Posted on by Fraser Cain

There Might Not Be Ice at the Moon’s Pole

Image credit: Cornell University

At the South Pole of the Moon, there is a region that is always in the shadow of craters which scientists have long believed could have deposits of water ice. Despite the fact that ice was detected by two spacecraft that orbited the moon, a new survey of the area by the giant Arecibo radio observatory has failed to find any surface deposits of ice. This doesn’t mean that the ice isn’t there, but it might be trapped in a large area under the surface, like lunar permafrost. Arecibo is a good instrument for detecting ice because it gives a very specific echo signature in the radio spectrum.

Despite evidence from two space probes in the 1990s, radar astronomers say they can find no signs of thick ice at the moon’s poles. If there is water at the lunar poles, the researchers say, it is widely scattered and permanently frozen inside the dust layers, something akin to terrestrial permafrost.

Using the 70-centimeter (cm)-wavelength radar system at the National Science Foundation’s (NSF) Arecibo Observatory, Puerto Rico, the research group sent signals deeper into the lunar polar surface — more than five meters (about 5.5 yards) — than ever before at this spatial resolution. “If there is ice at the poles, the only way left to test it is to go there directly and melt a small volume around the dust and look for water with a mass spectrometer,” says Bruce Campbell of the Center for Earth and Planetary Studies at the Smithsonian Institution.

Campbell is the lead author of an article, “Long-Wavelength Radar Probing of the Lunar Poles,” in the Nov. 13, 2003, issue of the journal Nature . His collaborators on the latest radar probe of the moon were Donald Campbell, professor of astronomy at Cornell University; J.F. Chandler of Smithsonian Astrophysical Observatory; and Alice Hine, Mike Nolan and Phil Perillat of the Arecibo Observatory, which is managed by the National Astronomy and Ionosphere Center at Cornell for the NSF.

Suggestions of lunar ice first came in 1996 when radio data from the Clementine spacecraft gave some indications of the presence of ice on the wall of a crater at the moon’s south pole. Then, neutron spectrometer data from the Lunar Prospector spacecraft, launched in 1998, indicated the presence of hydrogen, and by inference, water, at a depth of about a meter at the lunar poles. But radar probes by the 12-cm-wavelength radar at Arecibo showed no evidence of thick ice at depths of up to a meter. “Lunar Prospector had found significant concentrations of hydrogen at the lunar poles equivalent to water ice at concentrations of a few percent of the lunar soil,” says Donald Campbell. “There have been suggestions that it may be in the form of thick deposits of ice at some depth, but this new data from Arecibo makes that unlikely.”

Says Bruce Campbell, “There are no places that we have looked at with any of these wavelengths where you see that kind of signature.”

The Nature paper notes that if ice does exist at the lunar poles it would be considerably different from “the thick, coherent layers of ice observed in shadowed craters on Mercury,” found in Arecibo radar imaging. “On Mercury what you see are quite thick deposits on the order of a meter or more buried by, at most, a shallow layer of dust. That’s the scenario we were trying to nail down for the moon,” says Bruce Campbell. The difference between Mercury and the moon, the researchers say, could be due to the lower average rate of comets striking the lunar surface, to recent comet impacts on Mercury or to a more rapid loss of ice on the moon.

What makes the lunar poles good cold traps for water is a temperature of minus 173 degrees Celsius (minus 280 degrees Fahrenheit). The limb of the sun rises only about two degrees above the horizon at the lunar poles so that sunlight never penetrates into deep craters, and a person standing on the crater floor would never see the sun. The Arecibo radar probed the floors of two craters in permanent shadow at the lunar south pole, Shoemaker and Faustini, and, at the north pole, the floors of Hermite and several small craters within the large crater Peary. In contrast, Clementine focused on the sloping walls of Shackleton crater, whose floor can’t be “seen” from Earth. “There is a debate on how to interpret data from a rough, tilted surface,” says Bruce Campbell.

The Arecibo radar probe is a particularly good detector of thick ice because it takes advantage of a phenomenon known as “coherent backscatter.” Radar waves can travel long distances without being absorbed in ice at temperatures well below freezing. Reflections from irregularities inside the ice produce a very strong radar echo. In contrast, lunar soil is much more absorptive and does not give as strong a radar echo.

Original Source: Cornell News Release

Posted on by Fraser Cain

Mars Express is Nearly There

Image credit: ESA

The European Space Agency’s mission to Mars, Mars Express, is right on schedule to arrive at the Red Planet on December 25, 2003. The British-built Beagle 2 lander will also reach Mars the same day, but it will be released from Mars Express on December 19. Beagle 2 doesn’t have any propulsion system of its own, so it’s critical that Mars Express releases it on the right trajectory. It will plunge through Mars’ atmosphere, deploy a parachute, and then land on the surface with the help of an airbag. Assuming everything went well, it will then be able to start examining rocks searching for evidence of life.

Europe’s mission to the Red Planet, Mars Express, is on schedule to arrive at the planet on Christmas Day, 2003.

The lander, Beagle 2, is due to descend through the Martian atmosphere and touch down also on 25 December.

Mars Express is now within 20 million kilometres of the Red Planet and the next mission milestone comes on 19 December, when Mars Express will release Beagle 2. The orbiter spacecraft will send Beagle 2 spinning towards the planet on a precise trajectory.

Into orbit
Beagle has no propulsion system of its own, so it relies on correct aiming by the orbiter to find its way to the planned landing site, a flat basin in the low northern latitudes of Mars.

ESA engineers will then fire the orbiter’s main engine in the early hours of 25 December to put Mars Express into orbit around Mars (called Mars Orbit Insertion, or MOI).

Landing
When Beagle 2 begins its descent, it will be slowed by friction with the Martian atmosphere. Nearer to the surface, parachutes will deploy and large gas-filled bags will inflate to cushion the final touchdown. Beagle 2 should bounce to a halt on Martian soil early on Christmas morning.

The first day on Mars is important for the lander because it has only a few hours to collect enough sunlight with its solar panels to recharge its battery.

Waiting for signal
We then have to wait for the radio ‘life’ signal from Beagle 2, relayed through the US Mars Odyssey spacecraft, to see if the probe has survived the landing. This could take hours or even days.

If nothing is received on Christmas morning, the UK Jodrell Bank Telescope will search for the faint radio signal from Beagle 2 in the evening. The Mars Express orbiter can also search for the lander but, because of its orbit, it will not be in place to do this until early January.

If all goes well, Mars Express and Beagle 2 will then begin their main mission – trying to answer the questions of whether there has been water, and possibly life, on Mars.

Original Source: ESA News Release

Posted on by Fraser Cain

New Dark Matter Detectors

Image credit: Fermilab

Astronomers don’t know what Dark Matter is, but they can see the effect of its gravity on regular matter. One possibility is that it’s regular matter, but isn’t emitting enough light for us to see. Another idea is that Dark Matter is an exotic form of matter that’s much more massive than regular particles, but interact so weakly that they’re almost impossible to detect. Researchers with the Cryogenic Dark Matter Search II have set up a series of detectors in an old iron mine in Minnesota that’s shielded from cosmic radiation and might sense these particles.

Using detectors chilled to near absolute zero, from a vantage point half a mile below ground, physicists of the Cryogenic Dark Matter Search today (November 12) announced the launch of a quest that could lead to solving two mysteries that may turn out to be one and the same: the identity of the dark matter that pervades the universe, and the existence of supersymmetric particles predicted by particle physics theory. Scientists of CDMS II, an experiment managed by the Department of Energy’s Fermi National Accelerator Laboratory hope to discover WIMPs, or weakly interacting massive particles, the leading candidates for the constituents of dark matter-which may be identical to neutralinos, undiscovered particles predicted by the theory of supersymmetry.

“There’s this arrow from particle physics and this arrow from cosmology and they seem to be pointing to the same place,” said Case Western Reserve University’s Dan Akerib, deputy project manager of CDMS II. “Detection of a neutralino would be very big for cosmology and it would also be very big for particle physics.”

The CDMS II experiment, a collaboration of scientists from 12 institutions with support from DOE’s Office of Science and the National Science Foundation, uses a detector located deep underground in the historic Soudan Iron Mine in northeastern Minnesota. Experimenters seek signals of WIMPs, particles much more massive than a proton but interacting so weakly with other particles that thousands would pass through a human body each second without leaving a trace.

Remarkably, in the kind of convergence that gets physicists’ attention, the characteristics of this cosmic missing matter particle now appear to match those of the supersymmetric neutralino.

“Either that is a cosmic coincidence, or the universe is telling us something,” said Fermilab’s Dan Bauer, CDMS project manager.

By watching how galaxies spin-how gravity affects their contingent stars-astronomers have known for 70 years that the matter we see cannot constitute all the matter in the universe. If it did, galaxies would fly apart. Recent calculations indicate that ordinary matter containing atoms makes up only 4 percent of the energy-matter content of the universe. “Dark energy” makes up 73 percent, and an unknown form of dark matter makes up the last 23 percent.

“It is often said that this is the ultimate Copernican Revolution,” said David Caldwell, a physicist at the University of California at Santa Barbara and chair of the CDMS Executive Committee. “Not only are we not at the center of the universe, but we are not even made of the same stuff as most of the universe.”

Measurements of the cosmic microwave background, residual radiation left over from the Big Bang, have recently placed severe constraints on the nature and amount of dark matter. The lightweight neutrino can account for only a few percent of the missing mass. If neutrinos constituted the main component of dark matter, they would act on the cosmic microwave background of the universe in ways that the recent Wilkinson Microwave Anisotropy Probe should have observed-but did not.

Meanwhile, particle physicists have kept a lookout for particles that will extend the Standard Model, the theory of fundamental particles and forces. Supersymmetry, a theory that takes a big step toward the unification of all of the forces of nature, predicts that every matter particle has a massive supersymmetric counterpart. No one has yet seen one of these “superpartners.” Theory specifies the neutralino as the lightest neutral superpartner, and the most stable, a necessary attribute for dark matter. The neutralino’s predicted abundance and rate of interaction also make it a likely dark matter candidate, and Caldwell noted the impact that CDMS II could have.

“Discovery,” he said, “would be a great breakthrough, one of the most important of the century.”

Only occasionally would a WIMP hit the nucleus of a terrestrial atom, and the constant background “noise” from more mundane particle events-such as the common cosmic rays constantly showering the earth-would normally drown out these rare interactions. Placing the CDMS II detector beneath 740 meters of earth screens out most particle noise from cosmic rays. Chilling the detector to 50 thousandths of a degree above absolute zero reduces background thermal energy to allow detection of individual particle collisions. Fermilab’s Bauer estimates that with sufficiently low backgrounds, CDMS needs only a few interactions to make a strong claim for detection of WIMPs.

“The powerful technology we deploy allows an unambiguous identification of events in the crystals caused by any new form of matter,” said CDMS cospokesperson Bernard Sadoulet of the University of California at Berkeley.

Cospokesperson Blas Cabrera of Stanford University concurred.

“We believe we have the best apparatus in the world in terms of being able to identify WIMPs,” Cabrera said.

“This endeavor is a good example of cooperation between the DOE’s Office of High Energy Physics and the National Science Foundation in helping scientists address the origin of the dark matter in the universe,” said Raymond Orbach, Director of the Department of Energy’s Office of Science.

“CDMS II is the kind of innovative and pathbreaking research NSF is proud to support,” said Michael Turner, Assistant Director for Math and Physical Sciences at the National Science Foundation. “If it detects a signal it may tell us what the dark matter is and give us an important clue as to how gravity fits together with the other forces. This type of experiment shows how the universe can be used as a laboratory for getting at the some of the most basic questions we can ask as well as how DOE and NSF are working together.”

While CDMS II watches for WIMPs, scientists at Fermilab’s Tevatron particle accelerator will try to create neutralinos by smashing protons and antiprotons together.

“CDMS can tell us the mass and interaction rate of the WIMP,” said collaborator Roger Dixon of Fermilab. “But it will take an accelerator to tell us whether it’s a neutralino.”

CDMS II collaborators include Brown University, Case Western Reserve University, Fermi National Accelerator Laboratory, Lawrence Berkeley National Accelerator Laboratory, National Institute of Standards and Technology, Princeton University, Santa Clara University, Stanford University, University of California at Berkeley, University of California at Santa Barbara, University of Colorado at Denver, University of Minnesota.

Funding for the CDMS II experiment comes from the Office of Science of the U.S. Department of Energy and the Astronomy and Physics Division of the National Science Foundation.

Fermilab is a national laboratory funded by the Office of Science of the U.S. Department of Energy and operated by Universities Research Association, Inc.

Original Source: Fermilab News Release

Posted on by Fraser Cain

Pleiades Could Be Three Objects Colliding Together

Image credit: NOAO

The Pleiades star cluster has long been a favorite of astronomers, as it’s clearly visible with the naked eye, and looks even better in small telescopes and binoculars. The cluster’s wispy appearance comes from the fact that the stars are surrounded by a faint nebula. By tracking the motion of the stars and the cloud, a team of astronomers have discovered that the area is being formed by multiple clouds colliding together in the same region.

The naked-eye Pleiades star cluster has long been known to professional and amateur astronomers for the striking visible nebulosity that envelopes the cluster?s brightest stars, scattering their light like fog around a streetlamp.

Radio and infrared observations in the 1980s established that this nebulosity results from a chance encounter by the young stars of the Pleiades with an interstellar cloud, rather than being caused by debris from the cluster?s formation. New data obtained at Kitt Peak National Observatory suggest that the Pleiades are actually encountering two clouds, giving rise to an extraordinary and previously unknown occurrence: a three-body collision in the vast emptiness of interstellar space.

This new perspective on the motion of interstellar gas near the cluster comes from high-resolution spectra obtained at an adjunct facility of Kitt Peak?s 2.1-meter telescope known as the Coud? Feed. The investigator was Richard White of Smith College in Northampton, MA, who worked in collaboration with students from Smith College and Amherst College.

?The idea of the Pleiades and one gas cloud in an interstellar train wreck already made this nearby cluster an especially interesting region for astronomers seeking to understand the details of physical and chemical processes in the interstellar medium,? White says. ?The presence of a second cloud interacting with the first cloud and with the cluster creates a situation more like a three-car crash in a demolition derby, which makes the Pleiades altogether unique as natural laboratory.?

The time scale for the unfolding of the interstellar collisions in the Pleiades is several hundred thousand years. ?That is good news for those who enjoy the magnificent color images of the Pleiades images that grace textbooks and coffee table books, which suffer no danger of obsolescence,? White says. ?It is bad news for those who would like to see celestial fireworks unfolding from year to year.?

Known as the Seven Sisters for the seven stars said to be visible with the naked eye, the Pleiades (M45) consists of more than 500 stars roughly 100 million years old in a cluster located about 400 light-years from Earth.

Sodium atoms in gas found between Earth and the stars absorb two specific wavelengths of yellow starlight (the same wavelengths of yellow light emitted by low-pressure sodium streetlamps). Because of the Doppler effect (analogous to the shift in siren pitch produced when an ambulance is moving toward or away from a listener), the motion of the gas along our line of sight produces subtle shifts in the observed wavelengths.

In a paper published in the October 2003 Astrophysical Journal Supplement, White interprets the new observations of sodium atoms in the Pleiades region in the context of other recent observations of the Pleiades region. These observations include significant new optical images of the Pleiades from the Burrell Schmidt telescope on Kitt Peak, published earlier this year in the Astrophysical Journal by Steven Gibson of the University of Calgary and Kenneth Nordsieck of the University of Wisconsin, and radio maps of neutral hydrogen that formed part of Gibson?s doctoral thesis.

The orientation of features in the optical and radio imagery provides clues to gas and dust motions across the sky, which can be combined with the spectroscopically measured velocities from Kitt Peak to allow astronomers to reconstruct the three-dimensional configuration of the interstellar matter near the Pleiades.

The sodium absorption lines reveal that there always is one feature between Earth and the Pleiades stars, moving toward the cluster with a line of sight velocity of about 10 kilometers per second. White associates this feature with the Taurus-Auriga interstellar cloud complex, the bulk of which lies about 40 light-years to the east.

Toward some stars, however, there are two or more absorption features. White argues that a shock-wave from the collision between the Pleiades and gas associated with the Taurus-Auriga complex can account for splitting of one feature into three in some areas, primarily on the south and east sides of the Pleiades. However, the presence of an additional feature in the data, primarily on the west side and moving into the cluster at about 12 kilometers per second, defies understanding unless a second cloud also is converging on the Pleiades, he concludes.

The only previously known three-body collisions in interstellar space are inferred close encounters by a star and a neighboring binary or triple star system within a globular cluster or in the cores of galaxies.

Previously released images of the Pleiades from Kitt Peak that amply demonstrate the surrounding nebulosity are available in the NOAO Image Gallery (linked above).

Located southwest of Tucson, AZ, Kitt Peak National Observatory is part of the National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under a cooperative agreement with the National Science Foundation.

Original Source: NOAO News Release

Posted on by Fraser Cain

Nearby Star is Forming a Jupiter-Like Planet

Image credit: UA

Astronomers from the University of Arizona have used a new technique called “nulling interferometry” to reveal the planetary disk around a newly-forming star. Incredibly, they discovered a gap in the disk, where a Jupiter-like planet is probably forming. This nulling technique works by combining the light from the central star in such a way that it gets canceled out. This allows fainter objects, such as dust and planets to be observed. The planet is likely several times the mass of Jupiter and orbits its star at about 1.5 billion kilometers.

University of Arizona astronomers have used a new technique called nulling interferometry to probe a dust disk around a young nearby star for the first time. They not only confirmed that the young star does have a protoplanetary disk — the stuff from which solar systems are born — but discovered a gap in the disk, which is strong evidence of a forming planet.

“It’s very exciting to find a star that we think should be forming planets, and actually see evidence of that happening,” said UA astronomer Philip Hinz.

“The bottom line is, we not only confirmed the hypothesis that this young star has a protoplanetary disk, we found evidence that a giant, Jupiter-like protoplanet is forming in this disk,” said Wilson Liu, a doctoral student and research assistant on the project.

“There’s evidence that this star is right on the cusp of becoming a main-sequence star,” Liu added. “So basically, we’re catching a star that is right at the point of becoming a main-sequence star, and it looks like it’s caught in the act of forming planets.”

Main-sequence stars are those like our sun that burn hydrogen at their cores.

Earlier this year, Hinz and Liu realized that observations of HD 100546 at thermal, or mid-infrared, wavelengths showed that the star had a dust disk.

Finding faint dust disks is “analogous to finding a lighted flashlight next to Arizona Stadium when the lights are on,” Liu said.

The nulling technique combines starlight in such a way that it is canceled out, creating a dark background where the star’s image normally would be. Because HD 100546 is such a young star, its dust disk is still relatively bright, about as bright as the star itself. The nulling technique is needed to distinguish what light comes from the star, which can be suppressed, and what comes from the extended dust disk, which nulling does not suppress.

Hinz and UA astronomers Michael Meyer, Eric Mamajek, and William Hoffmann took the observations in May 2002. They used BLINC, the only working nulling interferometer in the world, along with MIRAC, a state-of-the-art mid-infrared camera, on the 6.5-meter (21-foot) diameter Magellan telescope in Chile to study the roughly 10-million-year-old star in the Southern Hemisphere sky.

Typically, dust in disks around stars is uniformly distributed, forming a continuous, flattened, orbiting cloud of material that is hot on the inner edge but cold most of the distance to the frigid outer edge.

“The data reduction was complicated enough that we didn’t realize until later that there was an inner gap in the disk,” Hinz noted.

“We realized the disk appeared about the same size at warmer (10 micron) wavelengths and at colder (20 micron) wavelengths. The only way that could be is if there’s an inner gap.”

The most likely explanation for this gap is that it is created by the gravitational field of a giant protoplanet =AD an object that could be several times more massive than Jupiter. The researchers believe the protoplanet may be orbiting the star at perhaps 10 AU. (An AU, or astronomical unit, is the distance between Earth and the sun. Jupiter is about 5 AU from the sun.)

Astronomers from the Netherlands and Belgium had previously used the Infrared Space Observatory to study HD 100546, which is 330 light-years from Earth. They detected comet-like dust around the star and concluded that it might be a protoplanetary disk. But the European space telescope was too small to clearly see dust surrounding the star.

Hinz, who developed BLINC, has been using the nulling interferometer with two 6.5-meter telescopes for the past three years for his survey of nearby stars in search of protoplanetary systems. In addition to the Magellan telescope that covers the Southern Hemisphere, Hinz uses the 6.5-meter UA/Smithsonian MMT atop Mount Hopkins, Ariz., for the Northern Hemisphere sky.=20

Hinz developed BLINC as a technology demonstration for the Terrestrial Planet Finder mission, which is managed for NASA by the Jet Propulsion Laboratory, Pasadena, Calif. NASA, which funds Hinz’ survey, supports research on solar-system formation under its Origins program and is developing nulling interferometry for Terrestrial Planet Finder.

“Nulling interferometry is very exciting because it is one of only a few technologies that can directly image circumstellar environments,” Liu said.

Using MIRAC, the camera developed by William Hoffmann and others, was important because it is sensitive to mid-infrared wavelengths, Hinz said. Astronomers will have to look in mid-infrared wavelengths, which correspond to room temperatures, to find planets with liquid water and possible life, he said.

Hinz’ survey includes HD 100546 and other “Herbig Ae” stars, which are nearby young stars generally more massive than our sun, but are not yet main sequence stars powered by nuclear fusion.

Hinz and Liu plan to observe increasingly mature star systems, searching for ever-fainter circumstellar dust disks and planets, as they continue to improve nulling interferometry and adaptive optics technologies. Adaptive optics is a technique that eliminates the effects of Earth’s shimmering atmosphere from starlight.

Hinz and others at UA Steward Observatory are designing a nulling interferometer for the Large Binocular Telescope, which will view the sky with two 8.4-meter (27-foot) diameter mirrors on Mount Graham, Ariz., in 2005.

Original Source: UA News

Posted on by Fraser Cain

Spacedev Puts a Satellite Up for Sale on eBay

Image credit: SpaceDev

Satellite manufacturer SpaceDev announced today that it has put a satellite up for sale on the Internet auction site eBay. The high bidder will win a spacecraft built by SpaceDev, or an interested party can just “Buy it Now” for $9.5 million USD. The auction begins on Monday, November 10 and ends 10 days later. The default satellite will come with an Earth observation camera, but the winning bidder can supply additional payloads, name the satellite, and attend the launch.

SpaceDev (OTCBB: SPDV) is auctioning a world exclusive private space mission on eBay. This first of its kind eBay auction is being listed for the ten-day period of 8:00 PM (PST) Monday, November 10, through 8:00 PM (PST) Thursday, November 20th.

The SpaceDev space mission auction is at:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2572382454&category=45046&rd=1

Most earth orbiting small satellite missions can cost $25 million or more, not including the launch. To demonstrate the affordability of private space missions, SpaceDev has posted a ?Buy it Now? price of $9.5 million. The high bidder will win a spacecraft based on SpaceDev?s Maneuvering and orbit Transfer Vehicle (MTV?).

?I founded SpaceDev to accelerate the development of space, to get the public involved in space and to have fun,? said Jim Benson, SpaceDev founder and CEO. ?With our successful launch and operation of CHIPSat earlier this year, and after being competitively selected to provide safe hybrid rocket propulsion for manned space flight, we are offering this unique space mission to the public.?

The high bidder has the right to supply his or her own payload, to name the SpaceDev MTV? satellite and to name the mission. The winning bidder, which could be an individual, company or government agency, can also be involved in the mission design, satellite assembly and testing (including putting small personal items on the spacecraft), can attend the launch, and can participate in on-orbit operations.

The nominal payload is a camera that provides a view of the launch separation on-orbit, a buyer-controlled camera on the spacecraft looking back down on earth and into space 24 hours a day, or the buyer can supply a SpaceDev-approved payload. The microsatellite camera can be operated over the Internet by the winning bidder, similar to SpaceDev?s CHIPSat microsat, which is the world?s first orbiting node on the Internet. Specific terms are included in the eBay auction listing. Search eBay for ?SpaceDev.?

Original Source: SpaceDev News Release

Posted on by Fraser Cain

Gamma Ray Map of the Milky Way

Image credit: ESA

The European Space Agency’s Integral gamma-ray observatory has produced a new map of the Milky Way in the gamma-ray spectrum. Integral is looking for traces of radioactive aluminum, which gives off gamma rays with a specific wavelength. But the question is, what’s producing all this aluminum? Some astronomers believe these could be created by specific objects in the Milky Way, like Red Giant stars or hot blue stars. Another possibility is that it’s produced as part of supernova explosions. Integral will help get to the bottom of this mystery.

ESA’s gamma-ray observatory Integral is making excellent progress, mapping the Galaxy at key gamma-ray wavelengths.

It is now poised to give astronomers their truest picture yet of recent changes in the Milky Way’s chemical composition. At the same time, it has confirmed an ‘antimatter’ mystery at the centre of the Galaxy.

Since its formation from a cloud of hydrogen and helium gas, around 12 000 million years ago, the Milky Way has gradually been enriched with heavier chemical elements. This has allowed planets and, indeed, life on Earth to form.

Today, one of those heavier elements – radioactive aluminium – is spread throughout the Galaxy and, as it decays into magnesium, gives out gamma rays with a wavelength known as the ‘1809 keV line.’ Integral has been mapping this emission with the aim of understanding exactly what is producing all this aluminium.

In particular, Integral is looking at the aluminium ‘hot spots’ that dot the Galaxy to determine whether these are caused by individual celestial objects or the chance alignment of many objects.

Astronomers believe that the most likely sources of the aluminium are supernovae (exploding high-mass stars) and, since the decay time of the aluminium is around one million years, Integral’s map shows how many stars have died in recent celestial history. Other possible sources of the aluminium include ‘red giant’ stars or hot blue stars that give out the element naturally.

To decide between these options, Integral is also mapping radioactive iron, which is only produced in supernovae. Theories suggest that, during a supernova blast, aluminium and iron should be produced together in the same region of the exploding star. Thus, if the iron’s distribution coincides with that of the aluminium, it will prove that the overwhelming majority of aluminium comes indeed from supernovae.

These measurements are difficult and have not been possible so far, since the gamma-ray signature of radioactive iron is about six times fainter than that of the aluminium. However, as ESA’s powerful Integral observatory accumulates more data in the course of the next year, it will finally be possible to reveal the signature of radioactive iron. This test will tell astronomers whether their theories of how elements form are correct.

In addition to these maps, Integral is also looking deeply into the centre of the Galaxy, to make the most detailed map ever of ‘antimatter’ there.

Antimatter is like a mirror image to normal matter and is produced during extremely energetic atomic processes: for example, the radioactive decay of aluminium. Its signature is known as the ‘511 keV line.’ Even though Integral’s observations are not yet complete, they show that there is too much antimatter in the centre of the Galaxy to be coming from aluminium decay alone. They also show clearly that there must be many sources of antimatter because it is not concentrated around a single point.

There are many possible sources for this antimatter. As well as supernovae, old red stars and hot blue stars, there are jets from neutron stars and black holes, stellar flares, gamma-ray bursts and interaction between cosmic rays and the dusty gas clouds of interstellar space.

Chris Winkler, Integral’s Project Scientist, says: “We have collected excellent data in the first few months of activity but we can and will do much more in the next year. Integral’s accuracy and sensitivity have already exceeded our expectations and, in the months to come, we could get the answers to some of astronomy’s most intriguing questions.”

Original Source: ESA News Release

Posted on by Fraser Cain

No Newsletter for a Couple of Days

I just wanted to warn you that I’m probably not going to be able to email out the newsletter for the next couple of days. My high-speed Internet connection is down until Wednesday at the earliest, so all I’ve got is dial-up. I can update the website, but I can’t send out the newsletter without a high-speed connection.

I’ll keep updating the site, and then send out a monster edition in a couple of days.

Sorry for the inconvenience.

Fraser Cain
Publisher
Universe Today

Posted on by Fraser Cain

Big Dunes on Mars

Image credit: NASA/JPL

Mars has the largest volcano, the deepest canyon, and it’s got the biggest sand dunes. Several conditions on the Red Planet, including its low gravity, air pressure and sand probably contribute to the gigantic sand dunes that can form there. Dunes have been seen by the Mars Global Surveyor which reach twice as tall as they get on Earth. The Mars Exploration Rovers, currently on track to reach Mars in early 2004 will have cameras on board that may help scientists take a closer look at the sand that makes up these gigantic dunes.

Mars is kind of like Texas: things are just bigger there. In addition to the biggest canyon and biggest volcano in the solar system, Mars has now been found to have sand ripples twice as tall as they would be on Earth.

Initial measurements of some of the Red Planet’s dunes and ripples using stereo-images from the Mars Orbiter Camera onboard the Mars Global Surveyor have revealed ripple features reaching almost 20 feet high and dunes towering at 300 feet.

One way to imagine the taller dimension of ripples on Mars is to visualize sand ripples on Earth, then stretch out the vertical dimension to double height, without changing the horizontal dimension.

“They do seem higher in relation to ripples on Earth,” said Kevin Williams of the Smithsonian National Air and Space Museum. Williams will be presenting this latest insight into the otherworldly scale of Marscapes on Monday, Nov. 3 at the annual meeting of the Geological Society of America in Seattle, WA.

Ripples are common on Mars and usually found in low-lying areas and inside craters, says Williams. On Earth they tend to form in long parallel lines from sand grains being pushed by water or air at right angles to the ripple lines. Dunes, on the other hand, are formed when grains of sand actually get airborne and “saltate” (a word based on the Latin verb “to jump”). That leads to cusp-shaped, star-shaped, and other dune arrangements that allow materials to pile sand much higher.

How exactly Martian dunes and ripples form is still unknown, says Williams, since the images from space give us no clues to the grain sizes or whether they are migrating or moving in any way. Though there are Viking spacecraft images from almost 30 years ago to compare with, the images do not have the resolution to confirm whether ripples have moved much in that time. For now, the dimensions of ripple-forms on Mars are the only indications of whether they are large ripples or small dunes. Williams’ results came about from the advantageous combination of image parameters to get the first height measurements of these ripple-like features at the limit of image resolution.

According to Williams, it’s likely the doubled heights of Mars ripples relative to their spacing is made possible by the same thing that makes Mars’ volcanoes so tall: lower gravity. With about one-third the gravity of Earth, sand, silt, and dust can theoretically stack up higher before gravity causes a slope failure.

However, other differences could play roles in making these large piles of sand as well. “It could also be from different wind speeds, air densities or other factors,” said Williams. Mars has a perennially subfreezing, very thin atmosphere in which global dust storms have been known to obscure the surface from view.

The study of Mars dunes and ripples has been underway since Viking spacecraft images of Mars first revealed such features in the late 1970s and early 1980s, says Williams. The primary difficulty of the work continues to be in discerning the close-up details, like the exact heights of features and grain sizes. As with dunes and ripples on Earth, these wind-blown features could reveal a lot about local and regional weather and wind currents ? if more was known about ripple and dune building under the very un-Earthlike conditions of Mars.

So far the only close-encounters humans have ever had with Martian dunes were with the Viking Landers and the Pathfinder mission, which sent the Sojourner rover trundling among Martian boulders. “There were some small dunes in the area of Pathfinder,” Williams said.

There are also likely to be ripples or small dunes within range of the far more mobile Mars Exploration Rovers now enroute to the Red Planet, Williams said. The Mars Exploration Rovers, Spirit and Opportunity, are larger and will be able to travel much further than Sojourner, making it more likely they will be taking a closer look at ripples as well as other geological features of Mars.

Original Source: Geological Society of America News Release

Posted on by Fraser Cain

Envisat Watches an Iceberg Break Up

Image credit: ESA

The European Space Agency’s Envisat Earth observation satellite captured images of a gigantic iceberg as it broke up during an Antarctic storm. The iceberg, called B-15A, was created in March 2000 when a Jamaican-sized chunk of ice broke away from the Ross Ice Shelf. It broke into smaller pieces shortly after that, but the largest chunk, B-15A grounded itself off the coast and stuck around for a few years. Finally in October, 2003, a giant storm helped split the iceberg up.

ESA’s Envisat satellite was witness to the dramatic last days of what was once the world’s largest iceberg, as a violent Antarctic storm cracked a 160-km-long floe in two.

A series of Envisat Advanced Synthetic Aperture Radar (ASAR) instrument images acquired between mid-September and October record how the bottle-shaped iceberg B-15A was split by the onslaught of powerful storms, waves and ocean currents as its own weight kept it fixed on the floor of Antarctica’s Ross Sea.

ASAR is especially useful for polar operations because its radar signal can pierce thick clouds and works through both day and night. Radar imagery charts surface roughness, so can easily differentiate between different ice types. Old ice ? as on the surface of B-15A ? is rougher than newly formed ice.

B-15A began its existence as B-15 in March 2000 – with an area of 11,655 sq km it was the world’s largest known iceberg. This Jamaica-sized floe was created when it broke away from the Ross Ice Shelf. The initial monster berg split into numerous pieces shortly afterwards, with the largest piece designated B-15A.

Like a wall of ice, B-15A remained a stubborn presence for the next two and a half years, diverting ocean currents. This caused increased ice around Ross Island that disrupted breeding patterns for the local penguin colony and required extra icebreaker activity to maintain shipping access to the US base at McMurdo Sound.

B-15A’s end came in sight on 7 October this year, as 120 kph winds buffeted the grounded iceberg during a storm. Two cracks ran into the heart of the iceberg from opposite ends until finally the entire berg gave way.

The larger of the two new pieces has inherited the name B-15A, and the smaller berg named B-15J. They remain largely locked in place, some 3,800 kilometres south of New Zealand. The bergs could persist there for many years ? a GPS station has been placed on the 3,496 sq km B-15A to enable study of its future progress.

Despite events such as these there is so far no conclusive evidence as to whether polar ice is actually thinning. Next year will see the launch of ESA?s CryoSat mission, a dedicated ice-watching satellite designed to map precise changes in the thickness of polar ice-sheets and floating sea-ice.

CryoSat will be the first satellite to be launched as part of the Agency?s Living Planet Programme. This small research mission will carry a radar altimeter that is based on a heritage from existing instruments, but with several major enhancements to improve the measurement of icy surfaces.

By determining rates of ice-thickness change CryoSat will contribute to our understanding of the relationship between the Earth?s ice cover and global climate.

Original Source: ESA News Release