Posted on by Fraser Cain

March 29 Total Eclipse

Partial solar eclipse across the United States on May 10, 1994. Image credit: Sky & Telescope Click to enlarge
Those lucky enough to live in parts of Africa, Turkey and Central Asia will experience a total eclipse of the Sun on Wednesday, March 29, 2006. Even larger areas of the Earth will get to see the Sun dim in a partial solar eclipse, from Brazil to China. If you’re lucky enough to be watching from the thin path of totality, the Sun will be completely obscured by the Moon, making the corona visible like a fiery ring.

On Wednesday, March 29, 2006, a total eclipse of the Sun will sweep across parts of West and North Africa, Turkey, and Central Asia. The eclipse will be partial across a much wider region, including most of Africa, all of Europe, and much of western and southern Asia.

The accompanying maps provided by Sky & Telescope magazine tell the story. They will help skywatchers in those regions of the world to plan their activities for the big day.

A solar eclipse happens when the Moon crosses the face of the Sun as seen from your viewpoint on Earth. The globe map shows the entire region of Earth that will be touched by any part of this eclipse, including the complete path of totality: where the Sun will become completely covered by the Moon. As the map shows, the total eclipse starts at sunrise at the tip of Brazil, crosses the Atlantic in the morning, the Sahara Desert at midday, Turkey in the afternoon, and ends at sunset in Central Asia. Red lines on the globe map indicate how much of the Sun’s diameter is covered at maximum partial eclipse. Purple lines tell when this happens, in Universal Time (UT; also called Greenwich Mean Time or GMT).

The close-up map of Europe and the Middle East gives more detail. Here, blue and red lines tell the start and end times of partial eclipse, respectively, again in UT/GMT. The partial eclipse for any site is at its maximum halfway between these times. The black lines on the map tell the percentage of the Sun’s diameter that will be covered at maximum eclipse.

Although a partial solar eclipse can’t hold a candle to a total one, it’s a memorable celestial event in its own right. Can you see a change in the illumination of the landscape around you? A partial eclipse has to be surprisingly deep to alter the light visibly, because our eyes are very good at adjusting to ambient light levels. But when this does happen, the world seems to take on an odd, silvery feel like no other. Look for crescent-shaped dapplings on the ground where sunlight shines through leaves. In a safely solar-filtered telescope (see below), look for mountain silhouettes on the Moon’s dark edge. Look too for a difference between the Moon’s complete darkness and the not-so-complete darkness of any sunspots that the edge of the Moon approaches.

Warning: Never look at the bright surface of the Sun without proper eye protection! Examples are special “eclipse glasses” properly designed for the purpose, a #14 rectangular arc-welder’s filter, or special astronomers’ solar filters (see our list of solar filter suppliers). Staring at the bright Sun can burn your retina, leaving a permanent blind spot in the center of your vision. The only reason a partial eclipse poses a special danger is because it can prompt people to look directly at the Sun, something they wouldn’t normally do. See our complete descriptions of the various ways to watch safely, including the “projection method” using a pinhole, binoculars, or a telescope.

Looking while the Sun is totally eclipsed, on the other hand, is safe. At that time, of course, none of the Sun’s bright surface is in view.

People who’ve never tried photographing a solar eclipse before can get fine results by following Sky & Telescope’s tips for photographers.

More on this particular eclipse appears in the January and March 2006 issues of Sky & Telescope, the Essential Magazine of Astronomy.

For detailed local predictions at any given location, please see NASA’s Web site for this eclipse.

Original Source: Sky and Telescope

Posted on by Fraser Cain

Giant Protoplanets Should Get Destroyed

Inward migration of a group of protoplanets, where they’re represented by white circles. Image credit: QMUL Click to enlarge
Astronomers think they’ve got a handle on many aspects of planetary formation. But two British researchers have discovered a problem with the formation of gas giant planets. Under their model, the cores of these massive planets should be drawn inward by their parent star in only 100,000 years – not nearly enough time to form into a stable orbit. It could be that the first generations of planets never get past the “clump” stage before they’re destroyed. It’s only the later generations that actually survive long enough to become planets.

Two British astronomers, Paul Cresswell and Richard Nelson present new numerical simulations in the framework of the challenging studies of planetary system formation. They find that, in the early stages of planetary formation, giant protoplanets migrate inward in lockstep into the central star. Their results will soon be published in Astronomy & Astrophysics.

In an article to be published in Astronomy & Astrophysics, two British astronomers present new numerical simulations of how planetary systems form. They find that, in the early stages of planetary formation, giant protoplanets migrate inward in lockstep into the central star.

The current picture of how planetary systems form is as follows: i) dust grains coagulate to form planetesimals of up to 1 km in diameter; ii) the runaway growth of planetesimals leads to the formation of ~100 ? 1000 km-sized planetary embryos; iii) these embryos grow in an “oligarchic” manner, where a few large bodies dominate the formation process, and accrete the surrounding and much smaller planetesimals. These “oligarchs” form terrestrial planets near the central star and planetary cores of ten terrestrial masses in the giant planet region beyond 3 astronomical units (AU).

However, these theories fail to describe the formation of gas giant planets in a satisfactory way. Gravitational interaction between the gaseous protoplanetary disc and the massive planetary cores causes them to move rapidly inward over about 100,000 years in what we call the “migration” of the planet in the disc. The prediction of this rapid inward migration of giant protoplanets is a major problem, since this timescale is much shorter than the time needed for gas to accrete onto the forming giant planet. Theories predict that the giant protoplanets will merge into the central star before planets have time to form. This makes it very difficult to understand how they can form at all.

For the first time, Paul Cresswell and Richard Nelson examined what happens to a cluster of forming planets embedded in a gaseous protoplanetary disc. Previous numerical models have included only one or two planets in a disc. But our own solar system, and over 10% of the known extrasolar planetary systems, are multiple-planet systems. The number of such systems is expected to increase as observational techniques of extrasolar systems improve. Cresswell and Nelson’s work is the first time numerical simulations have included such a large number of protoplanets, thus taking into account the gravitational interaction between the protoplanets and the disc, and among the protoplanets themselves.

The primary motivation for their work is to examine the orbits of protoplanets and whether some planets could survive in the disc for extended periods of time. Their simulations show that, in very few cases (about 2%), a lone protoplanet is ejected far from the central star, thus lengthening its lifetime. But in most cases (98%), many of the protoplanets are trapped into a series of orbital resonances and migrate inward in lockstep, sometimes even merging with the central star.

Cresswell and Nelson thus claim that gravitational interactions within a swarm of protoplanets embedded in a disc cannot stop the inward migration of the protoplanets. The “problem” of migration remains and requires more investigation, although the astronomers propose several possible solutions. One may be that several generations of planets form and that only the ones that form as the disc dissipates survive the formation process. This may make it harder to form gas giants, as the disc is depleted of the material from which gas giant planets form. (Gas giant formation may still be possible though, if enough gas lies outside the planets’ orbits, since new material may sweep inward to be accreted by the forming planet). Another solution might be related to the physical properties of the protoplanetary disc. In their simulations, the astronomers assumed that the protoplanetary disc is smooth and non-turbulent, but of course this might not be the case. Large parts of the disc could be more turbulent (as a consequence of instabilities caused by magnetic fields), which may prevent inward migration over long time periods.

This work joins other studies of planetary system formation that are currently being done by a European network of scientists. Our view of how planets form has drastically changed in the last few years as the number of newly discovered planetary systems has increased. Understanding the formation of giant planets is currently one of the major challenges for astronomers.

Original Source: Astronomy & Astrophysics

Posted on by Fraser Cain

Spitzer Sees Distant Galaxy Clusters

Spitzer spots galactic clusters bonding back when the universe was about 4.6 billion years old. Image credit: NASA Click to enlarge
NASA’s Spitzer Space Telescope recently turned up clusters of galaxies located 7-9 billion light years from Earth. These galaxies are located at the very limits of Spitzer’s observing ability with its 85-centimeter (33-inch) telescope. Galaxy clusters are some of the largest structures in the Universe, consisting of thousands of galaxies and trillions of stars. This discovery gives astronomers more evidence about what kinds of structures existed in the early Universe.

Astronomers using NASA’s Spitzer Space Telescope have conducted a cosmic safari to seek out a rare galactic species. Their specimens — clusters of galaxies in the very distant universe — are few and far between, and have hardly ever been detected beyond a distance of 7 billion light-years from Earth.

To find the clusters, the team carefully sifted through Spitzer infrared pictures and ground-based catalogues; estimated rough distances based on the cluster galaxies’ colors; and verified suspicions using a spectrograph instrument at the W.M. Keck Observatory in Hawaii.

Ultimately, the expedition resulted in quite a galactic catch — the most distant galaxy cluster ever seen, located 9 billion light-years away. This means the cluster lived in an era when the universe was a mere 4.5 billion years old. The universe is believed to be 13.7 billion years old.

“Detecting a galaxy cluster 9 billion light-years away is very exciting,” said the study’s lead investigator, Dr. Peter Eisenhardt of NASA’s Jet Propulsion Laboratory. “It’s really amazing that Spitzer’s 85-centimeter telescope can see 9 billion years back in time.”

Using the same methods, the astronomers also found three other clusters living between 7 and 9 billion light-years away.

“Spitzer is an excellent instrument for detecting very distant galaxy clusters because they stand out so brightly in the infrared,” said co-investigator Dr. Mark Brodwin, also of JPL. “You can think of these distant galaxy cluster surveys as a game of ‘Where’s Waldo?’ With an optical telescope you can spot ‘Waldo,’ or the distant galaxy clusters, by carefully searching for them amongst a sea of faint galaxies.”

“But in the Spitzer data, it’s as though Waldo is wearing a bright neon hat and can be easily picked out of the crowd,” Brodwin added.

Galaxy clusters are the largest gravitationally bound structures in the universe. A typical cluster can contain thousands of galaxies and trillions of stars. Because of their huge size and mass, they are relatively rare. For example, if Earth were to represent the entire universe, then countries would be the equivalent of galaxies, and continents would be the galaxy clusters.

Galaxy clusters grow like snowballs, picking up new galaxies from gravitational interactions over billions of years. For this reason, team members say these behemoths should be even rarer in the very distant universe.

“The ultimate goal of this research is to find out when the galaxies in this and other distant clusters formed,” said co-investigator Dr. Adam Stanford, of the University of California at Davis. Stanford is the lead author of a paper on the most distant galaxy cluster’s discovery, which was published in the December 2005 issue of Astrophysical Journal Letters.

This is the second time Eisenhardt and Stanford have broken the record for capturing the most distant galaxy cluster. Both say they accidentally broke the record in 1997 when they detected a cluster located 8.7 billion light-years away. The discovery was made by a deep survey of a 0.03-degree patch of sky, or an area significantly smaller than a pea held out at arms length, for 30 nights at the Kitt Peak National Observatory in Arizona.

“We were lucky in 1997 because we weren’t looking for galaxy clusters and found the most distant one ever detected in a very small patch of sky,” said Stanford. “Because galaxy clusters are so massive and rare, you typically need to deeply survey a large area of sky to find them.”

“With Spitzer’s great infrared sensitivity we surveyed more deeply in 90 seconds than we could in hours of exposure in the 1997 observations, and we used this advantage to survey a region 300 times larger,” adds Eisenhardt.

The 9 billion-year-old cluster is just one of 25 the team captured on their Spitzer safari. They are currently preparing for more observations this spring at the W.M. Keck Observatory to confirm the distance of additional galaxy clusters from their sample. According to Eisenhardt, some of the clusters awaiting confirmation may be even more distant than the current record holder.

Original Source: Spitzer Space Telescope

Posted on by Fraser Cain

Defending Against Radiation

The sun is a major source of radiation for life on Earth. Image credit: NASA/ESA/SOHO. Click to enlarge
Space travel has its dangers. One of the biggest risks will come from the various types of radiation that flood space. Scientists are learning how life on Earth has evolved different kinds of tricks to resist radiation. Some animals and plants have evolved protective covering or pigmentation, but some forms of bacteria can actually repair damage to its DNA from radiation. Future space travelers might take advantage of these techniques to minimize the harm they get from long exposure.

In Star Wars and Star Trek movies, people travel between planets and galaxies with ease. But our future in space is far from assured. Issues of hyperdrive and wormholes aside, it doesn’t seem possible that the human body could withstand extended exposure to the harsh radiation of outer space.

Radiation comes from many sources. Light from the sun produces a range of wavelengths from long-wave infrared to short-wavelength ultraviolet (UV). Background radiation in space is composed of high-energy X-rays, gamma rays and cosmic rays, which all can play havoc with the cells in our bodies. Since such ionizing radiation easily penetrates spacecraft walls and spacesuits, astronauts today must limit their time in space. But being in outer space for even a short time greatly increases their odds of developing cancer, cataracts, and other radiation-related health problems.

To overcome this problem, we may find some useful tips in nature. Many organisms already have devised effective strategies to protect themselves from radiation.

Lynn Rothschild of the NASA Ames Research Center says that radiation has always been a danger for life on Earth, and so life had to find ways to cope with it. This was especially important during the Earth’s earliest years, when the ingredients for life were first coming together. Because our planet did not initially have much oxygen in the atmosphere, it also lacked an ozone (O3) layer to block out harmful radiation. This is one reason why many believe life originated underwater, since water can filter out the more damaging wavelengths of light.

Yet photosynthesis ? the transformation of sunlight into chemical energy ? developed relatively early in the history of life. Photosynthetic microbes like cyanobacteria were using sunlight to make food as early as 2.8 billion years ago (and possibly even earlier).

Early life therefore engaged in a delicate balancing act, learning how to use radiation for energy while protecting itself from the damage that radiation could cause. While sunlight is not as energetic as X-rays or gamma rays, the UV wavelengths are preferentially absorbed by DNA bases and by the aromatic amino acids of proteins. This absorption can damage cells and the delicate DNA strands that encode the instructions for life.

“The problem is, if you’re going to access solar radiation for photosynthesis, you’ve got to take the good with the bad — you’re also exposing yourself to the ultraviolet radiation,” says Rothschild. “So there’s various tricks that we think early life used, as life does today.”

Besides hiding under liquid water, life makes use of other natural UV radiation barriers such as ice, sand, rocks, and salt. As organisms continued to evolve, some were able to develop their own protective barriers such as pigmentation or a tough outer shell.

Thanks to photosynthetic organisms filling the atmosphere with oxygen (and thereby generating an ozone layer), most organisms on Earth today don’t need to contend with high energy UV-C rays, X-rays or gamma rays from space. In fact, the only organisms known to survive space exposure ? at least in the short term – are bacteria and lichen. Bacteria need some shielding so they won’t get fried by the UV, but lichen have enough biomass to act as a protective spacesuit.

But even with a good barrier in place, sometimes radiation damage does occur. The lichen and bacteria hibernate while in space ? they do not grow, reproduce, or engage in any of their normal living functions. Upon return to Earth, they exit this dormant state and, if there was damage inflicted, proteins in the cell work to piece together DNA strands that were broken apart by radiation.

The same damage control occurs with organisms on Earth when they’re exposed to radioactive materials such as uranium and radium. The bacterium Deinococcus radiodurans is the reigning champion when it comes to this sort of radiation repair. (Complete repair is not always possible, however, which is why radiation exposure can lead to genetic mutations or death.)

“I live in eternal hope of unseating D. radiodurans,” says Rothchild. Her search for radiation-resistant microorganisms has brought her to Paralana hot spring in Australia. Uranium-rich granite rocks emit gamma rays while lethal radon gas bubbles up from the hot water. Life in the spring is therefore exposed to high levels of radiation ? both below, from the radioactive materials, and above, from the intense UV light of the Australian sun.

Rothschild learned about the hot spring from Roberto Anitori of Macquarie University’s Australian Centre for Astrobiology. Anitori has been sequencing the 16S ribosomal RNA genes and culturing the bacteria that live quite happily in the radioactive waters. Like other organisms on Earth, the Paralana cyanobacteria and other microbes may have devised barriers to shield themselves from the radiation.

“I have noticed a tough, almost silicone-like layer on some of the microbial mats there,” says Anitori. “And when I say “silicon-like,” I mean the sort you use on window pane edging.”

“Apart from possible shielding mechanisms, I suspect that the microbes at Paralana also have good DNA repair mechanisms,” adds Anitori. At the moment, he can only speculate about the methods used by the Paralana organisms to survive. However, he does plan to closely investigate their radiation resistance strategies later this year.

In addition to Paralana, Rothschild’s investigations have brought her to extremely arid regions in Mexico and the Bolivian Andes. As it turns out, many organisms that evolved to live in deserts are also quite good at surviving radiation exposure.

Prolonged water loss can cause DNA damage, but some organisms have evolved efficient repair systems to combat this damage. It’s possible that these same dehydration repair systems are used when the organism needs to repair radiation-inflicted damage.

But such organisms may be able to avoid damage altogether simply by being dried out. The lack of water in desiccated, dormant cells makes them much less susceptible to the effects of ionizing radiation, which can harm cells by producing free radicals of water (hydroxyl or OH radical). Because free radicals have unpaired electrons, they eagerly try to interact with DNA, proteins, lipids in cell membranes, and anything else they can find. The resulting wreckage can lead to organelle failure, block cell division, or cause cell death.

Eliminating the water in human cells is probably not a practical solution for us to minimize our radiation exposure in space. Science fiction has long toyed with the idea of putting people into suspended animation for long space journeys, but turning humans into shriveled, dried-out raisins and then rehydrating them back to life isn’t medically possible – or very appealing. Even if we could develop such a procedure, once the human raisinettes were rehydrated they would again be susceptible to radiation damage.

Perhaps someday we can genetically engineer humans to have the same super radiation-repair systems as microorganisms like D. radiodurans. But even if such tinkering with the human genome was possible, those hardy organisms aren’t 100 percent resistant to radiation damage, so health problems would persist.

So of the three known mechanisms that life has devised to combat radiation damage – barriers, repair, and desiccation – the most immediately practical solution for human spaceflight would be to devise better radiation barriers. Anitori thinks his studies of the Paralana Spring organisms could someday help us engineer such barriers.

“Perhaps we will be taught by nature, mimicking some of the shielding mechanisms used by microbes,” he states.

And Rothschild says radiation studies also could provide some important lessons as we look toward establishing communities on the moon, Mars, and other planets.

“When we start to build human colonies, we’re going to take organisms with us. You’re ultimately going to want to grow plants, and possibly make an atmosphere on Mars and on the moon. We may not want to spend the effort and the money to protect them completely from the UV and cosmic radiation.”

In addition, says Rothschild, “humans are just full of microbes, and we couldn’t survive without them. We don’t know what effect the radiation will have on that associated community, and that may be more of a problem than the direct effect of radiation on the humans.”

She believes her studies also will be useful in the search for life on other worlds. Assuming that other organisms in the universe also are based on carbon and water, we can postulate what sort of extreme conditions they could survive in.

“Each time we find an organism on Earth that can live further and further into an environmental extreme, we’ve increased the size of that envelope of what we know life can survive within,” says Rothschild. “So if we go to a place on Mars that has a certain radiation flux, desiccation, and temperature, we can say, ‘There are organisms on Earth that can live under those conditions. There’s nothing that precludes life from living there.’ Now, whether life is there or not is another matter, but at least we can say this is the minimum envelope for life.”

For instance, Rothschild thinks life could be possible in the salt crusts on Mars, which are similar to salt crusts on Earth where organisms find shelter from solar UV. She also looks at life living under ice and snow on Earth, and wonders if organisms could live a comparatively radiation-protected existence under the ice of Jupiter’s moon Europa.

Original Source: NASA Astrobiology

Posted on by Fraser Cain

Hazy Layers on Titan

Titan’s multiple hazy layers. Image credit: NASA/JPL/SSI Click to enlarge
This is a composite photograph consisting of 24 photos taken by Cassini of Saturn’s moon Titan. Up at the top of Titan it’s possible to see several layers of clouds in the atmosphere. The top layer is at an altitude of 500 km (300 miles) and probably consists of water ice. Why the atmosphere is separate like this is still a mystery, but scientists think it might have something to do with waves in the atmosphere.

This composite of 24 images from the Cassini spacecraft shows multiple layers in Titan’s stratospheric haze. The most prominent layer is located about 500 kilometers (300 miles) above the surface and is seen at all latitudes, encircling the moon. The material in this layer is probably a condensed substance, possibly water ice.

Several other layers are most apparent in the north polar hood (at top), but this view also shows some at other latitudes. The mechanisms that produce these layers are not understood, but waves in the atmosphere are thought to play a significant role.

The images in this composite were taken over a period of 23 minutes. The images were processed to enhance fine detail and then were combined to create this view. North on Titan (5,150 kilometers, or 3,200 miles across) is up.

The images were taken in visible light with the narrow-angle camera on Jan. 27, 2006 at a distance of approximately 2.3 million kilometers (1.4 million miles) from Titan and at a Sun-Titan-spacecraft, or phase, angle of 155 degrees. Image scale is 13 kilometers (8 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

Is Dark Matter Made up of Sterile Neutrinos?

The Guitar nebula. Image credit: Palomar Observatory. Click to enlarge
Since it makes up a large part of the Universe, you’d think we’d know what dark matter is by now. Sorry, it’s still a mystery, but new theories are coming out all the time. An international team of researchers are now theorizing that dark matter could be a class of particles known as “sterile neutrinos”. These particles, formed right at the Big Bang, could account for the Universe’s missing mass, and would have the handy side effect of speeding up the early formation of stars.

Dark matter may have played a major role in creating stars at the very beginnings of the universe. If that is the case, however, the dark matter must consist of particles called “sterile neutrinos”. Peter Biermann of the Max Planck Institute for Radio Astronomy in Bonn, and Alexander Kusenko, of the University of California, Los Angeles, have shown that when sterile neutrinos decay, it speeds up the creation of molecular hydrogen. This process could have helped light up the first stars only some 20 to 100 million years after the big bang. This first generation of stars then ionised the gas surrounding them, some 150 to 400 million years after the big bang. All of this provides a simple explanation to some rather puzzling observations concerning dark matter, neutron stars, and antimatter.

Scientists discovered that neutrinos have mass through neutrino oscillation experiments. This led to the postulation that “sterile” neutrinos exist – also known as right-handed neutrinos. They do not participate in weak interactions directly, but do interact through their mixing with ordinary neutrinos. The total number of sterile neutrinos in the universe is unclear. If a sterile neutrino only has a mass of a few kiloelectronvolts (1 keV is a millionth of the mass of a hydrogen atom), that would explain the huge, missing mass in the universe, sometimes called “dark matter”. Astrophysical observations support the view that dark matter is likely to consist of these sterile neutrinos.

Biermann and Kusenko’s theory sheds light on a number of still unexplained astronomical puzzles. First of all, during the big bang, the mass of neutrinos created in the Big Bang would equal what is needed to account for dark matter. Second, these particles could be the solution to the long-standing problem of why pulsars move so fast.

Pulsars are neutron stars rotating at a very high velocity. They are created in supernova explosions and normally are ejected in one direction. The explosion gives them a “push”, like a rocket engine. Pulsars can have velocities of hundreds of kilometres per second – or sometimes even thousands. The origin of these velocities remains unknown, but the emission of sterile neutrinos would explain the pulsar kicks.

The Guitar Nebula contains a very fast pulsar. If dark matter is made of particles which reionized the universe – as Biermann and Kusenko suggest – the pulsar’s motion could have created this cosmic guitar.

Third, sterile neutrinos can help explain the absence of antimatter in the universe. In the early universe, sterile neutrinos could have “stolen” what is called the “lepton number” from plasma. At a later time, the lack of lepton number was converted to a non-zero baryon number. The resulting asymmetry between baryons (like protons) and antibaryons (like antiprotons) could be the reason why the universe has no antimatter.

“The formation of central galactic black holes, as well as structure on subgalactic scales, favours sterile neutrinos to account for dark matter. The consensus of several indirect pieces of evidence leads one to believe that the long sought-after dark-matter particle may, indeed, be a sterile neutrino”, says Peter Biermann

Original Source: Max Planck Society

Posted on by Fraser Cain

Debris Filled Craters on Mars

This photograph was taken by ESA’s Mars Express spacecraft. It shows a mountain in the eastern Hellas Planitia region with craters partly filled with debris. It’s possible that the mountain was covered by glaciers in the past, which filled up the craters with ice and debris; the debris remained after the glaciers retreated. The craters are largely free of meteorite impacts inside, so it’s believed they filled with debris less than a few million years ago.

This video and accompanying images, taken by the High Resolution Stereo Camera (HRSC) on board ESA’s Mars Express spacecraft, show an unusual flow deposit on the floors of two adjacent impact craters in the eastern Hellas Planitia region, indicating possible glacial processes.

The stereo capability of the HRSC makes it possible to animate 3D anaglyph images, based on digital elevation models. The image data have been acquired during Mars Express orbit 451 from an altitude of 590 kilometres with an original resolution of 29 metres per pixel.

The unusual ‘hourglass’-shaped structure is located in the southern-hemisphere highland terrain of Promethei Terra at the eastern rim of the Hellas Basin, at about latitude 38 South and longitude 104 East.

Most likely the surface morphology is formed by the ‘creep’ of ice and debris, similar to either terrestrial rock glacier landforms or debris covered glaciers which are commonly found in high latitudes and alpine regions.

‘Talus’ material (or ‘scree’, the broken rocks that lie on a steep mountainside or at the base of a cliff) and ice-rich debris accumulated at the base of the remnant massif and filled the upper bowl-shaped impact crater which is approximately nine kilometres wide. The debris-ice mixture then flowed through a breach in the crater rim into a 17-kilometre wide crater, 500 metres below, taking advantage of the downward slope.***image4:left***

Of particular interest is the age of these surfaces, which seem to be fairly intact over a wide area. It has been shown recently that there is some evidence that glaciers were shaping the Martian surface at mid latitudes and even near the equator until a few million years ago.

Typical evidence for a significant loss of volatiles, such as pits and other depressions can be observed on all debris surfaces surrounding the remnant massif.

The statistical analysis of the number of craters formed by meteorite impacts used for age determination also shows that part of the surface with its present-day glacial characteristics was formed only a few million years ago.

Original Source: Mars Express

Posted on by Fraser Cain

Astrophoto: The Planet Jupiter by Mike Salway

The Planet Jupiter by Mike Salway
Thirty years ago the clearest views of the planet Jupiter could only be obtained from multi-million dollar robotic space probes, like the twin Voyager missions sent to survey the outer planets. As recently as five years ago, the atmosphere still hopelessly blurred views of Jupiter, or any other planet, seen from the surface of the Earth through telescopes. All of that has changed thanks to the digital revolution in photography. Now, people with the interest, a modest telescope and a common web camera can learn to take planetary portraits that rival some the best from NASA.

The accompanying photographs of Jupiter and its moon Ganymede, in orbit around the Sun, 365 million miles from our planet, were produced by Mike Salway, an Australian amateur astronomer using a unguided 10 inch Dobsonian telescope and a ToUCam web camera. The pictures were produced from images taken on March 12, 2006. The clarity of each image is similar to pictures taken by Voyager after it had traveled over 90 percent of the distance from Earth to Jupiter.

Taking planetary images from the ground using modest equipment is still a daunting challenge that requires patience, ingenuity and talent. For example, each of the three pictures featured here required Mike to take 450 separate exposures at five frames per second over a space of ninety seconds. Using commercially available software to pick out the best frames, Mike was able to identify the clearest images from each set, digitally combine then enhance them and produce one final picture.

Mike not only captured this trio of beautiful images, he created a short sixteen-frame movie showing the planet in rotation! Each frame is separated by approximately five minutes; therefore the movie spans the planet’s rotation over a period of almost an hour and a half. The clarity of this animation also harks back to those taken as Voyager approached Jupiter in 1979.

One of the three images has been arrowed to indicate the location of a new storm in Jupiter’s atmosphere that has taken on the same hues and characteristics of the Great Red Spot – a storm that has persisted for over three hundred years. Nicknamed Red Jr, this new disturbance is still quite huge and capable of swallowing several Earths.

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 Mark Mortimer

Book Review: Universe


Big topics need big books. You can’t get a much bigger topic than the universe, and the book edited by Martin Rees entitled Universe – The Definitive Visual Guide fits the bill for size. This is a large book in dimensions and content. It covers most of the interesting lore in cosmology and astronomy and is chock full of pictures, explanations and trivia of astronomical history. Big is the order of the day and big appetites will be well satiated after reading this.

The universe is the be all and end all. Having a visual reference doesn’t come easy for such a scope, especially when much lies outside our eye’s realm. The universe is all of space and all of time. It is all of matter and all of energy. Our eyes can detect some of the matter and energy on Earth. But, we don’t see quarks or super galaxy cluster filaments. Yet we know they exist. We also can’t see the opaque universe at the beginning of time or the appearance of the universe after its deep freeze. Yet we believe that these also have a place in our existence. Hence, with imagination and the power of knowledge, we can represent images and concepts on flat pieces of paper to visualize the entire universe.

This book is billed as a definitive visual guide. As such, readers get exciting descriptive answers to almost every relevant astronomical question. The book has three main sections. The introduction establishes the physical basis for the universe; its size, its matter, its inter-relations. This continues with descriptions on man’s interactions, from choosing binoculars to describing the space race. Following this extensive and in-depth introduction is a section on the material objects. There are planets, stars, galaxies and all the rest that amateur and professional astronomers have detected and mapped. The last section provides the standard information on night sky viewing. All 88 constellations and monthly night sky charts fill the pages in wonderful detail. This one-stop book is an excellent reference for space related visual images.

Calling a book a definitive visual guide is risky. Often books with this title quickly find themselves in the sell-off bin of the store as they contain little more than stock footage. There is lots of stock footage in this book, but principally because there is only one main source, NASA. Nevertheless, this isn’t a constraint, as many other sources like the Galaxy Picture Library and the Anglo Australian Observatory contribute. Further, this book doesn’t showcase any source. Images are woven throughout the text to glorify the subject matter rather than the group or machine behind the camera shutter. With judicious editing, it is not the source that sparkles but the subject of the pictures.

As much as Martin Rees is billed as the general editor, there is obviously more here than one person could conveniently accomplish. In all, the book lists 19 editors with many others contributing. With so many cooks, there is the concern that the broth may spoil. Not in this case. There is little duplication. The hundreds of pages and multitude of topics blend into each other in harmony. The section describing the planets is particularly nice, as some of the most recent images from the Huygens probe and the Mars explorers grace the pages. Each page spread itself is 30 by 50 cm, hence allowing for majestic sweeps of other worlds. Dominant features of every photographed planet and many moons are described as if for a travelogue. Chasms, canals, peaks and striations are named, located and graced with a sense of shape and importance. This same attention to detail extends in the following section to stars, nebula, supernova and black holes. Most alluring of all though is the preponderance of choice images. After all, this book is called a definitive visual guide.

Being big with lots of pictures, however, doesn’t always make for a stimulating book. This visual guide is no different. It is dry like an encyclopaedia. You won’t sit for hours in your favourite reading chair. It is both too heavy to hold comfortably and too staid. There is no plot to capture the imagination. Like a reference, it simply states particulars then heads off to the next topic. Understandably, the universe is so big there is little opportunity to diverge. In any case, the pages are very well appointed, not too busy nor too sparse. The topics are current and with enough depth to satisfy the generalist. It is an excellent reference source for the backyard astronomer preparing for their evening viewing. Or, it can provide a rich background for young researchers.

Our universe, from an astronomer’s perspective, is a wonderful, visual cornucopia. The book Universe – The Definitive Visual Guide edited by Martin Rees aims to satisfy the appetites for those branching into this domain. This big book does justice to the largess of the universe.

Review by Mark Mortimer

Read more reviews online or purchase a copy from Amazon.com

Posted on by Fraser Cain

What’s Up This Week – March 20 – March 26, 2006

M44: The Beehive. Image credit: NOAO/AURA/NSF. Click to enlarge.
Greetings, fellow SkyWatchers! This week brings darker skies, bright star clusters, meteor showers, unusual nebulae and a chance to participate in G.L.O.B.E. at Night! Whether you use a telescope, binoculars, or just your eyes – you’ll find a wealth of astronomy activities this week. So turn an eye to the sky, because….

Here’s what’s up!

Monday, March 20 – Tonight the obscure constellation of Cancer is now well placed for observation – so why not compare views of the two Messier clusters found there? They’re both binocular and telescope easy!

M44 is one of the most easily recognized studies in the night sky. Like the Pleiades and Hyades in Taurus, Praesepe, “The Manger,” comes to us as a discovery from antiquity. Its myths include one about two neighboring bright stars – Asellus Australis and Asellus Borealis. These two stars are said to be donkeys taking meals from the manger. Known to amateur astronomers as “the Beehive Cluster,” Galileo was the first to discern its stellar nature. Even with his modest scope, he resolved around forty of its brightest members. Modern telescopes have determined that at least 200 of the 350 or more stars visually associated with M44 move together and are a part of the 700 million year old open cluster.

Open cluster M67 is little less than a fist width southeast of M44, or about a finger-width west of visual star – Acubens (Alpha Cancri). Five times further away than M44, and at 3.5 billion years of age, M67 is one of the oldest open clusters in our galaxy. Its brightest stars have already gone “white dwarf” after long ago exhausting their nuclear fuel. You’ll notice it’s quite dense and surprisingly faint for a Messier study. Its discoverer, Johann Gottfried Koehler, was unable to resolve any stars! Today’s telescopes resolve dozens – even hundreds – of cluster members while most binoculars will find it to appear quite “galactic!”

Be on the lookout for Antares as it and the Moon rise together. There will be an occultation tonight, so be sure to check IOTA for times and details in your area.

Tuesday, March 21 – How about one last open cluster before going galaxy hunting? Our study – M48 – is roughly 3 degrees southeast of Zeta Monocerotis. Like M44 in Cancer, M48 lies within the limits of unaided sight. Its brightest member is a spectral type A star, intrinsically some 70 times brighter than our own Sun, but it only appears close to 9th magnitude thanks to 1500 light-years separating us. M48 is quite large, and will show several dozen stars within reach of small scopes and binoculars.

Spring has arrived and with it comes the time of galaxies. To celebrate this new astronomical season, have a look at NGC 2903. Located about a finger-width south-southeast of Lambda Leonis, this 8.9 magnitude tilted spiral looks very much like a slightly fainter version of M81 in Ursa Major. Larger scopes easily catch hints of the galaxy’s spiral extensions and all will show considerable brightening toward the very expansive core region!

Wednesday, March 22 – Born on this day in 1799 was Friedrich Argelander, a compiler of star catalogues. Argelander also studied variable stars and created the first international astronomical organization entitled simply the “Astronomical Society.”

If you’d like to join in an Astronomical Society event, then take the time to visit the Astronomical League webpages and participate in the National Optical Astronomy Observatory (NOAO) call to all observers to participate in G.L.O.B.E. at Night program. No special equipment is needed and your observations “count”!

With a later moonrise tonight, let’s have a look at two meteor showers. We’ll start first with the Camelopardalids. These have no definite peak, and a screaming fall rate of only one per hour. They do have one claim to fame however – these are the slowest meteors known – arriving at a speed of only 7 kilometers per second!

Far more interesting will be to watch for the peak of the March Geminids. These were first discovered and recorded in 1973, then confirmed in 1975. With a much improved fall rate of about 40 per hour, these faster meteors will be fun to follow. When you do see a bright streak, trace it back to its point of origin. Did you see a Camelopardalid? Or a March Geminid?

While out, let’s use the late rise of the Moon to our advantage and head about 2 degrees northeast of star 13 in Monoceros. Our study will be NGC 2261 – more commonly known as “Hubble’s Variable Nebula.” Named for Edwin Hubble, this 10th magnitude object is very blue in appearance through larger apertures, and a true enigma. The fueling star, the variable R Monocerotis, does not display a normal stellar spectrum and may be a proto-planetary system. R is usually lost in the high surface brightness of the “comet-like” structure of the nebula, yet the nebula itself varies with no predictable timetable – perhaps due to dark masses shadowing the star. We do not even know how far away it is, because there is no detectable parallax!

Thursday, March 23 – Today in 1840, the first photograph of the Moon was taken. The daguerreotype plate was exposed by American astronomer and medical doctor, J. W. Draper. Draper’s fascination with chemical responses to light also led him to another first — a photo of the Orion Nebula.

Tonight let’s have a look at a study in light and dark as we view our large binocular and telescope study for this evening. You’ll find it located roughly halfway between Sirius and Alpha Monocerotis – NGC 2359. Known as “Thor’s Helmut,” this bubble-like emission nebula was blown into existence by the superheated blue giant star in its center. NGC 2359 spans about 30 light-years some 15,000 light-years away. The supercharging Wolf-Rayet star produces high speed stellar winds which may have interacted with a nearby molecular cloud giving this strange nebula its curved shape. At magnitude 11, “Thor’s Helmut” is an unusual observation to add to your collection of “head gear.”

Friday, March 24 – Today is the birthday of Walter Baade. Born in 1893, Baade was the first to resolve the Andromeda galaxy’s companions into individual stars and developed the concept of the two types of stellar populations in galaxies. Among his many achievements, Baade is also well known for discovering an area towards our galactic center (M24) which is relatively free of dust, now known as “Baade’s Window.”

Although “Baade’s Window” is a summer sky study, we can take the time this evening to study an area on the opposite side of the sky. Astronomers use a celestial coordinate system based on “hours:minutes:seconds” for east-west location (right ascension – RA) and “degrees” for north-south (declination – DEC) position. It just so happens that should you turn eye, binoculars, or telescope to a RA-DEC location completely complimentary to the center of Baade’s Window (RA=6hrs:16mins, DEC=18.29 degrees) you will find yourself about mid-way between 3.2 magnitude Mu Geminorum and 4.4 magnitude Nu Orionis. And it is precisely there that you will see something that is almost completely the opposite of what can be seen in Baade’s Window – which is to say, “not much.”

Saturday, March 25 – Today in 1655, Titan – Saturn’s largest satellite – was discovered by Christian Huygens. 350 years later, a probe named for Huygens captured the attention of the world as it descended by parachute onto Titan’s surface and sent back information on that distant moon. Huygens also went on to discover Saturn’s ring system in 1655. So while Saturn still rides high in the sky, make your own return visit and tour Saturn’s rings and satellites. The siren song of Titan awaits you!

Also on this date in 1951, 21 cm wavelength radiation from atomic hydrogen in the Milky Way was first detected. 1420 MHz H I, neutral – but non-molecular, hydrogen studies continue to form the basis of large parts of modern radio astronomy. Milky Way H I regions are generally free of stars since they heat the stable hydrogen gases and cause them to emit light. Using 21 cm radio-telescopy, astronomers can map the distribution of non-stellar matter in the interstellar medium – the vast regions of space between the stars. Because radio waves can penetrate dust also found in the interstellar medium, we know much more about the distribution of hydrogen gas in our galaxy than would otherwise be possible.

Although stable hydrogen gas is invisible optically, its presence is especially concentrated along the disk of our galaxy in its vast spiral arms. One such region is associated with the Orion Complex. So take some time to scan the sky due south of 3.4 magnitude Eta Orionis and note how few stars are visible between it and 4.2 magnitude 29 Orionis – some 5 and a half degrees away. Such regions are known to have high concentrations of 21 cm radiation caused by hydrogen gas that has yet to begin coalescing into new Suns such as our own.

Sunday, March 26 – Tonight, let’s have a look at the “Eight-burst Planetary.” But, we have to warn you, it isn’t easy for the northern hemisphere. Start by locating Alpha Hydrae. Now drop more than a hand span due south to Psi in Vela. With Psi centered at low power, you can simply wait a little less than half an hour for NGC 3132 to “drift” into the field, or move due east 7 degrees. Either way should reveal this superb 8th magnitude “Southern Ring Nebula!” Look for a “tilt” in brightness across this 2000 light-year distant ring plus its central star. Use high power – this one is less than half the size of the famed “Northern Ring Nebula” – M57.

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