Posted on by Fraser Cain

Astrophoto: Zodiacal Light by Tony and Daphne Hallas


Zodiacal Light by Tony and Daphne Hallas

The night sky, from a dark location, is filled with many sights full of wonder to urban dwellers: the slow moving glint of a satellite solar array, the flash and occasional sonic repercussion of a meteor flailing overhead, the arc of combined luminosity from the Milky Way’s remote suns and the glow from high altitude cirrus present in Earth’s atmosphere. But at certain times of the year a few hours after sunset or before sunrise, a soft triangular shape will appear from the horizon extending upward that may lead you to believe the moon or the sun is about to rise. This explanation has passed through the minds of observers since antiquity and is called the false dawn… but, it is another thing altogether.

The Sun rules over a vast empire in the sky and around it circles a cortege of loyal subjects – noble planets with waists of varying proportion, their attendant moons in tow like guards and helpful servants, countless asteroids which make up the sky’s gentry and intermittent tourists on holiday from the kingdom’s outer provinces- the comets. But in between the sun and just outside the influence of Earth’s orbit is a vast cloud of interplanetary dust– crumbs fallen from the table during the feast of the solar system’s creation. Each tiny particle may be separated from its neighbor by up to five miles, thus this nebula is very thin. But its presence is apparent when sunlight glints off each fragment and you are standing beneath an exceptionally dark, clear night sky at the right time of the year.

Because the dust that creates this phenomenon resides within the same plane as the planets, it projects itself against the same constellations that the planets also pass, thus it is now known as the Zodiacal Light.

For those in the Northern Hemisphere, the best time to see this unique apparition is a few hours after sunset in the west between February and March and a few hours before dawn during October, over in the east. If you live in the Southern Hemisphere the best western view is during the evening from August to September or in the east during the early morning hours throughout April.

Over time, the dust that forms this cloud slowly spirals inward toward the sun. It is believed that the cloud regenerates itself from the debris that results in the collision of larger orbiting particles and from the tails of comets.

This exceptional picture of the Zodiacal Light was recently produced by Tony and Daphne Hallas from a location at Modoc Plateau, which lies in the northeast corner of California as well as parts of Oregon and Nevada. This area is one of the darkest sites in the continental United States and is home to a mile-high expanse of lava flows, cinder cones, pine forests and seasonal lakes. Daphne and Tony took this image with a Canon 20D digital camera using a 16-35mm f/2.8 lens.

Do you have photos you’d like to share? Post them to the Universe Today astrophotography forum or email them, and we might feature one in Universe Today.

Written by R. Jay GaBany

Posted on by Fraser Cain

Building an Antimatter Spaceship

A spacecraft powered by a positron reactor would resemble this artist's concept of the Mars Reference Mission spacecraft. Credit: NASA

If you’re looking to build a powerful spaceship, nothing’s better than antimatter. It’s lightweight, extremely powerful and could generate tremendous velocity. However, it’s enormously expensive to create, volatile, and releases torrents of destructive gamma rays. NASA’s Institute for Advanced Concepts is funding a team of researchers to try and design an antimatter-powered spacecraft that could avoid some of those problems.

Most self-respecting starships in science fiction stories use anti matter as fuel for a good reason – it’s the most potent fuel known. While tons of chemical fuel are needed to propel a human mission to Mars, just tens of milligrams of antimatter will do (a milligram is about one-thousandth the weight of a piece of the original M&M candy).

However, in reality this power comes with a price. Some antimatter reactions produce blasts of high energy gamma rays. Gamma rays are like X-rays on steroids. They penetrate matter and break apart molecules in cells, so they are not healthy to be around. High-energy gamma rays can also make the engines radioactive by fragmenting atoms of the engine material.

The NASA Institute for Advanced Concepts (NIAC) is funding a team of researchers working on a new design for an antimatter-powered spaceship that avoids this nasty side effect by producing gamma rays with much lower energy.

Antimatter is sometimes called the mirror image of normal matter because while it looks just like ordinary matter, some properties are reversed. For example, normal electrons, the familiar particles that carry electric current in everything from cell phones to plasma TVs, have a negative electric charge. Anti-electrons have a positive charge, so scientists dubbed them “positrons”.

When antimatter meets matter, both annihilate in a flash of energy. This complete conversion to energy is what makes antimatter so powerful. Even the nuclear reactions that power atomic bombs come in a distant second, with only about three percent of their mass converted to energy.

Previous antimatter-powered spaceship designs employed antiprotons, which produce high-energy gamma rays when they annihilate. The new design will use positrons, which make gamma rays with about 400 times less energy.

The NIAC research is a preliminary study to see if the idea is feasible. If it looks promising, and funds are available to successfully develop the technology, a positron-powered spaceship would have a couple advantages over the existing plans for a human mission to Mars, called the Mars Reference Mission.

“The most significant advantage is more safety,” said Dr. Gerald Smith of Positronics Research, LLC, in Santa Fe, New Mexico. The current Reference Mission calls for a nuclear reactor to propel the spaceship to Mars. This is desirable because nuclear propulsion reduces travel time to Mars, increasing safety for the crew by reducing their exposure to cosmic rays. Also, a chemically-powered spacecraft weighs much more and costs a lot more to launch. The reactor also provides ample power for the three-year mission. But nuclear reactors are complex, so more things could potentially go wrong during the mission. “However, the positron reactor offers the same advantages but is relatively simple,” said Smith, lead researcher for the NIAC study.

Also, nuclear reactors are radioactive even after their fuel is used up. After the ship arrives at Mars, Reference Mission plans are to direct the reactor into an orbit that will not encounter Earth for at least a million years, when the residual radiation will be reduced to safe levels. However, there is no leftover radiation in a positron reactor after the fuel is used up, so there is no safety concern if the spent positron reactor should accidentally re-enter Earth’s atmosphere, according to the team.

It will be safer to launch as well. If a rocket carrying a nuclear reactor explodes, it could release radioactive particles into the atmosphere. “Our positron spacecraft would release a flash of gamma-rays if it exploded, but the gamma rays would be gone in an instant. There would be no radioactive particles to drift on the wind. The flash would also be confined to a relatively small area. The danger zone would be about a kilometer (about a half-mile) around the spacecraft. An ordinary large chemically-powered rocket has a danger zone of about the same size, due to the big fireball that would result from its explosion,” said Smith.

Another significant advantage is speed. The Reference Mission spacecraft would take astronauts to Mars in about 180 days. “Our advanced designs, like the gas core and the ablative engine concepts, could take astronauts to Mars in half that time, and perhaps even in as little as 45 days,” said Kirby Meyer, an engineer with Positronics Research on the study.

Advanced engines do this by running hot, which increases their efficiency or “specific impulse” (Isp). Isp is the “miles per gallon” of rocketry: the higher the Isp, the faster you can go before you use up your fuel supply. The best chemical rockets, like NASA’s Space Shuttle main engine, max out at around 450 seconds, which means a pound of fuel will produce a pound of thrust for 450 seconds. A nuclear or positron reactor can make over 900 seconds. The ablative engine, which slowly vaporizes itself to produce thrust, could go as high as 5,000 seconds.

One technical challenge to making a positron spacecraft a reality is the cost to produce the positrons. Because of its spectacular effect on normal matter, there is not a lot of antimatter sitting around. In space, it is created in collisions of high-speed particles called cosmic rays. On Earth, it has to be created in particle accelerators, immense machines that smash atoms together. The machines are normally used to discover how the universe works on a deep, fundamental level, but they can be harnessed as antimatter factories.

“A rough estimate to produce the 10 milligrams of positrons needed for a human Mars mission is about 250 million dollars using technology that is currently under development,” said Smith. This cost might seem high, but it has to be considered against the extra cost to launch a heavier chemical rocket (current launch costs are about $10,000 per pound) or the cost to fuel and make safe a nuclear reactor. “Based on the experience with nuclear technology, it seems reasonable to expect positron production cost to go down with more research,” added Smith.

Another challenge is storing enough positrons in a small space. Because they annihilate normal matter, you can’t just stuff them in a bottle. Instead, they have to be contained with electric and magnetic fields. “We feel confident that with a dedicated research and development program, these challenges can be overcome,” said Smith.

If this is so, perhaps the first humans to reach Mars will arrive in spaceships powered by the same source that fired starships across the universes of our science fiction dreams.

Original Source: NASA News Release

Posted on by Fraser Cain

Titan and Epimetheus Behind the Rings

Titan and small Epimetheus behind Saturn’s rings. Image credit: NASA/JPL/SSI. Click to enlarge
This Cassini photograph shows Saturn’s large, smoggy moon Titan partly obscured by the planet’s rings. Another of Saturn’s moons, tiny Epimetheus, is visible as a dot just to the left of Titan. Cassini took this photograph on March 9, 2006 when it was approximately 4.1 million kilometers (2.5 million miles) from Titan.

This poetic scene shows the giant, smog-enshrouded moon Titan behind Saturn’s nearly edge-on rings. Much smaller Epimetheus (116 kilometers, or 72 miles across) is just visible to the left of Titan (5,150 kilometers, or 3,200 miles across).

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on March 9, 2006, at a distance of approximately 4.1 million kilometers (2.5 million miles) from Titan. The image scale is 25 kilometers (16 miles) per pixel on Titan. The brightness of Epimetheus was enhanced for 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 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

Mars Reconnaissance Orbiter Adjusts its Orbit

The large Argyre Basin in Mars’ southern hemisphere. Image credit: NASA/JPL/MSSS. Click to enlarge
NASA’s Mars Reconnaissance Orbiter has sent back some new test images of the Martian surface, at a resolution of 2.5 metres/pixel. Once it reaches its final science orbit, the spacecraft will be 10 times closer to the planet, and the images will be even higher resolution. The spacecraft fired its thrusters on Wednesday to adjust its orbit so that it passed through Mars’ atmosphere. This maneuver is called aerobraking, and the spacecraft will make many of these passes over the next 6 months.

Researchers today released the first Mars images from two of the three science cameras on NASA’s Mars Reconnaissance Orbiter.

Images taken by the orbiter’s Context Camera and Mars Color Imager during the first tests of those instruments at Mars confirm the performance capability of the cameras. The test images were taken from nearly 10 times as far from the planet as the spacecraft will be once it finishes reshaping its orbit. Test images from the third camera of the science payload were released previously.

“The test images show that both cameras will meet or exceed their performance requirements once they’re in the low-altitude science orbit. We’re looking forward to that time with great anticipation,” said Dr. Michael Malin of Malin Space Science Systems, San Diego. Malin is team leader for the context camera and principal investigator for the Mars Color Imager.

The cameras took the test images two weeks after the orbiter’s March 10 arrival at Mars and before the start of “aerobraking,” a process of reshaping the orbit by using controlled contact with Mars’ atmosphere. This week, the spacecraft is dipping into Mars’ upper atmosphere as it approaches the altitude range that it will use for shrinking its orbit gradually over the next six months.

The orbiter is currently flying in very elongated loops around Mars. Each circuit lasts about 35 hours and takes the spacecraft about 27,000 miles (43,000 kilometers) away from the planet before swinging back in close.

On Wednesday, a short burn of intermediate sized thrusters while the orbiter was at the most distant point nudged the spacecraft to pass from approximately 70 miles (112 kilometers) to within 66 miles (107 kilometers) of Mars’ surface.

“This brings us well into Mars’ upper atmosphere for the drag pass and will enable the mission to start reducing the orbit to its final science altitude,” said Dan Johnston of NASA’s Jet Propulsion Laboratory, Pasadena, Calif., deputy mission manager.

After hundreds of passes through the upper atmosphere, the drag will gradually reduce the far point of the orbit until the spacecraft is in a nearly circular orbit every two hours.

After the spacecraft gets into the proper orbit for its primary science phase, the six science instruments on board will begin their systematic examination of Mars. The Mars Color Imager will view the planet’s entire atmosphere and surface every day to monitor changes in clouds, wind-blown dust, polar caps and other variable features.

Images from the Context Camera will have a resolution of 20 feet (6 meters) per pixel, allowing surface features as small as a basketball court to be discerned. The images will cover swaths 18.6 miles (30 kilometers) wide.

The Context Camera will show how smaller areas examined by the High Resolution Imaging Science Experiment Camera — which will have the best resolution ever achieved from Mars orbit — and by the mineral-identifying Compact Reconnaissance Imaging Spectrometer fit into the broader landscape. It will also allow scientists to watch for small-scale changes, such as newly cut gullies, in the broader coverage area.

The new test images from the Context Camera and the Mars Color Imager are available online at www.nasa.gov/mro , www.msss.com/mro/ctx/images/2006/04/13/ and www.msss.com/mro/marci/images/2006/04/13/ .

For more detailed information about Mars Reconnaissance Orbiter, see http://mars.jpl.nasa.gov/mro .

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

Original Source: NASA News Release

Posted on by Fraser Cain

The Strange Nebula Around Eta Carinae

One of the five PHOENIX spectrograph of Eta Carinae. Image credit: Gemini Observatory/AURA. Click to enlarge
Eta Carinae is an unusual variable star just 8,000 light years away from Earth. It’s about 100 times more massive than our Sun – one of the most massive known – and it shines about 5 million times brighter than the Sun. It’s surrounded by an unusual cloud of material known as the Homunculus Nebula, which astronomers believe was created by successive explosions on the star’s surface. The Gemini Observatory has revealed a shockwave of expanding material moving through space at 500 km/second (310 miles/s).

Although the Homunculus Nebula around the massive star Eta Carinae has been the subject of intense study for many years, it has always been reluctant to divulge its innermost secrets. However, an important chapter in the recent evolution of this unique star was revealed when Nathan Smith (University of Colorado) used the high-resolution infrared spectrograph PHOENIX on the Gemini South telescope to observe the bipolar nebula surrounding Eta Carinae.

Multi-slit spectroscopy allowed Smith to reconstruct both the geometry and the velocity structure of the expanding gas in the nebula based on the behavior of the molecular line of hydrogen H2 at 2.1218 microns and the atomic line of ionized iron [Fe II] at 1.6435 microns.

Analysis of the PHOENIX spectrum shows a very well-defined shell structure expanding ballistically at about 500 kilometers per second. A “thick,” warm inner dust shell traced by [Fe II] emission is surrounded by a cooler and denser outer shell that is traced by strong H2 emission. Even though the outer H2 skin is remarkably thin and uniform it contains about 11 solar masses of gas and dust ejected over a period of less than five years. The Gemini spectra show that the density in the outer shell may reach 107 particles per cm3.

The spatio-kinematic structure of H2 emission at the pinched waist of the nebula helps explain the unusual and complex structures seen in other high-resolution images. The current shape of the Homunculus nebula is of two well-defined polar lobes outlined by an outer massive shell of gas and dust. Smith states that these Gemini/PHOENIX data indicate that most of the mass lost during the Great Eruption of the mid-nineteenth century was limited to the high latitudes of the star, with almost all of the mechanical energy escaping between 45 degrees and the pole.

“The mass distribution in the nebula indicates that its shape is a direct result of an aspherical explosion from the star itself, instead of being pinched at the waist by the surrounding circumstellar material,” said Smith.

For more details read “The Structure of the Homunculus: I. Shape and Latitutude Dependence from H2 and [Fe II] velocity Maps of Eta Carinae,” by Nathan Smith, The Astrophysical Journal, in press or at astro-ph/0602464.

Original Source: Gemini Observatory

Posted on by Fraser Cain

Mars Rovers Head for New Sites After Studying Layers

Coarse-grained layers inside Mars’ Gusev Crater. Image credit: NASA/JPL/Cornell. Click to enlarge
NASA engineers have moved the Spirit Mars rover to a safe North-facing slope to ride out the Martian winter. Since the rover is in the Southern hemisphere, it gets much less sunlight during the Winter. This maneuver was made more difficult because its right-front wheel has stopped working – the robot is dragging it along like an anchor. Spirit requires a good angle towards the sun to catch energy from the Sun onto its solar panels. It needs to store enough electricity to run the overnight heaters that protect its electronics.

NASA’s Mars rover Spirit has reached a safe site for the Martian winter, while its twin, Opportunity, is making fast progress toward a destination of its own.

The two rovers recently set out on important — but very different — drives after earlier weeks inspecting sites with layers of Mars history. Opportunity finished examining sedimentary evidence of ancient water at a crater called “Erebus,” and is now rapidly crossing flat ground toward the scientific lure of a much larger crater, “Victoria.”

Spirit studied signs of a long-ago explosion at a bright, low plateau called “Home Plate” during February and March. Then one of its six wheels quit working, and Spirit struggled to complete a short advance to a north-facing slope for the winter. “For Spirit, the priority has been to reach a safe winter haven,” said Dr. Steve Squyres of Cornell University, Ithaca, N.Y., principal investigator for the Mars Exploration Rover project.

The rovers have operated more than eight times as long as their originally planned three-month explorations on Mars. Each has driven more than 6.8 kilometers (4.2 miles) about 11 times as far as planned. Combined, they have returned more than 150,000 images. Two years ago, the project had already confirmed that at least one place on Mars had a wet and possibly habitable environment long ago. The scientific findings continue.

Opportunity spent most of the past four months at Erebus, a highly eroded impact crater about 300 meters (1,000 feet) in diameter, where the rover found extensive exposures of thin, rippled layering interpreted as a fingerprint of flowing water. “What we see at Erebus is a thicker interval of wetted sediment than we’ve seen anywhere else,” said Dr. John Grotzinger of the California Institute of Technology, “The same outcrops also have cracks that may have formed from wetting and drying.”

In mid-March, Opportunity began a 2-kilometer (1.6-mile) trek from Erebus to Victoria, a crater about 800 meters (half a mile) across, where a thick sequence of sedimentary rocks is exposed. In the past three weeks, Opportunity has already driven more than a fourth of that distance.

At Home Plate, Spirit found coarse layering overlain by finer layering in a pattern that fits accumulation of material falling to the ground after a volcanic or impact explosion. In one place, the layers are deformed where a golfball-size rock appears to have fallen on them while they were soft. “Geologists call that a ‘bomb sag,’ and it is strong evidence for some kind of explosive origin,” Squyres said. “We would like to have had time to study Home Plate longer, but we needed to head for a north-facing slope before winter got too bad.”

Spirit is in Mars’ southern hemisphere, where the sun is crossing lower in the northern sky each day. The rovers rely on solar power. The amount available will keep dropping until the shortest days of the Mars winter, four months from now. To keep producing enough electricity to run overnight heaters that protect vital electronics, Spirit’s solar panels must be tilted toward the winter sun by driving the rover onto north-facing slopes. However, on March 13 the right-front wheel’s drive motor gave out. Spirit has subsequently driven about 80 meters (262 feet) using five wheels and dragging the sixth, but an initial route toward a large hill proved impassable due to soft ground. Last week, the team chose a smaller nearby ridge, dubbed “Low Ridge Haven,” as the winter destination. Spirit reached the ridge Sunday and has a favorable 11-degree tilt toward the north.

“We have to use care choosing the type of terrain we drive over,” Dr. Ashitey Trebi-Ollennu, a rover planner at NASA’s Jet Propulsion Laboratory, Pasadena, Calif., said about the challenge of five-wheel driving. In tests at JPL, the team has been practicing a maneuver to gain additional tilt by perching the left-front wheel on a basketball-size rock.

Spending eight months or so at Low Ridge Haven will offer time for many long-duration studies that members of the science team have been considering since early in the mission, said Dr. Ray Arvidson of Washington University in St. Louis, deputy principal investigator. These include detailed mapping of rocks and soils; in-depth determination of rock and soil composition; monitoring of clouds and other atmospheric changes; watching for subtle surface changes due to winds; and learning properties of the shallow subsurface by tracking surface-temperature changes over a span of months.

JPL, a division of the California Institute of Technology, Pasadena, manages the Mars Exploration Rover Project for the NASA Science Mission Directorate.

For images and information about the rovers, see http://www.nasa.gov/rovers or http://marsrovers.jpl.nasa.gov .

For information about NASA and agency programs on the Web, visit http://www.nasa.gov .

Original Source: NASA News Release

Posted on by Mark Mortimer

Book Review: Destination Moon


Perhaps Krafft Ehricke put it best when he said if God wanted us to be a spacefaring race, He would have given us a Moon. The Apollo Space Program validated this statement by placing astronauts on the lunar surface. Rod Pyle in his book entitled Destination Moon � The Apollo Missions in the Astronauts’ Own Words brings back those heady days when anything seemed possible, if only we had the will.

Today, with NASA’s sights reset upon our Moon, there are many people with the desire to revisit their earlier sojourns to the same locale. A generation has matured without experiencing the euphoria of proving that the Earth is round, that it orbits the Sun and that people can walk on land other than of Earth. The Apollo Space Program showed that the universe is indeed a big place and that people aren’t inherently constrained to one little planet. Using technology of the day, stronauts rocketed up to the Moon, studied the geology and drove vehicles about the surface. Twelve people stood on the surface, surveyed the landscape, poked and prodded the rocks and left foot prints. Hundreds of thousands of others helped put them there. Those times were indeed heady for humankind.

Pyle’s objective with his book is to transport the reader back to that time of breathless wonder, to enjoy and (re) experience the Apollo program as those who did firsthand. To achieve this, he uses a picture book format with a superb collection of photographs culled from thousands of original negatives. Vibrant, evocative photographs fill the pages. Square images take up the whole page, while rectangular images expand across two. Most are in colour, though many of the views of the lunar surface look black and white for obvious reasons. The clarity of each is sharp, well depicting the memorable moment, and strongly evocative of the times. With the emotion transfixed on the many displayed faces, it is very easy to return to the times of Apollo.

The book’s title is also accurate when it states that the missions are discussed in the astronauts’ own words. This is because Pyle uses the astronauts’ mission dialogue and interviews straight from NASA. These are the astronauts own words but they contain nothing original. However, the translation’s of Pete Conrad singing are particularly humorous and the chosen passages highlight the flavour of the particular mission. Throughout these dialogues, brief explanatory notes orient the reader and put the dialogue in context. In all, these provide a valuable reference when viewing the photographs.

Pyle uses a chronological format through the book. He begins with outlines of Apollo 1, 7 and 8, the preparations for flight, the testing and the experience of failure. Next he combines Apollo 9 and 10 and the success of all up testing. Then he dedicates a chapter for each of the following 7 missions. With the description of each mission, he includes the official crew pictures to remind the reader of the human element. He closes with a chapter describing Al Bean’s artwork and thoughts on spaceflight and the future. In addition to including the crew pictures for each mission, there are many spectacular photographs of the lunar surface. In the words of Buzz Aldrin, these really show the magnificent desolation of the topology. Photographs address many other times in the mission, such as pre-launch, the lunar module ascension to the command module, and, the return capsule hitting the water. With all these well chosen, striking pictures, this book makes a wonderful gift to someone who hasn’t partaken in the experience or anyone who wants to re-fresh the feelings of optimism from those days.

Walking on the Moon’s surface is possible, people have already done it! Rod Pyle in his book entitled Destination Moon � The Apollo Missions in the Astronauts’ Own Words provides dramatic evidence of this. He lets photographs do most of the talking as he returns the reader to the exciting days when people walked on the Moon. We may soon return.

Review by Mark Mortimer

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

Posted on by Fraser Cain

Swirly Stormy Saturn

Dynamic Saturn. Image credit: NASA/JPL/SSI. Click to enlarge
Saturn, up close and personal. In this Cassini image, you can see the subtle, swirling storms that roll across Saturn’s atmosphere. Unlike the Earth, Saturn is still a planet in formation; it’s continuing to slowly contract, which generates the massive amounts of heat that drive its dramatic weather systems. Cassini took this photograph on March 7, 2006 when it was 2.9 million kilometers (1.8 million miles) from Saturn.

Streamers, swirls and vortices roll across the dynamic face of Saturn.

Unlike Earth, where most of the weather is driven by the Sun, Saturn’s storms and circulation are driven in part by internal heating. Amazingly, the planet is still contracting (ever so slightly) from its formation, more than 4.5 billion years ago. This gravitational contraction liberates energy in the form of heat.

The image was taken in polarized infrared light with the Cassini spacecraft narrow-angle camera on March 7, 2006, at a distance of approximately 2.9 million kilometers (1.8 million miles) from Saturn. The image scale is 17 kilometers (10 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

Mars Wants You to Have a Nice Day

This is a photograph of the unusually happy Galle Crater on Mars. ESA’s Mars Express took a series of 5 images shaped like strips which were then assembled on computer to build up a single photograph. Galle Crater is 230 km (143 miles) across, and located on the eastern rim of the Argyre Planitia impact basin on Mars.

These images, taken by the High Resolution Stereo Camera (HRSC) on board ESA’s Mars Express spacecraft, show the Galle Crater, an impact crater located on the eastern rim of the Argyre Planitia impact basin on Mars.

The HRSC obtained these images during orbits 445, 2383, 2438, 2460 and 2493 with a ground resolution ranging between 10-20 metres per pixel, depending on location within the image strip.

The images show Crater Galle lying to the east of the Argyre Planitia impact basin and south west of the Wirtz and Helmholtz craters, at 51 degrees South and 329 degrees East.

The images of the 230 km diameter impact crater are mosaics created from five individual HRSC nadir and colour strips, each tens of kilometres wide.

A large stack of layered sediments forms an outcrop in the southern part of the crater. Several parallel gullies, possible evidence for liquid water on the Martian surface, originate at the inner crater walls of the southern rim.

Crater Galle, named after the German astronomer J.G. Galle (1812-1910), is informally known as the ‘happy face’ crater.

The ‘face’ was first pointed out in images taken during NASA’s Viking Orbiter 1 mission.

***image4:left***Its interior shows a surface which is shaped by ‘aeolian’ (wind-caused) activity as seen in numerous dunes and dark dust devil tracks which removed the bright dusty surface coating.

The colour scenes, false-colour and near true-colour, have been derived from three HRSC colour and nadir channels gathered during five overlapping orbits. The perspective views have been calculated from a mosaic of digital terrain models derived from the stereo channels.

The black-and-white high-resolution image mosaic was derived from the nadir channel which provides the highest detail of all channels. The resolution has been decreased for use on the Internet, to around 50 m per pixel.

Original Source: ESA Mars Express

Posted on by Fraser Cain

Hubble Finds Xena’s Only a Little Bigger Than Pluto

An artist’s illustration of Xena with its moon. Image credit: NASA Click to enlarge
The powerful Hubble Space Telescope has finally been brought to bear on the newly discovered 10th planet (aka Xena), to help answer the question: is it really bigger than Pluto? Hubble is the only instrument that can make an actual visible light observation of Xena’s diameter. Hubble found that Xena is is about 2400 km (1,490 miles) across, which makes it only 113 km (70 miles) larger than Pluto. This makes the 10th planet unusually bright, probably covered in brilliant white methane snow.

For the first time, NASA’s Hubble Space Telescope has seen distinctly the “tenth planet,” currently nicknamed “Xena,” and has found that it is only slightly larger than Pluto.

Though previous ground-based observations suggested that Xena’s diameter was about 30 percent greater than Pluto, Hubble observations taken Dec. 9 and 10, 2005, showed Xena’s diameter as 1,490 miles (with an uncertainty of 60 miles). Pluto’s diameter, as measured by Hubble, is 1,422 miles.

“Hubble is the only telescope capable of getting a clean visible-light measurement of the actual diameter of Xena,” said Mike Brown, planetary scientist at the California Institute of Technology in Pasadena, Calif. Brown’s research team discovered Xena, officially cataloged as 2003 UB313, and its results have been accepted for publication in the Astrophysical Journal.

Only a handful of images were required to determine Xena’s diameter. Located 10 billion miles from Earth with a diameter a little more than half the width of the United States, the object is 1.5 pixels across in Hubble’s view. That’s enough to make a precise size measurement.

Because Xena is smaller than previously thought, but comparatively bright, it must be one of the most reflective objects in the solar system. The only object more reflective is Enceladus, a geologically active moon of Saturn whose surface is continuously recoated with highly reflective ice by active geysers.

Xena’s bright reflectivity is possibly due to fresh methane frost on its surface. The object may have had an atmosphere when it was closer to the sun, but as it moved to its current location farther away this atmosphere would have “frozen out,” settling on the surface as frost.

Another possibility is that Xena leaks methane gas continuously from its warmer interior. When this methane reaches the cold surface, it immediately freezes solid, covering craters and other features to make it uniformly bright to Hubble’s telescopic eye.

Xena’s takes about 560 years to orbit the sun, and it is now very close to aphelion (the point on its orbit that is farthest from the sun).Brown next plans to use Hubble and other telescopes to study other recently discovered Kuiper Belt objects that are almost as large as Pluto and Xena. The Kuiper Belt is a vast ring of primordial icy comets and larger bodies encircling Neptune’s orbit.

Finding that the largest known Kuiper Belt object is a virtual twin to Pluto may only further complicate the debate about whether to categorize the large icy worlds that populate the belt as planets. If Pluto were considered to be the minimum size for a planet, then Xena would fulfill this criterion, too. In time, the International Astronomical Union will designate the official name.

The Hubble Space Telescope is an international cooperative project between NASA and the European Space Agency. The Space Telescope Science Institute in Baltimore conducts Hubble science operations. The Institute is operated for NASA by the Association of Universities for Research in Astronomy, Inc., Washington

For electronic images and more Hubble news, visit: http://www.nasa.gov/hubble

Original Source: NASA News Release

Update, Pluto is no longer a planet. Why is Pluto not a planet?