediments is the smoking gun that something quite dramatic happened to the interplanetary dust population 8.2 million years ago,” says Farley, the Keck Foundation Professor of Geochemistry at Caltech and chair of the Division of Geological and Planetary Sciences. “It’s one of the biggest dust events of the last 80 million years.”

Interplanetary dust is composed of bits of rock from a few to several hundred microns in diameter produced by asteroid collisions or ejected from comets. Interplanetary dust migrates toward the sun, and en route some of this dust is captured by the Earth’s gravitational field and deposited on its surface.

Presently, more than 20,000 tons of this material accumulates on Earth each year, but the accretion rate should fluctuate with the level of asteroid collisions and changes in the number of active comets. By looking at ancient sediments that include both interplanetary dust and ordinary terrestrial sediment, the researchers for the first time have been able to detect major dust-producing solar system events of the past.

Because interplanetary dust particles are so small and rare in sediment-significantly less than a part per million-they are difficult to detect using direct measurements. However, these particles are extremely rich in helium 3, in comparison with terrestrial materials. Over the last decade, Ken Farley has measured helium 3 concentrations in sediments formed over the last 80 million years to create a record of the interplanetary dust flux.

To assure that the peak was not a fluke present at only one site on the seafloor, Farley studied two different localities: one in the Indian Ocean and one in the Atlantic. The event is recorded clearly at both sites.

To find the source of these particles, William F. Bottke and David Nesvorny of the SwRI Space Studies Department in Boulder, Colorado, along with David Vokrouhlicky of Charles University, studied clusters of asteroid orbits that are likely the consequence of ancient asteroidal collisions.

“While asteroids are constantly crashing into one another in the main asteroid belt,” says Bottke, “only once in a great while does an extremely large one shatter.”

The scientists identified one cluster of asteroid fragments whose size, age, and remarkably similar orbits made it a likely candidate for the Earth-dusting event. Tracking the orbits of the cluster backwards in time using computer models, they found that, 8.2 million years ago, all of its fragments shared the same orbital orientation in space. This event defines when the 100-mile-wide asteroid called Veritas was blown apart by impact and coincides with the spike in the interplanetary seafloor sediments Farley had found.

“The Veritas disruption was extraordinary,” says Nesvorny. “It was the largest asteroid collision to take place in the last 100 million years.”

As a final check, the SwRI-Czech team used computer simulations to follow the evolution of dust particles produced by the 100-mile-wide Veritas breakup event. Their work shows that the Veritas event could produce the spike in extraterrestrial dust raining on the Earth 8.2 million years ago as well as a gradual decline in the dust flux.

“The match between our model results and the helium 3 deposits is very compelling,” Vokrouhlicky says. “It makes us wonder whether other helium 3 peaks in oceanic cores can also be traced back to asteroid breakups.”

This research was funded by NASA’s Planetary Geology and Geophysics program and received additional financial support from Czech Republic grant agency and the National Science Foundation’s COBASE program. The Nature paper is titled “A late Miocene dust shower from the breakup of an asteroid in the main belt.”

Original Source: caltech News Release

Posted on by Fraser Cain

Juventae Chasma on Mars

The depression of Juventae Chasma taken by HRSC. Image credit: ESA Click to enlarge
These images, taken by the High Resolution Stereo Camera (HRSC) on board ESA’s Mars Express spacecraft, show the depression of Juventae Chasma, cut into the plains of Lunae Planum on Mars.

The HRSC obtained these images during orbit 243 with a ground resolution of approximately 23.4 metres per pixel. The scenes show the region of Lunae Planum, at approximately 5? South and 297? East.

The depression of Juventae Chasma, located north of Valles Marineris, cuts more than 5000 metres into the plains of Lunae Planum. The floor of Juventae Chasma is partly covered by dunes.

In the valley, to the north-east, there is a mountain composed of bright, layered material. This mountain is approximately 2500 metres high, it has a length of 59 kilometres and a width of up to 23 kilometres.

The OMEGA spectrometer on board Mars Express will be able to confirm that this mountain is indeed composed of sulphate deposits. The colour scenes have been derived from the three HRSC-colour channels and the nadir channel.

***image4:left***The perspective views have been calculated from the digital terrain model derived from the stereo channels. The 3D anaglyph image was calculated from the nadir and one stereo channel. Image resolution has been decreased for use on the internet.

Original Source: ESA Mars Express

Posted on by Fraser Cain

Kuiper Belt-Like Disks Around Two Nearby Stars

Two debris disks resemble the Kuiper Belt. Image credit: UC Berkeley Click to enlarge
A survey by NASA’s Hubble Space Telescope of 22 nearby stars has turned up two with bright debris disks that appear to be the equivalent of our own solar system’s Kuiper Belt, a ring of icy rocks outside the orbit of Neptune and the source of short-period comets.

The debris disks encircling these stars fall into two categories – wide and narrow belts – that appear to describe all nine stars, including the sun, which are known to have debris disks linked to planet formation. In fact, the sharp outer edges of the narrow belts, such as the Kuiper Belt in our solar system, may be a tip-off to the existence of a star-like companion that continually grooms the edge, in the same way that shepherding moons trim the edges of debris rings around Saturn and Uranus.

Research astronomer Paul Kalas, professor of astronomy James Graham and graduate student Michael Fitzgerald of the University of California, Berkeley, along with Mark C. Clampin of Goddard Space Flight Center in Greenbelt, Md., will report their discovery and conclusions in the Jan. 20 issue of Astrophysical Journal Letters.

The newfound stellar disks, each about 60 light years from Earth, bring to nine the number of stars with dusty debris disks observable at visible wavelengths. The new ones are different, however, in that they are old enough – more than 300 million years – to have settled into stable configurations akin to the stable planet and debris orbits in our own solar system, which is 4.6 billion years old. The other seven, except for the sun, range from tens of millions to 200 million years old – young by solar standards.

In addition, the masses of the stars are closer to that of the sun.

“These are the oldest debris disks seen in reflected light, and are important because they show what the Kuiper Belt might look like from the outside,” said Kalas, the lead researcher. “These are the types of stars around which you would expect to find habitable zones and planets that could develop life.”

Most debris disks are lost in the glare of the central star, but the high resolution and sensitivity of the Hubble Space Telescope’s Advanced Camera for Surveys has made it possible to look for these disks after blocking the light from the star. Kalas has discovered debris disks around two other stars (AU Microscopii and Fomalhaut) in the past two years, one of them with the Hubble telescope, and has studied details of most of the other known stars with disks.

“We know of 100-plus stars that have infrared emission in excess of that emitted from the star, and that excess thermal emission comes from circumstellar dust,” Kalas said. “The hard part is obtaining resolved images that give spatial information. Now, two decades after they were first discovered, we are finally beginning to see the dust disks. These recent detections are really a tribute to all the hard work that went into upgrading Hubble’s instruments during the last servicing mission.”

The small sampling already shows that such disks fall into two categories: those with a broad belt, wider than about 50 astronomical units; and narrow ones with a width of between 20 and 30 AU and a sharp outer boundary, probably like our own Kuiper Belt. An astronomical unit, or AU, is the average distance between the Earth and sun, about 93 million miles. Our Kuiper Belt is thought to be narrow, extending from the orbit of Neptune at 30 AU to about 50 AU.

Most of the known debris disks seem to have a central area cleared of debris, perhaps by planets, which are likely responsible for the sharp inner edges of many of these belts.

Kalas and Graham speculate that stars also having sharp outer edges to their debris disks have a companion – a star or brown dwarf, perhaps – that keeps the disk from spreading outward, similar to the way that Saturn’s moons shape the edges of many of the planet’s rings.

“The story of how you make a ring around a planet could be the same as the story of making rings around a star,” Kalas said. Only one of the nine stars is known to have a companion, but then, he said, no one has yet looked at most of these stars to see if they have faint companions at large distances from the primary star.

He suggests that a stray star passing by may have ripped off the edges of the original planetary disk, but a star-sized companion would be necessary to keep the remaining disk material, such as asteroids, comets and dust, from spreading outward.

If true, that would mean that the sun also has a companion keeping the Kuiper Belt confined within a sharp boundary. Though a companion star has been proposed before – most recently by UC Berkeley physics professor Richard Muller, who dubbed the companion Nemesis – no evidence has been found for such a companion.

A key uncertainty, Kalas said, is that while we can see many of the large planetesimals in our Kuiper Belt, we can barely detect the dust.

“Ironically, our own debris disk is the closest, yet we know the least about it,” he said. “We would really like to know if dust in our Kuiper Belt extends significantly beyond the 50 AU edge of the larger objects. When we acquire this information, only then will we be able to place our sun correctly in the wide or narrow disk categories.”

The star survey by Kalas, Graham, Fitzgerald and Clampin was one of the first projects of the Advanced Camera for Surveys aboard the Hubble, which was installed in 2002. The 22 stars were observed over a two year period ending in September 2004. The stars with debris disks detectable in visible light were HD 53143, a K star slightly smaller than the sun but about 1 billion years old, and HD 139664, an F star slightly larger than the sun but only 300 million years old.

“One is a K star and the other is an F star, therefore they are more likely to form planetary systems with life than the massive and short-lived stars such as beta-Pictoris and Fomalhaut,” he noted. “When we look at HD 53143 and HD 139664, we may be looking at astrophysical mirrors to our Kuiper Belt.”

The disk around the oldest of the two stars, HD 53143, is wide like that of beta-Pictoris (beta-Pic), which was the first debris disk ever observed, about 20 years ago, and AU Microscopii (AU Mic), which Kalas discovered last year. Both beta-Pic and AU Mic are about 10 million years old.

The disk around HD 139664, however, is a narrow belt, similar to the disk around the star Fomalhaut, which Kalas imaged for the first time early last year. HD 139664 has a very sharp outer edge at 109 AU, similar to the sharp outer edge of our Kuiper Belt at 50 AU. The belt around HD 139664 starts about 60 AU from the star and peaks in density at 83 AU.

“If we can understand the origin of the sharp outer edge around HD 139664, we might better understand the history of our solar system,” Kalas said.

The research was supported by grants from NASA through the Space Telescope Science Institute.

Original Source: UC Berkeley News Release