Posted on by Fraser Cain

Water detection at Gusev crater described

Color picture of Gusev crater. Image credit: ESA Click to enlarge
A large team of NASA scientists, led by earth and planetary scientists at Washington University in St. Louis details the first solid set of evidence for water having existed on Mars at the Gusev crater, exploration site of the rover Spirit.

Using an array of sophisticated equipment on Spirit, Alian Wang, Ph.D., Washington University senior research scientist in earth and planetary sciences in Arts & Sciences, and the late Larry A. Haskin, Ph.D., Ralph E. Morrow Distinguished University Professor of earth and planetary sciences, found that the volcanic rocks at Gusev crater near Spirit’s landing site were much like the olivine-rich basaltic rocks on Earth, and some of them possessed a coating rich in sulfur, bromine, chlorine and hematite, or oxidized iron. The team examined three rocks and found their most compelling evidence in a rock named Mazatzal.

The rock evidence indicates a scenario where water froze and melted at some point in Martian history, dissolving the sulfur, chlorine and bromine elements in the soil. The small amount of acidic fluids then react with the rocks buried in the soil and formed these highly oxidized coatings.

Trench-digging rover

During its traverse from landing site to Columbia Hills, the rover Spirit dug three trenches, allowing researchers to detect relatively high levels of magnesium sulfate comprising more than 20 percent of the regolith ? soil containing pieces of small rocks ? within one of the trenches, the Boroughs trench. The tight correlation between magnesium and sulfur indicates an open hydrologic system ? these ions had been carried by water to this site and deposited.

Spirit’s fellow rover Opportunity earlier had detected a history of water at another site on Mars, Meridiani planum. This study (by Haskin et al.) covered the investigation of Spirit rover sols (a sol is a Martian day) 1 through 156, with the major discoveries occurring after sol 80. After the findings were confirmed, Spirit traversed to the Columbian hills, where it found more evidence indicating water. The science team is currently planning for sol 551 operation of Spirit rover, which is only 55 meters away from the summit of Columbia Hills.

Spirit was on sol 597 on Sept 6 and on the summit of Husband Hill.

“We will stay on the summit for a few weeks to finish our desired investigations, then go downhill to explore the south inner basin, especially the so-called ‘home-plate,’ which could be a feature of older rock or a filled-in crater,” Wang said. “We will name a major geo-feature in the basin after Larry.”

Buried again and again

“We looked closely at the multiple layers on top of the rock Mazatzal because it had a very different geochemistry and mineralogy,” said Wang. “This told us that the rock had been buried in the soil and exposed and then buried again several times over the history. There are chemical changes during the burial times and those changes show that the soil had been involved with water.

“The telltale thing was a higher proportion of hematite in the coatings. We hadn’t seen that in any previous Gusev rocks. Also, we saw very high chlorine in the coating and very high bromine levels inside the rock. The separation of the sulfur and chlorine tells us that the deposition of chlorine is affected by water.”

While the multilayer coatings on rock Mazatzal indicates a temporal occurrence of low quantity water associated with freezing and melting of water, the sulfate deposition at trench sites indicates the involvement of a large body of water.

“We examined the regolith at different depths within the Big Hole and the Boroughs trenches and saw an extremely tight correlation between magnesium and sulfur, which was not observed previously,” Wang said. “This tells us that magnesium sulfate formed in these trench regoliths. The increasing bromine concentration and the separation of chlorine from sulfur also suggests the action of water. We don’t know exactly how much water is combined with that. The fact that the magnesium sulfate is more than 20 percent of the examined regolith sample says that the magnesium and sulfur were carried by water to this area from another place, and then deposited as magnesium sulfate. A certain amount of water would be needed to accomplish that action.”

Original Source: WUSTL News Release

Posted on by Fraser Cain

Future Titan Mission Shield Blasted By Radiation

Solar power heats NASA space shield material. Image credit: Bill Congdon, Applied Research Associates. Click to enlarge
For the last two years, tests have been conducted at Sandia National Laboratories? National Solar Thermal Test Facility to see how materials used for NASA?s future planetary exploration missions can withstand severe radiant heating.

The tests apply heat equivalent to 1,500 suns to spacecraft shields called Advanced Charring Ablators. The ablators protect spacecraft entering atmospheres at hypersonic speeds.

The test facility includes a 200-ft. ?solar tower? surrounded by by a field of hundreds of sun-tracking mirror arrays called heliostats. The heliostats direct sunlight to the top of the tower where the test objects are affixed.

Under a work agreement, researchers at Sandia and Applied Research Associates, Inc. are conducting the tests for NASA Marshall?s In-Space Propulsion/Aerocapture Program. The R&D effort is tied to NASA?s plan for a future Titan mission with an orbiter and lander. Titan is Saturn?s largest moon.

The tests are led by Sandia solar tower expert Cheryl Ghanbari and Bill Congdon, project principal investigator for Applied Research Associates, Inc.

Solar power heats NASA space shield material. The tests apply heat equivalent to 1,500 suns to spacecraft shields. (Photo courtesy of Bill Congdon, Applied Research Associates, Inc.)
Download 300dpi JPEG image, ?solar-heat.jpg,? 376K (Media are welcome to download/publish this image with related news stories.)The tests are designed to simulate atmospheric heating of spacecraft that enter Titan, including low levels of convective heating combined with relatively high levels of thermal radiation.

The primary ablator candidates for the Titan mission are low-density silicones and phenolics, all under 20 pounds-per-cubic-foot density.

To date, more than 100 five-inch diameter samples have been tested in the solar environment inside the tower?s wind tunnel using a large quartz window.

Congdon says because of Titan?s relatively high radiation environment, some initial concerns had to be put to rest through testing. He says radiation might penetrate in-depth within the ablator, causing an increased ?apparent? thermal conductivity and degrading insulation performance.

?Radiation could also generate high-pressure gasses within the ablator leading to spallation,? Congdon says.

?We have been testing at the solar tower to see how the candidate Titan materials can withstand the expected range of heating conditions,? Ghanbari says. ?Titan has a nitrogen-rich atmosphere and nitrogen is used in the tests to similarly reduce ablator oxidation, while energy from the sun-tracking heliostats is focused on the samples.?

Congdon says ground tests are necessary to understand and model surface ablation of the materials that will be severely heated during Titan entry.

During thermal radiation testing conducted in the solar tower, all of these concerns were addressed and found not to be a problem for the ablators of interest.

About the tests

The National Solar Thermal Test Facility consists of an eight-acre field of 220 solar-collection heliostats and a 200-ft.-tall tower that receives the collected energy at one of several test bays. A single heliostat includes 25 mirrors that are each four feet square. Total collection area of 220 heliostats is 88,000-square feet.

Because the heliostats are individually computer controlled, test radiation can be a shaped pulse as well as a square wave in terms of intensity vs. time, says Ghanbari.

Test samples are mounted high in the receiver tower, and the heliostats direct the sunlight upward to irradiate the sample surface. The samples are mounted in a water-cooled copper plate inside the wind tunnel with a quartz window that allows entry of the concentrated radiation.

Exposure is controlled by a fast-moving shutter and by pre-programmed heliostat movement. Radiation flux is calibrated before and after each test by a radiometer installed to occupy the same position as the test sample. Cooling effects from imposed surface flows are calibrated via a flat-plate slug calorimeter.

The materials are subjected to square pulse environments at flux levels of 100 and 150 W/cm2 for time periods that far exceed predicted flight durations for such high heating. They are also tested to ?exact? flux vs. time environments (simulating actual flight conditions) using programmed heliostat focusing at the solar tower facility.

The material samples are installed in the tower?s wind tunnel and exposed to the solar beam at flux levels up to 150 W/cm2, which is approximately 1,500 times the intensity of the sun on earth on a clear day. During exposure, air blows past the sample at about mach 0.3 with a high-speed nitrogen sub-layer close to the sample surface.

Ghanbari says tests can be conducted only during about four hours midday bracketing solar noon. Haze, clouds, and high winds that affect the heliostats can degrade test conditions.

Current results

?All of the candidate materials showed no spallation and very good thermal performance to these imposed environments,? Congdon says. Recently, five 12-inch by 12-inch panel samples were tested on top of the tower. Up to 20 additional 12-inch panels will be tested late in the summer followed by testing of 2-foot by 2-foot panels later in the year.

Additional tests for convective heating have been conducted on identical material samples at the Interaction Heating Facility (IHF) at NASA?s Ames Research Center.

Origianl Source: Sandia National Labs

Posted on by Fraser Cain

Earth-Like Planets Should Be Easy Spot While They’re Forming

***image***Astronomers looking for earth-like planets in other solar systems ? exoplanets ? now have a new field guide thanks to earth and planetary scientists at Washington University in St. Louis.

Bruce Fegley, Ph.D., Washington University professor of earth and planetary sciences in Arts & Sciences, and Laura Schaefer, laboratory assistant, have used thermochemical equilibrium calculations to model the chemistry of silicate vapor and steam-rich atmospheres formed when earth-like planets are undergoing accretion . During the accretion process, with surface temperatures of several thousands degrees Kelvin (K), a magma ocean forms and vaporizes.

“What you have are elements that are typically found in rocks in a vapor atmosphere,” said Schaefer. “At temperatures above 3,080 K, silicon monoxide gas is the major species in the atmosphere. At temperatures under 3,080 K, sodium gas is the major species. These are the indicators of an earth-like planet forming.”

At such red-hot temperatures during the latter stages of the exoplanets’ formation, the signal should be distinct, said Fegley.

“It should be easily detectable because this silicon monoxide gas is easily observable,” with different types of telescopes at infrared and radio wavelengths, Fegley said.

Schaefer presented the results at the annual meeting of the Division of Planetary Sciences of the American Astronomical Society, held Sept. 4-9 in Cambridge, England. The NASA Astrobiology Institute and Origins Program supported the work.

Forming a maser

Steve Charnley, a colleague at NASA AMES, suggested that some of the light emitted by SiO gas during the accretion process could form a maser ? Microwave Amplification by Stimulation Emission of Radiation. Whereas a laser is comprised of photons in the ultraviolet or visible light spectrum, masers are energy packets in the microwave image.

Schaefer explains: “What you basically have is a clump of silicon monoxide gas, and some of it is excited into a state higher than ground level. You have some radiation coming in and it knocks against these silicon monoxide molecules and they drop down to a lower state.

“By doing that, it also emits another photon, so then you essentially have a propagating light. You end up with this really very high intensity illumination coming out of this gas.”

According to Schaefer, the light from newly forming exoplanets should be possible to see.

“There are natural lasers in the solar system,” she said. “We see them in the atmospheres of Mars and Venus, and also in some cometary atmospheres.”

In recent months, astronomers have reported earth-like planets with six to seven times the mass of our earth. While they resemble a terrestrial planet like earth, there has not yet been a foolproof method of detection. The spectra of silicon monoxide and sodium gas would be the indication of a magma ocean on the astronomical object, and thus an indication a planet is forming, said Fegley.

The calculations that Fegley and Schaefer used also apply to our own earth. The researchers found that during later, cooler stages of accretion (below 1,500 K), the major gases in the steam-rich atmosphere are water, hydrogen, carbon dioxide, carbon and nitrogen, with the carbon converting to methane as the steam atmosphere cools.

Original Source: WUSTL News Release

Posted on by Fraser Cain

Asteroid Ceres Could Have Large Amounts of Water

Hubble tracks Ceres. Image credit: NASA/ESA Click to enlarge
Observations of 1 Ceres, the largest known asteroid, have revealed that the object may be a “mini planet,” and may contain large amounts of pure water ice beneath its surface.

The observations by NASA’s Hubble Space Telescope also show that Ceres shares characteristics of the rocky, terrestrial planets like Earth. Ceres’ shape is almost round like Earth’s, suggesting that the asteroid may have a “differentiated interior,” with a rocky inner core and a thin, dusty outer crust.

“Ceres is an embryonic planet,” said Lucy A. McFadden of the Department of Astronomy at the University of Maryland, College Park and a member of the team that made the observations. “Gravitational perturbations from Jupiter billions of years ago prevented Ceres from accreting more material to become a full-fledged planet.”

The finding will appear Sept. 8 in a letter to the journal Nature. The paper is led by Peter C. Thomas of the Center for Radiophysics and Space Research at Cornell University in Ithaca, N.Y., and also includes project leader Joel William Parker of the Department of Space Studies at Southwest Research Institute in Boulder, Colo.

Asteroid Ceres is approximately 580 miles (930 kilometers) across, about the size of Texas. It resides with tens of thousands of other asteroids in the main asteroid belt. Located between Mars and Jupiter, the asteroid belt probably represents primitive pieces of the solar system that never managed to accumulate into a genuine planet. Ceres comprises 25 percent of the asteroid belt’s total mass. However, Pluto, our solar system’s smallest planet, is 14 times more massive than Ceres.

The astronomers used Hubble’s Advanced Camera for Surveys to study Ceres for nine hours, the time it takes the asteroid to complete a rotation. Hubble snapped 267 images of Ceres. From those snapshots, the astronomers determined that the asteroid has a nearly round body. The diameter at its equator is wider than at its poles. Computer models show that a nearly round object like Ceres has a differentiated interior, with denser material at the core and lighter minerals near the surface. All terrestrial planets have differentiated interiors. Asteroids much smaller than Ceres have not been found to have such interiors.

The astronomers suspect that water ice may be buried under the asteroid’s crust because the density of Ceres is less than that of the Earth’s crust, and because the surface bears spectral evidence of water-bearing minerals. They estimate that if Ceres were composed of 25 percent water, it may have more water than all the fresh water on Earth. Ceres’ water, unlike Earth’s, would be in the form of water ice and located in the mantle, which wraps around the asteroid’s solid core.

Besides being the largest asteroid, Ceres also was the first asteroid to be discovered. Sicilian astronomer Father Giuseppe Piazzi spotted the object in 1801. Piazzi was looking for suspected planets in a large gap between the orbits of Mars and Jupiter. As more such objects were found in the same region, they became known as “asteroids” or “minor planets”.

Original source: Hubble News Release

Posted on by Fraser Cain

Biblis Patera Volcano

Biblis Patera. Image credit: ESA Click to enlarge
This image, taken by the High Resolution Stereo Camera (HRSC) on board ESA?s Mars Express spacecraft, shows the Biblis Patera volcano, located in the western part of the Tharsis rise on Mars.

The HRSC obtained this image during orbit 1034 with a ground resolution of approximately 10.8 metres per pixel. The scene shows the region of Biblis Patera, at approximately 2.0? North and 236.0? East.

Located between Olympus Mons and Tharsis Montes, the volcano Biblis Patera is 170 kilometres long, 100 kilometres wide and rises nearly three kilometres above its surroundings.

The bowl-shaped depression (the ?caldera?) may have been formed as the result of collapse of the magma chamber during eruptions of the volcano. The caldera has a diameter of 53 kilometres and extends to a maximum depth of roughly 4.5 kilometres.

The morphology of the caldera suggests that multiple collapse events have occurred.The radial depressions and faint concentric circles on the flanks of the volcano are most likely faults associated with the formation of Biblis Patera.

In the south-west (top left), the linear features extending north-west to south-east appear to be faults. Surrounding Biblis Patera there are more faults with a similar orientation and which may be related to the formation of the Tharsis Rise.

Biblis Patera is older than the surrounding plains, which consist of lava flows originating from Pavonis Mons (the middle one of the Tharsis Montes volcanoes). In the main colour image, clouds obscure the surface to the north-east of the caldera (bottom right), making it appear grey and less reddish-orange in colour.

The stereo and colour capability and the high-resolution coverage of extended areas with the HRSC allow the improved study of the complex geological evolution of the Red Planet.

By supplying new image data for volcanoes like Biblis Patera, the HRSC provides scientists with the opportunity to better understand the morphology and volcanic history of Mars.

Data from the HRSC, coupled with information from other instruments on Mars Express and other missions, improves our understanding of this fascinating planet.

Original Source: ESA Mars Express

Posted on by Fraser Cain

Surprising Insights Into Comet Tempel 1

Comet Tempel 1. Image credit: NASA/JPL Click to enlarge
Painting by the numbers is a good description of how scientists create pictures of everything from atoms in our bodies to asteroids and comets in our solar system. Researchers involved in NASA’s Deep Impact mission have been doing this kind of work since the mission’s July 4th collision with comet Tempel 1.

“Prior to our Deep Impact experiment, scientists had a lot of questions and untested ideas about the structure and composition of the nucleus, or solid body of a comet, but we had almost no real knowledge,” said Deep Impact principal investigator Dr. Michael A’Hearn, a professor of astronomy at the University of Maryland, College Park. “Our analysis of data produced by Deep Impact is revealing a great deal, much of it rather surprising.”

For example, comet Tempel 1 has a very fluffy structure that is weaker than a bank of powder snow. The fine dust of the comet is held together by gravity. However, that gravity is so weak, if you could stand on the bank and jump, you would launch yourself into space.

Another surprise for A’Hearn and his colleagues was the evidence of what appears to be impact craters on the surface of the comet. Previously, two other comets had their nuclei closely observed and neither showed evidence of impact craters.

“The nucleus of Tempel 1 has distinct layers shown in topographic relief ranging from very smooth areas to areas with features that satisfy all the criteria for impact craters, including varying size,” A’Hearn said. “The problem in stating with certainty that these are impact craters is that we don’t know of a mechanism by which some comets would collide with the flotsam and jetsam in our solar system, while others would not.?

According to A’Hearn, one of the more interesting findings may be the huge increase in carbon-containing molecules detected in spectral analysis of the ejection plume. This finding indicates comets contain a substantial amount of organic material, so they could have brought such material to Earth early in the planet’s history when strikes by asteroids and meteors were common.

Another finding is the comet interior is well shielded from the solar heating experienced by the surface of the comet nucleus. Mission data indicate the nucleus of Tempel 1 is extremely porous. Its porosity allows the surface of the nucleus to heat up and cool down almost instantly in response to sunlight. This suggests heat is not easily conducted to the interior and the ice and other material deep inside the nucleus may be pristine and unchanged from the early days of the solar system, just as many scientists had suggested.

“The infrared spectrometer gave us the first temperature map of a comet, allowing us to measure the surface’s thermal inertia, or ability to conduct heat to the interior,” said Dr. Olivier Groussin, the University of Maryland research scientist who generated the map.

It is this diligent and time consuming analysis of spectral data that is providing much of the “color” with which Deep Impact scientists are painting the first ever detailed picture of a comet. For example, researchers recently saw emission bands for water vaporized by the heat of the impact, followed a few seconds later by absorption bands from ice particles ejected from below the surface and not melted or vaporized.

“In a couple of seconds the fast, hot moving plume containing water vapor left the view of the spectrometer, and we are suddenly seeing the excavation of sub-surface ice and dust,” said Deep Impact co-investigator Dr. Jessica Sunshine, with Science Applications International Corporation, Chantilly, Va. “It is the most dramatic spectral change I’ve ever seen.”

These findings are published in the September 9 issue of the journal Science, and were presented this week at the Division for Planetary Sciences meeting in Cambridge, England. Mission scientists are filling in important new portions of a cometary picture that is still far from finished.

The University of Maryland is responsible for overall Deep Impact mission science, and project management is handled by JPL. The spacecraft was built for NASA by Ball Aerospace & Technologies Corporation, Boulder, Colo. JPL is a division of the California Institute of Technology, Pasadena, Calif.

For more information about the Deep Impact mission on the Internet, visit: http://www.nasa.gov/deepimpact .

original Source: NASA News Release

Posted on by Fraser Cain

Saturn’s Deep Dynamic Clouds

Infrared mapping of Saturn’s clouds by Cassini. Image credit: NASA/JPL/SSI Click to enlarge
Cassini scientists have discovered an unexpected menagerie of clouds lurking in the depths of Saturn’s complicated atmosphere.

“Unlike the hazy, broad, global bands of clouds regularly seen in Saturn’s upper atmosphere, many of the deeper clouds appear to be isolated, localized features,” said Dr. Kevin H. Baines, a member of the visual and infrared mapping spectrometer team from NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “They come in a large variety of sizes and shapes, including circular and oval shapes, donut shapes, and swirls.”

These clouds are deep in the atmosphere, about 30 kilometers (19 miles) underneath the upper clouds usually seen on Saturn. They also behave differently from those in the upper atmosphere and are made of different materials. They are made of either ammonium hydrosulfide or water, but not ammonia — generally thought to comprise the upper clouds.

Scientists are using the motions of these clouds to understand the dynamic weather of Saturn’s deep atmosphere and get a three-dimensional global circulation picture of Saturn. They have mapped low-altitude winds over nearly the entire planet. Comparing these winds to the winds at higher altitudes has led them to conclude that substantial wind shears exist at Saturn’s equator. These shears are similar to wind shear observed by Galileo at Jupiter, indicating that similar processes occur on both planets. The new wind speeds measured by the mapping spectrometer shows that winds blow about 275 kilometers per hour (170 miles per hour) faster deeper down than in the upper atmosphere.

Besides the donut-shaped and other localized cloud systems, dozens of planet girdling lanes of clouds also appear in the new images. Such lanes — known as “zones”– are commonly seen in the upper clouds of Saturn and the other large planets. However, these deeper-level lanes are surprisingly narrow and more plentiful than seen elsewhere, including the upper clouds of Saturn. They also have a much more thread-like structure than normally seen in Jupiter or Saturn’s upper atmosphere, with many of the thread-like structures and swirls connected to discrete cloud “cells,” which look like convective cells on Earth.

The visual and infrared mapping spectrometer took high-resolution, near-infrared images of the deep clouds during four close passes of Saturn between February and July of this year. The images were at a wavelength seven times greater than visible to the human eye and five times greater than available to the Cassini visual camera.

The scientists used a new technique that allowed them to image the deep clouds silhouetted against the background radiation of heat generated by the planet’s interior. Until now, imaging clouds in the depths of Saturn has not been practical since upper-level hazes and clouds obscure the view.

“Instead of using sunlight as the source of radiation for imaging the deep clouds residing underneath the obscuring layer of upper-level clouds, we developed a new technique that uses Saturn’s own thermal heat as a source of light,” said Baines. “It’s like looking down at a well-lit city from an aircraft at night, and seeing the black areas against the city lights, which tells you there is a cloud there blocking the light. Saturn emits its own radiant glow, which looks much like the glow of city lights at night.”

Tracking these thermally-backlit clouds for several days enabled the determination of wind speeds at the deepest levels ever measured on Saturn.

“Understanding cloud development in the depths of Saturn will sharpen our understanding of global circulation throughout Saturn and of the major planets,” said Baines.

These findings were presented in a news briefing at the 37th Annual Meeting of the Division for Planetary Sciences meeting held this week in Cambridge, England.

More information on the Cassini-Huygens mission is available at http://saturn.jpl.nasa.gov and http://www.nasa.gov/cassini .

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA’s Science Mission Directorate, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL. The visual and infrared mapping spectrometer team is based at the University of Arizona.

Original Source: NASA/JPL/SSI News Release

Posted on by Fraser Cain

What’s Up This Week – September 5 – September 11, 2005

NGC 6822. Image credit: Local Group Galaxies Team/NOAO/AURA/NSF. Click to enlarge.
Monday, September 5 – Tonight the Moon will be an exceptional sighting since it will only appear on the western horizon for a very short time after sunset. If you’re looking for a lunar challenge, then look no further than crater Petavius about one third the distance up from southern cusp. This ancient crater is a wonderland of details when on the terminator. Look for rugged walls interrupted by crater Wrottsley on the northwest corner and the elongated Palitzsch on the southeast. If conditions are stable, power up to look for a massive, multi-peaked central mountain region, along with with a deep scar – Rimae Petavius – cutting diagonally across the waved floor.

With the Moon leaving the scene well before full sky dark, our study for this evening is strictly a telescopic challenge for skilled observers. Set your sites about 2 degrees northeast of easy double 54 Sagittarii, and let’s have a look at NGC 6822.

Often referred to as “Barnard’s Galaxy”, for its discoverer (E.E. Barnard – 1884), this usual customer is actually a member of our local galaxy group. For the 4″ to 6″ telescope, this 1.7 million light year distant object will not be easy, but can be achieved with good conditions. Lower power is essential in even larger scopes, and those into the 12″ to 16″ range will see the NGC 6822 burst into stunning resolution. This author has found that “Barnard’s Galaxy” almost appears like an open cluster overlaid with nebulosity, but the experienced eye will clearly see that the “shine” behind the stars is galactic in nature. It’s a very clumpy and unusual galaxy – one that I think you will very much enjoy. Be sure to look for small, pale blue planetary nebula, NGC 6818 in the same field to the north/northwest. This pair rocks!

Tuesday, September 6 – Today celebrates the founding of the Astronomical and Astrophysical Society of America. Started in 1899, it is now known as the American Astronomical Society.

Tonight’s Moon will be very young. Can you spot its very slender crescent at twilight? You’ll find it less than two degrees away from Jupiter. If you chose to observe it, let’s go further south than last night’s study and have a look at Furnerius. Far more shallow and less impressive than Petavius, Furnerius will fade into obscurity as the days go by. This flooded old crater has no central peak, but it does have a much younger crater that has punched a hole in its lava-filled floor. Look for the long “crack” which extends from Furnerius’ north shore to the crater rim. Perhaps it was caused by the impact? Sharp-eyed observers with good conditions and high power will also spot a multitude of small craters both within and caught along Furnerius’ walls. For binocular viewers, can you spot challenging craters Stevenus to the north and Fraunhofer to the south?

Deep Sky binocular observers – I have not forgotten you. Although I cannot hand you an unusual study such as “Barnard’s Galaxy”, what I can point you toward is an open cluster in Cygnus that will look very similar. Aim your binoculars roughly halfway between Gamma (the central star in the “cross”) and Eta (the next brightest due south). The NGC 6871 is truly remarkable in low power, wide field instruments. You will see around a dozen 7th to 9th magnitude star set in an arc and the area will be surrounded by glow of cluster members beyond your resolution. For those who observe with only your eyes? You’ll see it as a brighter patch against the glow of the Milky Way. It’s a beauty!

Wednesday, September 7 – For our friends in southern Africa, tonight gives you an opportunity to witness an astounding event as the Moon occults brilliant Venus for your location. This is a “don’t miss” opportunity, so please check this IOTA webpages for times and locations. Wishing you the best!

For the rest of us? Don’t hide inside at sunset as the crescent Moon, Jupiter, Venus and Spica will make a wonderful appearance on the western horizon. Look for Venus less than a degree away from the Moon!

While we’re out, let’s have a look at the surface of Selene and head once again toward the confusing southern cusp. Tonight’s challenge will be an usual series of craters known as the Rheita Valley. Look for this unusual feature about one third the distance up from the southern cusp. On the terminator you will spy a collection of three craters which we will study at a later date – from north to south, Metius, Fabricus and Jannsen. From Metius, look northeast for the small crater with the thick walls and small central peak. This is Rheita. Along Rheita’s west wall, look for an unsual marking that appears to be a long runnel cut though the rugged terrain. This 500 kilometer long feature looks as though it might have been the result of a series of impacts that are much older than Rheita itself. You will notice that they appear to lap over one another, ending as they progress through older southern crater Young.

Thursday, September 8 – Today in 1966, a legend was born as the television program, “Star Trek” premiered. Its enduring legend, created by Gene Roddenberry, was instrumental to inspiring several generation’s interest in space, astronomy, and technology. The long running series still airs, along with many movie and series sequels. May it continue to “live long and prosper”.

Still hanging tough on sorting out southern lunar features? Then let’s challenge you a bit further as we head south again tonight in search of Piccolomini. Start by identifying the three-ring circus of Theophilus, Cyrillus and Catherina on the terminator at the western edge of Mare Nectaris. Remember our unofficially named lunar ridge, known as Dorsae Beaumont? Good. Then follow it south across Mare Nectaris and see where it ends in shallow crater Beaumont. Further south you will see the ruined ring of Fracastorius on the mare’s southern edge. Keep moving south, because the next major crater you see will be Piccolomini. This is one outstanding little crater with its very thick walls and brilliant central peak. Congratulations on identifying it!

Now, relax. Tonight the Piscid meteor stream will reach its expected maximum of around 5 meteors per hour. This particular shower favours the southern hemisphere. While this branch of the Piscids is a rather unstudied, unusual and diffuse stream that is active all month, the fairly early set of tonight’s Moon will aid you in keeping an eye out for “shooting stars” emanating in the southeast for the northern hemisphere viewers.

Friday, September 9 – In this day in 1839, John Herschel marks history as he made the very first glass plate photograph – and we’re glad he did! The photo was of the famous 40-foot telescope of John’s father, William Herschel. The scope had not been used in decades and was disassembled shortly after its photograph was taken. Later in 1892, one this same day, Edward Emerson Barnard was busy at Lick Observatory as he discovered Jupiter’s innermost moon – Amalthea.

So are you ready to tour the Southern Highlands again? Then let’s start by relocating full disclosed Theophilus, Cyrillus and Catherina. Head southwest until you spot a very magnificent old crater on the terminator. Congratulations! You’ve just identified Maurolycus. Look for several intruding craters on its northern and southern walls. Now power up! Inside of Maurolycus are several small interior punchmarks, but look closely at its southern and eastern wall. Can you see where the strike that formed Maurolycus has actually partially eclipsed a much older crater? Look at where the three come together, sharing a triple border with crater Barocius to the southeast.

Saturday, September 10 – Today is the birthday of James E. Keeler. Born in 1857, American Keeler was a pioneer in the field of spectroscopy and astrophysics. In 1895, Keeler proved that different areas in Saturn’s rings rotate at different velocities. This clearly showed the Saturn’s rings were not solid, but were instead a collection of smaller particles in independent orbit. Can you spot the “Ring King” in Gemini this morning before dawn?

Tonight for most observers, keep a watch on the waxing Moon as you’ll discover that Antares is less than half a degree away to the south.

And speaking of south, let’s walk the Highlands again! Tonight we are heading due west of Maurolycus for an awesome crater on the terminator – Stofler. Stofler is easy to recognize, because this is one battered crater with some very, very steep walls. Stofler itself is old, and probably would have had a smooth floor had it not been the site of some very nasty impacts. Look at its southeastern wall, where you will see two overlaying craters that are the result of meteoroids slamming into the surface. If that weren’t enough, look further at the southern wall where you will see that four more have punched holes in Stofler’s structure. The west wall is the last remaining untouched bridge, leaving the crater floor below it bathed in shadow from the lunar sunrise.

Sunday, September 11 – Today celebrates the birthday of Sir James Jeans. Born in 1877, English-born Jeans was an astronomical theoretician. During the beginning of the 20th century, Jeans worked out the fundamentals of gravitational collapse process. This is an important contribution to the understanding of the formation of solar systems, stars, and galaxies. With the 2005 success of Deep Impact, let’s turn back the hands of time. Twenty years ago on this date, ICE, the International Cometary Explorer, made history as it flew by Comet Giacobini-Zinner, making it the first mission to reach a comet.

Are you afraid to go south again? Then don’t be. Tonight we’ll be looking at a series of craters that lay along the terminator and border the emerging Mare Nubium. Staring just below the central point, look for a line of descending craters. From north to south, they are Ptlomaeus, Alphonsus, Arzachel, tiny Thebit, Purbach and Walter. Congratulations! You’ve learned more lunar features this week than most folks learn in a year. Be sure to look for Tycho even further south and right on the terminator. Tonight its resemblance to an old analog telephone dial is remarkable. Enjoy it now, because you won’t see it this way tomorrow!

Lunacy has returned. No problem! We’ll just study the Moon until skies turn dark again. Until then? May all your journeys be at light speed… ~Tammy Plotner

Posted on by Fraser Cain

Cassini Scientists Make New Ring Discoveries

Saturn Rings. Image credit: NASA/JPL/SSI Click to enlarge
Cassini scientists today (5th September 2005) announced a host of fantastic new results from the spacecraft’s first season of prime ring viewing, including some unexpected findings on Saturn’s rings. These include new structures in Saturn’s diffuse rings, clumps and knots in the F ring – some of which may be small moons – and a completely unexpected spiral ring around the planet in the vicinity of the F ring.

The findings are illustrated in processed images and movies being released today and found at http://ciclops.org, http://saturn.jpl.nasa.gov and http://www.nasa.gov/cassini.

First in the line of new discoveries is that parts of the D ring (Saturn’s innermost ring) have relocated and dimmed. Images show one of the major discrete ring structures in the D ring has changed in brightness and moved inward towards Saturn by as much as 200 kilometres (124 miles). A change over the 25 years since the NASA Voyager spacecraft flybys indicates very short evolutionary lifetimes in the D ring and is of great interest to ring scientists who have been hoping that Cassini would yield information about ring ages and lifetimes.

Dr. Matt Hedman, an imaging team associate at Cornell University, Ithaca, N.Y. said, “I think our Cassini images of the D ring are providing new information about the dynamics and lifetimes of ring particles in a new regime, very close to the planet.”

The delicate G ring encircles the planet at about 170,000 kilometres (106,000 miles) from Saturn’s centre. Cassini scientists have now found a discontinuous bright ring segment, or ‘arc’, in this ring that bear at least a fleeting similarity to those imaged around Neptune in 1989 by NASA’s Voyager 2 spacecraft. Scientists think that long-lived arcs may be created or maintained by a nearby hidden moon. Another thought is that they formed as a result of a meteoroid impact.

Saturn’s tenuous D and G rings contain very little material, and the tiny, icy particles are the size of dust or smoke.

In examining the intriguing, knotted F ring, imaging team scientists have also discovered that the ghostly ringlets flanking the ring’s core are arranged into a spiral structure wound like a spring around the planet. Other spiralling structures seen in the main rings of Saturn, the density and bending waves, are initiated by the gravitational influence of an orbiting moon.

Density and bending waves move across the rings because of the way that relatively massive ring particles exert a gravitational influence on each other and can all move together. In contrast, the spiral structure contains very little mass and appears to originate from material somehow episodically ejected from the core of the F ring and then sheared out due to the different orbital speeds followed by the constituent particles.

“It is a big surprise to see a spiral arm in Saturn’s rings,” said Dr. Sebastien Charnoz, imaging team associate at the University of Paris. “It is very possible that the spiral is a consequence of moons crossing the F ring and spreading particles around, and may be telling us that the F ring might be a very unstable or even an ephemeral structure.”

In the same region, scientists continue to spot small, clump-like features that may be loosely-bound clumps of material or tiny moonlets. Some of them have been sighted for the better part of a year. The solid-or-not nature of these mysterious F ring objects may be determined by repeated sightings: moons will persist, while clumps are expected to dissipate with time.

“We have long suspected that small moons were hiding among the F ring’s strands and producing some of the structures that we see,” said Imaging Team Member Professor Carl Murray of Queen Mary, University of London. “But now the problem is that we are detecting objects that may be either solid moons controlling the ring, or just loose clumps of particles within the ring, and it’s hard to tell the difference. It is like trying to distinguish sheep dogs from sheep in a very large flock.”

A puzzling characteristic of at least two of the clumps/moons is that they appear to cross the F ring periodically. One of them, an object that was discovered last year (S/2004 S6), may be responsible for forming the spiral.

“If the orbit that we have computed for S/2004 S6 is correct, then it must periodically plow through the core of the F ring,” said Dr. Joseph Spitale, an imaging team associate at the Space Science Institute in Boulder, Colo. “The details of that interaction are not understood, but there probably are observable consequences, and maybe the F ring spiral is one of them.”

These ring results were acquired over the summer as Cassini was in a prime ring-viewing period where the spacecraft’s orbit was raised to look down on the rings. The discoveries began almost immediately, with the discovery in May of a tiny moonlet orbiting within the narrow Keeler Gap in Saturn’s outer A ring.

These and other results were presented in a press briefing at the 37th Annual Meeting of the Division for Planetary Sciences meeting held this week in Cambridge, England.

Original Source: PPARC News Release

Posted on by Fraser Cain

Star Gobbles Up Its Friend

Artist’s impression of a pulsar ‘eating’ a companion star. Image credit: ESA Click to enlarge
ESA’s Integral space observatory, together with NASA’s Rossi X-ray Timing Explorer spacecraft, has found a fast-spinning pulsar in the process of devouring its companion.

This finding supports the theory that the fastest-spinning isolated pulsars get that fast by cannibalising a nearby star. Gas ripped from the companion fuels the pulsar’s acceleration. This is the sixth pulsar known in such an arrangement, and it represents a ‘stepping stone’ in the evolution of slower-spinning binary pulsars into faster-spinning isolated pulsars.
“We’re getting to the point where we can look at any fast-spinning, isolated pulsar and say, ‘That guy used to have a companion’,” said Dr Maurizio Falanga, who led the Integral observations, at the Commissariat ? l’Energie Atomique (CEA) in Saclay, France.

‘Pulsars’ are rotating neutron stars, which are created in stellar explosions. They are the remnants of stars that were once at least eight times more massive than the Sun. These stars still contain about the mass of our Sun compactified into a sphere of only about 20 kilometres across.

This pulsar, called IGR J00291+5934, belongs to a category of ‘X-ray millisecond pulsars’, which pulse with the X-ray light several hundred times a second, one of the fastest known. It has a period of 1.67 milliseconds which is much smaller that most other pulsars that rotate once every few seconds.

Neutron stars are born rapidly spinning in collapses of massive stars. They gradually slow down after a few hundred thousand years. Neutron stars in binary star systems, however, can reverse this trend and speed up with the help from the companion star.

For the first time ever, this speeding-up has been observed in the act. “We now have direct evidence for the star spinning faster whilst cannibalising its companion, something which no one had ever seen before for such a system,” said Dr Lucien Kuiper from the Netherlands Institute for Space Research (SRON), in Utrecht.

A neutron star can remove gas from its companion star in a process called ‘accretion’. The flow of gas onto the neutron star makes the star spin faster and faster. Both the flow of gas and its crashing upon the neutron star surface releases much energy in the form of X-ray and gamma radiation.

Neutron stars have such a strong gravitational field that light passing by the star changes its direction by almost 100 degrees (in comparison light passing by the Sun is deflected by an angle which is 200 thousands times smaller). “This ‘gravitational bending’ allows us to see the back side of the star,” points out Prof. Juri Poutanen from the University of Oulu, Finland.

“This object was about ten times more energetic than what is usually observed for similar sources,” said Falanga. “Only some kind of monster emits at these energies, which corresponds to a temperature of almost a billion degrees.”

From a previous Integral result, scientists deduced that because the neutron star has a strong magnetic field, charged particles from its companion are channeled along the magnetic field lines until they slam into the neutron star surface at one of its magnetic poles, forming ‘hot spots’. The very high temperatures seen by Integral arise from this very hot plasma over the accretion spots.

IGR J00291+5934 was discovered by Integral during a routine scan of the sky on 2 December 2004, in the outer reaches of our Milky Way galaxy, when it suddenly flared. On the day after, scientists accurately clocked the neutron star with the Rossi X-ray Timing Explorer.

Rossi observations revealed that the companion is already a fraction the size of our Sun, perhaps as small as 40 Jupiter masses. The binary orbit is 2.5 hours long (as opposed to the year long Earth-Sun orbit). The full system is very tight; both stars are so close that they will fit into the radius of the Sun. These details support the theory that the two stars are close enough for accretion to take place and that the companion star is being cannibalised.

“Accretion is expected to cease after a billion of years or so,” said Dr Duncan Galloway of the Massachusetts Institute of Technology, USA, responsible for the Rossi observations. “This Integral-Rossi discovery provides more evidence of how pulsars evolve from one phase to another – from an initially slowly spinning binary neutron star emitting high energies, to a rapidly spinning isolated pulsar emitting in radio wavelengths.”

The discovery is the first of its kind for Integral (four of the first five rapidly spinning X-ray pulsars were discovered by Rossi). This bodes well in the combined search for these rare objects. Integrals’s sensitive detectors can identify relatively dim and distant sources and so, knowing where to look, Rossi can provide timing information through a dedicated observation extending over the entire two-week period of the typical outburst.

Original Source: ESA Portal