Posted on by Fraser Cain

Studying the Health of the Great Barrier Reef from Space

The Great Barrier Reef, photographed by Envisat. Image credit: ESA. Click to enlarge.
Australian researchers have found Envisat’s MERIS sensor can detect coral bleaching down to ten metres deep. This means Envisat could potentially monitor impacted coral reefs worldwide on a twice-weekly basis.

Coral bleaching happens when symbiotic algae living in symbiosis with living coral polyps (and providing them their distinctive colours) are expelled. The whitening coral may die with subsequent impacts on the reef ecosystem, and thus fisheries, regional tourism and coastal protection. Coral bleaching is linked to sea temperatures above normal summer maxima and to solar radiation. Bleaching may take place on localised and mass scales ? there was an extensive bleaching event in 1998 and 2002 likely linked to El Ni?o events.

“An increase in frequency of coral bleaching may be one of the first tangible environmental effects of global warming,” states Dr. Arnold Dekker of Australia’s Commonwealth Scientific and Industrial Research Organisation?s (CSIRO) Wealth from Oceans Flagship program.”The concern is that coral reefs might pass a critical bleaching threshold beyond which they are unable to regenerate.”

Aerial or boat-based observation is the current method of detecting bleaching, but many reefs are either inaccessible or simply too large (the Great Barrier Reef has an area of 350 000 square kilometres) for an event that happens within a fortnight. Bleached corals may rapidly be colonised by blue-green to brown algae, more difficult to distinguish from live coral.

Repetitive, objective and broad-scale satellite coverage is the alternative. At this week’s MERIS/AATSR Workshop in Frascati, Italy, the CSIRO team presented initial results using Envisat’s Medium Resolution Imaging Spectrometer (MERIS). MERIS acquires images in 15 different spectral bands at 300 m resolution.

“Coral bleaching needs to be mapped at the global scale,” Dekker adds. “High-spatial resolution satellites can only do it on a few reefs due to cost and coverage constraints. We need a system that has appropriate coverage and revisit frequency, with a sufficient amount of spectral bands and sensitivity. There is no more suitable system than MERIS.”

The team studied Heron Island reef at the southern end of the Great Barrier Reef, site of a University of Queensland research station. Validating MERIS Full Resolution mode results, they found that observed changes in live coral cover were correlated to an existing bleaching event.

Theoretical studies indicate that for each complete 300-metre pixel of coral under one metre of water it is possible to detect a 2% bleaching of live coral. MERIS should remain sensitive to detecting from 7-8% bleached coral even under ten metres of water.

“MERIS Full Resolution covers the world every three days, a bottleneck for global monitoring could be data processing,” Dekker concludes. “However satellite sensors measuring sea surface temperature such as Envisat’s Advanced Along Track Scanning Radiometer (AATSR) can be applied to prioritise reefs that are subject to sea temperature heating anomalies-thus focusing the MERIS based bleaching detection.

Australia’s Great Barrier Reef Marine Park Authority has expressed interest in the project. Australian scientists plan to progress to perform MERIS monitoring of bleaching events up to the scale of the whole Great Barrier Reef.

Original Source: ESA News Release

Posted on by Fraser Cain

What’s Up This Week – October 3 – October 9, 2005

The Helix Nebula. Image credit: NOAO/AURA/NSF. Click to enlarge.
Monday, October 3 – Today marks a terrific event as viewers in Africa had a chance to witness an annular solar eclipse. Many parts of both Europe and Asia were also treated to a partial eclipse as well, so be sure the check the pages of Mr. Eclipse for links to times, locations, images, etc.

For those of us who didn’t get to see the solar ring, let’s look for a ring of another type. Tonight’s dark sky object is a difficult one for northern observers and is truly a challenge. Around a handspan south of Zeta Aquarii and just a bit west of finderscope star Upsilon is a remarkably large area of nebulosity that is very well suited to large binoculars, rich field telescopes and wide field eyepieces. Are you ready to walk into the “Helix”?

Known as NGC 7293, this faint planetary nebula “ring” structure is around half the size of the full Moon. While its total magnitude of 6.5 and large size should denote an easy find, the “Helix” is anything but easy because of its low surface brightness nature. Binoculars will show it as a large, round, hazy spot while small telescopes with good seeing conditions will have a chance to outshine larger ones by using lower power eyepieces to pick up this braided ring structure.

As one of the very closest of planetary nebula, the NGC 7392 is very similar in structure to the famous “Ring” – M57. It is a spherical shell of gas lighted by an extremely hot, tiny central star that’s only around 2% of our own Sun’s diameter – yet exceeds a surface temperature of over 100,000 kelvin. Can you resolve it? Best of luck!

Tuesday, October 4 – Today in 1957, the USSR made history as Sputnik 1 became the first manmade object to orbit the earth.

Orbiting a bit further out is the new comet in town – C/2005 E2 (McNaught). Located in the southeastern portion of southern Saggitarius, E2 is around five degrees east of Alpha Corona Australis and just a breath south. Now holding a magnitude of an estimated 12, our new friend will be climbing northwards rather quickly in the weeks ahead and will begin to brighten as it curves its way northeastward toward the M55 at month’s end. How soon can you spot it?

Wednesday, October 5 – Today marks the birthdate of Robert Goddard. Born 1882, Goddard is known as the father of modern rocketry – and with good reason.

In 1907, Goddard came into the public eye as a cloud of smoke erupted from the basement of the physics building in Worcester Polytechnic Institute where he had just fired a powder rocket. By 1914, he had patented the use of liquid rocket fuel and two or three stage solid fuel rockets. His work continued as he sought methods of putting equipment ever higher and by 1920 had envisioned his rockets reaching the Moon. Among his many achievements, he proved that a rocket would work in a vacuum and by 1926 had the first scientific equipment along for the ride. By 1932, Goddard was guiding those flights and by 1937 had the motors pivoting on gimbals and controlled gyroscopically. His lifetime of work went pretty much unnoticed until the dawn of the “Space Age”, but in 1959 (14 years after his death) he received his acclaim at last as NASA’s Goddard Space Flight Center was established in his memory.

Tonight, challenge yourself visually to see if you can find the very slender crescent of the Moon. This will be quite difficult for more northern observers, but you’ll find it about half a fist width below Venus.

Also today in 1923, Edwin Hubble was busy discovering the first Cepheid variable in M31, the Andromeda Galaxy. Although this might not seem like much, at the time it proved that “spiral nebulae” were indeed independant galaxies that greatly resembled our own. With the Moon not harming tonight’s skies, take the time to truly study the Andromeda Galaxy – not just look at it. With patience you will find that it stretches across several fields of view in even modest telescopes and contains a wealth of details.

Thursday, October 6 – Tonight SkyWatchers are urged to look west after sunset as the tender crescent Moon nears the sparkling Venus. Do you see “Earthshine?”

If you chose to look at the lunar surface, you will see the emerging Mare Crisium area and the line of prominent craters which stretch to the north – Cleomides, Burckhardt, Geminus and Messala. Just south of central begins the smooth, grey seas of Mare Fecunditatis with the lovely old Langrenus caught on its eastern edge. Look further south for Petavius.

Friday, October 7 – Today is the birthdate of Niels Bohr. Born in 1855, Danish-born Bohr became the pioneer atomic physicist.

Tonight is the peak of the Piscids meteor shower, so keep watch on the radiant area near Aries. The fall rate is around 15 per hour and they’ll streak through at 28 kilometers per second.

Tonight on the lunar surface, be sure to catch this opportunity to study details around crater Proclus on Mare Crisium’s western shore. This amazing little crater is home to many lunar transient phenomena and will develop a bright ray system in the days ahead.

Right now we are only one month away from opposition with Mars and gaining on the “God of War” at a speed of 20,000 miles every day. By the time you have finished with lunar observations, you’ll see it blazing its way up around 90 minutes after sunset and arriving on the scene around 5 minutes earlier each night and gaining in brightness. This author highly encourages you to wait until Mars has cleared most atmospheric disruption and observe. The details that can be seen on the Red Planet’s surface are stunning! Even the smallest of aperture can resolve out dark markings and one polar cap, but for those of you with larger scopes? I promise you that you cannot look away. It is that incredibly detailed.

Saturday, October 8 – Today marks the birthday of Ejnar Hertzsprung. Born 1873, Hertzsprung was a Danish astronomer who first proved the existence of giant and dwarf stars in the early 1900s. His work included the relationship between color and luminosity, but wasn’t truly recognized until it was recovered by Henry Russell and now is a familiar part of all our studies as the Hertzsprung-Russell diagram. His use of absolute magnitudes will come into play tonight as we have a look at the sixth brightest star in the sky – Capella.

Now rising in the east at nightfall, Alpha Auriga is often called the “Goat Star” and is the nearest to the pole of all the first magnitude stars in the night sky. If it were not 45 light years away, it would be 160 times brighter than our own Sun! Like most stars, Capella is a multiple system that contains at least 4 members that are far too close to be resolved by our ordinary means.

While you’re out, be sure to turn your scope towards the Moon as old favourites – Posidonius, Theophilus, Cyrillus and Catherina – are waiting for you!

Sunday, October 9 – Tonight is the peak of the Draconid meteor shower whose radiant is near the westering constellation of Hercules. This particular shower can be quite impressive when comet Giacobinni-Zinner passes near Earth. When this happens, the fall rate jumps to 200 per hour and has even been known to reach 1000!

So what am I going to tell you that no one else has? Comet Giacobinni-Zinner reached perihelion on July 2nd of this year and is still less than 2 AU away. 😉

Until next week? May all your journeys be at light speed…. ~Tammy Plotner

Posted on by Fraser Cain

10th Planet has a Moon

Artist illustration of the 10th planet and its moon. Image credit: Caltech. Click to enlarge.
The newly discovered 10th planet, 2003 UB313, is looking more and more like one of the solar system’s major players. It has the heft of a real planet (latest estimates put it at about 20 percent larger than Pluto), a catchy code name (Xena, after the TV warrior princess), and a Guinness Book-ish record of its own (at about 97 astronomical units-or 9 billion miles from the sun-it is the solar system’s farthest detected object). And, astronomers from the California Institute of Technology and their colleagues have now discovered, it has a moon.

The moon, 100 times fainter than Xena and orbiting the planet once every couple of weeks, was spotted on September 10, 2005, with the 10-meter Keck II telescope at the W.M. Keck Observatory in Hawaii by Michael E. Brown, professor of planetary astronomy, and his colleagues at Caltech, the Keck Observatory, Yale University, and the Gemini Observatory in Hawaii. The research was partly funded by NASA. A paper about the discovery was submitted on October 3 to Astrophysical Journal Letters.

“Since the day we discovered Xena, the big question has been whether or not it has a moon,” says Brown. “Having a moon is just inherently cool-and it is something that most self-respecting planets have, so it is good to see that this one does too.”

Brown estimates that the moon, nicknamed “Gabrielle”-after the fictional Xena’s fictional sidekick-is at least one-tenth of the size of Xena, which is thought to be about 2700 km in diameter (Pluto is 2274 km), and may be around 250 km across.

To know Gabrielle’s size more precisely, the researchers need to know the moon’s composition, which has not yet been determined. Most objects in the Kuiper Belt, the massive swath of miniplanets that stretches from beyond Neptune out into the distant fringes of the solar system, are about half rock and half water ice. Since a half-rock, half-ice surface reflects a fairly predictable amount of sunlight, a general estimate of the size of an object with that composition can be made. Very icy objects, however, reflect a lot more light, and so will appear brighter-and thus bigger-than similarly sized rocky objects.

Further observations of the moon with NASA’s Hubble Space Telescope, planned for November and December, will allow Brown and his colleagues to pin down Gabrielle’s exact orbit around Xena. With that data, they will be able to calculate Xena’s mass, using a formula first devised some 300 years ago by Isaac Newton.

“A combination of the distance of the moon from the planet and the speed it goes around the planet tells you very precisely what the mass of the planet is,” explains Brown. “If the planet is very massive, the moon will go around very fast; if it is less massive, the moon will travel more slowly. It is the only way we could ever measure the mass of Xena-because it has a moon.”

The researchers discovered Gabrielle using Keck II’s recently commissioned Laser Guide Star Adaptive Optics system. Adaptive optics is a technique that removes the blurring of atmospheric turbulence, creating images as sharp as would be obtained from space-based telescopes. The new laser guide star system allows researchers to create an artificial “star” by bouncing a laser beam off a layer of the atmosphere about 75 miles above the ground. Bright stars located near the object of interest are used as the reference point for the adaptive optics corrections. Since no bright stars are naturally found near Xena, adaptive optics imaging would have been impossible without the laser system.

“With Laser Guide Star Adaptive Optics, observers not only get more resolution, but the light from distant objects is concentrated over a much smaller area of the sky, making faint detections possible,” says Marcos van Dam, adaptive optics scientist at the W.M. Keck Observatory, and second author on the new paper.

The new system also allowed Brown and his colleagues to observe a small moon in January around 2003 EL61, code-named “Santa,” another large new Kuiper Belt object. No moon was spotted around 2005 FY9-or “Easterbunny”-the third of the three big Kuiper Belt objects recently discovered by Brown and his colleagues using the 48-inch Samuel Oschin Telescope at Palomar Observatory. But the presence of moons around three of the Kuiper Belt’s four largest objects-Xena, Santa, and Pluto-challenges conventional ideas about how worlds in this region of the solar system acquire satellites.

Previously, researchers believed that Kuiper Belt objects obtained moons through a process called gravitational capture, in which two formerly separate objects moved too close to one another and become entrapped in each other’s gravitational embrace. This was thought to be true of the Kuiper Belt’s small denizens-but not, however, of Pluto. Pluto’s massive, closely orbiting moon, Charon, broke off the planet billions of years ago, after it was smashed by another Kuiper Belt object. Xena’s and Santa’s moons appear best explained by a similar origin.

“Pluto once seemed a unique oddball at the fringe of the solar system,” Brown says. “But we now see that Xena, Pluto, and the others are part of a diverse family of large objects with similar characteristics, histories, and even moons, which together will teach us much more about the solar system than any single oddball ever would.”

Original Source: Caltech News Release

Posted on by Fraser Cain

Space Tourist and New Crew Arrive at the Space Station

Greg Olsen and the crews of Expedition 11 and 12. Image credit: NASA. Click to enlarge.
The Soyuz spacecraft with the 12th international space station crew, Commander William McArthur and Flight Engineer Valery Tokarev, docked with the orbiting laboratory at 1:27 a.m. EDT Monday.

With them was American Greg Olsen, the third private citizen in space, flying under a contract with the Russian Federal Space Agency. He will spend about eight days on the station.

They launched from the Baikonur Cosmodrome in Kazakhstan just before midnight on Friday.

Olsen will conduct scientific experiments on the station, and then return to Earth with Expedition 11. That crew, Commander Sergei Krikalev and NASA Science Officer John Phillips, has been on the orbiting laboratory since April.

They will undock Oct. 10 in the Soyuz TMA that brought them to the station April 16. Landing is scheduled for 9:08 p.m. EDT that day in the steppes of Kazakhstan, winding up their 180-day increment.

McArthur, 54, a retired Army colonel, is a veteran of three shuttle flights, including one to the station and one to the Russian space station Mir. Tokarev, 52, a colonel in the Russian Air Force, is a veteran of one spaceflight, to the international space station aboard a space shuttle.

Hatches were opened at 4:36 a.m. EDT. After hugs and greetings with the traditional bread and salt, they got a safety briefing from the Expedition 11 crew. In extensive handover briefings during their eight days together, they will get training on systems and experiments on the station and on the Canadarm2 robotic arm.

During their six months on the station McArthur and Tokarev will do two or three spacewalks. The first, from the Quest airlock in U.S. spacesuits, is planned for early November. Tasks include installation of a camera group and retrieval of the station’s floating potential probe.

That will be McArthur’s third spacewalk and the first for Tokarev.

About two weeks later the crewmembers will board their Soyuz spacecraft and move it from the Pirs docking compartment to a docking port on the Zarya module. That will clear the Pirs for use of its airlock in a spacewalk using Russian Orlan suits in December.

That spacewalk will focus on retrieving scientific experiments and photography of a micrometeoroid monitoring system and the Soyuz descent module’s multilayer insulation.

A third spacewalk early next year in U.S. spacesuits is under consideration.

McArthur and Tokarev also are scheduled to welcome an unpiloted Progress cargo craft to the station, just in time for Christmas. That Progress will bring fuel, equipment, supplies, water, oxygen and air to the station. Docking is planned for Dec. 23.

Station maintenance will occupy considerable time. They will continue scientific investigations aboard the orbiting laboratory, as well as a program of scientific education activities and Earth observations.

Their replacements, the 13th crew of the station, are scheduled to arrive in March.

Original Source: NASA News Release

Posted on by Mark Mortimer

Book Review: Echo of the Big Bang

Scientist now accept that the cosmic microwave background (CMB) radiation results from the big bang. This knowledge was slow in developing. In 1920, Shapley and Curtis debated whether the universe is bigger than the Milky Way Galaxy. Yet, pieces of the puzzle kept falling into place, such as the red-shift indicating an expanding universe. However, we knew by then that mass attracts, so why are stars moving away? For resolution, Einstein introduced a cosmological constant (which he later refuted). The accidental discovery of the CMB in 1964 firmly set the stage for the inflationary theory of the universe, yet knowing its existence wasn’t enough. To delve deeper, NASA first sponsored COBE (from 1976 to 1991) then picked WMAP to “drive down the margin of error and nail down the physical characteristics…expansion rate, geometry, matter density, matter to dark matter ratio…”. Thus cosmology follows the typical tale of scientific advancement; the piecing together of little clues to develop an overarching paradigm.

The technical information that relates to the CMB is humongous. This book is not. Lemonick chooses to go the route of simplicity in conveying the scientific details. For the most part, references come with minimal description. For example, the reader is left to wonder about the relative worth of HEMT’s (high electron mobility transistors) to bolometres as the electronic detector of choice. Or for another, we read of omega, the mass/energy density that relates to dark matter and dark energy and to the shape of the universe. There are some standard descriptions, such as of topology and its doughnuts, but that is all. As cosmology combines the skills of many disciplines, this level of detail is necessary for this size book.

Rather than concentrating on the technical aspects, Lemonick emphasises the people. This is sensible as Lemonick is not a cosmological theoretician, he is a broadsheet science writer. Using a mostly chronological ordering, he presents the prerequisite characters of WMAP and many of the COBE mission as well. We read of anxiety in building the satellite, preoccupation leading to gallbladder surgery, and sleepless nights necessary for processing data. By nicely adding emotion to the description of the scientists, Lemonick puts in a real human flavour. This lightens the topic, but if you’re not interested in the side details, such as procurement strategies for high end electronics, this can be a bit off putting.

Further, continual side steps into this trivia or some person’s characteristic traits makes this book hard to classify. At times, it seems quite eloquent, such as the setting described as “…after a mild winter, the brilliance of the campus in full bloom is almost overwhelming”. This same style relates to system testing where the satellite is “…plunged down to extreme cold, vibrated, bombarded with simulate microwave signals, blasted with sound waves from gigantic loudspeakers four feet across”. With these, the reading is simple but the overall sense is of a smooth series of factoids presented one after the other. Once finished, the reader should feel quite prepared for a game of Trivial Pursuit, the Cosmology Edition (if it exists).

If you’re looking for a well written, entertaining science book that is easy to pick up and put down, this is it. There’s enough substance to keep you interested while sitting on the bus commuting into work. However, there’s not enough to over embellish the lore of cosmology, the established traits of the pertinent scientists or typify the build out of scientific satellites. A clearer title or a clarifying sub title would have been helpful.

Well, how much are discoveries worth? A satellite can answer fundamental questions about our existence, but only if we want to pay the piper. The WMAP mission was such a story as with a ceiling cost, it successfully answered specific cosmologic questions. Michael Lemonick in his book Echo of the Big Bang brings to us the story of this mission, the people involved and the challenges of high-end electronics. In combining a sense of history with the warmth of personalities he gives the average person a great introduction into cosmology and high end science.

Review by Mark Mortimer

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

Posted on by Fraser Cain

Ballooning on Mars

Artist illustration of a balloon floating above Mars. Image credit: ESA/Global Aerospace. Click to enlarge.
Mars rovers, Spirit and Opportunity, have, by now, spent almost two years on the surface of Mars. They traveled several miles each, frequently stopping and analyzing scientific targets with their cameras, spectrometers and other instruments to uncover evidence of liquid water on Mars in the past. Their mission is a smashing success for NASA.

But what if NASA had a platform on Mars that was able to cover these distances in a matter of hours instead and study the rocks on the surface in the same detail as rovers do? Scientific return from such a vehicle would be immense scientists would be able to study the whole planet in greater detail in a time span of a single year.

While orbiters can look at virtually any point on the surface of a planet, they lack the resolution provided by instruments on rovers or landers. Rovers, on the other hand, have limited mobility and cannot travel very far from their landing site. As the atmosphere of Mars is very thin, an airplane at Mars would last for just an hour until it runs out of fuel.

Global Aerospace Corporation of Altadena, CA proposes that the Mars exploration vehicle combining the global reach similar to that of orbiters and high resolution observations enabled by rovers could be a balloon that can be steered in the right direction and that would drop small science packages over the target sites. The concept being developed by the Global Aerospace Corporation is funded by the NASA Institute for Advanced Concepts (NIAC).

Balloons have been long recognized as unique, scientific platforms due to their relatively low cost and low power consumption. Two balloons flew in the atmosphere of Venus in 1984. In the past the inability to control the path of Mars balloons has limited their usefulness, and therefore scientific interest in their use.

Global Aerospace Corporation has designed an innovative device, called Balloon Guidance System (BGS) that enables steering a balloon through the atmosphere. The BGS is an aerodynamic surface a wing that hangs on a several kilometer-long tether below the balloon. The difference in winds at different altitudes create a relative wind at the latitude of the BGS wing, which in turn creates a lifting force. This lifting force is directed sideways and can be used to pull the balloon left or right relative to the prevailing winds.

Floating just several kilometers above the surface of Mars, the guided Mars balloons can observe rock formations, layerings in canyon walls and polar caps, and other features at very high resolution using relatively small cameras. They can be directed to fly over specific targets identified from orbital images and to deliver small surface laboratories, that will analyze the site at the level of detail rovers would do. Instruments at the balloon’s gondola can also measure traces of methane in the atmospheric and follow its increasing concentrations to the source on the ground. This way the search for existing or extinct life on Mars can be accelerated.

Original Source: NASA Astrobiology

Posted on by Fraser Cain

Keck Can Turn Down Starlight to See Planetary Disks

The massive Keck telescope on Hawaii’s Mauna Kea. Image credit: NASA/JPL. Click to enlarge.
Are we alone in the universe? Are there planets like Earth around other ?suns? that might harbor life? Thanks to a recent technology breakthrough on a key NASA planet-finding project, the dream of answering those questions is no longer light-years away.

On a crystal clear, star-filled night at Hawaii?s Keck Observatory in Mauna Kea, NASA engineers successfully suppressed the blinding light of three stars, including the well-known Vega, by 100 times. This breakthrough will enable scientists to detect the dim dust disks around stars, where planets might be forming. Normally the disks are obscured by the glare of the starlight.

Engineers accomplished this challenging feat with the Keck Interferometer, which links the observatory?s two 10-meter (33-feet) telescopes. By combining light from the telescopes, the Keck Interferometer has a resolving power equivalent to a football-field sized telescope. The ?technological touchdown? of blocking starlight was achieved by adding an instrument called a ?nuller.?

This setup may eventually help scientists select targets for NASA?s envisioned Terrestrial Planet Finder missions. The success of those potential future missions, one observing in visible light and one in infrared, depends on being able to find Earth-like planets in the dust rings around stars.

?We have proven that the Keck Interferometer can block light from nearby stars, which will allow us to survey the amount of dust around them,? said Dr. James Fanson, project manager for the Keck Interferometer at NASA’s Jet Propulsion Laboratory. That survey will begin in late 2006 after the team refines the nuller?s sensitivity level.

Combined information from all of NASA?s planet-hunting missions will provide a complete picture of possible Earth-like planets: how big they are, whether they are warm enough for life, and if their atmospheres and surfaces show chemical signatures of current life.

?People have been talking about whether there are other earths out there for 2,500 years. Only now are we developing the technology to go find out,? said Michael Devirian, manager of NASA?s Navigator Program at JPL, which is investigating potential planet-exploring missions.

So far, scientists around the world have found 150 planets orbiting other stars. Most are giants, like Jupiter; none is as small as Earth. Scientists believe the best odds of finding life outside our solar system are on Earth-sized planets, particularly those with the right temperature, density and chemistry.

More information on NASA?s planet-finding missions, including the Keck Interferometer and Terrestrial Planet Finder is at http://planetquest.jpl.nasa.gov.

JPL manages the Keck Interferometer and the Terrestrial Planet Finder missions for NASA?s Science Mission Directorate, Washington. JPL is a division of the California Institute of Technology in Pasadena. The W.M. Keck Observatory is funded by California Institute of Technology, the University of California and NASA, and is managed by the California Association for Research in Astronomy, Kamuela, Hawaii.

Original Source: NASA/JPL News Release

Posted on by Fraser Cain

Vivid View of Spongy Hyperion

Saturn’s moon Hyperion. Image credit: NASA/JPL/SSI. Click to enlarge.
Cassini performed back-to-back flybys of Saturn moons Tethys and Hyperion last weekend, coming closer than ever before to each of them. Tethys has a scarred, ancient surface, while Hyperion is a strange, spongy-looking body with dark-floored craters that speckle its surface.

New images, mosaics and a movie of these bodies are available at http://saturn.jpl.nasa.gov , http://www.nasa.gov/cassini and http://ciclops.org .

Images of Tethys taken during Cassini’s close approach to the moon on Sept. 24, 2005, reveal an icy land of steep cliffs and craters. Cassini photographed the moon’s south pole, a region not seen by NASA’s Voyager spacecraft.

A giant rift called Ithaca Chasma cuts across the disk of Tethys. Much of the topography in this region, including that of Ithaca Chasma, has been thoroughly hammered by impacts. This appearance suggests that the event that created Ithaca Chasma happened very long ago.

Near a prominent peaked crater named Telemachus are the remnants of a very old crater named Teiresias. The ancient impact site is badly overprinted and eroded by impact weathering and degradation. All that remains is a circular pattern of hummocks that mark where the old crater rim existed. Many of the fresh-appearing craters exhibit unusually bright crater floors, in contrast to the dark-floored craters seen on Saturn’s oddly tumbling moon Hyperion.

Images of Hyperion taken on Sept. 26 show a surface dotted with craters and modified by some process, not yet understood, to create a strange, “spongy” appearance, unlike the surface of any other Saturn moon.

A false-color image of Hyperion reveals crisp details and variations in color across the strange surface that might represent differences in the composition of materials. Hyperion has a notably reddish tint when viewed in natural color.

Scientists are extremely curious to learn what the dark material is that fills many craters on this moon. Features within the dark terrain, including a 200-meter-wide (650-feet) impact crater surrounded by rays and numerous bright-rimmed craters, indicate that the dark material may be only tens of meters thick with brighter material beneath.

Scientists will also be examining Cassini’s sharp views in hopes of determining whether there have been multiple episodes of landslides on Hyperion. Such “downslope” movement is evident in the filling of craters with debris and the near elimination of many craters along the steeper slopes. Answers to these questions may help solve the mystery of why this object has evolved different surface forms from other moons of Saturn.

Cassini flew by Hyperion at a distance of only 500 kilometers (310 miles). Hyperion is 266 kilometers (165 miles) across, has an irregular shape, and spins in a chaotic rotation. Much of its interior is empty space, explaining why scientists call Hyperion a rubble-pile moon. This flyby was Cassini’s only close encounter with Hyperion in the prime mission four-year tour. Over the next few months, scientists will study the data in more detail.

Cassini flew by Tethys at a distance of approximately 1,500 kilometers (930 miles) above the surface. Tethys is 1,071 kilometers (665 miles) across and will be visited again by Cassini in the summer of 2007.

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 Cassini-Huygens 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 team is based at the Space Science Institute, Boulder, Colo.

Original Source: NASA/JPL/SSI News Release