Posted on by Fraser Cain

Star Clusters Could Be Galaxy Remnants

Globular star clusters are like spherical cathedrals of light – collections of millions of stars lumped into a space only a few dozen light-years across. If the Earth resided within a globular cluster, our night sky would be alight with thousands of stars more brilliant than Sirius.

Our own Milky Way Galaxy currently holds about 200 globular clusters, but once possessed many more. According to the hierarchical theory of galaxy formation, galaxies have grown larger over time by consuming smaller dwarf galaxies and star clusters. And sometimes, it seems that the unfortunate prey is not swallowed whole but instead is munched like a peach, stripped of its outer layers to leave behind only the pit. New research by Paul Martini (Harvard-Smithsonian Center for Astrophysics) and Luis Ho (Observatories of the Carnegie Institution of Washington) shows that some globular clusters may be remnants of dwarf galaxies that were stripped of their outer stars, leaving only the galaxy’s nucleus behind.

Martini and Ho reported their results in the July 20, 2004, issue of The Astrophysical Journal.

Their findings hint at an important yet puzzling connection between the largest globular clusters and the smallest dwarf galaxies. “Star clusters and galaxies are quite different from a structural standpoint – star clusters are much more centrally concentrated, for example – and so the mechanisms that form them must be quite different. Identification of star clusters in the same mass range as galaxies is a very important step toward understanding how both types of objects form,” says Martini.

For their investigation, the team studied 14 globular clusters in the large elliptical galaxy Centaurus A (NGC 5128) using the 6.5-meter-diameter Magellan Clay telescope at Carnegie’s Las Campanas Observatory, Chile. The clusters were selected for their brightness, and since brighter clusters tend to contain more stars and more mass, were expected to be massive. Yet their results surprised even Martini and Ho, showing that the globular clusters of Centaurus A are much more massive than most globulars in the Local Group of galaxies (which includes the Milky Way and the Andromeda Galaxy).

“The essence of our findings is that these 14 globulars are 10 times more massive than the smaller globulars in our neighborhood, and whatever process makes them can produce some really huge objects – they begin to overlap with the smallest galaxies,” says Martini.

Martini also points out the recent discovery of a suspected intermediate-mass black hole in the Andromeda Galaxy globular cluster known as G1, which offers further evidence linking globular clusters to dwarf galaxies. The presence of a moderate-sized black hole is more understandable if it once occupied the center of a dwarf galaxy – a galaxy that lost its outer stars to the pull of Andromeda, leaving it only a shadow of its former self.

Ho, a co-discoverer of the intermediate-mass black hole in G1, adds, “One of the most surprising findings is that the black hole in G1 obeys the same tight correlation between black hole mass and host galaxy mass that has been well established for supermassive black holes in the centers of big galaxies. This puzzling result is more understandable if G1 was once the nucleus of a larger galaxy. A very interesting question is whether some of the massive clusters in Centaurus A also contain central black holes.”

Although most of our Galaxy’s globular clusters are much smaller than those of Centaurus A, the largest Milky Way globulars (such as the omega Centauri star cluster) rival those of the elliptical galaxy. The similarities between massive globulars in both galaxies may point to similar formation mechanisms. Future studies of these most massive globular clusters will explore connections between the formation processes for star clusters and galaxies.

Centaurus A is located approximately 12.5 million light-years away. It is about 65,000 light-years across and is more massive than the Milky Way and Andromeda galaxies put together. Centaurus A possesses a total of about 2000 globular clusters – more than all of the galaxies in the Local Group combined. Recent Spitzer Space Telescope observations of Centaurus A uncovered evidence that it merged with a spiral galaxy about 200 million years ago.

Original Source: Harvard-Smithsonian CfA News Release

Posted on by Fraser Cain

Genesis Heads for Home

Thirty days before its historic return to Earth with NASA’s first samples from space since the Apollo missions, the Genesis spacecraft successfully completed its twentieth trajectory maneuver.

At 12:00 Universal Time (5:00 a.m. Pacific Daylight Time), Mon., August 9, Genesis fired its 90 gram (.2 pound) thrusters for a grand total of 50 minutes, changing the solar sampler’s speed by 1.4 meters per second (about 3.1 miles per hour). The maneuver required half a kilogram (1.1 pounds) of hydrazine monopropellant to complete.

“It was a textbook maneuver,” said Ed Hirst, Genesis’s mission manager at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “After sifting through all the post-burn data, I expect we will find ourselves right on the money.”

The Genesis mission was launched in August of 2001 on a journey to capture samples from the storehouse of 99 percent of all the material in our solar system — the Sun. The samples of solar wind particles, collected on ultra-pure wafers of gold, sapphire, silicon and diamond, will be returned for analysis by Earth-bound scientists. The samples Genesis provides will supply scientists with vital information on the composition of the Sun, and will shed light on the origins of our solar system.

Helicopter flight crews, navigators and mission engineers continue to prepare for the return of the Genesis spacecraft on September 8. On that date, Genesis will dispatch a sample return capsule that will re-enter Earth’s atmosphere for a planned mid-air capture at the U.S. Air Force Utah Test and Training Range. To preserve the delicate particles of the Sun in their prisons of silicon, gold, sapphire and diamond, specially trained helicopter pilots will snag the return capsule from mid-air using the space-age equivalent of a fisherman’s rod and reel. The flight crews for the two helicopters assigned for Genesis capture and return are comprised of former military aviators and Hollywood stunt pilots.

JPL manages the Genesis mission for NASA’s Space Mission Directorate, Washington, DC. Lockheed Martin Space Systems, Denver, developed and operates the spacecraft. JPL is a division of the California Institute of Technology, the home institute of Genesis’s principal investigator Dr. Don Burnett.

More information about Genesis is available at http://genesismission.jpl.nasa.gov/. More information about the actual capture and return process is available at http://www.genesismission.org/mission/recgallery.html.

Original Source: NASA/JPL News Release

Posted on by Fraser Cain

Hubble Sees a Gas Cavity in Space

In this unusual image, NASA’s Hubble Space Telescope captures a rare view of the celestial equivalent of a geode ? a gas cavity carved by the stellar wind and intense ultraviolet radiation from a hot young star.

Real geodes are baseball-sized, hollow rocks that start out as bubbles in volcanic or sedimentary rock. Only when these inconspicuous round rocks are split in half by a geologist, do we get a chance to appreciate the inside of the rock cavity that is lined with crystals. In the case of Hubble’s 35 light-year diameter “celestial geode” the transparency of its bubble-like cavity of interstellar gas and dust reveals the treasures of its interior.

The object, called N44F, is being inflated by a torrent of fast-moving particles (called a “stellar wind”) from an exceptionally hot star once buried inside a cold dense cloud. Compared with our Sun (which is losing mass through the so-called “solar wind”), the central star in N44F is ejecting more than a 100 million times more mass per second. The hurricane of particles moves much faster at about 4 million miles per hour (7 million kilometers per hour), as opposed to about 0.9 million miles per hour (1.5 million kilometers per hour) for our Sun. Because the bright central star does not exist in empty space but is surrounded by an envelope of gas, the stellar wind collides with this gas, pushing it out, like a snowplow. This forms a bubble, whose striking structure is clearly visible in the crisp Hubble image.

The nebula N44F is one of a handful of known interstellar bubbles. Bubbles like these have been seen around evolved massive stars (Wolf-Rayet stars), and also around clusters of stars (where they are called “super-bubbles”). But they have rarely been viewed around isolated stars, as is the case here.

On closer inspection N44F harbors additional surprises. The interior wall of its gaseous cavity is lined with several four- to eight-light-year-high finger-like columns of cool dust and gas. (The structure of these “columns” is similar to the Eagle Nebula’s iconic “pillars of creation” photographed by Hubble a decade ago, and is seen in a few other nebulae as well). The fingers are created by a blistering ultraviolet radiation from the central star. Like windsocks caught in a gale, they point in the direction of the energy flow. These pillars look small in this image only because they are much farther away from us than the Eagle Nebula’s pillars.

N44F is located about 160,000 light-years in our neighboring dwarf galaxy the Large Magellanic Cloud, in the direction of the southern constellation Dorado. N44F is part of the larger N44 complex, which is a large super-bubble, blown out by the combined action of stellar winds and multiple supernova explosions. N44 itself is roughly 1,000 light-years across. Several compact star-forming regions, including N44F, are found along the rim of the central super-bubble.

This image was taken with Hubble’s Wide Field Planetary Camera 2 in March 2002, using filters that isolate light emitted by sulfur (shown in blue, a 1,200-second exposure) and hydrogen gas (shown in red, a 1,000-second exposure).

Original Source: Hubble News Release

Posted on by Fraser Cain

Wallpaper: Little Ghost Nebula

Known to amateur astronomers as the ‘Little Ghost Nebula’, because it appears as a small, ghostly cloud surrounding a faint dying star, NGC 6369 lies in the direction of the constellation Ophiuchus.

The NASA/ESA Hubble Space Telescope has took this image of the planetary nebula NGC 6369, at a distance estimated to be between about 2000 and 5000 light-years from Earth.

When a star with a mass similar to that of our own Sun nears the end of its lifetime, it expands in size to become a ‘red giant’. The red-giant stage ends when the star expels its outer layers into space, producing a faintly glowing nebula.

Astronomers call such an object a planetary nebula, because its round shape resembles that of a planet when viewed with a small telescope.

The Hubble photograph of NGC 6369, captured with the Wide Field Planetary Camera 2 (WFPC2) in 2002, reveals remarkable details of the ejection process that are not visible from ground-based telescopes because of the blurring produced by the Earth’s atmosphere.

The remnant stellar core in the centre is now sending out a flood of ultraviolet (UV) light into the surrounding gas. The prominent blue-green ring, nearly a light-year in diameter, marks the location where the energetic UV light has stripped electrons off of atoms in the gas. This process is called ionisation.

In the redder gas at larger distances from the star, where the UV light is less intense, the ioniszation process is less advanced. Even farther outside the main body of the nebula, one can see fainter wisps of gas that were lost from the star at the beginning of the ejection process.

This colour image has been produced by combining WFPC2 pictures taken through filters that isolate light emitted by three different chemical elements with different degrees of ionisation.

The doughnut-shaped blue-green ring represents light from ionised oxygen atoms that have lost two electrons (blue) and from hydrogen atoms that have lost their single electrons (green). Red marks emission from nitrogen atoms that have lost only one electron. Our own Sun may eject a similar nebula, but not for another 5000 million years.

The gas will expand away from the star at about 15 miles per second, dissipating into interstellar space after some 10 000 years. After that, the remnant stellar member in the centre will gradually cool off for millions of years as a tiny white dwarf star, and eventually wink out.

Original Source: ESA News Release

Posted on by Fraser Cain

How the Solar Wind Gets Past the Earth’s Shield

ESA?s quartet of space-weather watchers, Cluster, has discovered vortices of ejected solar material high above the Earth. The superheated gases trapped in these structures are probably tunnelling their way into the Earth?s magnetic ?bubble?, the magnetosphere. This discovery possibly solves a 17-year-mystery of how the magnetosphere is constantly topped up with electrified gases when it should be acting as a barrier.

The Earth?s magnetic field is our planet?s first line of defence against the bombardment of the solar wind. The solar wind itself is launched from the Sun and carries the Sun?s magnetic field throughout the Solar System. Sometimes this magnetic field is aligned with Earth?s and sometimes it points in the opposite direction.

When the two fields point in opposite directions, scientists understand how ?doors? in Earth?s field can open. This phenomenon, called ?magnetic reconnection?, allows the solar wind to flow in and collect in the reservoir known as the boundary layer. On the contrary, when the fields are aligned they should present an impenetrable barrier to the flow. However, spacecraft measurements of the boundary layer, dating back to 1987, present a puzzle because they clearly show that the boundary layer is fuller when the fields are aligned than when they are not. So how is the solar wind getting in?

Thanks to the data from the four formation-flying spacecraft of ESA?s Cluster mission, scientists have made a breakthrough. On 20 November 2001, the Cluster flotilla was heading around from behind Earth and had just arrived at the dusk side of the planet, where the solar wind slides past Earth?s magnetosphere. There it began to encounter gigantic vortices of gas at the magnetopause, the outer ?edge? of the magnetosphere.

?These vortices were really huge structures, about six Earth radii across,? says Hiroshi Hasegawa, Dartmouth College, New Hampshire who has been analysing the data with help from an international team of colleagues. Their results place the size of the vortices at almost 40 000 kilometres each, and this is the first time such structures have been detected.

These vortices are known as products of Kelvin-Helmholtz instabilities (KHI). They can occur when two adjacent flows are travelling with different speeds, so one is slipping past the other. Good examples of such instabilities are the waves whipped up by the wind slipping across the surface of the ocean. Although KHI-waves had been observed before, this is the first time that vortices are actually detected.

When a KHI-wave rolls up into a vortex, it becomes known as a ?Kelvin Cat?s eye?. The data collected by Cluster have shown density variations of the electrified gas, right at the magnetopause, precisely like those expected when travelling through a ?Kelvin Cat?s eye?.

Scientists had postulated that, if these structures were to form at the magnetopause, they might be able to pull large quantities of the solar wind inside the boundary layer as they collapse. Once the solar wind particles are carried into the inner part of the magnetosphere, they can be excited strongly, allowing them to smash into Earth?s atmosphere and give rise to the aurorae.

Cluster?s discovery strengthens this scenario but does not show the precise mechanism by which the gas is transported into Earth?s magnetic bubble. Thus, scientists still do not know whether this is the only process to fill up the boundary layer when the magnetic fields are aligned. For those measurements, Hasegawa says, scientists will have to wait for a future generation of magnetospheric satellites.

Original Source: ESA News Release

Posted on by Fraser Cain

Cassini’s View of Tiny Hyperion

Image credit: NASA/JPL/SSI
This image represents Cassini?s best view yet of Saturn?s battered and chaotically rotating little moon Hyperion (266 kilometers, 165 miles across). Cassini was, at the time, speeding away from the Saturn system on its initial long, looping orbit.

Hyperion has an irregular shape and is known to tumble erratically in its orbit. Cassini is slated to fly past this moon on September 26, 2005.

The image was taken in visible light with the narrow angle camera on July 15, 2004, from a distance of about 6.7 million kilometers (4.1 million miles) from Hyperion and at a Sun- Hyperion-spacecraft, or phase, angle of 95 degrees. The image scale is 40 kilometers (25 miles) per pixel. The image has been magnified by a factor of four to aid visibility.

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 Office of Space Science, Washington, D.C. The imaging team is based at the Space Science Institute, Boulder, Colorado.

For more information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov and the Cassini imaging team home page, http://ciclops.org.

Original Source: CICLOPS News Release

Posted on by Fraser Cain

Photograph the Perseids Tonight

The annual Perseid meteor shower will peak the night of August 11. Members of the news media are presented with an excellent opportunity to witness and photograph the event.

The best views of the meteor shower will be from dark, rural locations. The darker the observing site, the easier it will be to observe or photograph the meteors. Most of the best sites in Southern California are in the desert and mountain areas located east of the major cities.

Meteor photography should not begin until it is completely dark, after 9 p.m. Early in the evening meteors will appear in the northeastern part of the sky. As the night progresses, the meteors will be more numerous and can appear anywhere in the sky. Most of the meteor shower activity will take place after midnight, when observers may see them at the rate of about one per minute.

Meteors occur at random times and locations in the sky. The best technique for capturing them photographically involves using a standard 35-mm camera that has a “B” or bulb setting. The camera needs to be securely fastened to a tripod. A cable release will allow for control the exposures with a minimum of vibration. Film with a speed of ISO 400, 800, or 1000 is recommended. Avoid using a telescope or a telephoto lens,because they reveal only a tiny fraction of the sky, thus greatly reducing your chances of catching a meteor. On the other hand, wide-angle lenses are more likely to catch a meteor, although the meteor will appear small on the photographic image. A 50mm lens is probably a good compromise.

To photograph the meteors, pick an area of the sky, focus on infinity and start the exposure. Those shooting with film may wish to hold the exposure until a meteor is captured, end the exposure, and then start another. Any interesting foreground objects in the shot can be nicely “painted in” to the picture with a flashlight beam shining on them. Don’t be afraid to experiment.

Photographers shooting digitally have some advantages and disadvantages over those shooting with film. Digital photography provides the photographer with rapid feedback as to how the exposures are going. However, it should be noted that for most digital cameras, longer exposures mean more noise in the image. This can be defeated by either taking short exposures (less than a minute) or taking a dark frame of the same length as your exposures of the sky. This dark frame can later be subtracted with a program such as Photoshop.

For anyone attempting to capture the meteor shower on video, the International Meteor Organization recommends using a fast lens and a powerful image intensifier. Specific details are online at http://www.imo.net/video/

Cloud-free skies are essential to having the best view of the meteor shower. The National Weather Service often does not provide the kind of forecast necessary for astronomical observations. A good choice is to check out the Clear Sky Clock. A list of all of the Clear Sky Clock sites in California can be found online at

http://cleardarksky.com/csk/prov/California_clocks.html

An explanation of how to read the data is provided on the web page. Simply choose a site close to where you will observe the meteor shower. Should clouds intervene, it is important to remember that the shower lasts for several nights, giving you another opportunity.

Original Source: Caltech News Release

Posted on by Fraser Cain

One Year to Go for Mars Reconnaissance Orbiter

With one very busy year remaining before launch, the team preparing NASA’s next mission to Mars has begun integrating and testing the spacecraft’s versatile payload. Possible launch dates from Cape Canaveral, Fla., for NASA’s Mars Reconnaissance Orbiter begin Aug. 10, 2005. The spacecraft will reach Mars seven months later to study the surface, subsurface and atmosphere with the most powerful instrument suite ever flown to the red planet.

“Mars Reconnaissance Orbiter is a quantum leap in our spacecraft and instrument capabilities at Mars,” said James Graf, the mission’s project manager at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “Weighing 2,180 kilograms [4,806 pounds] at launch, the spacecraft will be the largest ever to orbit Mars. The data rate from the orbiter at Mars back to Earth will be three times faster than a high-speed residential telephone line. This rate will enable us to return a tremendous amount of data and dramatically increase our understanding of this mysterious planet.”

JPL’s Dr. Richard Zurek, project scientist for Mars Reconnaissance Orbiter, said, “This capability is needed to achieve the higher-resolution imaging, spectral mapping, atmospheric profiling and subsurface probing that will allow us to follow up on the exciting discoveries of the current Mars missions.”

Workers at Lockheed Martin Space Systems, Denver, have been building the orbiter for more than a year and have reached the final assembly stage. Flight software is 96 percent complete. Assembly of the launch vehicle, an Atlas V, has begun at the same facility where the orbiter is being completed and tested. This will be the first interplanetary mission hitched to an Atlas since 1973. The Mars Reconnaissance Orbiter team now numbers about 175 people at Lockheed Martin and 110 at JPL.

Kevin McNeill, Lockheed Martin’s program manager for the orbiter, said, “Our team has completed integration and testing of a majority of the spacecraft’s subsystems. In the next few months, we’ll integrate and test the science instruments on the orbiter, followed by environmental testing through early next year. We look forward to getting to the Cape next spring and integrating with the Atlas V launch vehicle. We’re all very excited about getting to Mars and returning data for the science teams to evaluate.”

The spacecraft’s six science instruments are in the final stages of assembly, testing and calibration at several locations for delivery in coming weeks. The payload also includes a relay telecommunications package called Electra and two technology demonstrations to support planning of future Mars missions. “Electra was integrated with the spacecraft and tested in July,” Graf said. “The next payload elements to be integrated will be the Mars climate sounder and the compact reconnaissance imaging spectrometer for Mars.” The climate sounder, from JPL, will quantify the martian atmosphere’s vertical variations in water vapor, dust and temperature; the imaging spectrometer, from Johns Hopkins Applied Physics Laboratory of Laurel, Md., will scan the surface to look for water-related minerals at unprecedented scales, extending discoveries made by NASA’s Mars Exploration Rovers.

The largest telescopic camera ever sent into orbit around another planet, called the high resolution imaging science experiment, will reveal Mars surface features as small as a kitchen table. Ball Aerospace, Boulder, Colo., is building it for the University of Arizona, Tucson. The orbiter will also carry three other cameras. Two come from Malin Space Sciences, San Diego: the context camera for wide-swath, high-resolution pictures, and the Mars multi-color imager with its fish-eye lens for tracking changes in weather and variations in atmospheric ozone. An optical navigation camera from JPL will use positions of Mars’ two moons to demonstrate precision navigation for future missions.

The Italian Space Agency is providing the orbiter’s shallow radar sounding instrument, designed to probe below the surface to discover evidence of underground layers of ice, rock and, perhaps, melted water.

Another technology demonstration from JPL will allow comparison of a higher-frequency, more-efficient radio band with the band commonly used for interplanetary communications. This may allow future missions to return more data with the same expended power.

NASA?s chief scientist for Mars, Dr. Jim Garvin, added, “We build our science strategy for Mars around the next-generation reconnaissance this spacecraft is to provide, with its revolutionary remote sensing payload, and we are proud of the impressive progress to date by our Mars Reconnaissance Orbiter team. Mars Reconnaissance Orbiter will tell us where we must send our next wave of robotic explorers, including the Mars Science Laboratory, as well as paving the way for human exploration.”

The Mars Reconnaissance Orbiter mission is managed by JPL, a division of the California Institute of Technology, Pasadena, for the NASA Science Mission Directorate, Washington. Lockheed Martin Space Systems is the prime contractor for the project.

Original Source: NASA/JPL News Release

Posted on by Fraser Cain

Cargo Ship Blasts Off

An unpiloted Russian cargo ship blasted off this morning from the Baikonur Cosmodrome in Kazakhstan on a three-day journey to deliver almost three tons of food, fuel, oxygen, water and supplies to the residents of the International Space Station.

The ISS Progress 15 craft lifted off on time from the Central Asian launch site at 12:03 a.m. CDT (503 GMT), and less than 10 minutes later settled into orbit. Moments after that, automatic commands deployed its solar arrays and navigational antennas.

As the Progress launched, Expedition 9 Commander Gennady Padalka and Flight Engineer and NASA Science Officer Mike Fincke were asleep. The Station was flying just to the southwest of Baikonur at an altitude of 230 statute miles at the time of launch.

Two engine firings were scheduled overnight to raise and refine the Progress? orbit and its path to the ISS for an automated docking Saturday morning at 12:02 a.m. CDT (502 GMT) at the aft port of the Zvezda Service Module. The Progress is loaded with 1521 pounds of propellant, 110 pounds of oxygen and air to replenish the Station?s atmosphere, 926 pounds of water and more than 3000 pounds of spare parts, life support system components and experiment hardware.

Among the spare parts launched today to the Station are new pumps for the U.S. spacesuits onboard that experienced cooling problems in early June while being prepared for a spacewalk to repair a failed power controller. The suits are undergoing troubleshooting in the hope they can be placed back into service in the near future. The repair spacewalk was eventually conducted in Russian Orlan spacesuits on June 30.

Also on the Progress are clothing articles for the next residents that will occupy the Station. Expedition 10 Commander and NASA Science Officer Leroy Chiao and Flight Engineer Salizhan Sharipov are scheduled to launch Oct. 9 on the Soyuz TMA-5 vehicle from Baikonur to begin a six-month stay on the complex, replacing Padalka and Fincke.

Information on the crew’s activities aboard the Space Station, future launch dates, as well as Station sighting opportunities from anywhere on the Earth, is available on the Internet at:

http://spaceflight.nasa.gov/

Details on Station science operations can be found on an Internet site administered by the Payload Operations Center at NASA’s Marshall Space Flight Center in Huntsville, Ala., at:

http://scipoc.msfc.nasa.gov/

The next ISS status report will be issued on Friday, August 13, or earlier, if events warrant.

Original Source: NASA Status Report

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Perspective View of Olympus Mons

This perspective view, taken by the High Resolution Stereo Camera (HRSC) on board ESA’s Mars Express spacecraft, shows the complex caldera of Olympus Mons on Mars, the highest volcano in our Solar System.

Olympus Mons has an average elevation of 22 kilometres and the caldera, or summit crater, has a depth of about 3 kilometres. The data was retrieved during orbit 143 of Mars Express on 24 February 2004. The view is looking north.

The curved striations on the left and foreground, in the southern part of the caldera, are tectonic faults. After lava production has ceased the caldera collapsed over the emptied magma chamber. Through the collapse the surface suffers from extension and so extensional fractures are formed.

The level plain inside the crater on which these fractures can be observed represents the oldest caldera collapse. Later lava production caused new caldera collapses at different locations (the other circular depressions). They have partly destroyed the circular fracture pattern of the oldest one.

This perspective view of the caldera was calculated from the digital elevation model derived from the stereo channels and combined with the nadir and colour channels of the HRSC.

Original Source: ESA News Release