Posted on by Fraser Cain

Science Team Determines Composition of Asteroid Itokawa

Asteroid Itokawa. Image credit: JAXA. Click to enlarge
Itokawa, a spud-shaped, near-Earth asteroid, consists mainly of the minerals olivine and pyroxene, a mineral composition similar to a class of stony meteorites that have pelted Earth in the past.

This asteroid ingredient list, published in Science, comes courtesy of Hayabusa, the spacecraft launched in 2003 by the Japanese Aerospace Exploration Agency (JAXA). The mission of Hayabusa is to bring back first-ever samples from an asteroid to better understand their role as building blocks of the solar system.

Itokawa, an elongated rocky object nearly as long as five football fields, circles the sun more than 321 million miles away from Earth. Along with a few hundred known asteroids, Itokawa’s orbit is close to Earth’s orbit and was discovered by the Lincoln Near-Earth Asteroid (LINEAR) program, which detects near-Earth asteroids and provides advance warning if any are bound for Earth. Itokawa doesn’t currently pose such a threat, but its close proximity made it a tempting scientific target.

A near-infrared spectrometer aboard Hayabusa helped identify Itokawa’s mineralogy, mostly a mixture of the rock-forming minerals olivine and pryroxene, and possibly some plagioclase and metallic iron. But to truly understand what they had, the team turned to Takahiro Hiroi, a Brown University researcher who is expert in determining the composition of asteroids and meteorites, bits of asteroids that have fallen to Earth.

Hiroi is a senior research associate in the Department of Geological Sciences at Brown and the operations manager of the University’s NASA-funded Reflectance Experiment Laboratory (RELAB). For the Hayabusa project, Hiroi obtained samples of meteorites from museums, measured them at RELAB, and compared these results with spectral data from Itokawa.

Hiroi was able to determine that the mineral composition of the surface of Itokawa was similar to that of LL chondrites, a common class of stony meteorites relatively low in metallic iron. This link helped the team place a probable source of origin for Itokawa: the inner portion of the main asteroid belt, a ring of tens of thousands of rocks orbiting the sun between Mars and Jupiter.

Using Hayabusa data, the team was also able to better describe the surface of Itokawa. Much of it is studded with boulders, although the asteroid contains a smoother area known as Muses Sea. This diversity of terrain, the team concludes, may be the result of past meteoroid impacts and space weathering, a rock-altering process due to bombardments by dust particles and solar wind.

“We’ve never had a close-up look at such a small asteroid until now,” Hiroi said. “Large asteroids such as Eros are completely covered with a thick regolith, a blanket of looser material created by space weathering. With Itokawa, we believe we have witnessed a developing stage of the formation of this regolith. And these boulders sitting on Itokawa are no different from the meteorites that have fallen on Earth. So we may be seeing an earlier stage of asteroid evolution, of a type that has touched this planet.”

NASA and JAXA funded the work.

Original Source: Brown University

Posted on by Fraser Cain

Titan Behind the Rings

Titan behind Saturn’s icy ring. Image credit: NASA/JPL/SSI Click to enlarge
Titan peeks from behind Saturns rings in this recent Cassini photograph. The dark Enke gap and narrow F-ring are visible. Cassini took this image on April 28, 2006 when it was approximately 1.8 million kilometers (1.1 million miles) from Titan.

Saturn’s largest moon, Titan, peaks out from under the planet’s rings of ice.

This view looks toward Titan (5,150 kilometers, or 3,200 miles across) from slightly beneath the ringplane. The dark Encke gap (325 kilometers, or 200 miles wide) is visible here, as is the narrow F ring.

Images taken using red, green and blue spectral filters were combined to create this natural color view. The images were taken with the Cassini spacecraft narrow-angle camera on April 28, 2006 at a distance of approximately 1.8 million kilometers (1.1 million miles) from Titan. Image scale is 11 kilometers (7 miles) per pixel on Titan.

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

Metal in Planets Depends on Their Stars

Correlation between the heavy elements in transiting planets and the metallicity of their parents. Image credit: A&A. Click to enlarge
Of the 188 extrasolar planets discovered, 10 are transits; we see them because they dim their parent star as they pass in front. This gives astronomers an opportunity to study the actual composition of these planets. European astronomers have discovered that the metal content of these “hot Jupiters” depends on the amount of metal in their parent star, which changes the size of their cores.

A team of European astronomers, led by T. Guillot (CNRS, Observatoire de la Cote d’Azur, France), will publish a new study of the physics of Pegasids (also known as hot Jupiters) in Astronomy & Astrophysics. They found that the amount of heavy elements in Pegasids is correlated to the metallicity of their parent stars. This is a first step in understanding the physical nature of the extrasolar planets.

Up to now, astronomers have discovered 188 extrasolar planets, among which 10 are known as “transiting planets”. These planets pass between their star and us at each orbit. Given the current technical limitations, the only transiting planets that can be detected are giant planets orbiting close to their parent star known as “hot Jupiters” or Pegasids. The ten transiting planets known thus far have masses between 110 and 430 Earth masses (for comparison, Jupiter, with 318 Earth masses, is the most massive planet in our Solar System).

Although rare, transiting planets are the key to understanding planetary formation because they are the only ones for which both the mass and radius can be determined. In principle, the obtained mean density can constrain their global composition. However, translating a mean density into a global composition needs accurate models of the internal structure and evolution of planets. The situation is made difficult by our relatively poor knowledge of the behaviour of matter at high pressures (the pressure in the interiors of giant planets is more than a million times the atmospheric pressure on Earth). Of the nine transiting planets known up to April 2006, only the least massive one could have its global composition determined satisfactorily. It was shown to possess a massive core of heavy elements, about 70 times the mass of the Earth, with a 40 Earth-mass envelope of hydrogen and helium. Of the remaining eight planets, six were found to be mostly made up of hydrogen and helium, like Jupiter and Saturn, but their core mass could not be determined. The last two were found to be too large to be explained by simple models.

Considering them as an ensemble for the first time, and accounting for the anomalously large planets, Tristan Guillot and his team found that the nine transiting planets have homogeneous properties, with a core mass ranging from 0 (no core, or a small one) up to 100 times the mass of the Earth, and a surrounding envelope of hydrogen and helium. Some of the Pegasids should therefore contain larger amounts of heavy elements than expected. When comparing the mass of heavy elements in the Pegasids to the metallicity of the parent stars, they also found a correlation to exist, with planets born around stars that are as metal-rich as our Sun and that have small cores, while planets orbiting stars that contain two to three times more metals have much larger cores. Their results will be published in Astronomy & Astrophysics.

Planet formation models have failed to predict the large amounts of heavy elements found this way in many planets, so these results imply that they need revising. The correlation between stellar and planetary composition has to be confirmed by further discoveries of transiting planets, but this work is a first step in studying the physical nature of extrasolar planets and their formation. It would explain why transiting planets are so hard to find, to start with. Because most Pegasids have relatively large cores, they are smaller than expected and more difficult to detect in transit in front of their stars. In any case, this is very promising for the CNES space mission COROT to be launched in October, which should discover and lead to characterization of tens of transiting planets, including smaller planets and planets orbiting too far from their star to be detected from the ground.

What of the tenth transiting planet? XO-1b was announced very recently and is also found to be an anomalously large planet orbiting a star of solar metallicity. Models imply that it has a very small core, so that this new discovery strengthens the proposed stellar-planetary metallicity correlation.

Original Source: NASA Astrobiology

Posted on by Fraser Cain

Aram Chaos on Mars

This false colour image, taken by ESA’s Mars Express spacecraft, shows the heavily eroded Aram Chaos region on Mars. The region is a 280-km (174-mile) wide circular structure located between two outflow channels. Scientists think that the eastern portion of the nearby Valles Marineris was responsible for torrents of ice and water that chopped up the landscape millions of years ago.

These images, taken by the High Resolution Stereo Camera (HRSC) on board ESA’s Mars Express spacecraft, show Aram Chaos, 280-km-wide circular structure characterized by chaotic terrain.

The HRSC obtained these images during orbit 945 with a ground resolution of approximately 14 metres per pixel. The images show the region of Aram Chaos, at approximately 2 North and 340 East.

Aram Chaos is a 280-km-wide almost-circular structure located between the outflow channel Ares Vallis and Aureum Chaos. It is one of many regions located east of Valles Marineris and characterized by chaotic terrain.

As the name ‘chaos’ suggests, this terrain comprises large-scale remnant massifs, large relief masses that have been moved and weathered as a block. These are heavily eroded and dominate the circular morphology, or structure, which may have formed during an impact. As seen in the colour image, these remnant massifs range from a few kilometres to approximately ten kilometres wide and have a relative elevation of roughly 1000 metres.

The western region of the colour image is characterized by brighter material, which seems to be layered and could be the result of sedimentary deposition. Distinct layering, causing a terrace-like appearance, is also visible east of this brighter material and in the relatively flat region located in the northwest of the colour image.

***image4:left***Some scientists believe that the numerous chaotic regions located in the eastern part of Valles Marineris were the source of water or ice thought to have created the valleys that extend into Chryse Planitia. These regions are particularly interesting because they may yield clues to the relationship between Valles Marineris, the chaotic terrain, the valleys and the Chryse basin.

The colour scenes have been derived from the three HRSC-colour channels and the nadir channel. The perspective view has been calculated from the digital terrain model derived from the stereo channels. The anaglyph image was calculated from the nadir and one stereo channel.

Original Source: ESA Mars Express

Posted on by Fraser Cain

Saturn’s Moon Enceladus Rolled Over

An illustration of the interior of Saturn’s moon Enceladus. Image credit: NASA. Click to enlarge
Saturn’s moon Enceladus has a strange hot spot at its southern pole; a region that should be one of its coldest places. Scientists think that warm material inside the moon created an instability. The moon eventually rolled over, repositioning the spot at its southern pole. Other bodies in the Solar System, such as Uranus’ moon Miranda, have probably undergone similar rolls in the past.

Saturn’s moon Enceladus – an active, icy world with an unusually warm south pole ? may have performed an unusual trick for a planetary body. New research shows Enceladus rolled over, literally, explaining why the moon’s hottest spot is at the south pole.

Enceladus recently grabbed scientists’ attention when the Cassini spacecraft observed icy jets and plumes indicating active geysers spewing from the tiny moon’s south polar region.

“The mystery we set out to explain was how the hot spot could end up at the pole if it didn’t start there,” said Francis Nimmo, assistant professor of Earth sciences, University of California, Santa Cruz.

The researchers propose the reorientation of the moon was driven by warm, low-density material rising to the surface from within Enceladus. A similar process may have happened on Uranus’ moon Miranda, they said. Their findings are in this week’s journal Nature.

“It’s astounding that Cassini found a region of current geological activity on an icy moon that we would expect to be frigidly cold, especially down at this moon’s equivalent of Antarctica,” said Robert Pappalardo, co-author and planetary scientist at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “We think the moon rolled over to put a deeply seated warm, active area there.” Pappalardo worked on the study while at the University of Colorado.

Rotating bodies, including planets and moons, are stable if more of their mass is close to the equator. “Any redistribution of mass within the object can cause instability with respect to the axis of rotation. A reorientation will tend to position excess mass at the equator and areas of low density at the poles,” Nimmo said. This is precisely what happened to Enceladus.

Nimmo and Pappalardo calculated the effects of a low-density blob beneath the surface of Enceladus and showed it could cause the moon to roll over by up to 30-degrees and put the blob at the pole.

Pappalardo used an analogy to explain the Enceladus rollover. “A spinning bowling ball will tend to roll over to put its holes — the axis with the least mass — vertically along the spin axis. Similarly, Enceladus apparently rolled over to place the portion of the moon with the least mass along its vertical spin axis,” he said.

The rising blob (called a “diapir”) may be within either the icy shell or the underlying rocky core of Enceladus. In either case, as the material heats up it expands and becomes less dense, then rises toward the surface. This rising of warm, low-density material could also help explain the high heat and striking surface features, including the geysers and “tiger-stripe” region suggesting fault lines caused by tectonic stress.

Internal heating of Enceladus probably results from its eccentric orbit around Saturn. “Enceladus gets squeezed and stretched by tidal forces as it orbits Saturn, and that mechanical energy is transformed into heat energy in the moon’s interior,” added Nimmo.

Future Cassini observations of Enceladus may support this model. Meanwhile, scientists await the next Enceladus flyby in 2008 for more clues.

This research was supported by grants from NASA. The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL, a division of Caltech, manages the mission for NASA’s Science Mission Directorate. The Cassini orbiter was designed, developed and assembled at JPL.

For images and information about the Cassini mission, visit: http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov .

Original Source: NASA News Release

Posted on by Fraser Cain

Astrophoto: NGC 4631 by Bernd Wallner

NGC 4631 by Bernd Wallner
People have populated the night sky with animals, mythical heroes, and scientific instruments by connecting the stars into constellations. Similar leaps of imagination have also led observers to give names to nebulas and galaxies based on their resemblance. Thus, M51 is called the Whirlpool Galaxy, M27 is named the Dumbbell Nebula and M57 is known as the Ring. NGC 4631 reminded someone of a Whale, complete with barnacles, and like a harpoon the name stuck to it.

NGC 4631 is an enormous spiral galaxy about the same size as the Milky Way but, by chance, it is turned to us so that we only see its edge. Vast veins of dark dust are visible crisscrossing its length. This matter is a fundamental ingredient to create future solar generations. Not surprisingly, the dark lanes are intermingled with the bright red and blue glows of young star clusters that have just left their nebula nests.

Slightly to the left of center is the golden tale-tale glow of this galaxy’s central region. It’s a side view that’s partially obscured by the front edge of spiral arms we see. Images from the Chandra X-Ray Observatory have shown that NGC 4631 has a halo of hot gases blown from clusters of massive stars in this area. The Milky Way has a similar halo, too.

NGC 4631 belongs to a group of galaxies that are approximately 25 million light years from Earth in the direction of the northern constellation Canes Venatici. The fourteen members of this gathering are located so close together that they interact with each other gravitationally. For example, the small oval shaped companion galaxy seen in this picture may have previously been much larger but lost matter to NGC 4631 as a price for approaching too close and being captured. Also, a slight warp, or curve, is noticeable in this galaxy’s profile. It is thought to be caused by the gravitational tug of other galaxies in this group. Even more noticeable is the effect this galaxy has on one of its neighbors, NGC 4656 (located close-by but outside this picture’s field of view). It is a galaxy so disturbed that it has been named the Hockey Stick.

Bernd Wallner took this beautiful picture of NGC 4631 over three late-April nights this year from his private observatory near Burghausen. Bavaia, Germany. Bernd used his 24-inch Cassegrain reflector telescope and an 11 mega-pixel camera to record 70 separate images that were digitally combined to form this eight and a half hour exposure.

Do you have photos you’d like to share? Post them to the Universe Today astrophotography forum or email them, and we might feature one in Universe Today.

Written by R. Jay GaBany

Posted on by Fraser Cain

The Ozone Layer’s Recovering

The Antarctic ozone hole. Image credit: NASA.
Over the last few decades, scientists have been tracking the depletion of the ozone layer in the Earth’s atmosphere. A large hole still opens up over Antarctica, but ozone levels worldwide have stopped declining. The question is why. The relatively recent reduction of ozone-destroying gasses shouldn’t make an improvement so quickly. NASA scientists think that atmospheric wind patterns could be transferring ozone around the planet, helping with the recovery. At this rate, we’ll return to 1980 levels between 2030 and 2070.

Think of the ozone layer as Earth’s sunglasses, protecting life on the surface from the harmful glare of the sun’s strongest ultraviolet rays, which can cause skin cancer and other maladies.

People were understandably alarmed, then, in the 1980s when scientists noticed that manmade chemicals in the atmosphere were destroying this layer. Governments quickly enacted an international treaty, called the Montreal Protocol, to ban ozone-destroying gases such as CFCs then found in aerosol cans and air conditioners.

Today, almost 20 years later, reports continue of large ozone holes opening over Antarctica, allowing dangerous UV rays through to Earth’s surface. Indeed, the 2005 ozone hole was one of the biggest ever, spanning 24 million sq km in area, nearly the size of North America.

Listening to this news, you might suppose that little progress has been made. You’d be wrong.

While the ozone hole over Antarctica continues to open wide, the ozone layer around the rest of the planet seems to be on the mend. For the last 9 years, worldwide ozone has remained roughly constant, halting the decline first noticed in the 1980s.

The question is why? Is the Montreal Protocol responsible? Or is some other process at work?

It’s a complicated question. CFCs are not the only things that can influence the ozone layer; sunspots, volcanoes and weather also play a role. Ultraviolet rays from sunspots boost the ozone layer, while sulfurous gases emitted by some volcanoes can weaken it. Cold air in the stratosphere can either weaken or boost the ozone layer, depending on altitude and latitude. These processes and others are laid out in a review just published in the May 4th issue of Nature: “The search for signs of recovery of the ozone layer” by Elizabeth Westhead and Signe Andersen.

Sorting out cause and effect is difficult, but a group of NASA and university researchers may have made some headway. Their new study, entitled “Attribution of recovery in lower-stratospheric ozone,” was just accepted for publication in the Journal of Geophysical Research. It concludes that about half of the recent trend is due to CFC reductions.

Lead author Eun-Su Yang of the Georgia Institute of Technology explains: “We measured ozone concentrations at different altitudes using satellites, balloons and instruments on the ground. Then we compared our measurements with computer predictions of ozone recovery, [calculated from real, measured reductions in CFCs].” Their calculations took into account the known behavior of the sunspot cycle (which peaked in 2001), seasonal changes in the ozone layer, and Quasi-Biennial Oscillations, a type of stratospheric wind pattern known to affect ozone.

What they found is both good news and a puzzle.

The good news: In the upper stratosphere (above roughly 18 km), ozone recovery can be explained almost entirely by CFC reductions. “Up there, the Montreal Protocol seems to be working,” says co-author Mike Newchurch of the Global Hydrology and Climate Center in Huntsville, Alabama.

The puzzle: In the lower stratosphere (between 10 and 18 km) ozone has recovered even better than changes in CFCs alone would predict. Something else must be affecting the trend at these lower altitudes.

The “something else” could be atmospheric wind patterns. “Winds carry ozone from the equator where it is made to higher latitudes where it is destroyed. Changing wind patterns affect the balance of ozone and could be boosting the recovery below 18 km,” says Newchurch. This explanation seems to offer the best fit to the computer model of Yang et al. The jury is still out, however; other sources of natural or manmade variability may yet prove to be the cause of the lower-stratosphere’s bonus ozone.

Whatever the explanation, if the trend continues, the global ozone layer should be restored to 1980 levels sometime between 2030 and 2070. By then even the Antarctic ozone hole might close–for good.

Original Source: NASA News Release

Posted on by Fraser Cain

Finding a Fourth Dimension

Braneworld challenges Einstein’s general relativity. Image credit: NASA. Click to enlarge
Scientists have been intrigued for years about the possibility that there are additional dimensions beyond the three we humans can understand. Now researchers from Duke and Rutgers universities think there’s a way to test for five-dimensional theory (4 spatial dimensions plus time) of gravity that competes with Einstein’s General Theory of Relativity. This extra dimension should have effects in the cosmos which are detectable by satellites scheduled to launch in the next few years.

Scientists at Duke and Rutgers universities have developed a mathematical framework they say will enable astronomers to test a new five-dimensional theory of gravity that competes with Einstein’s General Theory of Relativity.

Charles R. Keeton of Rutgers and Arlie O. Petters of Duke base their work on a recent theory called the type II Randall-Sundrum braneworld gravity model. The theory holds that the visible universe is a membrane (hence “braneworld”) embedded within a larger universe, much like a strand of filmy seaweed floating in the ocean. The “braneworld universe” has five dimensions — four spatial dimensions plus time — compared with the four dimensions — three spatial, plus time — laid out in the General Theory of Relativity.

The framework Keeton and Petters developed predicts certain cosmological effects that, if observed, should help scientists validate the braneworld theory. The observations, they said, should be possible with satellites scheduled to launch in the next few years.
If the braneworld theory proves to be true, “this would upset the applecart,” Petters said. “It would confirm that there is a 4th dimension to space, which would create a philosophical shift in our understanding of the natural world.”

The scientists’ findings appeared May 24, 2006, in the online edition of the journal Physical Review D. Keeton is an astronomy and physics professor at Rutgers, and Petters is a mathematics and physics professor at Duke. Their research is funded by the National Science Foundation.

The Randall-Sundrum braneworld model — named for its originators, physicists Lisa Randall of Harvard University and Raman Sundrum of Johns Hopkins University — provides a mathematical description of how gravity shapes the universe that differs from the description offered by the General Theory of Relativity.

Keeton and Petters focused on one particular gravitational consequence of the braneworld theory that distinguishes it from Einstein’s theory.

The braneworld theory predicts that relatively small “black holes” created in the early universe have survived to the present. The black holes, with mass similar to a tiny asteroid, would be part of the “dark matter” in the universe. As the name suggests, dark matter does not emit or reflect light, but does exert a gravitational force.

The General Theory of Relativity, on the other hand, predicts that such primordial black holes no longer exist, as they would have evaporated by now.

“When we estimated how far braneworld black holes might be from Earth, we were surprised to find that the nearest ones would lie well inside Pluto’s orbit,” Keeton said.

Petters added, “If braneworld black holes form even 1 percent of the dark matter in our part of the galaxy — a cautious assumption — there should be several thousand braneworld black holes in our solar system.”

But do braneworld black holes really exist — and therefore stand as evidence for the 5-D braneworld theory?

The scientists showed that it should be possible to answer this question by observing the effects that braneworld black holes would exert on electromagnetic radiation traveling to Earth from other galaxies. Any such radiation passing near a black hole will be acted upon by the object’s tremendous gravitational forces — an effect called “gravitational lensing.”

“A good place to look for gravitational lensing by braneworld black holes is in bursts of gamma rays coming to Earth,” Keeton said. These gamma-ray bursts are thought to be produced by enormous explosions throughout the universe. Such bursts from outer space were discovered inadvertently by the U.S. Air Force in the 1960s.

Keeton and Petters calculated that braneworld black holes would impede the gamma rays in the same way a rock in a pond obstructs passing ripples. The rock produces an “interference pattern” in its wake in which some ripple peaks are higher, some troughs are deeper, and some peaks and troughs cancel each other out. The interference pattern bears the signature of the characteristics of both the rock and the water.

Similarly, a braneworld black hole would produce an interference pattern in a passing burst of gamma rays as they travel to Earth, said Keeton and Petters. The scientists predicted the resulting bright and dark “fringes” in the interference pattern, which they said provides a means of inferring characteristics of braneworld black holes and, in turn, of space and time.

“We discovered that the signature of a fourth dimension of space appears in the interference patterns,” Petters said. “This extra spatial dimension creates a contraction between the fringes compared to what you’d get in General Relativity.”

Petters and Keeton said it should be possible to measure the predicted gamma-ray fringe patterns using the Gamma-ray Large Area Space Telescope, which is scheduled to be launched on a spacecraft in August 2007. The telescope is a joint effort between NASA, the U.S. Department of Energy, and institutions in France, Germany, Japan, Italy and Sweden.

The scientists said their prediction would apply to all braneworld black holes, whether in our solar system or beyond.

“If the braneworld theory is correct,” they said, “there should be many, many more braneworld black holes throughout the universe, each carrying the signature of a fourth dimension of space.”

Original Source: Duke University

Posted on by Fraser Cain

Minerals Stop Transfering Heat at the Earth’s Core

Magnesiowustite crystals lose the ability of infrared transmission when squashed. Image credit: JHU/NASA. Click to enlarge
Researchers from the Carnegie Institution’s Geophysical Laboratory have discovered that certain minerals stop conducting infrared light as they near the Earth’s core. Even though they transmit infrared light perfectly well on the surface, they actually absorb it when crushed by the intense pressures near the Earth’s core. This discovery will help scientists better understand the flow of heat in the Earth’s interior, as well as helping to develop new models of planetary formation and evolution.

Minerals crunched by intense pressure near the Earth’s core lose much of their ability to conduct infrared light, according to a new study from the Carnegie Institution’s Geophysical Laboratory. Since infrared light contributes to the flow of heat, the result challenges some long-held notions about heat transfer in the lower mantle, the layer of molten rock that surrounds the Earth’s solid core. The work could aid the study of mantle plumes-large columns of hot upwelling magma believed to produce features such as the Hawaiian Islands and Iceland.

Crystals of magnesiowustite, a common mineral within the deep Earth, can transmit infrared light at normal atmospheric pressures. But when squashed to over half a million times the pressure at sea level, these crystals instead absorb infrared light, which hinders the flow of heat. The research will appear in the May 26, 2006 issue of the journal Science.

Carnegie staff members Alexander Goncharov and Viktor Struzhkin, with postdoctoral fellow Steven Jacobsen, pressed crystals of magnesiowustite using a diamond anvil cell-a chamber bound by two superhard diamonds capable of generating incredible pressure. They then shone intense light through the crystals and measured the wavelengths of light that made it through. To their surprise, the compressed crystals absorbed much of the light in the infrared range, suggesting that magnesiowustite is a poor conductor of heat at high pressures.

“The flow of heat in Earth’s deep interior plays an important role in the dynamics, structure, and evolution of the planet,” Goncharov said. There are three primary mechanisms by which heat is likely to circulate in the deep Earth: conduction, the transfer of heat from one material or area to another; radiation, the flow of energy via infrared light; and convection, the movement of hot material. “The relative amount of heat flow from these three mechanisms is currently under intense debate,” Goncharov added.

Magnesiowustite is the second most common mineral in the lower mantle. Since it does not transmit heat well at high pressures, the mineral could actually form insulating patches around much of the Earth’s core. If that is the case, radiation might not contribute to overall heat flow in these areas, and conduction and convection might play a bigger role in venting heat from the core.

“It’s still too early to tell exactly how this discovery will affect deep-Earth geophysics,” Goncharov said. “But so much of what we assume about the deep Earth relies on our models of heat transfer, and this study calls a lot of that into question.”

Original Source: Carnegie Institution

Posted on by Fraser Cain

What’s Up This Week – May 29 – June 4, 2006

M83: “The Southern Pinwheel”. Image credit: Bill Schoening/NOAO/AURA/NSF. Click to enlarge.
Greetings, fellow SkyWatchers! Let’s hope clear skies have returned to your area as we begin the week with a look at the incredible M83. As the Moon returns, we’ll study the features and be in for some excitement as it occults asteroid Vesta. Stay tuned as we go globular and catch some “shooting stars” because…

Here’s what’s up!

Monday, May 29 – Today in 1919, a total eclipse of the Sun occurred and stellar measurements taken along the limb agreed with predictions based on Einstein’s General Relativity theory – a first! Although we call it gravity, the space-time curve deflects the light of stars near the limb, causing their apparent position to differ slightly. Unlike today’s astronomy, at that time you could only observe stars near the Sun’s limb (less than an arc second) during an eclipse. It’s interesting to note that even Newton had his own theories on light and gravitation which also predicted deflection!

With tonight’s thin moon setting early, let’s have a look at the superb “Southern Pinwheel” galaxy – M83. You’ll find it a little more than a fist width south-southeast of Gamma Hydrae.

Pictures of M83 are often used to show budding astronomers what our own galaxy would look like if it were “out there” rather than “all around us.” In astrophotos, M83 shows a luminous central core with two broad bars of almost equally intense light extending outward across from one another. These act as trunks for the gnarled growth of the galaxy’s main spiral arms. Well away from the core, three spiral extensions are seen coiling outward to ultimately dissipate into space. But, that’s where the comparison with our own galaxy ends. This 15 million light-year distant, 30,000 light-year diameter class SB spiral is but a miniature of our giant spiral!

As you observe M83 tonight take the time to look for the structure described above – the round central core region, lateral bars, and spiraling extensions. More aperture means more light, and more detail.

Something new? First re-locate M5 in Serpens then head 3 degrees east. There you will find the brightest galaxy (NGC 5846) of a half dozen or so clustered around 4.6 magnitude 110 Virginis. These include NGCs 5850, 5831, 5838, 5854, 5813, and NGC 5806. These seven galaxies range in magnitude from 10.2 to 11.8 – and all are within the range of a mid-size scope.

Tuesday, May 30 – Tonight we’ll begin our studies by checking out the slender crescent of the Moon. To the north you will see the eastern edge of Mare Crisium beginning to emerge. The bright point on the shoreline is Promontorium Agarum with shallow crater Condorcet to its east. Look along the shore of the mare for a mountain to the south known as Mons Usov. Just to its north Luna 24 landed and directly to its west are the remains of Luna 15. Can you spot tiny crater Fahrenheit nearby?

Once the Moon has set, let’s revisit a spectacular globular cluster well suited to all instruments – M5. To find M5 easily, head southeast of Arcturus and north of Beta Librae and identify 5 Serpentis. At low power, or in binoculars, you will see this handsome globular in the same field to the northwest.

First discovered while observing a comet by Gottfried Kirch and his wife in 1702, Charles Messier found it on his own on May 23, 1764. Although Messier said it was a round nebula that “doesn’t contain any stars,” even small scopes can resolve the curved patterns of stars that extend from M5’s bright nucleus. Binoculars will reveal it with ease. For a real challenge, large telescopes can look for 11.8 magnitude globular Palomar 5 about 40′ south of the star 4 Serpentis. Under very dark, clear skies, M5 can just be glimpsed unaided, but telescopes will enjoy the rose-petal like star arcs of this 13 billion year old city of stars.

Wednesday, May 31 – Be very sure to check with IOTA for an awesome event on this Universal date. Why? Asteroid Vesta will be occulted by the Moon!

Tonight let’s return to Mare Crisium and look for some challenging features. Beginning on the south shore of Crisium, start by identifying crater Shaply trapped on the edge of the mare’s enclosure. To the southeast of Shaply you will see two small grey ovals. The northernmost is crater Firmicus with crater Apollonius to its south. Further south you will see the smooth grey area of Sinus Successus. If you look at the paler peninsula on Successus’ northern shore, you are seeing crater Ameghino and the landing area of the Luna 18 and Luna 20 missions.

If you’d like to take on another mission tonight, wait for the Moon to set and head towards Hercules for a high power view of a 9th magnitude planetary nebula – NGC 6210. This small disk won’t be easy to separate from neighboring stars without magnification. To find NGC 6210, locate Beta and Gamma Herculis. Draw an imaginary line between them and extend it around the same distance to the northeast. Around 6500 light-years away, NGC 6510 is one of the most active planetary nebulae. Hubble Space Telescope (HST) images show powerful hot jets of turbulent gas burrowing through an outer shell of cool gas.

Thursday, June 1 – Tonight let’s look on the lunar surface at the junction of Mare Fecunditatis and the edge of Mare Tranquillitatis. Here stands ancient Taruntius. Like a lighthouse guarding the shores, it stands on a mountainous peninsula overlooking the mare. Tonight it appears as a bright ring, but watch in the days ahead as this “lighthouse” shoots its brilliant beams across the desolate landscape nearly 175 kilometers.

To see another brilliant lighthouse, let’s head towards northern Hercules for a look at “the other Hercules Cluster” – M92. Discovered on December 27, 1777 by J. E. Bode, magnitude 6.5 M92 radiates with roughly half the brilliance of the Great Hercules Cluster – and this holds true intrinsically as well. About 900 light-years more distant than its famous neighbor, M13, the smaller M92 is still only 5,000 light-years away – “next door.”

M92 gives a splendid, well-resolved view in even small scopes. It dissolves into dozens of fainter members arrayed around a nebulous core radiating the combined light of over 150,000 suns. Like all globulars, higher magnification must be used to add contrast and reveal some of its brighter stellar components – especially near the core where this celestial “lighthouse” really gathers them in!

Friday, June 2 – For SkyWatchers tonight, have a look as Regulus is quite near Luna.

For telescope users, the Moon gives a wonderful opportunity to revisit ancient crater Posidonius. Its 84 kilometer by 98 kilometer expanse is easily seen in the most modest of optical instruments and it offers a wealth of details with its eroded walls and 1768 meter (5800 ft.) central peak. Look for a central crater attended by a fine curve of challenging mountain peaks to its east.

Continue southward from Posidonius along the edge of Mare Serenitatis to catch partially open crater Le Monnier. This ruined ring contains the remains of the Luna 21 mission – forever awaiting salvage in the grey sands along Le Monnier’s southern edge.

Even though skies are fairly bright, we can still get an impression of a very distant third globular cluster in Hercules. This one is small and faint – but with reason. NGC 6229 is almost 100,000 light-years away! If it were transported to the distance of M13 or M92 it would shine as bright as the latter and eclipse both in apparent size!

Due to great distance, the brightest stars associated with NGC 6229 are only within reach of large telescopes. This may explain why William Herschel interpreted the faint and slightly condensed glow of NGC 6229 as a planetary nebula when he discovered it May 12, 1787. The surprise of three globulars within the confines of Hercules may also explain why the globular cluster was mistaken as a comet discovery in 1819! Its stellar nature was only first resolved in the mid 1800s by the discoverer of Neptune – Louis d’Arrest.

Despite the Moon, larger scopes can find NGC 6229 between the stars 52 and 42 Hercules, a fist width north of Eta – the northeastern star of the Hercules Keystone.

Saturday, June 3 – If you’re up early, why not keep watch for the peak of the Tau Herculids meteor shower? With a radiant near Corona Borealis, the Earth will encounter this stream for about a month. Sharp-eyed observers can expect about 15 faint streaks per hour at its maximum.

Although it’s furthest from the Earth right now, did you see Selene during daylight today? Spectacular, isn’t it. Have you ever wondered if there was any place on the lunar surface that has never seen the light?

Directly in the center of the Moon is a dark floored area known as the Sinus Medii. South of that are two conspicuously large craters – Hipparchus to the north and ancient Albategnius to the south. Trace the terminator toward the south until you almost reach its point (cusp.) There you will see a black oval. This normal looking crater with brilliant west wall is ancient crater Curtius. Because of its high latitude, we never see its interior – and neither does the Sun! It is believed that the inner walls are quite steep. Because of this, Curtius’ deep interior hasn’t seen the light of day since its formation billions of years ago! Locked in perpetual darkness, scientists speculate there may be “lunar ice” inside its many cracks and crevasses crevices.

Because our Moon has no atmosphere, the entire surface is exposed to the vacuum of space. When sunlit, the surface reaches up to 385 K. Any exposed ice would immediately evaporate and be lost because the Moon’s weak gravity cannot hold it. Frozen matter can only exist on the moon within permanently shadowed areas. Curtius lies near the Moon’s south pole. Imaging has shown some 15,000 square kilometers where similar conditions could exist. But where does the “ice” come from? The lunar surface never ceases to be pelted by meteorites – most of which contain water. Many craters are formed by just such impacts. Hidden from sunlight, this frozen material can exist for millions of years!

Sunday, June 4 – How about a little lunar “prospecting?” Then let’s explore the northern equivalent to Curtius. Start by locating previous study crater Plato. North of Plato lies a long horizontal area of gray floor – Mare Frigoris. North of Frigoris you will see a “double crater.” This is the elongated diamond shape of Goldschmidt. Cutting across its western border is Anaxagoras. The lunar north pole isn’t far from Goldschmidt, and since Anaxagoras lies about one degree outside of the Moon’s theoretical “arctic” area, the lunar sun will never go high enough to clear the southernmost rim. Such “permanent darkness” must mean there’s ice! And for that very reason, NASA’s Lunar Prospector probe was sent to explore. Did it find what it was looking for? The answer is yes.

The probe discovered vast quantities of cometary ice secreted inside the crater’s depths. What’s the significance? Water is essential to life and its presence influences any plans to establish a base on the lunar surface. Will the sun ever shine on such a base? Quite probably. But down below, in the crater’s depths it never has, and never will…

Tonight let’s look at another distant world as we take another look at Jupiter. You don’t have to wait for the sky to actually get dark to view Jupiter. At magnitude -2.4, Jupiter can easily be found a half-hour after sunset. It won’t be long before it’s gone so enjoy those “Bands on the Run” while they last!

May all your journeys be at light speed… ~Tammy Plotner with Jeff Barbour.