Posted on by Fraser Cain

Full Frame Rhea

Saturn’s moon Rhea. Image credit: NASA/JPL/SSI Click to enlarge
Saturn’s moon Rhea is an alien ice world, but in this frame-filling view it is vaguely familiar. Here, Rhea’s cratered surface looks in some ways similar to our own Moon, or the planet Mercury. But make no mistake – Rhea’s icy exterior would quickly melt if this moon were brought as close to the Sun as Mercury. Rhea is 1,528 kilometers (949 miles) across.

Instead, Rhea preserves a record of impacts at its post in the outer solar system. The large impact crater at center left (near the terminator or boundary between day and night), called Izanagi, is just one of the numerous large impact basins on Rhea.

This view shows principally Rhea’s southern polar region, centered on 58 degrees South, 265 degrees West.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Aug. 1, 2005, at a distance of approximately 255,000 kilometers (158,000 miles) from Rhea and at a Sun-Rhea-spacecraft, or phase, angle of 62 degrees. Image scale is 2 kilometers (1.2 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

Radiation on the Moon

The surface of the Moon is exposed to space radiation. Image credit: NASA Click to enlarge
On the Moon, many of the things that can kill you are invisible: breathtaking vacuum, extreme temperatures and space radiation top the list.

Vacuum and temperature NASA can handle; spacesuits and habitats provide plenty of air and insulation. Radiation, though, is trickier.

The surface of the Moon is baldly exposed to cosmic rays and solar flares, and some of that radiation is very hard to stop with shielding. Furthermore, when cosmic rays hit the ground, they produce a dangerous spray of secondary particles right at your feet. All this radiation penetrating human flesh can damage DNA, boosting the risk of cancer and other maladies.

According to the Vision for Space Exploration, NASA plans to send astronauts back to the Moon by 2020 and, eventually, to set up an outpost. For people to live and work on the Moon safely, the radiation problem must be solved.

“We really need to know more about the radiation environment on the Moon, especially if people will be staying there for more than just a few days,” says Harlan Spence, a professor of astronomy at Boston University.

To carefully measure and map the Moon’s radiation environment, NASA is developing a robotic probe to orbit the Moon beginning in 2008. Called the Lunar Reconnaissance Orbiter (LRO), this scout will pave the way for future human missions not only by measuring space radiation, but also by hunting for frozen water and mapping the Moon’s surface in unprecedented detail. LRO is a key part of NASA’s Robotic Lunar Exploration Program, managed by the Goddard Space Flight Center.

One of the instruments onboard LRO is the Cosmic Ray Telescope for the Effects of Radiation (CRaTER).

“Not only will we measure the radiation, we will use plastics that mimic human tissue to look at how these highly energetic particles penetrate and interact with the human body,” says Spence, who is the Principal Investigator for CRaTER.

By placing the radiation detectors in CRaTER behind various thicknesses of a special plastic that has similar density and composition to human tissue, Spence and his colleagues will provide much-needed data: Except for quick trips to the Moon during the Apollo program, most human spaceflight has occurred near Earth where our planet’s magnetic field provides a natural shield. In low-Earth orbit, the most dangerous forms of space radiation are relatively rare. That’s good for astronauts, but it leaves researchers with many unanswered questions about what radiation does to human tissue. CRaTER will help fill in the gaps.

Out in deep space, radiation comes from all directions. On the Moon, you might expect the ground, at least, to provide some relief, with the solid body of the Moon blocking radiation from below. Not so.

When galactic cosmic rays collide with particles in the lunar surface, they trigger little nuclear reactions that release yet more radiation in the form of neutrons. The lunar surface itself is radioactive!

So which is worse for astronauts: cosmic rays from above or neutrons from below? Igor Mitrofanov, a scientist at the Institute for Space Research and the Russian Federal Space Agency, Moscow, offers a grim answer: “Both are worse.”

Mitrofanov is Principle Investigator for the other radiation-sensing instrument on LRO, the Lunar Exploration Neutron Detector (LEND), which is partially funded by the Russian Federal Space Agency. By using an isotope of helium that’s missing one neutron, LEND will be able to detect neutron radiation emanating from the lunar surface and measure how energetic those neutrons are.

The first global mapping of neutron radiation from the Moon was performed by NASA’s Lunar Prospector probe in 1998-99. LEND will improve on the Lunar Prospector data by profiling the energies of these neutrons, showing what fraction are of high energy (i.e., the most damaging to people) and what fraction are of lower energies.

With such knowledge in hand, scientists can begin designing spacesuits, lunar habitats, Moon vehicles, and other equipment for NASA’s return to the Moon knowing exactly how much radiation shielding this equipment must have to keep humans safe.

NASA News Release

Posted on by Fraser Cain

Tempel 1’s Ingredients

Astronomers using data from Spitzer and Deep Impact are preparing a comet “soup”. Image credit: NASA Click to enlarge
When Deep Impact smashed into comet Tempel 1 on July 4, 2005, it released the ingredients of our solar system’s primordial “soup.” Now, astronomers using data from NASA’s Spitzer Space Telescope and Deep Impact have analyzed that soup and begun to come up with a recipe for what makes planets, comets and other bodies in our solar system.

“The Deep Impact experiment worked,” said Dr. Carey Lisse of Johns Hopkins University’s Applied Physics Laboratory, Laurel, Md. “We are assembling a list of comet ingredients that will be used by other scientists for years to come.” Lisse is the team leader for Spitzer’s observations of Tempel 1. He presented his findings this week at the 37th annual meeting of the Division of Planetary Sciences in Cambridge, England.

Spitzer watched the Deep Impact encounter from its lofty perch in space. It trained its infrared spectrograph on comet Tempel 1, observing closely the cloud of material that was ejected when Deep Impact’s probe plunged below the comet?s surface. Astronomers are still studying the Spitzer data, but so far they have spotted the signatures of a handful of ingredients, essentially the meat of comet soup.

These solid ingredients include many standard comet components, such as silicates, or sand. And like any good recipe, there are also surprise ingredients, such as clay and chemicals in seashells called carbonates. These compounds were unexpected because they are thought to require liquid water to form.

“How did clay and carbonates form in frozen comets?” asked Lisse. “We don’t know, but their presence may imply that the primordial solar system was thoroughly mixed together, allowing material formed near the Sun where water is liquid, and frozen material from out by Uranus and Neptune, to be included in the same body.”

Also found were chemicals never seen before in comets, such as iron-bearing compounds and aromatic hydrocarbons, found in barbecue pits and automobile exhaust on Earth.

The silicates spotted by Spitzer are crystallized grains even smaller than sand, like crushed gems. One of these silicates is a mineral called olivine, found on the glimmering shores of Hawaii’s Green Sands Beach.

Planets, comets and asteroids were all born out of a thick soup of chemicals that surrounded our young Sun about 4.5 billion years ago. Because comets formed in the outer, chilly regions of our solar system, some of this early planetary material is still frozen inside them.

Having this new grocery list of comet ingredients means theoreticians can begin testing their models of planet formation. By plugging the chemicals into their formulas, they can assess what kinds of planets come out the other end.

“Now, we can stop guessing at what’s inside comets,” said Dr. Mike A’Hearn, principal investigator for the Deep Impact mission, University of Maryland, College Park. “This information is invaluable for piecing together how our own planets as well as other distant worlds may have formed.”

NASA’s Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer Space Telescope mission for NASA’s Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at Caltech. The University of Maryland, College Park, conducted the overall mission management for Deep Impact, and JPL handled project management for the mission for NASA’s Science Mission Directorate.

For more graphics and more information about Spitzer, visit http://www.spitzer.caltech.edu/Media/index.shtml .

Original source: NASA News Release

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