Posted on by Fraser Cain

Monstrous Stars Spawn a Community of Smaller Stars

Spitzer view of the Carina Nebula, a well known nebula containing newborn stars in the Milky Way. Image credit: Spitzer. Click to enlarge.
The saga of how a few monstrous stars spawned a diverse community of additional stars is told in a new image from NASA’s Spitzer Space Telescope.

The striking picture reveals an eclectic mix of embryonic stars living in the tattered neighborhood of one of the most famous massive stars in our Milky Way galaxy, Eta Carinae. Astronomers say that radiation and winds from Eta Carinae and its massive siblings ripped apart the surrounding cloud of gas and dust, shocking the new stars into being.

“We knew that stars were forming in this region before, but Spitzer has shown us that the whole environment is swarming with embryonic stars of an unprecedented multitude of different masses and ages,” said Dr. Robert Gehrz, University of Minnesota, Twin Cities, a member of the team that made the Spitzer observations.

The results were presented yesterday at the 206th meeting of the American Astronomical Society in Minneapolis by Dr. Nathan Smith, lead investigator of the Spitzer findings, University of Colorado, Boulder.

Previous visible-light images of this region, called the Carina Nebula, show cloudy finger-like pillars of dust, all pointing toward Eta Carinae at the center. Spitzer’s infrared eyes cut through much of this dust to expose incubating stars embedded inside the pillars, as well as new star-studded pillars never before seen.

Eta Carinae, located 10,000 light-years from Earth, was once the second brightest star in the sky. It is so massive, more than 100 times the mass of our Sun, it can barely hold itself together. Over the years, it has brightened and faded as material has shot away from its surface. Some astronomers think Eta Carinae might die in a supernova blast within our lifetime.

Eta Carinae’s home, the Carina Nebula, is also quite big, stretching across 200 light-years of space. This colossal cloud of gas and dust not only gave birth to Eta Carinae, but also to a handful of slightly less massive sibling stars. When massive stars like these are born, they rapidly begin to shred to pieces the very cloud that nurtured them, forcing gas and dust to clump together and collapse into new stars. The process continues to spread outward, triggering successive generations of fewer and fewer stars. Our own Sun may have grown up in a similar environment.

The new Spitzer image offers astronomers a detailed “family tree” of the Carina Nebula. At the top of the hierarchy are the grandparents, Eta Carinae and its siblings, and below them are the generations of progeny of different sizes and ages.

“Now we have a controlled experiment for understanding how one giant gas and dust cloud can produce such a wide variety of stars,” said Gehrz.

The false colors in the Spitzer picture correspond to different infrared wavelengths. Red represents dust features and green shows hot gas. Embryonic stars are yellow or white and foreground stars are blue. Eta Carinae itself lies just off the top of image. It is too bright for infrared telescopes to observe.

JPL manages the Spitzer Space Telescope mission for NASA’s Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena. JPL is a division of Caltech. Spitzer’s infrared array camera, which took the picture of the Carina Nebula, was built by NASA Goddard Space Flight Center, Greenbelt, Md.; its development was led by Dr. Giovanni Fazio, Smithsonian Astrophysical Observatory, Cambridge, Mass.

Additional information about the Spitzer Space Telescope is available at: http://www.spitzer.caltech.edu/spitzer.

Original Source: Spitzer News Release

Posted on by Fraser Cain

Andromeda is Three Times Larger Than Previously Believed

One small corner of the massive Andromeda galaxy (M31). Image credit: Subaru. Click to enlarge.
The lovely Andromeda galaxy appeared as a warm fuzzy blob to the ancients. To modern astronomers millennia later, it appeared as an excellent opportunity to better understand the universe. In the latter regard, our nearest galactic neighbor is a gift that keeps on giving.

Scott Chapman, from the California Institute of Technology, and Rodrigo Ibata, from the Observatoire Astronomique de Strasbourg in France, have led a team of astronomers in a project to map out the detailed motions of stars in the outskirts of the Andromeda galaxy. Their recent observations with the Keck telescopes show that the tenuous sprinkle of stars extending outward from the galaxy are actually part of the main disk itself. This means that the spiral disk of stars in Andromeda is three times larger in diameter than previously estimated.

At the annual summer meeting of the American Astronomical Society today, Chapman will outline the evidence that there is a vast, extended stellar disk that makes the galaxy more than 220,000 light-years in diameter. Previously, astronomers looking at the visible evidence thought Andromeda was about 70,000 to 80,000 light-years across. Andromeda itself is about 2 million light-years from Earth.

The new dimensional measure is based on the motions of about 3,000 of the stars some distance from the disk that were once thought to be merely the “halo” of stars in the region and not part of the disk itself. By taking very careful measurements of the “radial velocities,” the researchers were able to determine precisely how each star was moving in relation to the galaxy.

The results showed that the outlying stars are sitting in the plane of the Andromeda disk itself and, moreover, are moving at a velocity that shows them to be in orbit around the center of the galaxy. In essence, this means that the disk of stars is vastly larger than previously known.

Further, the researchers have determined that the nature of the “inhomogeneous rotating disk”-in other words, the clumpy and blobby outer fringes of the disk-shows that Andromeda must be the result of satellite galaxies long ago slamming together. If that were not the case, the stars would be more evenly spaced.

Ibata says, “This giant disk discovery will be very hard to reconcile with computer simulations of forming galaxies. You just don’t get giant rotating disks from the accretion of small galaxy fragments.”

The current results, which are the subject of two papers already available and a third yet to be published, are made possible by technological advances in astrophysics. In this case, the Keck/DEIMOS multi-object spectrograph affixed to the Keck II Telescope possesses the mirror size and light-gathering capacity to image stars that are very faint, as well as the spectrographic sensitivity to obtain highly accurate radial velocities.

A spectrograph is necessary for the work because the motion of stars in a faraway galaxy can only be detected within reasonable human time spans by inferring whether the star is moving toward us or away from us. This can be accomplished because the light comes toward us in discrete frequencies due to the elements that make up the star.

If the star is moving toward us, then the light tends to cram together, so to speak, making the light higher in frequency and “bluer.” If the star is moving away from us, the light has more breathing room and becomes lower in frequency and “redder.”

If stars on one side of Andromeda appear to be coming toward us, while stars on the opposite side appear to be going away from us, then the stars can be assumed to orbit the central object.

The extended stellar disk has gone undetected in the past because stars that appear in the region of the disk could not be known to be a part of the disk until their motions were calculated. In addition, the inhomogeneous “fuzz” that makes up the extended disk does not look like a disk, but rather appears to be a fragmented, messy halo built up from many previous galaxies’ crashing into Andromeda, and it was assumed that stars in this region would be going every which way.

“Finding all these stars in an orderly rotation was the last explanation anyone would think of,” says Chapman.

On the flip side, finding that the bulk of the complex structure in Andromeda’s outer region is rotating with the disk is a blessing for studying the true underlying stellar halo of the galaxy. Using this new information, the researchers have been able to carefully measure the random motions of stars in the stellar halo, probing its mass and the form of the elusive dark matter that surrounds it.

Although the main work was done at the Keck Observatory, the original images that posed the possibility of an extended disk were taken with the Isaac Newton Telescope’s Wide-Field Camera. The telescope, located in the Canary Islands, is intended for surveys, and in the case of this study, served well as a companion instrument.

Chapman says that further work will be needed to determine whether the extended disk is merely a quirk of the Andromeda galaxy, or is perhaps typical of other galaxies.

The main paper with which today’s AAS news conference is concerned will be published this year in The Astrophysical Journal with the title “On the Accretion Origin of a Vast Extended Stellar Disk Around the Andromeda Galaxy.” In addition to Chapman and Ibata, the other authors are Annette Ferguson, University of Edinburgh; Geraint Lewis, University of Sydney; Mike Irwin, Cambridge University; and Nial Tanvir, University of Hertfordshire.

Original Source: Caltech News Release

Posted on by Mark Mortimer

Book Review: Atlas: The Ultimate Weapon

The Atlas booster evolved directly from the melding of experienced German rocket scientists with the need of the United States to counter the USSR’s ability. That is, the United States needed an Intercontinental Ballistic Missile (ICBM). However, as much as the German’s had successfully produced the V2 rocket, there was a huge jump in requirements from the V2 to their needs. For instance, a much heavier payload had to accurately and quickly fly much further over the Earth’s surface and land within a few miles of a given target. And this was to happen within minutes from activation. The Atlas booster was one of the industries’ responses to this government need and this history takes the reader through many of the trials, tribulations and interesting moments that occurred in this evolution of rocket technology.

The goal of the Atlas project was to have a number of active squadrons of ICBMs, ready in an instant to retaliate. Yet, their main goal was to deter an aggressor so they would truly succeed by remaining unused. In a few short years, Convair achieved this goal but the technological advances soon outdated the Atlas booster. Here is where Walker emphasises the beauty of the design as, even with this end point, the Atlas booster went on to perform stellar work in another arena, the space program. Using the tried and true technology of the Atlas booster, men were placed in orbit, cameras were sent to the moon and many global observatories were lofted up. That is, even after launching all the stored Atlas boosters, Convair kept producing these boosters to satisfy general space launch needs.

Using the perspective of a managerial level expert in this industrial program, which he was, Chuck Walker takes the reader on through the concept stage and up to the end of life for the primary mission. His history commences with the state of world affairs that generated a request for proposal by the United States’ Air Force. Convair, an aeroplane manufacturer dabbling in rocketry, won. Walker then uses his own experience within Convair, as well as recollections of many other managers together with saved documentation, to prepare a valid general review.

We read how estimates had to be made for launch site construction even though the missile design was not complete. Materials got stressed to the boundaries of knowledge and beyond. Configuration management, tracking change requests and obtaining appropriate authority ranged from casual recognition during the design stages to almost stifling bureaucracy during installation. Equally, the test and trials start with pure guess work but with experience, processes and procedures ably verified capability and ensured safety. This transformation from novice to proud and knowledgeable initiate resonates throughout the text.

In addition to the actual missile fabrication and deployment, Walker includes many direct contributions from relevant people regarding events and relations with other companies and subcontractors. These views come almost singularly from Convair managerial personnel so there is likely some bias in the perspective. Negligible reference is given to the contributions from subcontractors such as Rocketdyne and its rocket engines or General Electric and its guidance package. Interactions with the customer, that is the United States Air Force, continually crop up to put the pace and level of work into perspective. An overseer company, Ramo-Wooldridge, also has many references as it performed reviews and secondary checks often to the consternation of Convair managers. In all, many personal relationships, well remembered expos?s and a few choice scenarios pleasantly enliven the staid details normally associated with the histories of equipment.

As with any historical review, this book follows a chronological order. However, many particular quotes make the time line seem jumpy. That is, contributor often refer to events discussed in earlier chapters or covered further along in the text. Also, given that Walker refers to the Atlas as a workhorse of the space program, there could have been more information on its usage as such, for example to discuss significant upgrades and accomplishments. Still, there are references for those wishing to explore further.

An Atlas booster put John Glenn into orbit, Surveyor-1 on the Moon and Pioneer-11 to Saturn. But, it began as a critical element in the United States’ policy of deterrence in the early 1960s when rocketry was still in its infancy. The book “Atlas The Ultimate Weapon” by Chuck Walker, with Joel Powell, writes up the history of the development of this weapon and in so doing describes the challenges in mass producing a state of the art ballistic rocket.

Order a copy online from Countdown Creations.

Review by Mark Mortimer.

Posted on by Fraser Cain

Carbon/Oxygen Stars Could Explode as Gamma Ray Bursts

Artist illustration of a gamma-ray burst. Image credit: NASA. Click to enlarge.
Observations by two of the world’s largest telescopes provide strong evidence that a peculiar type of exploding star may be the origin of elusive gamma-ray bursts that have puzzled scientists for more than 30 years.

A team of astronomers from Italy, Japan, Germany and the United States, including the University of California, Berkeley, conclude from observations with the Keck and Subaru telescopes in Hawaii that naked carbon/oxygen stars that flatten as they collapse into a black hole are good candidates for the source of gamma-ray bursts.

Though astronomers have observed a couple of bursts associated with this type of supernova – a Type Ic supernova sometimes called a hypernova – the theory of how a hypernova produces gamma rays is still speculative. The new observations, though not a smoking gun, provide a major piece of evidence that the theory, called the collapsar model, is correct. The model explains how an asymmetric exploding star produces a tight beam of matter and energy out of each pole that generates an intense burst of gamma rays, while the absence of a hydrogen and helium envelope would allow the blast to escape.

“It appears that to produce a gamma-ray burst, a core-collapse supernova needs to be both asymmetric in its explosion mechanism, so that there is a natural axis along which matter can more easily squirt, and free of a hydrogen envelope, so that the jet doesn’t have to pummel through a lot of material,” said co-author Alex Filippenko, UC Berkeley professor of astronomy.

The team, led by Paolo Mazzali of the Trieste Observatory in Italy and the Max-Planck Institute for Astrophysics in Garching, Germany, reported its findings in a paper appearing in the May 27 issue of Science.

The fact that a gamma-ray burst was not observed in association with this supernova is actually in accord with predictions, said UC Berkeley graduate student Ryan Foley, a member of the team.

“These observations suggest that the collapsar model is probably correct and that some of these Type Ic supernovae appear to be off-axis gamma-ray bursts, in which the gamma-ray burst is pointing in some direction other than Earth,” Foley said.

Gamma-ray bursts are brief but bright flashes of X-rays and gamma rays that seem to go off randomly in the sky about once a day, briefly outshining the sun a million trillion times. It took until 1997 to establish that they originate outside our Milky Way Galaxy, and only within the past few years have astronomers gotten tantalizing hints that the bursts are associated with supernovae.

Because they are so bright, gamma-ray bursts have to be a collimated beam, similar to but tighter than the cone of light emitted by a lighthouse. Otherwise, the energy in the explosion would be equivalent to instantaneously converting the mass of several suns into a fireball of energy.

The most popular scenario is that a collapsing star generates two highly collimated beams or jets of particles and energy that flash outward from the poles. The particles and energy generate a shock wave when they hit gas and dust around the star, which in turn accelerates particles to energies at which they emit high-energy light: gamma rays and X-rays. The initial burst fades over a few seconds, but the resulting shock waves (the “afterglow”) can be visible to optical, radio and X-ray telescopes for days after the explosion.

A possible candidate for the type of supernova that could produce a gamma-ray burst is the Type Ic supernova. Type Ic supernovae result from massive stars whose winds have shed their outer envelopes of hydrogen and often all their helium, or that have lost these outer layers to a binary companion. Only the core is left, composed of the elements produced by fusion in the star’s center – mostly carbon and oxygen but other heavy elements as well, down to a solid iron center.

The collapsar theory proposes that the solid iron sphere at the very core of the star collapses under gravity to a black hole, but that the split-second collapse takes place in a unique way. As the iron and surrounding matter fall inward, the spin of the core increases, flattening the in-falling material into a disk that flows inward along the equator. The congestion of in-falling matter pushes some of it right back out along the path of least resistance – the two blowholes at either pole.

The matter shot out from the poles rams into the other layers of the star, which it may not be able to penetrate. The lack of a hydrogen and helium envelope presumably increases the chances the jet will punch through.

“It has so much energy that it pushes through these outer layers of the star, which are of relatively small density compared to the disk of in-falling material in the center of the star,” said Foley. “Eventually, if it punches out, you have a gamma-ray jet. Some Type Ic supernovae may be failed gamma-ray bursts, which means the jet tried to push out, but there was too much material in the way, and it never actually broke out. That would explain why we don’t see gamma-ray bursts associated with some of these objects.”

If the theory is true, astronomers should see different things depending on whether the jet is aimed toward Earth or away from it. If the jet is coming out perpendicular to our line of sight, for example, no gamma-ray burst would be visible, but other aspects of the expanding supernova blast wave should be observable. In particular, the spectrum of the supernova a year or so after its explosion should show emission lines of elements, such as oxygen, that are split, one shifted slightly to lower wavelengths and the other shifted to higher wavelengths. The two lines would come from opposite sides of the expanding disk around the equatorial region of the remnant black hole, one Doppler shifted toward the red because it is moving away from us, the other blueshifted because it is moving toward us. Such split or double lines would not be visible from a polar perspective.

About two years ago, on Oct. 25, 2003, UC Berkeley researchers had discovered a Type Ic supernova using Filippenko’s automated supernova search telescope, the Katzman Automatic Imaging Telescope (KAIT) at the University of California’s Lick Observatory. Called SN 2003jd, the supernova was about 260 million light years away in the constellation Aquarius. Though no associated gamma-ray burst was recorded, the supernova appeared to be as bright as the supernovae previously associated with gamma-ray bursts, so the international team reporting this week in Science decided to look again at the supernova, taking its spectrum in search of double-peaked emission lines.

“These observations were actually guided by our theoretical predictions,” Mazzali said. “The idea was that a bright Type Ic supernova, not accompanied by a gamma-ray burst, could be just what we were looking for: an off-axis event which could confirm our predictions.”

Koji Kawabata from Hiroshima University, Ken’ichi Nomoto of the University of Tokyo and his colleagues observed the remnant nebula with the 8.2-meter Subaru telescope on Sept. 12, 2004, about 330 days after it blew. Subsequently, Filippenko and Foley turned the 10-meter Keck telescope on the nebula on Oct. 19, 2004, about 370 days after the initial explosion, to obtain spectral images with the Low Resolution Imaging Spectrometer (LRIS). Both telescopes sit atop Mauna Kea volcano on the island of Hawaii. Subaru is operated by the National Astronomical Observatory of Japan, while the Keck Observatory is operated by the California Association for Research in Astronomy, whose board of directors includes representatives from the California Institute of Technology (Caltech) and UC.

Kawabata, Mazzali and his team analyzed the spectra, revealing that they exhibit split oxygen and magnesium emission lines exactly as would be expected if the collapsar model of gamma-ray production were correct. This was the first Type Ic supernova to show split oxygen lines.

“Jets are a signature of the model, which means that not all explosions will be pointed directly at us. If every time we looked at these objects they appeared to be pointing at us, that would mean the model is probably flawed,” Foley said. “The model predicts that a certain percentage of these objects should look like this supernova (SN 2003jd). Now that we’ve found one of these, the credibility of the model has increased.”

To see such double oxygen lines, the supernova nebula would have to be viewed within 20 degrees of the expanding disk, a rare situation that could explain why other Type Ic supernovae, including some associated with a gamma-ray burst, do not show the split oxygen line.

“(Our observations) strengthen the connection between gamma-ray bursts and Type Ic supernovae by showing that the Type Ic SN 2003jd appears to indeed have been an asymmetric explosion whose main axis of ejection happened not to be pointing at us,” Filippenko said.

Other coauthors of the paper are Keiichi Maeda, Jinsong Deng and Nozomu Tominaga of the University of Tokyo; Enrico Ramirez-Ruiz of the Institute for Advanced Study in Princeton, New Jersey; Stefano Benetti of the Astronomical Observatory of Padova, Italy; Elena Pian of the Trieste Observatory; Youichi Ohyama of the Subaru Telescope; Masanori Iye of Japan’s National Astronomical Observatory; Thomas Matheson of the National Optical Astronomy Observatory in Tuscon, Ariz.; Lifan Wang of Lawrence Berkeley National Laboratory; and Avishay Gal-Yam of Caltech.

The work was supported in part by the National Science Foundation, the Japan Society for the Promotion of Science and Japan’s Ministry of Education, Culture, Sports, Science and Technology.

Original Source: Berkeley News Release

Posted on by Fraser Cain

Shuttle Getting an Upgraded Fuel Tank

Discovery rolls back to the Vehicle Assembly Building for an upgrade. Image credit: NASA. Click to enlarge.
The Space Shuttle Discovery is back in the Vehicle Assembly Building (VAB) at NASA’s Kennedy Space Center, Fla. The Shuttle will get a new, modified external fuel tank to ensure a safe Return to Flight mission (STS-114).

Discovery, carried by a Crawler Transporter, entered the VAB at 4:30 p.m. EDT. The 10-hour, 4.2 mile trip from Launch Pad 39B was briefly interrupted due to an over heated bearing on the Transporter. Today’s rollback was the 15th in Space Shuttle Program history.

“Rolling back Discovery was the right thing to do and demonstrates our commitment to a safe Return to Flight,” said Shuttle Program Manager Bill Parsons. “We will continue to focus on the processing milestones and complete the additional analysis we determined was required, so that we continue to move toward a launch during the July window.”

Technicians will de-mate Discovery from its External Tank (ET-120) and Solid Rocket Boosters on May 31. Discovery will be attached to ET-121 on June 7. ET-121 was originally scheduled to fly with the Shuttle Atlantis on the second Return to Flight mission (STS-121).

In the VAB, a new heater will be added to ET-121 on the feedline bellows. It is the part of the pipeline that carries liquid oxygen to the Shuttle’s main engines, to minimize potential ice and frost buildup. The tank also has several safety improvements, including an improved bipod fitting that connects it to the Orbiter.

In addition, NASA’s second redesigned tank has been outfitted with temperature sensors and accelerometers, used to measure vibration. These sensors will gather information about the tank’s performance during flight.

After the heater is added to ET-121 and the Shuttle is attached to its new propulsion elements, Discovery will roll back out to Launch Pad 39B in mid-June. Discovery’s payload, the Italian-built Multi-Purpose Logistics Module Raffaello, will be installed in the payload bay, while the Shuttle is on the pad.

Launch of Discovery for STS-114 is targeted for July 13. The launch window extends to July 31. During its 12-day mission, Discovery’s seven-person crew will test new hardware and techniques to improve Shuttle safety and deliver supplies to the International Space Station.

Video from the rollback will feed on NASA TV, available on the Web and via satellite in the continental U.S. on AMC-6, Transponder 9C, C-Band, at 72 degrees west longitude. The frequency is 3880.0 MHz. Polarization is vertical, and audio is monaural at 6.80 MHz. It’s available in Alaska and Hawaii on AMC-7, Transponder 18C, C-Band, at 137 degrees west longitude. The frequency is 4060.0 MHz. Polarization is vertical, and audio is monaural at 6.80 MHz. For NASA TV information and schedules on the Internet, visit: http://www.nasa.gov/ntv

Photos of the rollback are available on the Web at: http://mediaarchive.ksc.nasa.gov/index.cfm

For the latest information about NASA’s Return to Flight efforts, visit: http://www.nasa.gov/returntoflight

Original Source: NASA News Release

Posted on by Fraser Cain

Dark Spots on the Moon Show a Turbulent Solar System

The Moon and its dark spots. Image credit: NASA. Click to enlarge.
People of every culture have been fascinated by the dark “spots” on the Moon, which seem to compose the figure of a rabbit, frogs or the face of a clown. With the Apollo missions, scientists found that these features are actually huge impact basins that were flooded with now-solidified lava. One surprise was that these basins formed relatively late in the history of the early solar system – approximately 700 million years after the formation of the Earth and Moon. Many scientists now believe that these lunar impact basins bear witness to a huge spike in the bombardment rate of the planets – called the late heavy bombardment (LHB). The cause of such an intense bombardment, however, is considered by many to be one of the best-preserved mysteries of solar system history.

In a series of three papers published in this week’s issue of the journal Nature, an international team of planetary scientists, Rodney Gomes (National Observatory of Brazil), Harold Levison (Southwest Research Institute, United States), Alessandro Morbidelli (Observatoire de la C?te d’Azur, France) and Kleomenis Tsiganis (OCA and University of Thessaloniki, Greece) – brought together by a visitor program hosted at the Observatoire de la C?te d’Azur in Nice – proposed a model that not only naturally solves the mystery of the origin of the LHB, but also explains many of the observed characteristics of the outer planetary system.

This new model envisions that the four giant planets, Jupiter, Saturn, Uranus and Neptune, formed in a very compact orbital configuration, which was surrounded by a disk of small objects made of ice and rock (known as “planetesimals”). Numerical simulations by the Nice team shows that some of these planetesimals slowly leaked out of the disk due to the gravitational effects of the planets. The planets scattered these smaller objects throughout the solar system, sometimes outward and sometimes inward.

“As Isaac Newton taught us, for every action there is an equal and opposite reaction,” says Tsiganis. “If a planet throws a planetesimal out of the solar system, the planet moves toward the Sun, just a tiny bit, in compensation. If, on the other hand, the planet scatters the planetesimal inward, the planet jumps slightly farther from the Sun.”

Numerical simulations show that, on average, Jupiter moved inward while the other giant planets moved outward.

Initially, this was a very slow process, taking millions of years for the planets to move a small amount. Then, according to this new model, after 700 million years, the situation suddenly changed. At that time, Saturn migrated through the point where its orbital period was exactly twice that of Jupiter’s. This special orbital configuration caused Jupiter’s and Saturn’s orbits to suddenly become more elliptical.

“This caused the orbits of Uranus and Neptune to go nuts,” says Gomes. “Their orbits became very eccentric and they started to gravitationally scatter off each other – and Saturn too.”

The Nice team argues that this evolution of Uranus’ and Neptune’s orbits caused the LHB on the Moon. Their computer simulations show that these planets very quickly penetrated the planetesimal disk, scattering objects throughout the planetary system. Many of these objects entered the inner solar system where they peppered the Earth and Moon with impacts. In addition, the whole process destabilized the orbits of asteroids, which then would have also contributed to the LHB. Finally, the gravitational effects of the planetesimal disk caused Uranus and Neptune to evolve onto their current orbits.

“It’s very convincing,” says Levison. “We have made several dozen simulations of this process, and statistically the planets ended up on orbits very similar to the ones that we see, with the correct separations, eccentricities and inclinations. So, in addition to the LHB, we can also explain the orbits of the giant planets. No other model has ever accomplished either thing before.”

However, there was one more hurdle to overcome. The solar system currently contains a population of asteroids that follow essentially the same orbit as Jupiter, but lead or trail that planet by an angular distance of roughly 60 degrees. Computer simulations show that these bodies, known as the “Trojan asteroids,” would have been lost as the giant planets’ orbits changed.

“We sat around for months worrying about this problem, which seemed to invalidate our model,” says Morbidelli, “until we realized that if a bird can escape from an open cage, another one can come and nest in it.”

The Nice team found that some of the very objects that were driving the planetary evolution, and which caused the LHB, would also have been captured into Trojan asteroid orbits. In the simulations, the trapped Trojans turned out to reproduce the orbital distribution of the observed Trojans, which was unexplained up to now. The total predicted mass of the trapped objects was also consistent with the observed population.

Taken in total, the Nice team’s new model naturally explains the orbits of the giant planets, the Trojan asteroids and the LHB to unprecedented accuracy. “Our model explains so many things that we believe it must be basically correct,” says Mordibelli. “The structure of the outer solar system shows that the planets probably went through a shake up well after the planet formation process ended.”

Original Source: SWRI News Release

Posted on by Fraser Cain

Mysterious Spot on Titan Puzzles Astronomers

Titan and its strange spot viewed in different wavelengths. Image credit: NASA/JPL/SSI. Click to enlarge.
Saturn’s moon Titan shows an unusual bright spot that has scientists mystified. The spot, approximately the size and shape of West Virginia, is just southeast of the bright region called Xanadu and is visible to multiple instruments on the Cassini spacecraft.

The 483-kilometer-wide (300-mile) region may be a “hot” spot — an area possibly warmed by a recent asteroid impact or by a mixture of water ice and ammonia from a warm interior, oozing out of an ice volcano onto colder surrounding terrain. Other possibilities for the unusual bright spot include landscape features holding clouds in place or unusual materials on the surface.

“At first glance, I thought the feature looked strange, almost out of place,” said Dr. Robert H. Brown, team leader of the Cassini visual and infrared mapping spectrometer and professor at the Lunar and Planetary Laboratory, University of Arizona, Tucson. “After thinking a bit, I speculated that it was a hot spot. In retrospect, that might not be the best hypothesis. But the spot is no less intriguing.”

The Cassini spacecraft flew by Titan on March 31 and April 16. Its visual and infrared mapping spectrometer, using the longest, reddest wavelengths that the spectrometer sees, observed the spot, the brightest area ever observed on Titan.

Cassini’s imaging cameras saw a bright, 550-kilometer-wide (345-mile) semi-circle at visible wavelengths at this same location on Cassini’s December 2004 and February 2005 Titan flybys. “It seems clear that both instruments are detecting the same basic feature on or controlled by Titan’s surface,” said Dr. Alfred S. McEwen, Cassini imaging team scientist, also of the University of Arizona. “This bright patch may be due to an impact event, landslide, cryovolcanism or atmospheric processes. Its distinct color and brightness suggest that it may have formed relatively recently.”

Other bright spots have been seen on Titan, but all have been transient features that move or disappear within hours, and have different spectral (color) properties than this feature. This spot is persistent in both its color and location. “It’s possible that the visual and infrared spectrometer is seeing a cloud that is topographically controlled by something on the surface, and that this weird, semi-circular feature is causing this cloud,” said Dr. Elizabeth Turtle, Cassini imaging team associate, also from the Lunar and Planetary Laboratory.

“If the spot is a cloud, then its longevity and stability imply that it is controlled by the surface. Such a cloud might result from airflow across low mountains or outgassing caused by geologic activity,” said Jason Barnes, a postdoctoral researcher working with the visual and infrared mapping spectrometer team at the University of Arizona.

The spot could be reflected light from a patch of terrain made up of some exotic surface material. “Titan’s surface seems to be mostly dirty ice. The bright spot might be a region with different surface composition, or maybe a thin surface deposit of non-icy material,” Barnes added.

Scientists have also considered that the spot might be mountains. If so, they’d have to be much higher than the 100-meter-high (300-foot) hills Cassini’s radar altimeter has seen so far. Scientists doubt that Titan’s crust could support such high mountains.

The visual and infrared mapping spectrometer team will be able to test the hot spot hypothesis on the July 2, 2006, Titan flyby, when they take nighttime images of the same area. If the spot glows at night, researchers will know it’s hot.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov. For additional images visit the visual and infrared mapping spectrometer page at http://wwwvims.lpl.arizona.edu and the Cassini imaging team homepage http://ciclops.org .

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 visual and infrared mapping spectrometer team is based at the University of Arizona. The imaging team is based at the Space Science Institute in Boulder, Co.

Original Source: NASA/JPL News Release

Posted on by Fraser Cain

Podcast: Amateurs Help Find a Planet

Professional astronomers have got some powerful equipment at their disposal: Hubble, Keck, and Spitzer, just to name a few. But many discoveries rely on the work of amateurs, using equipment you could buy at your local telescope shop. And recently, amateurs helped discover a planet orbiting another star 15 thousand light-years away. Grant Christie is an amateur astronomer from Auckland New Zealand, and is part of the team that made the discovery.
Continue reading “Podcast: Amateurs Help Find a Planet”

Posted on by Fraser Cain

Audio: Amateurs Help Find a Planet

Artist illustration of an extrasolar planet. Image credit: CfA. Click to enlarge.
Listen to the interview: Microlens Planet Discovery (6.2 mb)

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Fraser Cain: Can you give me some background on the planet that you helped to discover?

Grant Christie: There’s still a bit of analysis to do on it to figure out exactly all its parameters, but it’s in the order of about 15,000 light-years away. That’s still being worked on, the distance. It’s quite a massive planet, probably in the order of about 2-3x the mass of Jupiter, and it’s orbiting at about 3 astronomical units away from its parent star. It’s not exactly like a familiar object, but if you could see it up close, it would probably look a bit like Jupiter. It would be about 3 times heavier, but not that much bigger because it would be more compressed by its gravity.

Fraser: The planets that have been discovered to date are within a few hundred light years of Earth. How were you able to find one 15,000 light-years away, expecially using backyard equipment?

Christie: With this discovery, we’re just part of a cog in a wheel, we’re part of a team, but it was using a method known as gravitational microlensing. That sounds like a bit of a mouthful, but essentially it uses a star as a lens to magnify a more distant star. This works if the two stars are exactly lined up as we see them from Earth. So we have a situation where we have a distant star somewhere in the halo – or the bulge – of the galaxy maybe 20,000 light-years from Earth. By chance, another star has come almost exactly in line between us and it. That intervening star’s gravity works like a lens and it amplifies the light of the more distant star. We can’t see them as two stars, they’re so close together, and no telescope on Earth can. But what we see is the magnification, or the amplification of the light from the distant star as it goes through that lens. All of that’s fine, some 600 of these microlensing events are detected each year currently. They in themselves aren’t that unusual, but it turns out that if you have a planet orbiting the lensing star – the one that’s intervened between us and the more distant one – then that planet hugely changes the characteristics of the lens. It changes the light amplification greatly. What we’re doing is simply measuring the brightness changes of the lens as these two stars come into alignment and then move out of alignment. It turns out that the one we were observing, the light was magnified by something like 50x over and above what was there before the lensing started. That brings faint stars that we normally couldn’t see with a small telescope up within our range. In the current case, the amplification brought it up to magnitude 18 in the visual wavelengths. That’s very close to our limit, but we were still able to do it.

Fraser: Was your team expecting to find evidence of a planet before you began any observations, or was that just a happy outcome?

Christie: It is largely a happy outcome. There’s a team based in Chile, a Polish team from Warsaw University let by Professor Udalski, and their job, their main function is to find microlensing events. They monitor millions of stars every night looking for stars that just seem to rise in brightness in a way that you’d expect from a lens. There are obviously lots of variable stars as well, which they have already tabulated, so they know about those. They’re detecting microlensing events. They’re detecting about 600 a year. They started observing this event in about March 17th, or thereabouts, and they noticed this star just starting to brighten – it had never brightened before – and they followed it. Each night as they took an observation, it appeared to brighten more and more, and as this process goes on they noticed that it was following a particular brightening curve that you’d expect from a microlensing event, so they were confident that it was a microlens. And then as we got closer into April, it started to show signs that it was departing from a pure simple lens you’d get from a single star all by itself; that’s a mathematically defined shape and if the photometry’s good, you can usually tell whether you’ve got a single lens or not. Around April 18th they started to notice a significant departure from that simple lens model, these are the guys running the OGLE team. They put out an alert that went to MicroFUN, who is a group we’re associated with. They run out of Ohio State University, led by Professor Andrew Gould there. We then received notification saying, it looks like there might be an anomoly with this microlensing event; try and observe it as much as possible. That’s really where we started our observations. By that stage it was faint, but it was still within reach of our telescopes. We were surprised that it actually was observable. I would have thought that it was too faint. Now I know that we can do work at a fainter limit than I’d previously thought. It was known by about April 20th that this microlensing event had a strong anomaly in it, which is the term they use, and we followed it for the following few days – probably about 3-4 days. It went through some very strong anomalies that really were a sign that was a planet present causing those anomolies. Most of these events you observe – I’ve done quite a few, probably 20 at least myself – turn out to be a simple lens, and there’s nothing surprising in them at all. The excitement of doing this sort of work is that you simply don’t know, nobody knows what you’re going to find. You start following one of these microlensing events as it reaches its maximum, and it’s at the maximum point, or close to it when the maximum sensitivity to a planet is going to be. We’re just not that interested in looking at them until you get very close to that maximum. And that’s when the networks really come are really start to saturate the light curve by covering them.

Fraser: So the stars have to be lined up quite nicely for the effect of the planet to show up.

Christie: Yes, they need to be nearly perfect. That creates a very high amplification. Some of the ones we’ve looked at have had amplifications where the light is magnified 800x. They’re not common, but when you get a very high amplification lens like that, when the alignment is nearly perfect, that’s when you’re most likely to find a planet if there’s one present.

Fraser: How sensitive can this technique be?

Christie: Some of the experts have said that had this planet not been bigger than Jupiter, it was the size of the Earth, these observations still would have detected it. I know there’s some debate about that amongst the academics in the teams, but broadly speaking, that’s probably an indication that this method can be very sensitive. And this event actually didn’t come up to be that bright. We’ve observed ones which have come up so bright you could see them in a little 6″ telescope.

Fraser: That’s amazing, though. I know people have been discussing different techniques that they might be able to see Earth-sized planets orbiting other stars, but to know that we might have a technique available right now is pretty impressive. I wanted to talk to you a bit about how amateurs can get involved in the discoveries in astronomy. Where are some avenues that people can get involved?

Christie: There are lots of ways you can get involved in observational astronomy, but in talking about photometry, which is a measurement of star brightness, you basically just need a telescope with as much aperture as you can afford. A decent sort of mounting and a CCD imaging camera. For below $10,000 you can set up a system that’s very capable, and can actually be really useful. There are lots of other things you can do in observational astronomy that don’t require that, but to do this sort of work, that’s what you’d need. We do work other than this microlensing work, we also measure the light changes of objects called cataclysmic variable stars. These are interesting objects that do a lot of flickering, and all sorts of things, and we’re part of a worldwide network that follows that kind of object. Generally, the common denomenator is the measurement of brightness over time of some star or object. That’s called photometry, and that’s primarily what we do.

Fraser: Congratulations on your team’s discovery of this new planet, and good luck with your work in the future.

Christie: You’re very welcome. I’d like to pay tribute to my co-worker here in New Zealand, Jennie McCormick, who uses the smallest telescope of all, and has done way over a thousand hours on this kind of work and deserves the recognition from her efforts put in.

Posted on by Fraser Cain

Saturn Reflects X-Rays from the Sun

Saturn viewed by Chandra in the X-Ray spectrum during a solar flare. Image credit: Chandra. Click to enlarge.
When it comes to mysterious X-rays from Saturn, the ringed planet may act as a mirror, reflecting explosive activity from the sun, according to scientists using NASA’s Chandra X-ray Observatory.

The findings stem from the first observation of an X-ray flare reflected from Saturn’s low-latitudes, the region that correlates to Earth’s equator and tropics.

Dr. Anil Bhardwaj, a planetary scientist at NASA’s Marshall Space Flight Center (MSFC), Huntsville, Ala., led the study team. The study revealed Saturn acts as a diffuse mirror for solar X-rays.

Counting photons, particles that carry electromagnetic energy including X-rays, was critical to this discovery. Previous studies revealed Jupiter, with a diameter 11 times that of Earth, behaves in a similar fashion. Saturn is about 9.5 times larger than Earth. It is twice as far from Earth as Jupiter.

“The bigger the planet and nearer to the sun, the more solar photons it will intercept; resulting in more reflected X-rays.” Bhardwaj said. “These results imply we could use giant planets like Jupiter and Saturn as remote-sensing tools. By reflecting solar activity back to us, they could help us monitor X-ray flaring on portions of the sun facing away from Earth’s space satellites.”

Massive solar explosions called flares often accompany coronal mass ejections, which emit solar material and a magnetic field. When directed toward Earth, these ejections can wreak havoc on communications’ systems from cell phones to satellites.

Even as the research appeared to solve one mystery, the source of Saturn’s X-rays, it fueled long standing questions about magnetic fields. Of the three magnetic planets in our solar system, Jupiter and Earth emit two general types of X rays, auroral emissions from polar regions and disk emissions from low latitudes. No research has observed unambiguous signatures of auroral X-ray emissions on Saturn.

“We were surprised to find no clear evidence of auroral X-ray emissions during our observations,” Bhardwaj said. “It is interesting to note that even as research solves some mysteries, it confirms there is much more we have to learn.”

The research appeared in the May 10, 2005 issue of Astrophysical J. Letters. the research team also included Ron Elsner of MSFC; Hunter Waite of the University of Michigan, Ann Arbor; Randy Gladstone of the Southwest Research Institute, San Antonio, Texas; Thomas Cravens of the University of Kansas, Lawrence; and Peter Ford from the Massachusetts Institute of Technology, Cambridge.

Bhardwaj is working at MSFC as a National Research Council scholar. MSFC manages the Chandra program for NASA’s Science Mission Directorate in Washington. Northrop Grumman of Redondo Beach, Calif., was the prime development contractor for the observatory. The Smithsonian Astrophysical Observatory controls science and flight operations from the Chandra X-ray Center in Cambridge, Mass.

Original Source: NASA News Release