Posted on by Fraser Cain

Fly Through of a Martian Canyon

Flight through Mariner Valley. Image credit: NASA/JPL. Click to enlarge.
NASA researchers have created a virtual fly through of Valles Marineris on Mars. This video was created by stitching together images taken by the Thermal Emission Imaging System multi-band camera on NASA’s Mars Odyssey spacecraft. The images showed details as small as 300 meters (1,000 feet) across, and were taken during in infrared during the Martian daytime. The final images were coloured on computer to approximate how the landscape would look to the human eye.

A new view of the biggest canyon in the solar system, merging hundreds of photos from NASA’s Mars Odyssey orbiter, offers scientists and the public an online resource for exploring the entire canyon in detail.

This canyon system on Mars, named Valles Marineris, stretches as far as the distance from California to New York. Steep walls nearly as high as Mount Everest give way to numerous side canyons, possibly carved by water. In places, walls have shed massive landslides spilling far out onto the canyon floor.

A simulated fly-through using the newly assembled imagery is available online. The fly-through plus tools for wandering across and zooming into the large image are also available.

“We picked Valles Marineris to make this first mosaic because it’s probably the most complex, interesting feature on the entire planet,” said Dr. Phil Christensen of Arizona State University, Tempe. He is the principal investigator for Mars Odyssey’s versatile camera, the Thermal Emission Imaging System. “To understand many of the processes on Mars — erosion, landsliding and the effects of water — you really need to have a big-picture view but still be able to see the details.”

Small parts of the canyon have been seen at higher resolution, but at 100 meters (328 feet) per pixel, the new view has sharper resolution than any previous imaging of the entire canyon.

In addition to the completed mosaic of Valles Marineris images, the camera team has also prepared an online data set of nearly the entire planet of Mars at 232 meters (760 feet) per pixel, the most detailed global view of the red planet. The team plans to post 100-meter-resolution mosaics of other regions of Mars in coming months.

Odyssey reached Mars in 2001. The Thermal Emission Imaging System began observing the planet systematically in February 2002 both in visible wavelengths and in infrared wavelengths, which are better for seeing surface details through Mars’ atmospheric dust. As the spacecraft passes over an area, the camera records images of swaths 32 kilometers wide (20 miles wide). More than three years of observations made at infrared wavelengths during Martian daytime are combined into the assembled view of Valles Marineris and the global image data set.

Mars Odyssey is managed by NASA’s Jet Propulsion Laboratory, a division of the California Institute of Technology, Pasadena, for NASA’s Science Mission Directorate, Washington. Lockheed Martin Space Systems, Denver, is the prime contractor for the project and built the spacecraft. The orbiter began an extended mission in August 2004 after successfully completing its primary mission.

Original Source: NASA/JPL News Release

Posted on by Fraser Cain

Super Earths Might Be Common

Artist illustration of a super Earth. Image credit: CfA. Click to enlarge.
Nearly all the extrasolar planets discovered have been Jupiter-sized or larger. But astronomers from the Harvard-Smithsonian Center for Astrophysics think that super-earths – rocky planets several times larger that our planet – might actually be much more common. Based on the recent discovery of a super-earth around a red dwarf star 9,000 light-years away, the research team calculated that there are probably 3 times as many of these planets than the larger gas giants.

Astronomers have discovered a new “super-Earth” orbiting a red dwarf star located about 9,000 light-years away. This newfound world weighs about 13 times the mass of the Earth and is probably a mixture of rock and ice, with a diameter several times that of Earth. It orbits its star at about the distance of the asteroid belt in our solar system, 250 million miles out. Its distant location chills it to -330 degrees Fahrenheit, suggesting that although this world is similar in structure to the Earth, it is too cold for liquid water or life.

Orbiting almost as far out as Jupiter does in our solar system, this “super-Earth” likely never accumulated enough gas to grow to giant proportions. Instead, the disk of material from which it formed dissipated, starving it of the raw materials it needed to thrive.

“This is a solar system that ran out of gas,” says Harvard astronomer Scott Gaudi of the Harvard-Smithsonian Center for Astrophysics (CfA), a member of the MicroFUN collaboration that spotted the planet.

The discovery is being reported today in a paper posted online at http://arxiv.org/abs/astro-ph/0603276 and submitted to The Astrophysical Journal Letters for publication.

Gaudi performed extensive data analysis that confirmed the existence of the planet. Further analysis simultaneously ruled out the presence of any Jupiter-sized world in the distant solar system.

“This icy super-Earth dominates the region around its star that, in our solar system, is populated by the gas giant planets,” said first author Andrew Gould (Ohio State University), who leads MicroFUN.

The team also calculates that about one-third of all main sequence stars may have similar icy super-Earths. Theory predicts that smaller planets should be easier to form than larger ones around low-mass stars. Since most Milky Way stars are red dwarfs, solar systems dominated by super-Earths may be more common in the Galaxy than those with giant Jupiters.

This discovery sheds new light on the process of solar system formation. Material orbiting a low-mass star accumulates into planets gradually, leaving more time for the gas in the protoplanetary disk to dissipate before large planets have formed. Low-mass stars also tend to have less massive disks, offering fewer raw materials for planet formation.

“Our discovery suggests that different types of solar systems form around different types of stars,” explains Gaudi. “Sun-like stars form Jupiters, while red dwarf stars only form super-Earths. Larger A-type stars may even form brown dwarfs in their disks.”

Astronomers found the planet using a technique called microlensing, an Einsteinian effect in which the gravity of a foreground star magnifies the light of a more distant star. If the foreground star possesses a planet, the planet’s gravity can distort the light further, thereby signaling its presence. The precise alignment required for the effect means that each microlensing event lasts for only a brief time. Astronomers must monitor many stars closely to detect such events.

Microlensing is sensitive to less massive planets than the more common planet-finding methods of radial velocity and transit searches.

“Microlensing is the only way to detect Earth-mass planets from the ground with current technology,” says Gaudi. “If there had been an Earth-mass planet in the same region as this super-Earth, and if the alignment had been just right, we could have detected it. By adding one more two-meter telescope to our arsenal, we may be able to find up to a dozen Earth-mass planets every year.”

The OGLE (Optical Gravitational Lensing Experiment) collaboration initially discovered the microlensed star in April 2005 while peering in the direction of the galactic center, where both foreground and background stars are widespread. OGLE identifies several hundred microlensing events per year, however only a small fraction of those events yield planets. Gaudi estimates that with one or two additional telescopes located in the southern hemisphere to monitor the galactic center, the planet count could jump drastically.

The discovery was made by 36 astronomers, including members of the MicroFUN, OGLE, and Robonet collaborations. The name of the planet is OGLE-2005-BLG-169Lb. OGLE-2005-BLG-169 refers to the 169th microlensing event discovered by the OGLE Collaboration toward the Galactic bulge in 2005, and “Lb” refers to a planetary mass companion to the lens star.

Crucial roles in the discovery were played by OGLE team leader Andrzej Udalski of Warsaw University Observatory and graduate students Deokkeun An of Ohio State and Ai-ying Zhou of Missouri State University. Udalski noticed that this microlensing event was reaching a very high magnification on May 1, and he quickly alerted the MicroFUN group to this fact, since high magnification events are known to be very favorable for planet detection. MicroFUN’s regular telescopes were unable to get many images, so MicroFUN leader Gould called the MDM Observatory in Arizona where An and Zhou were observing. Gould asked An and Zhou to obtain a few measurements of the star’s brightness over the course of the night, but instead An and Zhou made more than 1000 measurements. This large number of MDM measurements was crucial for the determination the observed signal must really be due to a planet.

Original Source: CfA News Release

Posted on by Fraser Cain

Pluto and Its Moons Were Born Together

Pluto and its three moons. Image credit: Hubble. Click to enlarge.
New photographs from the Hubble Space Telescope provide evidence that Pluto and its three moons probably formed at the same time, out of the same material. Scientists believe that the 4 objects were created when two Pluto-sized Kuiper Belt objects collided together. Hubble revealed that that Pluto and its moons have identical colours; exactly what you’d expect from this kind of an origin.

Using new Hubble Space Telescope observations, a research team led by Dr. Hal Weaver of the Johns Hopkins University Applied Physics Laboratory and Dr. Alan Stern of Southwest Research Institute has found that Pluto’s three moons are essentially the same color – boosting the theory that the Pluto system formed in a single, giant collision.

Publishing their findings in an International Astronomical Union Circular (No. 8686), the team determined that Pluto’s two “new” satellites, discovered in May 2005 and provisionally called S/2005 P 1 and S/2005 P 2, have identical colors to one another and are essentially the same, neutral color as Charon, Pluto’s large moon discovered in 1978.

All three satellites have surfaces that reflect sunlight with equal efficiency at all wavelengths, which means they have the same color as the Sun or Earth’s moon. In contrast, Pluto has more of a reddish hue.

The new observations were obtained March 2 with the high-resolution channel of the Hubble’s Advanced Camera for Surveys. The team determined the bodies’ colors by comparing the brightness of Pluto and each moon in images taken through a blue filter with those taken through a green/red filter. The images are available on the Hubble Web site at http://hubblesite.org/newscenter/newsdesk/archive/releases/2006/15/image/.

“The high quality of the new data leaves little doubt that the hemispheres of P1 and P2 that we observed have essentially identical, neutral colors,” says Weaver.

The new results further strengthen the hypothesis that Pluto and its satellites formed after a collision between two Pluto-sized objects nearly 4.6 billion years ago. “Everything now makes even more sense,” says Stern. “If all three satellites presumably formed from the same material lofted into orbit around Pluto from a giant impact, you might well expect the surfaces of all three satellites to have similar colors.”

The researchers hope to make additional Hubble color observations, in several more filters, to see if the similarity among the satellites persists to longer (redder) wavelengths. They have proposed to obtain compositional information on the new satellites by observing them at near-infrared wavelengths, where various ice and mineral absorptions are located. The researchers also hope to better refine the orbits of P1 and P2 and measure the moons’ shapes and rotational periods.

The Hubble observations were made in support of NASA’s New Horizons mission to Pluto and the Kuiper Belt. New Horizons launched on Jan. 19, 2006, and will fly through the Pluto system in July 2015, providing the first close-up look at the ninth planet and its moons. Stern leads the mission and science team as principal investigator; Weaver serves as the mission’s project scientist. The Johns Hopkins University Applied Physics Laboratory, Laurel, Md., manages the mission for NASA’s Science Mission Directorate and operates the New Horizons spacecraft. For more information on the mission, visit http://pluto.jhuapl.edu.

The other members of the Hubble Space Telescope-Pluto satellite observing team include Max Mutchler of the Space Telescope Science Institute, Baltimore; Drs. William Merline, John Spencer, Andrew Steffl, Elliot Young and Leslie Young of Southwest Research Institute, Boulder, Colo.; and Dr. Marc Buie of Lowell Observatory, Flagstaff, Ariz.

Original Source: JHUAPL News Release

Update: Pluto is not a planet.

Posted on by Fraser Cain

What’s Up This Week – March 13 – March 19, 2006

What's Up 2006

Download our free “What’s Up 2006” ebook, with entries like this for every day of the year.


Greetings, fellow SkyWatchers! Although the Moon is back “en force”, this will still be an exciting week filled with events such as an eclipse, meteor shower and bright, beautiful star clusters.

Here’s what’s up!

Archival image of Percival Lowell. Click to enlarge.
Monday, March 13 – On this day in 1781, Uranus was discovered by William Herschel. 74 years later, in 1855, Percival Lowell was born.

Originally named “the Georgium Sidus,” Uranus was previously catalogued as a faint 6th magnitude star by John Flamsteed in 1690 and designated as 34 Tauri. Herschel came upon this same “star” – then located in the constellation Gemini – while doing a double star search using a homemade 6″ speculum-mirrored reflector. Imagine his surprise when the “star” revealed itself as a small greenish globe!

Percival Lowell was born to a distinguished Boston family with ties to Harvard University. Lowell graduated with honors in mathematics from that same institution in 1876. After traveling throughout the Far East, Lowell’s imagination was set on fire by Giovanni Schiaparelli’s observation of “canali” on Mars. In 1894, Lowell moved to Flagstaff, Arizona and established the Lowell Observatory. Over the next 15 years, he observed Mars with a passion few astronomers could ever hope to match for any single study. During this period, Lowell wrote several books developing the idea of an extinct race of Martians responsible for various artificial features he thought he had observed on the planet’s surface.

Tonight the great Grimaldi, found in the central region of the moon near the terminator is the best lunar feature for binoculars. If you would like to see how well you have mastered your telescopic skills, then let’s start there. About one Grimaldi length south, you’ll see a narrow black ellipse with a bright rim. This is Rocca. Go the same distance again (and a bit east) to spot a small, shallow crater with a dark floor. This is Cruger, and its lava-filled interior is very similar to another study – Billy. Now look between them. Can you see a couple of tiny dark markings? Believe it or not, this is called Mare Aestatis. It’s not even large enough to be considered a medium-sized crater, but is a mare!

Tuesday, March 14 – Today is the birthday of Albert Einstein. Born in 1879, Einstein was later hailed as one of the finest scientific minds of our times. In 1921, Einstein won the Physics Nobel Prize based on work completed 15 years earlier associated with the photoelectric effect – a natural phenomenon now regularly used to accumulate light to image the most distant things in the Universe. Even more significantly, Einstein developed a theory of gravity based on the curvature of space and time caused by the distribution of matter and another theory (of mass-energy conversion) which accounted for the prodigious and sustainable energy output of the stars.

Tonight is the Full Moon. In many cultures, it is known as the “Worm Moon.” As ground temperatures begin to warm and produce a thaw in the northern hemisphere, earthworms return and encourage the return of robins. For the Indians of the far north, this was also considered the “Crow Moon.” The return of the black bird signaled the end of winter. Sometimes it has been called the “Crust Moon” because warmer temperatures melt existing snow during the day, leaving it to freeze at night. Perhaps you may have also heard it referred to as the “Sap Moon.” This marks the time of tapping maple trees to make syrup. To early American settlers, it was called the “Lenten Moon” and was considered to be the last full Moon of winter. For those of us in northern climes, let’s hope so!

But for viewers almost the world over, tonight’s Moon will hold a far greater significance as it passes through a portion of the Earth’s shadow known as the penumbra. Eclipse time? You bet. For viewers in Asia, India and the western portion of Australia, you’ll get to see the Moon pass through this shadow just as it sets for your local time. For Europe and Africa? You’re in luck as the entire event can be seen from your area. For the majority of both North and South America, the eclipse will be underway as the Moon rises, but you can watch it slide out of the shadow long before it sets. Unfortunately, the western-most portion of the Americas will not see anything.

While a penumbral eclipse is not known to be particularly exciting – this one is deep. The edge of the Moon will just graze the inner umbral shadow. As a rule of thumb, remember that the Moon moves about its own diameter each hour, so the very beginning of a penumbral eclipse will be difficult to notice. Slowly and steadily, the coloration will begin to change and even inexperienced SkyWatchers will notice that something is different. It’s a very relaxing experience and we wish you clear skies!

Wednesday, March 15 – Today celebrates the birth of Nicolas Lacaille. Born in 1713, Lacaille’s measurements confirmed the Earth’s equatorial bulge. He also named the fifteen southern constellations, and a lunar feature honors his life’s work. Although the Moon will be bright, we can still have a look at the crater named for Lacaille. Start by heading towards the lunar south central region. Dominating the scene will be brilliant crater Tycho. From there, it’s north to the eastern shores of Mare Nubium, where you will see the bright ring of Thebit. Shallow Lacaille resides to the east and will be a challenge to make out under the low contrast conditions.

While skies remain bright all night, we can still have a look at an open cluster easily located in northeastern Orion. This 5.9 magnitude scattered group of stars may have been first observed by Giovanni Batista Hodierna in the mid-17th century. While bright enough to have been a Messier object, William Herschel added it to his log of discoveries on October 15, 1784, as H VIII.24. Of the 30 known stars associated with this 3,600 light-year distant group, the brightest is 50 million years old. Despite lunar interference, a half-dozen of the cluster’s very brightest members can be seen in small scopes at mid-range powers. Look for NGC 2169 slightly less than a fist width north-northeast of Betelguese and slightly south of Xi and Nu Orionis.

Thursday, March 16 – On this day in 1926, Robert Goddard launched the first liquid-fuel rocket. He first showed his potential in 1907 when a cloud of smoke rose from a powder rocket fired off in the basement of the physics building in Worcester Polytechnic Institute. Needless to say, the school took an immediate interest in the work of this student! Thankfully Robert was not expelled and a lifetime career in rocketry followed. Goddard was also the first person to realize the full spectrum of possibilities associated with missiles and space flight, and his life was completely dedicated to bringing his visions to realization. While most of Goddard’s achievements went unrecognized for many years, tonight we celebrate his name and passion for the space sciences. His first flight may have only gone 12 meters, but forty years later on this same date the Gemini 8 performed the first orbital docking – a maneuver that could have never happened without Goddard’s work!

Tonight, let’s have a look at an ancient walled plain – Gauss. Located north of Mare Crisium, this oblong crater should be divided by the terminator for most viewers tonight. Its east wall will be quite bright and the west wall outlined by a black arc. It is a very old crater, and if you up the magnification, you will see its ruined, cracked floor riddled with numerous small craterlets.

While out, be on watch for the Corona-Australids meteor shower. While the fall rate is low, about 5 to 7 per hour, our friends in the southern hemisphere stand the best chance with this one.

While we’re out, let’s have a look at another fine study on Messier’s list – M50. Described as “heart-shaped” by some observers, those with larger telescopes will see enough members of this 5.9 magnitude open cluster to note two main “petals” of stars arcing outward to the north and southeast. Several tenth magnitude stars congregate toward the center of this 3,200 light-year distant cluster while numerous 11th and 12th magnitude members dance around them in chains and arcs. Look for at least one luminous red giant and a half dozen yellow giants among this 80 million year-old, 20 light-year diameter study.

Friday, March 17 – On this day in 1958, the first solar-powered spacecraft was launched. Christened Vanguard 1, it was an engineering test satellite. From its orbital position, the data taken from its transmissions helped to refine the true shape of the Earth.

While out observing, turn a scope towards Saturn and see if you can begin to make out faint structure in the ring system. On a fine night of “seeing,” you should easily be able to make out the shadow of the planet’s globe cast the planet casts against its posterior ring plane. Look for the shadow of the ring itself softening the view of the planet’s northern equatorial region.

As the Moon rises tonight, look for bright Spica to accompany it. For some lucky viewers, this will be an occultation! Please check with IOTA for details in your area.

Saturday, March 18 – Today in 1965, the first spacewalk was performed by Alexei Leonov onboard the Soviet Voskhod spacecraft. The “walk” lasted around 20 minutes and Alexei had problems re-entering the spacecraft because his space suit had inflated. Imagine his fear as he let air leak out of his suit in order to squeeze back inside. Later when the crew of two landed off target in the heavily forested Ural Mountains, the pair had to spend the night in the woods surrounded by wolves. It took over twenty-four hours before they were located, then workers had to chop their way through the forest to recover them on skis. Brave men on the frontiers of human exploration of space!

Tonight let’s honor their courage by going after something really tough – but certainly not dangerous. Start with Castor and head 3 degrees north-northeast to center on 4.9 magnitude Omicron Geminorum. Now move north another 4 degrees to locate a widely spaced east-west oriented pair of 8th magnitude stars in the constellation Lynx. Look nearby for the faint whisper of luminosity associated with one of the most fascinating studies in the heavens – 10.4 magnitude globular cluster NGC 2419 – the famed “Intergalactic Wanderer.”

First discovered by William Herschel on New Year’s Eve 1788, the Intergalactic Wanderer may or may not just be “passing through” the Milky Way region. – Even as a member of our galaxy’s entourage of clusters and satellite dwarf galaxies, it is one of the most distant. Outside of our own galaxy at around 300,000 light-years!

Small scopists take heart. NGC 2419 can be seen on dark sky occasions in instruments as small as a spotting scope – although you will need to avert your vision to see it. How is that possible? NGC 2419 is intrinsically one of the brightest globular clusters we know of. Be sure to catch this one before moonrise!

Sunday, March 19 – With time to spare before Luna lights up the night, let’s go south and locate a fine reflecting nebula – NGC 2467 – in northern Puppis. Sometimes referred to as the “skull and crossbones nebula,” this billowing cloud of gas and dust is easily found less than a finger-width south-southeast of 3.5 magnitude Xi Puppis. Even a small telescope will find this expansive, star-studded emission nebula a real beauty! Those with larger apertures should look for neighboring splotches of nebulosity illuminated by small groupings of stars – some of which are part of a newly forming open cluster.

Keep in mind while observing NGC 2467 that we are seeing it from a great distance. At 17,000 light-years, this expansive region of star formation is some 10 times farther away than the Great Nebula in Orion. If it were the same distance away, NGC 2467 would dwarf M42!

May all your journeys be at light speed… ~Tammy Plotner. Additional writing by Jeff Barbour @ astro.geekjoy.com.

Posted on by Fraser Cain

NASA Orbiter Arrives at Mars

NASA’s Mars orbiter approaching Mars. Image credit: NASA/JPL Click to enlarge
Mars added a new satellite today, when NASA’s Mars Reconnaissance Orbiter arrived at the Red Planet. The spacecraft fired its engines for 27 minutes shortly before arrival to slow it down a little, just enough so that Mars could capture it with its gravity. Over the next seven months, the spacecraft will pass through Mars’ atmosphere 550 times, slowing itself down further through a process called aerobraking. After having settled into its final orbit, it will search for signs of water and scout out future landing locations.

NASA’s Mars Reconnaissance Orbiter has begun its final approach to the red planet after activating a sequence of commands designed to get the spacecraft successfully into orbit.

The sequence began Tuesday and will culminate with firing the craft’s main thrusters for about 27 minutes on Friday — a foot on the brakes to reduce velocity by about 20 percent as the spacecraft swings around Mars at about 5,000 meters per second (about 11,000 miles per hour). Mission controllers at NASA’s Jet Propulsion Laboratory, Pasadena, Calif., and Lockheed Martin Space Systems, Denver, are monitoring the events closely.

“We have been preparing for years for the critical events the spacecraft must execute on Friday,” said JPL’s Jim Graf, project manager. “By all indications, we’re in great shape to succeed, but Mars has taught us never to get overconfident. Two of the last four orbiters NASA sent to Mars did not survive final approach.”

Mars Reconnaissance Orbiter will build upon discoveries by five successful robots currently active at Mars: NASA rovers Spirit and Opportunity, NASA orbiters Mars Global Surveyor and Mars Odyssey, and the European Space Agency’s Mars Express orbiter. It will examine Mars’ surface, atmosphere and underground layers in great detail from a low orbit. It will aid future missions by scouting possible landing sites and relaying communications. It will send home up to 10 times as much data per minute as any previous Mars mission.

First, it must get into orbit. The necessary thruster burn will begin shortly after 1:24 p.m. Pacific Time on Friday. Engineers designed the burn to slow the spacecraft just enough for Mars’ gravity to capture it into a very elongated elliptical orbit. A half-year period of more than 500 carefully calculated dips into Mars’ atmosphere — a process called aerobraking — will use friction with the atmosphere to gradually shrink the orbit to the size and nearly-circular shape chosen for most advantageous use of the six onboard science instruments.

“Our primary science phase won’t begin until November, but we’ll actually be studying the changeable structure of Mars’ atmosphere by sensing the density of the atmosphere at different altitudes each time we fly through it during aerobraking,” said JPL’s Dr. Richard Zurek, project scientist for the mission.

Additional information about Mars Reconnaissance Orbiter is available online at: http://www.nasa.gov/mro

The 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, Denver, is the prime contractor for the project and built the spacecraft.

Original Source: NASA News Release

Posted on by Fraser Cain

GIOVE A Transmits Loud and Clear

Chilbolton Observatory. Image credit: ESA Click to enlarge
After a successful launch on 28 December 2005, GIOVE A began transmitting navigation signals on 12 January 2006. Work is currently being performed to check the quality of these signals.

In space, the success of a mission relies on the achievement of a series of milestones. This is especially true for a pioneering mission such as GIOVE A, the first Galileo satellite, launched late last year under the European Space Agency’s responsibility.

Manufacture, launch, reaching final orbit and transmission of first signals: all these key steps were met by the satellite, which is now going to achieve its first goal, the filing for the frequencies allocated to Galileo by the International Telecommunication Union (ITU).

After launch and platform commissioning, GIOVE A started signal transmission on 12 January and the quality of these signals is now being checked. This checking process is employing several facilities, including the Navigation Laboratory at ESA’s European Space Research and Technology Centre (ESTEC), in the Netherlands, the ESA ground station at Redu, in Belgium, and the Rutherford Appleton Laboratory (RAL) Chilbolton Observatory in the United Kingdom.

Chilbolton’s 25 metre antenna makes it possible to acquire the signals from GIOVE A and verify they conform to the Galileo system’s design specification. Each time the satellite is visible from Chilbolton, the large antenna is activated and tracks the satellite. GIOVE A orbits at an altitude of 23 260 kilometres, making a complete journey around the Earth in 14 hours and 22 minutes.

Every orbital pass provides an opportunity to analyse the signals from the satellite. The quality of the signals transmitted by GIOVE A will have an important influence on the accuracy of the positioning information that will be provided by the user receivers on the ground, so a detailed check-out of the signal properties is mandatory. The signal quality can be affected by the environment of the satellite in its orbit and by the propagation path of the signals travelling from space to ground. Additionally, the satellite signals must not create interference with services operating in adjacent frequency bands, and this is also being checked.

The engineers at Chilbolton have means to observe and record in real time the spectrum of the signals transmitted by GIOVE A. Several measurements are performed relating to transmitted signal power, centre frequency and bandwidth, as well as the format of the navigation messages generated on-board. This allows the analysis of the satellite transmissions in the three frequency bands which are reserved for it and confirmation that GIOVE A is transmitting that which is expected of it.

The GIOVE A mission also represents an opportunity for the testing of a key element of the future Galileo system, the user receivers. The first Galileo experimental receivers, manufactured by Septentrio of Belgium, were installed at the Redu and Chilbolton In Orbit Test Stations and at the Guildford, United Kingdom, premises of Surrey Satellite Technology Limited (SSTL), the manufacturer of the satellite and now in charge of its control in orbit.

A meticulous task, sometimes tedious, but essential for the progress of the project, ensuring that Galileo, the joint civilian navigation initiative from the European Space Agency and the European Commission, can offer the value added services which will fundamentally depend on the quality of the transmitted signals.

Original Source: ESA Portal

Posted on by Fraser Cain

Merging White Dwarfs Create Helium Stars

Harlan J. Smith Telescope. Image credit: Marty Harris/McDonald Observatory. Click to enlarge
An international group of astronomers has used the Hubble Space Telescope to determine the origin of an unusual class of objects called extreme helium stars. These objects are formed when two white dwarf stars merge together. Since they were first discovered more than 60 years ago, less than two dozen have found. They contain almost no hydrogen, and are dominated by helium and other heavier elements. When two white dwarf stars merge together, the resulting star swells up to become a supergiant star rich in helium.

An international group of astronomers including Dr. David L. Lambert, director of The University of Texas at Austin McDonald Observatory, has used Hubble Space Telescope to determine the origin of a very unusual and rare type of star. The group’s studies indicate that the so-called “extreme helium stars” are formed by the merger of two white dwarf stars. The work has been published in the February 10 issue of The Astrophysical Journal.

The team was led by Dr. Gajendra Pandey of the Indian Institute of Astrophysics (IIA) in Bangalore, and also includes Dr. C. Simon Jeffery of Armagh Observatory in Northern Ireland, and Professor N. Kameswara Rao, also of IIA.

“It’s taken more than 60 years after the first discovery at McDonald to get some idea of how these formed,” Rao said. He has been studying these types of stars for more than 30 years. “We are now getting a consistent picture.”

The nature of the first extreme helium star, HD 124448, was discovered at McDonald Observatory in 1942 by Daniel M. Popper of The University of Chicago. Since then, fewer than two dozen of these stars have been identified. They are supergiant stars – less massive than the Sun but many times larger and hotter – and remarkable for their strange compositions. They contain almost no hydrogen, the most abundant chemical element in the universe, and the most basic component of all stars. Instead, they are dominated by helium, with significant amounts of carbon, nitrogen, and oxygen, and traces of all other stable elements.

The origin of extreme helium stars cannot be traced back to formation in a cloud of helium gas, since no such clouds exist in our Milky Way galaxy. Nuclear reactions in a star like the Sun convert hydrogen to helium to provide sunlight or starlight. Since the helium is confined the hot core of a star, the star must lose vast amounts of gas before the helium is at the star’s surface – and thus detectable by telescopes. No known mechanism inside the star can drive off the overlying layers to expose the helium.

Two decades ago, astronomers Ronald Webbink and Icko Iben of the University of Illinois introduced the theory that extreme helium stars formed from the merger of two white dwarfs.

White dwarfs are the end product of the evolution of stars like the Sun. They don’t contain much hydrogen. Some are rich in helium, and others in carbon and oxygen. A pair of white dwarfs can result from the evolution of a normal binary star (two normal stars in orbit around each other).

Webbink and Iben supposed that, in some cases, one star in the binary may evolve as a helium-rich white dwarf, and the other as a carbon-oxygen-rich white dwarf. Over billions of years of orbiting each other, the two stars lose energy and move steadily closer to each other. Eventually, the helium white dwarf is consumed by the more massive carbon-oxygen white dwarf. The resultant single star swells up to become a helium-rich supergiant star.

To test this theory, astronomers needed to uncover the exact chemical composition of extreme helium stars. This is what Pandey, Lambert, and their colleagues set out to do. They obtained crucial observations with NASA’s Hubble Space Telescope, and made supporting observations from the 2.7-meter Harlan J. Smith Telescope at McDonald Observatory and the 2.3-meter Vainu Bappu Telescope in India.

“As an aside,” Lambert said, “it’s interesting to note that the namesakes of these two telescopes, Harlan J. Smith and Vainu Bappu, were the very best of friends in graduate school at Harvard.” Later, Smith served as director of McDonald Observatory from 1963 to 1989. Vainu Bappu founded the Indian Institute of Astrophysics. “Today, with collaborations like this project,” Lambert said, “we’re maintaining the important international and personal ties that astronomy thrives upon.”

The group made detailed studies of the ultraviolet light coming from seven extreme helium stars with Hubble Space Telescope’s STIS instrument (the Space Telescope Imaging Spectrograph) and of the optical light from the telescopes in Texas and India. This data provided them with the specific amounts of at least two dozen different chemical elements present in each star they studied.

According to Rao, it is the advance in technology of being able to observe the spectra of these stars in ultraviolet light with Hubble that made this breakthrough study possible more than 60 years after extreme helium stars were discovered.

The Hubble results match up well with predicted compositions from models of the composition of a star formed through the merger of two white dwarf stars in which the helium-core white dwarf is torn apart, and forms a thick disk around the carbon-oxygen white dwarf. Then, in a process taking only a few minutes, the disk is gravitationally pulled into the carbon-oxygen white dwarf.

What happens next depends of the mass of the new, resulting star. If it is above a certain mass, called the Chandrasekar limit, it will explode (specifically, it will explode as a Type Ia supernova). However, if the mass is below this limit, the new merged star will balloon up into a supergiant, eventually becoming an extreme helium star.

Pandey, Lambert, Jeffery, and Rao plan to continue their research on extreme helium stars, using both the Smith and Hobby-Eberly Telescopes at McDonald Observatory. They hope to identify more extreme helium stars, and discover even more chemical elements in these stars.

This research was supported by grants from the Robert A. Welch Foundation of Houston, Texas and the Space Telescope Science Institute in Baltimore, Maryland.

Original Source: University of Texas at Austin

Posted on by Fraser Cain

Cometary Globule CG4

Cometary globule CG4. Image credit: NOAO. Click to enlarge
This object looks like a comet, but it’s actually a star forming region called CG4. Cometary globules like this are relatively small clouds of gas and dust in the Milky Way. CG4 is about 1,300 light years from Earth; its head is about 1.5 light-years across, and its tail is about 8 light-years long. The head of the nebula is opaque, but it’s illuminated by the light from the hot newly forming stars.

A dramatic new image of cometary globule CG4 marks the one-thousandth image posted to the online gallery hosted by the National Optical Astronomy Observatory.

The flower-like image of this star-forming region in Earth’s southern skies was taken by Travis Rector and Tim Abbott using a 64-megapixel Mosaic imaging camera on the National Science Foundation’s Victor M. Blanco telescope at Cerro Tololo Inter-American Observatory.

Cometary globules are isolated, relatively small clouds of gas and dust within the Milky Way. This example, called CG4, is about 1,300 light years from Earth. Its head is some 1.5 light-years in diameter, and its tail is about 8 light-years long. The dusty cloud contains enough material to make several Sun-sized stars. CG4 is located in the constellation of Puppis.

The head of the nebula is opaque, but glows because it is illuminated by light from nearby hot stars. Their energy is gradually destroying the dusty head of the globule, sweeping away the tiny particles which scatter the starlight. This particular globule shows a faint red glow from electrically charged hydrogen, and it seems about to devour an edge-on spiral galaxy (ESO 257-19) in the upper left. In reality, this galaxy is more than a hundred million light-years further away, far beyond CG4.

The image from the 4-meter telescope was taken in four filters, three of which are for blue, green and near-infrared light. The fourth is designed to isolate a specific color of red, known as hydrogen-alpha, which is produced by warm hydrogen gas.

The National Optical Astronomy Observatory (NOAO) consists of Kitt Peak National Observatory near Tucson, AZ; Cerro Tololo Inter-American Observatory near La Serena, Chile; and, the NOAO Gemini Science Center, the route for U.S. astronomers to observe with the Gemini North telescope in Hawaii and the Gemini South telescope in Chile. NOAO is operated by the Association of Universities for Research in Astronomy Inc. (AURA), under a cooperative agreement with the National Science Foundation.

Original Source: NOAO News Release

Posted on by Fraser Cain

SOHO Can See Right Through the Sun

The Sun. Image credit: NASA/ESA Click to enlarge
NASA researchers have developed a technique that allows them to look right through the Sun to see what’s happening on the other side. The Solar and Heliospheric Observatory (SOHO) can trace the sound waves caused by active regions on the opposite side of the Sun. This technique allows the researchers to be more prepared when large sunspots rotate around to face the Earth, and better predict active space weather.

NASA researchers using the Solar and Heliospheric Observatory (SOHO) spacecraft have developed a method of seeing through the sun to the star’s far side. The sun’s far side faces away from the Earth, so it is not directly observable by traditional techniques.

“This new method allows more reliable advance warning of magnetic storms brewing on the far side that could rotate with the sun and threaten the Earth,” said NASA-supported scientist Phil Scherrer of Stanford University, Stanford, Calif.

Magnetic storms resulting from violent solar activity disrupt satellites, radio communications, power grids and other technological systems on Earth. Advance warning can help planners prepare for operational disruptions. The sun rotates once every 27 days, as seen from Earth, and this means the evolution of active regions on the far side of the sun previously has not been detectable.

Many of these storms originate in groups of sunspots, or active regions – areas with high concentration of magnetic fields. Active regions situated on the near side of the sun, the one facing the Earth, can be observed directly. However, traditional methods provided no information about active regions developing on the other side of the sun. Knowing whether there are large active regions on the opposite side of the sun may greatly improve forecast of potential magnetic storms.

The new observation method uses SOHO’s Michelson Doppler Imager (MDI) instrument to trace sound waves reverberating through the sun to build a picture of the far side.

The sun is filled with many kinds of sound waves caused by the convective (boiling) motion of gas in its surface layers. The far side imaging method compares the sound waves that emanate from each small region on the far side with what was expected to arrive at that small region from waves that originated on the front side. An active region reveals itself because its strong magnetic fields speed up the sound waves. The difference becomes evident when sound waves originating from the front side and from the back side get out of step with one another.

“The original far-side imaging method only allowed us to see the central regions, about one-quarter to one-third of its total area,” Scherrer said. “The new method allows us to see the entire far side, including the poles.” Scherrer started an effort to use the new method to create full far-side images from archived MDI data collected since 1996. The project was completed in December 2005.

Douglas Biesecker of the National Oceanic and Atmospheric Administration’s Space Environment Center, Boulder, Colo., said, “With the new far side photo album going back to 1996, we can discover identifying characteristics of active regions. This will improve our ability to distinguish real active regions.”

SOHO is a cooperative project between the European Space Agency and NASA. For SOHO information and images on the Web, visit:
www.nasa.gov/vision/universe/solarsystem/soho_xray.html

Original Source: NASA News Release

Posted on by Fraser Cain

Liquid Water Might Be On Enceladus

Plumes of icy material extend above the polar region of Enceladus. Image credit: NASA/JPL/SSI Click to enlarge
Scientists have discovered geysers of liquid water streaming off Enceladus, one of Saturn’s moons, like a colder version of Yellowstone Hot Springs. Enceladus is one of the few objects in the Solar System that has volcanoes, joining the Earth, Io and possibly Neptune’s moon Triton. This occurrence of liquid water, right near the surface, raises the hopes that there could be life, like the ecosystems on Earth which exist around deep sea vents, using geothermal heat for energy.

NASA’s Cassini spacecraft may have found evidence of liquid water reservoirs that erupt in Yellowstone-like geysers on Saturn’s moon Enceladus. The rare occurrence of liquid water so near the surface raises many new questions about the mysterious moon.

“We realize that this is a radical conclusion — that we may have evidence for liquid water within a body so small and so cold,” said Dr. Carolyn Porco, Cassini imaging team leader at Space Science Institute, Boulder, Colo. “However, if we are right, we have significantly broadened the diversity of solar system environments where we might possibly have conditions suitable for living organisms.”

High-resolution Cassini images show icy jets and towering plumes ejecting large quantities of particles at high speed. Scientists examined several models to explain the process. They ruled out the idea that the particles are produced by or blown off the moon’s surface by vapor created when warm water ice converts to a gas. Instead, scientists have found evidence for a much more exciting possibility — the jets might be erupting from near-surface pockets of liquid water above 0 degrees Celsius (32 degrees Fahrenheit), like cold versions of the Old Faithful geyser in Yellowstone.

Mission scientists report these and other Enceladus findings in this week’s issue of Science.

“We previously knew of at most three places where active volcanism exists: Jupiter’s moon Io, Earth, and possibly Neptune’s moon Triton. Cassini changed all that, making Enceladus the latest member of this very exclusive club, and one of the most exciting places in the solar system,” said Dr. John Spencer, Cassini scientist, Southwest Research Institute, Boulder, Colo.

“Other moons in the solar system have liquid-water oceans covered by kilometers of icy crust,” said Dr. Andrew Ingersoll, imaging team member and atmospheric scientist at the California Institute of Technology, Pasadena, Calif. “What’s different here is that pockets of liquid water may be no more than tens of meters below the surface.”

Other unexplained oddities now make sense. “As Cassini approached Saturn, we discovered that the Saturnian system is filled with oxygen atoms. At the time we had no idea where the oxygen was coming from,” said Dr. Candy Hansen, Cassini scientist at NASA’s Jet Propulsion Laboratory in Pasadena. “Now we know that Enceladus is spewing out water molecules, which break down into oxygen and hydrogen.”

Scientists are also seeing variability at Enceladus. “Even when Cassini is not flying close to Enceladus, we can detect that the plume’s activity has been changing through its varying effects on the soup of electrically-charged particles that flow past the moon,” said Dr. Geraint H. Jones, Cassini scientist, magnetospheric imaging instrument, Max Planck Institute for Solar System Research, Katlenburg-Lindau, Germany.

Scientists still have many questions. Why is Enceladus currently so active? Are other sites on Enceladus active? Might this activity have been continuous enough over the moon’s history for life to have had a chance to take hold in the moon’s interior?

“Our search for liquid water has taken a new turn. The type of evidence for liquid water on Enceladus is very different from what we’ve seen at Jupiter’s moon Europa. On Europa the evidence from surface geological features points to an internal ocean. On Enceladus the evidence is direct observation of water vapor venting from sources close to the surface,” said Dr. Peter Thomas, Cassini imaging scientist, Cornell University, Ithaca, N.Y.

In the spring of 2008, scientists will get another chance to look at Enceladus when Cassini flies within 350 kilometers (approximately 220 miles), but much work remains after Cassini’s four-year prime mission is over.

“There’s no question that, along with the moon Titan, Enceladus should be a very high priority for us. Saturn has given us two exciting worlds to explore,” said Dr. Jonathan Lunine, Cassini interdisciplinary scientist, University of Arizona, Tucson, Ariz.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL, a division of the Caltech, manages the mission for NASA’s Science Mission Directorate. The Cassini orbiter was designed, developed and assembled at JPL.

For images and more information, visit: http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov.

Original Source: NASA News Release