Posted on by Fraser Cain

Gaps in Saturn’s Rings

Gaps in Saturn’s rings. Image credit: NASA/JPL/SSI Click to enlarge
Saturn’s rings throw imposing shadows and relegate parts of the planet’s northern regions to darkness. Three thin and bright arcs in this scene represent three well-known gaps in the immense ring system. From bottom to top here (and widest to thinnest) they are the Cassini Division, the Encke Gap and the Keeler Gap.

The image was taken in infrared light (752 nanometers) using the Cassini spacecraft wide-angle camera on Oct. 29, 2005, at a distance of approximately 446,000 kilometers (277,000 miles) from Saturn. The image scale is 23 kilometers (14 miles) per pixel. The image was contrast enhanced to improve visibility of features in the atmosphere.

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

Hayabusa’s Return Probably Delayed

An Orbit Synthesis Example for Hayabusa Return starting in 2007. Image credit: JAXA Click to enlarge
Hayabusa spacecraft currently undergoes the recovery operation to resume the communication with the ground stations. It was hit by an abrupt disturbing torque owing to the fuel leak that occurred before, and has been out of the ground contact since December 9th. The project team has a good expect to have the spacecraft resume the communication soon. However, the project is now not so sure to make the spacecraft return to earth in June of 2007 and has decided to lengthen the flight period for three years more to have it return to the Earth in June of 2010.

On December 8th, Usuda station observed the sudden shifts of the range-rate measurements at 4:13 UTC with the corresponding gradual decrease of signal intensity AGC (Automated Gain Controller) read. The measurement and the intensity change slowly and are currently estimated due to the out-gassing effect that derived from the fuel leak-out at the end of last month. The leak occurred on November 26th and 27th. Since the beacon signal communication resumed on 29th, the project has made an effort to exclude the vapor gas of the fuel from the spacecraft. The project has by now identified the out-gassing has successfully been performed, as its exponential acceleration decay has shown so far.

On December 8th, the spacecraft was under the resume operation phase for the chemical propulsion, and was given a slow spin whose period is about six minutes. From the beginning of December, the project has introduced the Xenon gas thruster control strategy for emergency, replacing the chemical propulsion system. But the control capability of it was not enough strong for the spacecraft to withstand the disturbance on December 8th. Current estimation says the spacecraft may be in a large coning motion and that is why the spacecraft has not responded to the commands sent from the ground station.

The spacecraft has been out of communication since December 9th. Analysis predicting the attitude property relating to both the Sun and Earth shows that there will be high possibility counted on for the resumption of the communication from the ground for several months or more ahead. However, the spacecraft may have to undergo another long term baking cycle before it starts the return cruise operation using ion engines aboard. And it is concluded that the commencement of the return cruise during December is found difficult. The project has determined that the return cruise should start from 2007 so that the spacecraft can return to the Earth in June of 2010, three years later than the original plan, as long as no immediate resumption tales place very soon.

The spacecraft operation will shift from the normal mode to the rescue mode for several months to one year long. Long term predict indicates high probability of having the spacecraft communicated with the ground station again, with the spacecraft captured well in the beam width of the Usuda deep space antenna.

The spacecraft will take the advantage of Xenon gas attitude control again after enough length of baking operation. The Xenon gas that remains is adequate for the return cruise devised by the ion engines carried by Hayabusa.

The Hayabusa web page will report anything updated, as soon as it becomes available.

(Supplement) Hayabusa Rescue Operation

Hayabusa spacecraft is designed to allow the spin-stabilization and the attitude will converge to a certain pure spin around its high gain antenna axis ultimately. About the current state affected by the disturbance on December 8th, the attitude is conceived not to meet either of the Sun and Earth geometry requirement in terms of power and communication.

Once the coning motion damps, there will be some high probability that the spacecraft spin attitude satisfies both the power and communication conditions in several months.

There will be little possibility that the spacecraft position is out of the deep space antenna beam width for at least several months.

The Hayabusa system is designed to be initialized even once the whole power is down. Actually, on November 29th, the Hayabusa system restarted as these procedures functioned as prescribed.

There has been come up with a new trajectory synthesis that makes the spacecraft return to the earth in June of 2010. Without immediate communication resumption, the project thinks it should take this new schedule soon.

Original Source: JAXA News Release

Posted on by Fraser Cain

Massive Gas Halos Surround Most Galaxies

XMM-Newton view of hot ionised gas halo in NGC 4631. Image credit: ESA Click to enlarge
Astronomers using ESA’s XMM-Newton observatory have found very hot gaseous haloes around a multitude of spiral galaxies similar to our Milky Way galaxy. These ‘ghost-like’ veils have been suspected for decades but remained elusive until now.

Galaxy ‘haloes’ are often seen in so-called ‘starburst’ galaxies, the locations of concentrated star formation, but the discovery of high-temperature haloes around non-starburst spiral galaxies opens the door to new types of measurements once only dreamed about.

For example, scientists can confirm models of galaxy evolution and infer the star-formation rate in galaxies like our own by ‘calculating backwards’ to estimate how many supernovae are needed to make the observed haloes.

“Most of these ghost-like haloes have never been confirmed before in X-ray energies because they are so tenuous and have a low-surface brightness,” said Ralph T?llmann, from the Ruhr University in Bochum, Germany, lead author of the results.

“We needed the high sensitivity and large light-collecting area of the XMM-Newton satellite to uncover these haloes.”

In starburst galaxies, which have prominent haloes, star formation and star death (supernovae) are concentrated in the core of the galaxy and occur during a short time period over the life of a galaxy. This intense activity forms a halo of gas around the entire galaxy, similar to a volcano sending out a plume.

So how can haloes form in the absence of intense star formation? T?llmann’s group say that the entire disk of a spiral galaxy can ‘simmer’ with star-formation activity. This is spread out over time and distance. Like a giant pot of boiling water, the steady activity of star formation over millions and millions of years percolates outward to form the galaxy halo.

Two of the best-studied galaxies so far out of a group of 32 are NGC 891 and NGC 4634, which are tens of millions of light years away in the constellations Andromeda and Coma Berenices, respectively.

The scientists noted that these observations do not support a recent model of galaxy halo formation, in which gas from the intergalactic medium rains down on the galaxy and forms the halo.

Galaxy halos contain about 10 million solar masses of gas. The scientists say it is a relatively straightforward calculation to determine how many supernovae are needed to create the halo. Supernovae are intricately tied to the rate of star formation in a given galaxy.

“With our data we will be able to establish for the first time a critical rate of star formation that needs to be exceeded in order to create such haloes,” said Dr Ralf-J?rgen Dettmar, a co-author also from Ruhr University.

Once these haloes have formed, the hot gas cools and can fall down onto the galaxy’s disk, the scientists said. The gas is involved in a new cycle of star formation, because pressure from this infalling gas triggers the collapse of gas clouds into new stars.

Some heavy elements might escape the halo into intergalactic space, depending on the energy of the supernovae. Further analysis of the chemical composition of the halo might reveal this.

This would determine the correctness of recent cosmological models on the evolution of galaxies, as well as provide evidence of how the elements necessary for life are distributed through the Universe.

Original Source: ESA Portal

Posted on by Fraser Cain

Buffy the Kuiper Belt Object

A view of Buffy’s and other Kuiper belt object orbits. Image credit: CFHT Click to enlarge
A team of astronomers working in Canada, France and the United States have discovered an unusual small body orbiting the Sun beyond Neptune, in the region astronomers call the Kuiper belt. This new object is twice as far from the Sun as Neptune and is roughly half the size of Pluto. The body’s highly unusual orbit is difficult to explain using previous theories of the formation of the outer Solar System.

Currently 58 astronomical units from the Sun (1 astronomical unit, or AU, is the distance between the Earth and the Sun), the new object never approaches closer than 50 AU, because its orbit is close to circular. Almost all Kuiper belt objects discovered beyond Neptune are between 30 AU and 50 AU away. Beyond 50 AU, the main Kuiper belt appears to end, and what few objects have been discovered beyond this distance have all been on very high eccentricity (non-circular) orbits. Most of these high-eccentricity orbits are the result of Neptune “flinging” the object outward by a gravitational slingshot. However, because this new object does not approach closer than 50 AU, a different theory is needed to explain its orbit. Complicating the problem, the object’s orbit also has an extreme tilt, being inclined (tilted) at 47 degrees to the rest of the Solar System.

The Discovery and Follow-up

The object, which received the official designation 2004 XR 190 in the International Astronomical Union’s official announcement, was discovered during routine operation of the Canada-France Ecliptic Plane Survey (CFEPS) running as part of the Legacy Survey on the Canada France Hawaii Telescope. For now, the discoverers are using the temporary nickname “Buffy” to identify the new object, although they have proposed a different official name in keeping with normal procedures for naming such objects.

Buffy was extracted from the mountain of Legacy Survey data (about 50 gigabytes per hour of operation) by powerful computers combing through the telescopic images and producing hundreds of candidates. Astronomers then sift through the candidates to identify the distant comets.

Astronomer Lynne Allen of the University of British Columbia was the first to lay eyes on the new object, as she completed the initial identification in the course of processing CFEPS data from December 2004. “It was quite bright compared to the usual Kuiper belt objects we find”, said Dr. Allen, “but what was more interesting was how far away it was.”

The object’s brightness implies it is likely between 500 and 1000 kilometers (300 to 600 miles) in diameter. Buffy is thus a very large Kuiper belt object, but about half a dozen are larger.

“We immediately realized that the object was about twice as far as Neptune from the Sun and that its orbit was potentially nearly circular,” said UBC professor Brett Gladman, who noticed the unusual nature of the object when determining its orbit, “but further observations were required.”

One to two years of observations of a Kuiper belt object are required before their orbits can be precisely measured. The first additional observations of Buffy came in October 2005 when Gladman and Phil Nicholson of Cornell University used the Hale 5-meter telescope to re-observe the object.

Measurement of Buffy’s new position proved that the orbit was not only extremely tilted, inclined (tilted) at 47 degrees to the plane of the planetary system (essentially tying the record for a Kuiper belt object) but confirmed that Buffy was unlike any other previously-known object because it was on a nearly circular orbit while at a very large distance.

More measurements of Buffy’s position on images from telescopes at Kitt Peak National Observatories in Arizona by team members Joel Parker (Southwest Research Institute), as well as JJ Kavelaars (National Research Council of Canada, Herzberg Institute of Astrophysics) and Wes Fraser (University of Victoria), through November 2005 refined the estimate for Buffy’s closest approach to the Sun. Additional observations, to further confirm the orbit, where then provided by the CFHT Legacy Survey project. Astronomers will need to wait until February 2006 to measure the fine details of the Buffy’s orbit.

The team have reported their find to the Minor Planet Center, the clearinghouse for astronomical measurements of new minor planets. “To find the first known object with a nearly circular orbit beyond 50 AU is indeed intriguing,” reacted Brian Marsden, director of the MPC.

Challenging Theories

Although it is neither the smallest, largest, nor most distant object discovered in this region, the new Kuiper belt object has a highly unusual orbit which challenges theories of the evolution of the Solar System.

Why is Buffy’s orbit considered so unusual? Only one other detected object, Sedna, remains further than 50 astronomical units (AUs) from the Sun throughout its entire orbit. However, Sedna is on a very elliptical orbit, swooping in to 76 AU before traveling back out beyond 900 AU. In contrast, Buffy spends all of its time in the narrow range between 52 and 62 AU from the Sun. Combined with the tilt in its orbit, this new object challenges current theories about the history of the early Solar System.

Astronomers have detected other Kuiper belt objects that spend most of their time beyond 50 AU. These are on very elliptical orbits, and almost all approach within 38 AU of the Sun. That close approach places those objects within the reach of the gravitational influence of Neptune. These objects are generally thought to have been scattered out to their present orbits by a gravitational slingshot with Neptune. This group of objects was thus called the “Scattered Disk”.

Prior to the discovery of Buffy, a few other Kuiper belt objects were discovered which spend much of their time beyond 50 AU like those in the “Scattered Disk”, yet did not approach within the gravitational reach of Neptune. This group has been named the “Extended Scattered Disk”. Two of its members are 1995 TL8 and 2000 YW134, which approach to 40 AU of the Sun but have fairly elliptical orbits that take them back out beyond 60 AU. Two more extreme examples of the “Extended Scattered Disk” are 2000 CR105, which approaches to 44 AU, and Sedna, which never comes closer to the Sun than 76 AU.

Due to their large eccentricities, these objects are likely to have been strongly perturbed by something, although it could not have been Neptune because they do not come close enough to be scattered by that planet’s gravitational force. As both Sedna and 2000 CR105 also travel beyond 500 AU from the sun, one theory is that after being scattered by Neptune, a passing star could have pulled their closest approaches away from the Sun.

Buffy is clearly a member of the “Extended Scattered Disk”. However, Buffy’s almost circular orbit makes it stand out from the other members. In addition, Buffy’s large orbital tilt is not so easily explained by the passing star idea. If a star could have affected Buffy so strongly, it should also have disrupted much of the main Kuiper belt as well. Since astronomers do not detect that strong disruption, a more complex theory is needed to explain Buffy’s orbit.

The elusive explanation may lie in side-effects from rearrangements of the Solar System early in its history. One possibility is that as Neptune’s orbit slowly expanded in the young Solar System, complex gravitational interactions could have caused some Kuiper belt orbits to circularize and tilt. While Buffy’s orbit could have been created this way, this theory would not seem to explain 2000 CR105 and Sedna. This new discovery is exciting because it causes us to rethink our understanding of how the Kuiper belt formed.

The Future

Over the last half decade, theories about the formation of our outer Solar System have been pushed to their limits: unusual Kuiper belt objects, like Buffy, which never come close to Neptune yet have high inclination must be explained.

Although theories that explain individual objects exist, reproducing the entire ensemble of known objects with one process poses a difficult challenge to current solar system models. Because the unusual objects, like Buffy, are very rare, astronomers are still scratching the surface of the dark corners of the Kuiper belt. Future large-scale surveys that systematically explore the Kuiper belt are the only way unlock the mysteries of what happened early in the history of our Solar System.

Original Source: Canada-France-Hawaii Telescope

Posted on by Fraser Cain

Strange Bulge in Saturn’s Rings

Saturn’s rings very close to edge-on. Image credit: NASA/JPL/SSI Click to enlarge
Viewing Saturn’s rings very close to edge-on produces some puzzling effects, as these two images of the F ring demonstrate.

The upper image was acquired from less than a tenth of a degree beneath the ringplane and shows a mysterious bulge. Such a feature has not been seen previously by the Cassini spacecraft from this angle. It is possible that, because of the very shallow viewing angle, the Cassini spacecraft’s view takes a long path through the ring, making very faint material visible. It also may be that an embedded object of a kilometer or so in size stirs up the neighboring ring particles to create a bulge. Alternatively, an impact into an embedded moonlet that was covered with debris could produce a cloud like this.

Images taken by the Voyager spacecrafts showed clumps that might have been produced in these ways. Cassini’s investigations will help to determine the vertical extent of such clumps and understand their origins.

The lower image was obtained from less than a hundredth of a degree beneath the ringplane. Across the center of the rings is a dark lane, giving them an appearance not unlike that of a spiral galaxy, seen edge-on.

Both images were taken using the clear spectral filters (predominantly visible light) on the Cassini spacecraft narrow-angle camera. The images have been magnified by a factor of two.

The top image was obtained at a distance of 3.6 million kilometers (2.2 million miles) from Saturn on Nov. 11, 2005 and shows wispy fractures on Dione’s trailing hemisphere. The image scale is 22 kilometers (14 miles) per pixel. The bottom image was acquired at a distance of 2.5 million kilometers (1.6 million miles) from Saturn on Nov. 5, 2005. The image scale is 15 kilometers (9 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

Plasma Engine Could Open Up Space Exploration

Helicon reactor in operation. Image credit: ESA Click to enlarge
ESA has confirmed the principle of a new space thruster that may ultimately give much more thrust than today?s electric propulsion techniques. The concept is an ingenious one, inspired by the northern and southern aurorae, the glows in the sky that signal increased solar activity.

?Essentially the concept exploits a natural phenomenon we see taking place in space,? says Dr Roger Walker of ESA?s Advanced Concepts Team. “When the solar wind, a ?plasma? of electrified gas released by the Sun, hits the magnetic field of the Earth, it creates a boundary consisting of two plasma layers. Each layer has differing electrical properties and this can accelerate some particles of the solar wind across the boundary, causing them to collide with the Earth?s atmosphere and create the aurora.”

In essence, a plasma double layer is the electrostatic equivalent of a waterfall. Just as water molecules pick up energy as they fall between the two different heights, so electrically charged particles pick up energy as they travel through the layers of different electrical properties.

Researchers Christine Charles and Rod Boswell at the Australian National University in Canberra, first created plasma double layers in their laboratory in 2003 and realised their accelerating properties could enable new spacecraft thrusters. This led the group to develop a prototype called the Helicon Double Layer Thruster.

The new ESA study, performed as part of ESA?s Ariadna academic research programme in association with Ecole Polytechnique, Paris, confirms the Australian findings by showing that under carefully controlled conditions, the double layer could be formed and remains stable, allowing the constant acceleration of charged particles in a beam. The study also confirmed that stable double layers could be created with different propellant gas mixtures.

?The collaboration has been absolutely excellent,? says Dr Pascal Chabert, of Laboratoire de Physique et Technologie des Plasmas, Ecole Polytechnique. ?It has been a real kick-off for me and has given me lots of new ideas for plasma propulsion concepts to investigate with the Advanced Concepts Team. The new direction for our laboratory had led to a patent on a promising new electric propulsion device called an Electronegative Plasma Thruster.?

To create the double layer, Chabert and colleagues created a hollow tube around which was wound a radio antenna. Argon gas was continuously pumped into the tube and the antenna transmitted helicoidal radio waves of 13 megahertz. This ionised the argon creating a plasma. A diverging magnetic field at the end of the tube then forced the plasma leaving the pipe to expand. This allowed two different plasmas to be formed, upstream within the tube and downstream, and so the double layer was created at their boundary. This accelerated further argon plasma from the tube into a supersonic beam, creating thrust.

Calculations suggest that a helicon double layer thruster would take up a little more space than the main electric thruster on ESA?s SMART-1 mission, yet it could potentially deliver many times more thrust at higher powers of up to 100 kW whilst giving a similar fuel efficiency.

In the next steps, ESA will now construct a detailed computer simulation of the plasma in and around the thruster and use the laboratory results to verify its accuracy, so that the in-space performance can be fully assessed and larger high power experimental thrusters can be investigated in the future.

Original Source: ESA Portal

Posted on by Fraser Cain

Spitzer Finds More than 100 New Star Clusters

The new star cluster found by GLIMPSE. Image credit: NASA Click to enlarge
Astronomers have at last found inner light! Only, they didn’t find it through the typical Earthly methods of meditation, exercise and therapy. Instead, the light was discovered inside our Milky Way galaxy after hours of deep self-reflection with NASA’s Spitzer Space Telescope.

The astronomers, who are members of the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) team, used Spitzer’s heat-seeking infrared eyes to gaze at the dust-drenched plane of our galaxy. When they did this, the galaxy’s obscuring clouds of gas and dust became transparent, revealing approximately 100 new star clusters, each containing tens to hundreds of stars.

According to lead investigator Emily Mercer, a graduate student at Boston University, Mass., the new clusters will tell astronomers a great deal about the structure of the Milky Way and star formation within the galaxy.

“These little guys were quite hard to find,” said Mercer. “The discovery required sophisticated computer sifting of GLIMPSE data and careful inspection of the Spitzer images.”

In the past, our galaxy wasn’t so quick to give up its stellar secrets. Because we sit inside its flat, spiral disk, most of the galaxy appears as a thick blurry band of light that stretches across the sky. Many of the stars in this galactic plane cannot be detected with visible-light or ultraviolet telescopes. That’s because the cool clouds of dust and gas that hover around the galaxy’s center and make up galactic spiral arms block their starlight from our view.

Two-thirds of the new star clusters were discovered through a computer method developed by Mercer and her advisor, Dr. Dan Clemens, also of Boston University. They used an algorithm to automatically sift through the GLIMPSE data for clusters. The rest were found using the traditional method of visually scrutinizing images for star clusters.

Mercer also found that there are nearly twice as many star clusters in the southern galactic plane, the portion of the galactic plane visible from the Earth’s southern hemisphere, as in the northern galactic plane. She suspects that this observation may help astronomers map the location of the Milky Way’s spiral arms.

“Emily has done a great job,” says Clemens. “Her computer method for finding clusters has proved to be the most successful automated effort to date.”

Both Clemens and Mercer are members of the multi-institutional GLIMPSE team, which is led by Dr. Edward Churchwell of the University of Wisconsin, Madison. The group was selected to survey the galactic plane with Spitzer’s infrared array camera in November 2000 as part of Spitzer’s Legacy program. So far, more than 30 million stars in the inner Milky Way have already been catalogued by GLIMPSE, and the team expects to identify more than 50 million stars by the end of the project.

“By making the galactic plane transparent, Spitzer opens a new door for astronomers to study the Milky Way,” says Churchwell. “Some of the most interesting science likely to come out of this project will be serendipitous discoveries, which will open up entirely new avenues of inquiry.”

Original Source: Spitzer Space Telescope

Posted on by Fraser Cain

Sirius’ White Dwarf Companion Weighed by Hubble

Sirius and its tiny companion. Image credit: Hubble. Click to enlarge
For astronomers, it’s always been a source of frustration that the nearest white-dwarf star is buried in the glow of the brightest star in the nighttime sky. This burned-out stellar remnant is a faint companion of the brilliant blue-white Dog Star, Sirius, located in the winter constellation Canis Major.

Now, an international team of astronomers has used the keen eye of NASA’s Hubble Space Telescope to isolate the light from the white dwarf, called Sirius B. The new results allow them to measure precisely the white dwarf’s mass based on how its intense gravitational field alters the wavelengths of light emitted by the star. Such spectroscopic measurements of Sirius B taken with a telescope looking through the Earth’s atmosphere have been severely contaminated by scattered light from the very bright Sirius.

“Studying Sirius B has challenged astronomers for more than 140 years,” said Martin Barstow of the University of Leicester, U.K., who is the leader of the observing team. “Only with Hubble have we at last been able to obtain the observations we need, uncontaminated by the light from Sirius, in order to measure its change in wavelengths.”

“Accurately determining the masses of white dwarfs is fundamentally important to understanding stellar evolution. Our Sun will eventually become a white dwarf. White dwarfs are also the source of Type Ia supernova explosions that are used to measure cosmological distances and the expansion rate of the universe. Measurements based on Type Ia supernovae are fundamental to understanding ‘dark energy,’ a dominant repulsive force stretching the universe apart. Also, the method used to determine the white dwarf’s mass relies on one of the key predictions of Einstein’s theory of General Relativity; that light loses energy when it attempts to escape the gravity of a compact star.”

Sirius B has a diameter of 7,500 miles (12,000 kilometers), less than the size of Earth, but is much denser. Its powerful gravitational field is 350,000 times greater than Earth’s, meaning that a 150-pound person would weigh 50 million pounds standing on its surface. Light from the surface of the hot white dwarf has to climb out of this gravitational field and is stretched to longer, redder wavelengths of light in the process. This effect, predicted by Einstein’s theory of General Relativity in 1916, is called gravitational redshift, and is most easily seen in dense, massive, and hence compact objects whose intense gravitational fields warp space near their surfaces.

Based on the Hubble measurements of the redshift, made with the Space Telescope Imaging Spectrograph, the team found that Sirius B has a mass that is 98 percent that of our own Sun. Sirius itself has a mass of two times that of the Sun and a diameter of 1.5 million miles (2.4 million kilometers).

White dwarfs are the leftover remnants of stars similar to our Sun. They have exhausted their nuclear fuel sources and have collapsed down to a very small size. Sirius B is about 10,000 times fainter than Sirius itself, making it difficult to study with telescopes on the Earth’s surface because its light is swamped in the glare of its brighter companion. Astronomers have long relied on a fundamental theoretical relationship between the mass of a white dwarf and its diameter. The theory predicts that the more massive a white dwarf, the smaller its diameter. The precise measurement of Sirius B’s gravitational redshift allows an important observational test of this key relationship.

The Hubble observations have also refined the measurement of Sirius B’s surface temperature to be 44,900 degrees Fahrenheit, or 25,200 degrees Kelvin. Sirius itself has a surface temperature of 18,000 degrees Fahrenheit (10,500 degrees Kelvin).

At 8.6 light-years away, Sirius is one of the nearest known stars to Earth. Stargazers have watched Sirius since antiquity. Its diminutive companion, however, was not discovered until 1862, when it was first glimpsed by astronomers examining Sirius through one of the most powerful telescopes of that time.

Details of the work were reported in the October 2005 issue of the Monthly Notices of the Royal Astronomical Society. Other participants on the team include Howard Bond of the Space Telescope Science Institute, Baltimore, Md.; Matt Burleigh of the University of Leicester; Jay Holberg and Ivan Hubeny of the University of Arizona; and Detlev Koester of the University of Kiel, Germany.

Original Source: HubbleSite News Release

Posted on by Fraser Cain

Thousands of Auroras on Mars

Location of aurora on Mars. Image credit: ESA Click to enlarge
Auroras similar to Earth’s Northern Lights appear to be common on Mars, according to physicists at the University of California, Berkeley, who have analyzed six years’ worth of data from the Mars Global Surveyor.

The discovery of hundreds of auroras over the past six years comes as a surprise, since Mars does not have the global magnetic field that on Earth is the source of the aurora borealis and the antipodal aurora australis.
plot of the 13,000 auroral events on Mars

According to the physicists, the auroras on Mars aren’t due to a planet-wide magnetic field, but instead are associated with patches of strong magnetic field in the crust, primarily in the southern hemisphere. And they probably aren’t as colorful either, the researchers say: The energetic electrons that interact with molecules in the atmosphere to produce the glow probably generate only ultraviolet light – not the reds, greens and blues of Earth.

“The fact that we see auroras as often as we do is amazing,” said UC Berkeley physicist David A. Brain, the lead author of a paper on the discovery recently accepted by the journal Geophysical Research Letters. “The discovery of auroras on Mars teaches us something about how and why they happen elsewhere in the solar system, including on Jupiter, Saturn, Uranus and Neptune.”

Brain and Jasper S. Halekas, both assistant research physicists at UC Berkeley’s Space Sciences Laboratory, along with their colleagues from UC Berkeley, the University of Michigan, NASA’s Goddard Space Flight Center and the University of Toulouse in France, also reported their findings in a poster presented Friday, Dec. 9, at the American Geophysical Union meeting in San Francisco.

Last year, the European spacecraft Mars Express first detected a flash of ultraviolet light on the night side of Mars and an international team of astronomers identified it as an auroral flash in the June 9, 2005, issue of Nature. Upon hearing of the discovery, UC Berkeley researchers turned to data from the Mars Global Surveyor to see if an on-board UC Berkeley instrument package – a magnetometer-electron reflectometer – had detected other evidence of auroras. The spacecraft has been orbiting Mars since September 1997 and since 1999 has been mapping from an altitude of 400 kilometers (250 miles) the Martian surface and Mars’ magnetic fields. It sits in a polar orbit that keeps it always at 2 a.m. when on the night side of the planet.

Within an hour of first delving into the data, Brain and Halekas discovered evidence of an auroral flash – a peak in the electron energy spectrum identical to the peaks seen in spectra of Earth’s atmosphere during an aurora. Since then, they have reviewed more than 6 million recordings by the electron reflectometer and found amid the data some 13,000 signals with an electron peak indicative of an aurora. According to Brain, this may represent hundreds of nightside auroral events like the flash seen by the Mars Express.

When the two physicists pinpointed the position of each observation, the auroras coincided precisely with the margins of the magnetized areas on the Martian surface. The same team, led by co-authors Mario H. Acu?a of NASA’s Goddard Space Flight Center and Robert Lin, UC Berkeley professor of physics and director of the Space Sciences Laboratory, has extensively mapped these surface magnetic fields using the magnetometer/reflectometer aboard the Mars Global Surveyor. Just as Earth’s auroras occur where the magnetic field lines dive into the surface at the north and south poles, Mars’ auroras occur at the borders of magnetized areas where the field lines arc vertically into the crust.

Of the 13,000 auroral observations so far, the largest seem to coincide with increased solar wind activity.

“The flash seen by Mars Express seems to be at the bright end of energies that are possible,” Halekas said. “Just as on Earth, space weather and solar storms tend to make the auroras brighter and stronger.”
Depiction of surface magnetic fields on Mars

Earth’s auroras are caused when charged particles from the sun slam into the planet’s protective magnetic field and, instead of penetrating to the ground, are diverted along field lines to the pole, where they funnel down and collide with atoms in the atmosphere to create an oval of light around each pole. Electrons are a big proportion of the charged particles, and auroral activity is associated with a physical process still not understood that accelerates electrons, producing a telltale peak in the spectrum of electron energies.

The process on Mars is probably similar, Lin said, in that solar wind particles are funneled around to the night side of Mars where they interact with crustal field lines. The ultraviolet light is produced when the particles hit carbon dioxide molecules.

“The observations suggest some acceleration process occurs like on Earth,” he said. “Something has taken the electrons and given them a kick.”

What that “something” is remains a mystery, though Lin and his UC Berkeley colleagues lean towards a process called magnetic reconnection, where the magnetic field traveling with the solar wind particles breaks and reconnects with the crustal field. The reconnecting field lines could be what flings the particles to higher energies.

The surface magnetic fields, Brain said, are produced by highly magnetized rock that occurs in patches up to 1,000 kilometers wide and 10 kilometers deep. These patches probably retain magnetism left from when Mars had a global field in a way similar to what occurs when a needle is stroked with a magnet, inducing magnetization that remains even after the magnet is withdrawn. When Mars’ global field died out billions of years ago, the solar wind was able to strip the atmosphere away. Only the strong crustal fields are still around to protect portions of the surface.

“We call them mini-magnetospheres, because they are strong enough to stand off the solar wind,” Lin said, noting that the fields extend up to 1,300 kilometers above the surface. Nevertheless, the strongest Martian magnetic field is 50 times weaker than the field at the Earth’s surface. It’s hard to explain how these fields are able to funnel and accelerate the solar wind efficiently enough to generate an aurora, he said.

Brain, Halekas, Lin and their colleagues hope to mine the Mars Global Surveyor data for more information on the auroras and perhaps join with the European team operating the Mars Express to get complementary data on the flashes that could solve the mystery of their origin.

“Mars Global Surveyor was designed for a lifetime of 685 days, but it has been very valuable for more than six years now, and we are still getting great results,” Lin observed.

The work was supported by NASA. Coauthors with Brain, Halekas, Lin and Acu?a are Laura M. Peticolas, Janet G. Luhmann, David L. Mitchell and Greg T. Delory of UC Berkeley’s Space Sciences Laboratory; Steve W. Bougher of the University of Michigan; and Henri R?me of the Centre d’Etude Spatiale des Rayonnements in Toulouse.

Original Source: UC Berkeley News Release

Posted on by Fraser Cain

What’s Up This Week – December 12 – December 18, 2005

Credit: Roger Warner
Monday, December 12 – Let’s hope observers in Eastern Siberia had the chance to catch the Moon occulting Mars!

Be sure to at least take binoculars out tonight and have a look at the cold and beautiful Moon. Trace its wonderful bright ray systems – such as those that extend from Tycho, Copernicus and Kepler. There is no astronomical target out there able to compete with the details you’ll find on the lunar surface!

Tuesday, December 13 – Set the alarm for 4:30 a.m. and bundle up to watch for your one good chance at the Geminid meter shower!
Today in 1920, the first stellar diameter was measured by Francis Pease with an interferometer at Mt. Wilson. His target? Betelgeuse! Tonight let’s defy the Moon and have a look at the giant star as we look towards the northeastern corner of Orion.

One of the largest known stars, the Hobbits called it “Borgil” – but in the ancient world the Arabs knew this star as “Beit Alguese.” Its bright variability was first noticed by Sir William Herschel in 1836, and followed through its near 6 year cycle of erratic changes. During the phases of expansion and contraction, at smallest Betelgeuse still exceeds the diameter of Earth’s orbit around our own Sun. For all of its size, you might think Betelgeuse to be massive – but it’s not. Although it exceeds Sol by 160 million times in volume, it has only about 20 times more physical mass!

Enjoy its red photons tonight…

Wednesday, December 14 – Today is a very busy day in the history of astronomy. Tycho Brahe was born in 1546. Brahe was a Danish pre-telescopic astronomer who established the first modern observatory in 1582 and gave Kepler his first job in the field. In 1962, Mariner 2 made a flyby of Venus and became the first successful interplanetary probe. And, in 1972, the last humans (so far) to have been on the lunar surface returned to Earth on this date. Eugene Cernan left the final bootprint at Taurus-Littrow and called it the “end of the beginning.”

Tonight will be one of the most hauntingly beautiful and mysterious displays of celestial fireworks all year – the Geminid meteor shower. First noted in 1862 by Robert P. Greg in England, and B. V. Marsh and Prof. Alex C. Twining of the United States in independent studies, the annual appearance of the Geminid stream was weak, producing no more than a few per hour, but it has grown in intensity during the last century and a half. By 1877 astronomers were realizing that a new annual shower was occurring with an hourly rate of about 14. At the turn of the century it had increased to an average of over 20, and by the 1930s to from 40 to 70 per hour. Only eight years ago observers recorded an outstanding 110 per hour during a moonless night… But this time we’re not so fortunate.

So why are the Geminids such a mystery? Most meteor showers are historic, documented and recorded for hundred of years, and we know them as being cometary debris. When astronomers first began looking for the Geminids’ parent comet, they found none. After decades of searching, it wasn’t until October 11, 1983 that Simon Green and John K. Davies, using data from NASA’s Infrared Astronomical Satellite, detected an orbital object which the next night was confirmed by Charles Kowal to match the Geminid meteoroid stream. But this was no comet, it was an asteroid.

Originally designated as 1983 TB, but later renamed 3200 Phaethon, this apparently rocky solar system member has a highly elliptical orbit that places it within 0.15 AU of the Sun about every year and half. But asteroids can’t fragment like a comet – or can they? The original hypothesis was that since Phaethon’s orbit passes through the asteroid belt, it may have collided with other asteroids, creating rocky debris. This sounded good, but the more we studied the more we realized the meteoroid “path” occurred when Phaethon neared the Sun. So now our asteroid is behaving like a comet, yet it doesn’t develop a tail.

So what exactly is this “thing?” Well, we do know that 3200 Phaethon orbits like a comet, yet has the spectral signature of an asteroid. By studying photographs of the meteor showers, scientists have determined that the meteors are more dense than cometary material but not as dense as asteroid fragments. This leads us to believe that Phaethon is probably an extinct comet that has gathered a thick layer of interplanetary dust during its travels, yet retains the ice-like nucleus. Until we are able to take physical samples of this “mystery,” we may never fully understand what Phaethon is, but we can fully appreciate the annual display it produces!

Thanks to the wide path of the stream, folks the world over get an opportunity to enjoy the show. The traditional peak time is tonight – as soon as the constellation of Gemini appears around mid-evening – and it lasts through tomorrow morning. The radiant for the shower is right around bright star Castor, but meteors can originate from many points in the sky. From around 2:00 a.m. until dawn (when our local sky window is aimed directly into the stream) it is possible that we can see about one “shooting star” every 30 seconds, but the Moon will significantly decrease the number of fainter meteors. The most successful of observing nights are ones where you are comfortable, so be sure to use a reclining chair or pad the ground while looking up. Best of luck spotting one of the incredible and mysterious Geminids!

Thursday, December 15 – Heads up for Australia and New Zealand! On this universal date, the Moon will occult bright star Beta Tauri. Please check with IOTA for times in your location. Clear skies, mates!

Today in 1970, Soviet Venera 7 performed a first as it made a successful soft landing on Venus and went into the history books as the first object to land on another planet.

Tonight why not take a few minutes after sunset to land your eyes on Venus? Even if you don’t use a telescope, you can’t miss its ultra-bright appearance to the southwest in the northern hemisphere. If you use a telescope – Power up! Can you tell what percentage of the planet is shadowed? Follow it to month’s end when it will only be 6% illuminated, because it will be a year and a half before we see it like that again!

Friday, December 16 – Today we celebrate the birth of the working-class hero astronomer, Edward Emerson (E.E.) Barnard, Born into hardship in 1857 in Nashville, Tennessee, he was home schooled and began work at age 9 as a photographer. His first telescope was made from a cardboard tube and discarded parts. Continuing to self-educate, he purchased his first telescope and supported himself through awards from comet discoveries. His reputation as an outstanding observer brought him a Fellowship to Vanderbilt College and eventually to the doors of Lick and Yerkes Observatory where his photographic and observational skills became unsurpassed.

While we most commonly recognize Barnard’s discoveries of dark nebulae, did you know that he also did extensive work on objects that we can easily observe? The hauntingly nebulosity in the Pleiades belongs to Barnard, as well as a companion star in the Trapezium. Take a look at the Andromeda Galaxy while you’re out tonight – despite the Moon. While Edward Holden took credit for much of Barnard’s work, his ability to photograph this galaxy with second-hand equipment, and to discover comets in the same way, helped pave the way into a new era of observing.
Saturday, December 17 – Before the Moon rises tonight, let’s turn our attention towards a very beautiful and lesser known open cluster – NGC 663. You’ll find it about one fingerwidth northeast of Delta Cassiopeiae…

This magnificent tornado-shaped collection of stars will be quite noticeable in binoculars and will resolve out more than a dozen members to a small telescope. Larger telescopes will fully resolve this magnitude 7 cluster and reveal color amongst its many stars.
For southern hemisphere observers, look a little more than a fistwidth southeast of Canopus for the incredible NGC 2516. Visible to the unaided eye, this cluster should be spectacular in binoculars or a small telescope! Look for a red star in its center…

Sunday, December 18 – With the later rise of the Moon tonight, take the time to do a quick tour of the skies with binoculars. It would be a great time to try to spot M33 – the “Pinwheel Galaxy” – about three fingerwidths southeast of Beta Andromedae.
If you’re still around when the Moon rises, be sure to take a look at the Mare Crisium area. The terminator will show just how much of a curve we view this feature on!

Until next week, ask for the Moon but keep reaching for the stars! Light speed… ~Tammy Plotner