Posted on by Fraser Cain

Kuiper Belt Moons Might Be More Common

Artist’s concept of Xena the Sun, appearing from a distance. Image credit: NASA/JPL-Caltech. Click to enlarge
In the not-too-distant past, the planet Pluto was thought to be an odd bird in the outer reaches of the solar system because it has a moon, Charon, that was formed much like Earth’s own moon was formed. But Pluto is getting a lot of company these days. Of the four largest objects in the Kuiper belt, three have one or more moons.

“We’re now beginning to realize that Pluto is one of a small family of similar objects, nearly all of which have moons in orbit around them,” says Antonin Bouchez, a California Institute of Technology astronomer.

Bouchez discussed his work on the Kuiper belt at the winter meeting of the American Astronomical Society (AAS).

Bouchez says that the puzzle for planetary scientists is that, as a whole, the hundreds of objects now known to inhabit the Kuiper belt beyond the orbit of Neptune have only about an 11 percent chance of possessing their own satellites. But three of the four largest objects now known in the region have satellites, which means that different processes are at work for the large and small bodies.

Experts have been fairly confident for a decade or more that Pluto’s moon Charon was formed as the result of an impact, but that the planet seemed unique in this. According to computer models, Pluto was hit by an object roughly one-half its own size, vaporizing some of the planet’s material. A large piece, however, was cleaved off nearly intact, forming Pluto’s moon Charon.

Earth’s moon is thought to have been formed in a similar way, though our moon most likely formed out of a hot disk of material left in orbit after such a violent impact.

Just in the last year, astronomers have discovered two additional moons for Pluto, but the consensus is still that the huge Charon was formed by a glancing blow with another body, and that all three known satellites-as well as anything else not yet spotted from Earth-were built up from the debris.

As for the other Kuiper belt objects, experts at first thought that the bodies acquired their moons only occasionally by snagging them through gravitational capture. For the smaller bodies, the 11 percent figure would be about right.

But the bigger bodies are another story. The biggest of all – and still awaiting designation as the tenth planet – is currently nicknamed “Xena.” Discovered by Caltech’s Professor of Planetary Science Mike Brown and his associates, Chad Trujillo of the Gemini Observatory and David Rabinowitz of Yale University, Xena is 25 percent larger than Pluto and is known to have at least one moon.

The second-largest Kuiper belt object is Pluto, which has three moons and counting. The third-largest is nicknamed “Santa” because of the time of its discovery by the Mike Brown team, and is known to have two moons.

“Santa is an odd one,” says Bouchez. “You normally would expect moons to form in the same plane because they would have accreted from a disk of material in orbit around the main body.

“But Santa’s moons are 40 degrees apart. We can’t explain it yet.”

The fourth-largest Kuiper belt object is nicknamed “Easterbunny” – again, because of the time the Brown team discovered it – and is not yet known to have a moon. But in April, Bouchez and Brown will again be looking at Easterbunny with the adaptive-optics rig on one of the 10-meter Keck telescopes, and a moon might very well turn up.

Original Source: NASA Astrobiology

Posted on by Fraser Cain

Hit and Run Planets

A heavily cratered lunar surface by bombarding asteroids. Image credit: NASA Click to enlarge
Hit-and-run collisions between embryonic planets during a critical period in the early history of the Solar System may account for some previously unexplained properties of planets, asteroids, and meteorites, according to researchers at the University of California, Santa Cruz, who described their findings in the January 12 issue of the journal Nature.

The four “terrestrial” or rocky planets (Earth, Mars, Venus, and Mercury) are the products of an initial period, lasting tens of millions of years, of violent collisions between planetary bodies of various sizes. Scientists have mostly considered these events in terms of the accretion of new material and other effects on the impacted planet, while little attention has been given to the impactor. (By definition, the impactor is the smaller of the two colliding bodies.)

But when planets collide, they don’t always stick together. About half the time, a planet-sized impactor hitting another planet-sized body will bounce off, and these hit-and-run collisions have drastic consequences for the impactor, said Erik Asphaug, associate professor of Earth sciences at UCSC and first author of the Nature paper.

“You end up with planets that leave the scene of the crime looking very different from when they came in–they can lose their atmosphere, crust, even the mantle, or they can be ripped apart into a family of smaller objects,” Asphaug said.

The remnants of these disrupted impactors can be found throughout the asteroid belt and among meteorites, which are fragments of other planetary bodies that have landed on Earth, he said. Even the planet Mercury may have been a hit-and-run impactor that had much of its outer layers stripped away, leaving it with a relatively large core and thin crust and mantle, Asphaug said. That scenario remains speculative, however, and requires additional study, he said.

Asphaug and postdoctoral researcher Craig Agnor used powerful computers to run simulations of a range of scenarios, from grazing encounters to direct hits between planets of comparable sizes. Coauthor Quentin Williams, professor of Earth sciences at UCSC, analyzed the outcomes of these simulations in terms of their effects on the composition and final state of the remnant objects.

The researchers found that even close encounters in which the two objects do not actually collide can severely affect the smaller object.

“As two massive objects pass near each other, gravitational forces induce dramatic physical changes–decompressing, melting, stripping material away, and even annihilating the smaller object,” Williams said. “You can do a lot of physics and chemistry on objects in the Solar System without even touching them.”

A planet exerts enormous pressure on itself through self-gravity, but the gravitational pull of a larger object passing close by can cause that pressure to drop precipitously. The effects of this depressurization can be explosive, Williams said.

“It’s like uncorking the world’s most carbonated beverage,” he said. “What happens when a planet gets decompressed by 50 percent is something we don’t understand very well at this stage, but it can shift the chemistry and physics all over the place, producing a complexity of materials that could very well account for the heterogeneity we see in meteorites.”

The formation of the terrestrial planets is thought to have begun with a phase of gentle accretion within a disk of gas and dust around the Sun. Embryonic planets gobbled up much of the material around them until the inner Solar System hosted around 100 Moon-sized to Mars-sized planets, Asphaug said. Gravitational interactions with each other and with Jupiter then tossed these protoplanets out of their circular orbits, setting off an era of giant impacts that probably lasted 30 to 50 million years, he said.

Scientists have used computers to simulate the formation of the terrestrial planets from hundreds of smaller bodies, but most of those simulations have assumed that when planets collide they stick, Asphaug said.

“We’ve always known that’s an approximation, but it’s actually not easy for planets to merge,” he said. “Our calculations show that they have to be moving fairly slowly and hit almost head-on in order to accrete.”

It is easy for a planet to attract and accrete a much smaller object than itself. In giant impacts between planet-sized bodies, however, the impactor is comparable in size to the target. In the case of a Mars-size impactor hitting an Earth-size target, the impactor would be one-tenth the mass but fully one-half the diameter of the Earth, Asphaug said.

“Imagine two planets colliding, one half as big as the other, at a typical impact angle of 45 degrees. About half of the smaller planet doesn’t really intersect the larger planet, while the other half is stopped dead in its tracks,” Asphaug said. “So there is enormous shearing going on, and then you’ve got incredibly powerful tidal forces acting at close distances. The combination works to pull the smaller planet apart even as it’s leaving, so in the most severe cases the impactor loses a large fraction of its mantle, not to mention its atmosphere and crust.”

According to Agnor, the whole problem of planet formation is highly complex, and unraveling the role played by hit-and-run fragmenting collisions will require further study. By examining planetary collisions from the perspective of the impactor, however, the UCSC researchers have identified physical mechanisms that can explain many puzzling features of asteroids.

Hit-and-run collisions can produce a wide array of different kinds of asteroids, Williams said. “Some asteroids look like small planets, not very disturbed, and at the other end of the spectrum are ones that look like iron-rich dog bones in space,” he said. “This is a mechanism that can strip off different amounts of the rocky material that composes the crust and mantle. What’s left behind can range from just the iron-rich core through a whole suite of mixtures with different amounts of silicates.”

One of the puzzles of the asteroid belt is the evidence of widespread global melting of asteroids. Impact heating is inefficient because it deposits heat locally. It is not clear what could turn an asteroid into a big molten blob, but depressurization in a hit-and-run collision might do the trick, Asphaug said.

“If the pressure drops by a factor of two, you can go from something that is merely hot to something molten,” he said.

Depressurization can also boil off water and release gases, which would explain why many differentiated meteorites tend to be free of water and other volatile substances. These and other processes involved in hit-and-run collisions should be studied in more detail, Asphaug said.

“It’s a new mechanism for planetary evolution and asteroid formation, and it suggests a lot of interesting scenarios that warrant further study,” he said.

Original Source: NASA Astrobiology

Posted on by Fraser Cain

The Stars That Shouldn’t Be

Optical image of the galaxy merger NGC 2782. Image credit: UA Steward Observatory. Click to enlarge
Arizona astronomers have discovered a population of what appear to be young star clusters where they aren’t supposed to be. The newborn stars appear to have formed in the debris of the NGC 2782 galaxy collision — debris that lacks what astronomers believe are some important ingredients needed to form stars.

A large, Milky Way-type galaxy collided with a much smaller galaxy in the NGC 2782 collision. It’s an example of the most common type of galaxy collision in the universe. Scientists believe that such collisions played an important role in the buildup of large galaxies in the early universe.

If confirmed, these newly discovered young star clusters and their environment could help shed light on the process of star formation, especially in the early universe in regions far from the crowded, active centers of galaxies.

Karen Knierman, a graduate student and Arizona/NASA Space Grant Fellow at The University of Arizona, and Patricia Knezek of the WIYN Consortium in Tucson, Ariz., are reporting the research at the American Astronomical Society meeting in Washington, D.C., today.

The astronomers found the star clusters by taking deep images of the galaxy collision with the 4 Megapixel CCD camera of the 1.8 meter (71-inch) Vatican Advanced Technology Telescope (VATT) at Mount Graham International Observatory in Arizona.

NGC 2782 lies about 111 million light years away toward the Lynx constellation. When the two galaxies of unequal mass collided about 200 million years ago, their gravitational pull ripped out two tails of debris with very different properties.

Beverly Smith of Eastern Tennessee University and collaborators studied the optical and gas properties of these two tails and published their results in 1994 and 1999. Studying the gas properties tells astronomers about neutral hydrogen gas and molecular gas — both important ingredients in star formation. Smith and collaborators found that the optically bright eastern tail has some neutral hydrogen gas and molecular gas at the base of the tail, and an optically bright, but gas-poor concentration at the end of the tail. The optically faint western tail is rich in neutral hydrogen gas, but has no molecular gas.

Knierman and Knezek found blue star clusters younger than 100 million years along both tails, indicating that those stars formed within the tails after the galaxy collision began.

“That’s surprising because the western tail lacks molecular gas, one of the key ingredients for star formation,” Knierman said.

Star clusters are thought to form from the collapse of giant molecular gas clouds. If this is the case, astronomers would expect to see remnants of the molecular gas which helped give birth to the stars.

Given Smith’s earlier observations of gas in the debris tails, Knierman and Knezek expected they might see star formation in the eastern tail, where molecular gas is clearly present. But they didn’t expect to see star formation in the western tail, where no molecular gas was detected. Finding young star clusters in the western tail should prompt astronomers to question their current models of star formation, the Arizona team said.

“Do we still need a model of giant molecular gas clouds?” Knierman asked. “Or do we need a different model – perhaps one with smaller clumps of molecular gas that might have been destroyed or blown away when these energetic young stars formed?”

Finding unexpected young star clusters in the western tail could help explain why stars form in other places where there may be little molecular gas, like the outer edges of the Milky Way galaxy or in the debris of other galaxy collisions, Knierman and Knezek noted.

“This has important implications in how star formation proceeded when our universe was young and galaxy collisions were much more common than they are today,” Knierman said.

“Only recently have we become aware of the importance of the merging of small galaxies with larger systems in creating galaxies like our own Milky Way,” Knezek added.

Original Source: UA News Release

Posted on by Nancy Atkinson

Bringing Stardust Home

Stardust’s sample return capsule, safely back on Earth. Image credit: NASA/JPL. Click to enlarge.
NASA’s Stardust spacecraft is now back home, having traveled 4.6 billion kilometers (3 billion miles) and successfully completed its mission in space. On January 15, Stardust’s Sample Return Capsule (SRC) landed safely in the Utah desert, containing samples of a comet’s coma and interstellar dust particles. Stardust was launched in 1999, and in January 2004, the spacecraft performed a risky and historic flyby of Comet Wild 2 to capture the samples and take pictures of the comet’s nucleus.

The trickiest part of the mission, however, may have been guiding the spacecraft back home. The Stardust Navigation Team at NASA’s Jet Propulsion Laboratory in California has been working around the clock for the past few weeks, preparing to bring Stardust’s SRC back through Earth’s atmosphere to land in the US Air Force’s Utah Test and Training Range, southwest of Salt Lake City.

For a successful re-entry and landing, the Navigation team had to target the capsule’s entry to a specific point in the Earth’s atmosphere to within eight 100ths of a degree. One mission manager compared that feat to hitting the eye of a sewing needle from across the room.

Throughout the mission the Stardust scientists have heralded the performance of this desk-sized spacecraft. But members of the Navigation Team have maintained that Stardust’s design provided unprecedented navigation challenges during its entire 7- year mission, culminating with the Earth return.

“Navigating this spacecraft has always been extremely difficult because the attitude control thrusters are all mounted on the same side of the spacecraft,” said Neil Mottinger, a member of the Navigation and Entry, Descent and Landing teams.

The thrusters provide gentle pushes that allow a spacecraft to maintain the correct position while in flight. Normally, most spacecraft have their thrusters placed equally around all sides, but Stardust’s thrusters were positioned so the plume of the thrusters wouldn’t contaminate the particle collector.

“This ‘unbalanced’ thruster design causes a velocity change every time the spacecraft needed to control its attitude, which can occur hundreds of times a day,” said Christopher Potts, the Technical Supervisor of the Flight Path Control Group. “Each thruster pulse is extremely small, but the large number adds up to a significant effect on the trajectory.”

Consequently, the Navigation team needed to closely monitor the daily activity of the spacecraft. “It’s a little like trying to catch a knuckleball,” said Potts, “as the spacecraft trajectory changed noticeably as it reacted to its local space environment.”

Mottinger said that in some aspects, the spacecraft was almost like a bucking bronco. “It was impossible to predict when the thrusters would fire during normal spacecraft operations,” he said, “let alone the times when it would go into a safe mode, firing the thrusters quite frequently to obtaining a ‘safe’ attitude, awaiting further instructions from Earth.”

Both Mottinger and Potts said that in the past few weeks, the Navigation team has gone through tests, training and several full rehearsals for the spacecraft’s return. “We spent a large amount of time postulating what could go wrong,” Potts said, “and making sure there was an appropriate response to correct the problem.”

But with the Navigation Team’s diligent guidance, the SRC landed perfectly, much to the delight and relief of everyone involved with Stardust. Stardust Project Manager Thomas Duxbury said at a press conference following the landing, “This thing went like clockwork. We released this capsule from our spacecraft and it hit the atmosphere exactly on time.”

Mottinger said the hard work the team put in was definitely worth the rewards. “This team has to be exhausted,” he said. “It’s been a real challenge to predict where the spacecraft was headed and fine-tune the entry. I’m in awe of everyone on the Navigation Team who made all this happen.”

Stardust’s SRC will be brought to a clean room at the Johnson Space Center in Houston to be opened. Scientists from around the world will be able to study the thousands of particles of cometary and interstellar dust, many smaller than the width of a human hair. The particles were collected from the coma or “tail,” a cloud of gas and dust that surrounds a comet.

Comets are intriguing bodies, formed in the outer regions of the solar system. Scientists consider comets to be the best samples available of the original building blocks of our solar system, and that the particles Stardust returned should be able to tell us about the conditions of the early solar system.

To determine the makeup of the collected particles, scientists will cut the samples into even smaller pieces and investigate them with powerful microscopes. Stardust scientists are recruiting volunteers to search for the interstellar dust particles using virtual microscopes.

The collector is about the size and shape of a tennis racquet, and is made of a unique substance called Aerogel. Aerogel is made of silicon, but is 99.8% air, so it is the least dense man-made substance. It feels like an extremely light, very fine, dry sponge, and it has the ability to capture fast moving dust. It’s very strong, and easily survived the capsule’s landing on solid ground.

Mottinger and Potts both look forward to seeing the results that the study of Stardust’s samples will bring.

“The entire Navigation team realized we were responsible for delivering a ‘priceless’ cargo of pristine cometary material samples from a comet’s coma,” said Potts. “These samples represent a glimpse back in time at the early formation of the solar system. There’s little doubt that new science discoveries will be made which will influence the direction of future space exploration.”

Written by Nancy Atkinson

Posted on by Fraser Cain

What’s Up This Week – January 16 – January 22, 2006

What's Up 2006

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

M44. Image credit: NOAO/AURA/NSF. Click to enlarge.
Monday, January 16 – Although the early rise of tonight’s Moon will hamper the Delta Cancrid meteor shower, be on the lookout for fast moving meteors appearing to radiate from an area just west of the “Beehive” – M44. It’s a minor shower, with a fall rate of about 4 per hour, but it’s fun to catch one!

While we’re watching, take a look at M44 with binoculars or a low power telescope. You’ll find it in the center of the triangle of bright stars, Pollux, Regulus, and Procyon, and it is usually visible to the unaided eye from dark sky locations. Better known as the “Beehive,” M44 shows several dozen stars through binoculars. Through the scope, the cluster reveals up to 100 stars! Of the 400 known members, most congregate in an elliptical “swarm” spanning 15 light-years. The “Beehive” is only slightly more distant than the Pleiades at 500 light-years away. Thanks to its advanced stellar evolution, it contains several red giants, leading astronomers to believe it is around 400 million years old.

After moonrise, have a look at the lunar surface as the terminator reaches the edge of Mare Crisium in the northeastern quarter. Depending on your viewing time, you may have the opportunity to spot small craters Alhazen and Hansen on its eastern edge. Look for a long “wrinkle” creasing Crisium’s smooth sands. Such lunar features are known as dorsae. Dorsa Tetyaev and Dorsa Harker come together along Mare Crisium’s eastern shore. Look for south-central Dorsa Termier and Dorsum Oppel along Crisium’s west bank. These frozen “waves” of lava are millions of years old.

Tuesday, January 17 – With time to spare before Moon rise tonight, let’s hunt down that “wascally wabbit” Lepus and have a look at M79. Let Alpha and Beta be your guide as you drop the same distance between them to the south for double star ADS3954 and this cool little globular cluster.

Discovered by Pierre M?chain in 1780, M79 is not large, nor bright, but is visible in binoculars. Large telescopes will find it well resolved with a rich core area. Around 50,000 light-years away, this particular globular is very low in variables and recedes from us at a “rabbit” speed of 118 miles per second. But, don’t worry – it will remain visible for a very long time!

Now, take a quick look at tonight’s Moon. The terminator has advanced through Mare Crisium and looks like a gigantic “bite” taken out of the lunar edge.

Wednesday, January 18 – If you are up before dawn, why not spend a moment looking at the sky? Although the Moon will still be bright, stay on watch for meteors belonging to the Coma Berenicid shower. The fall rate is very modest with only one or two per hour, but these are among the very fastest meteors known. Blazing through the atmosphere at 65 kilometers per second, the trails will point back to the Coma Berenices star cluster east of Leo.

Since we’ll have early dark skies, let’s have a look at a single star – R Leporis. Because it is variable, ranging in magnitude from 5.5 to 11.7, R may or may not be visible to the unaided eye tonight. Use a telescope, or binoculars, to locate it west of Mu. Look for a line of three dim stars and choose the centermost.

Most commonly known as “Hind’s Crimson Star,” this long term, pulsating red variable was discovered in 1845 by J.R. Hind. Its light changes by a factor of 250 times during its period of 432 days, but R Leporis can sometimes stall while brightening. As an old red star, R takes on a unique ruby-red color as it dims. To understand carbon stars, picture a kerosene lamp burning with its wick up high. This “high burn” causes the glass to smoke, dimming the light and changing the color. Although this example is simplistic, it hints at how carbon stars work. When it sloughs off the soot? It brightens again!

“Hind’s Crimson Star” is believed to be about 1500 light-years distant and moving slowing away from us at about 32 km per second. No matter how “bright” you find it tonight, its unusually deep red color makes it a true pleasure.

Thursday, January 19 – Johann Bode was born today in 1747. Bode publicized the Titus-Bode law, a nearly geometric progression of the distances of the planets from the Sun, and made a number of discoveries of deepsky studies objects. Also born today in 1851, was Jacobus Kapteyn. Kapteyn studied the distribution and motion of almost half a million stars and created the first modern model of the size and structure of the Milky Way Galaxy.

Tonight in celebration of them both, let’s have a first look at a pair of circumpolar galaxies known as “Bode’s Nebulae.” Discovered by Johann in 1774, the galaxies known as M81 and M82 were first described by him as “nebulous.” In Bode’s time, it was thought such patches were solar systems in formation, but by Kapteyn’s time in the late 1800’s, astronomers were beginning understand the mechanics of stellar motion in the Milky Way galaxy. While M81 and M82 are not in good sky position right now, you can still track them down in binoculars. Look for the bowl of the “Big Dipper” and draw an imaginary line from Phecda to Dubhe (the southeastern and northwestern stars) and extend it the same distance northwest. Fade ever so slightly toward Polaris and enjoy this bright pair of island universes sharing space in the night.

Friday, January 20 – Born this day in 1573 was Simon Mayr. Although Mayr’s name is not widely recognized, we know the names he has given to Jupiter’s satellites. During 1609 and 1610, Mayr was observing moons of Jupiter at about the same time as Galileo. Though discovery was credited to Galileo, Mayr was given the honor of naming them. If you’re up before dawn, look for Jupiter in the constellation Libra and see if you can spot Io, Ganymede, Callisto and Europa for yourself!

Early dark skies mean a chance for serious study, and tonight our target will be a challenge. Head towards Zeta Ceti and neighboring Chi Ceti. When you’ve identified Chi, power up and look north-northwest to locate small, 11.8 magnitude galaxy NGC 681. It might be small and faint, but it’s a great example of barred spiral seen near edge-on. Mid-sized scopes will see little detail, but large instruments reveal a broad equatorial dust lane. At a distance of 55 million light-years, this peculiar galaxy is a rare sight. All its stars move at the same orbital speed around the core – hinting at vast quantities of unseen, mysterious “dark matter!”

Saturday, January 21 – John Couch Adams was born today in 1792. Adams, along with Urbain Le Verrier, mathematically predicted the existence of Neptune. Also born today in 1908 was Bengt Stromgren – developer of the theory of ionization nebulae (H II regions). Tonight we’ll take a look at an ionization nebula as we return for a more in-depth look at M42.

Known as “The Great Orion Nebula,” let’s learn what makes it glow. M42 is a great cloud of gas spanning more than 20,000 times the size of our own solar system and its light is mainly florescent. For most observers, it appears to have a slight greenish color – caused by oxygen being stripped of electrons by radiation from nearby stars. At the heart of this immense region is an area known as the “Trapezium” – its four brightest stars form perhaps the most celebrated multiple star system in the night sky. The Trapezium itself belongs to a faint cluster of stars now approaching main sequence and resides in an area of the nebula known as the “Huygenian Region” (named after 17th century astronomer and optician Christian Huygens who first observed it in detail).

Buried amidst the bright ribbons and curls of this cloud of predominately hydrogen gas are many star forming regions. Appearing like “knots,” these Herbig-Haro objects are thought to be stars in the earliest stages of condensation. Associated with these objects are a great number of faint red stars and erratically luminous variables – young stars, possibly of the T Tauri type. There are also “flare stars,” whose rapid variations in brightness mean an ever changing view.

While studying M42, you’ll note the apparent turbulence of the area – and with good reason. The “Great Nebula’s” many different regions move at varying speeds. The rate of expansion at the outer edges may be caused by radiation from the very youngest stars present. Although M42 may have been luminous for as long as 23,000 years, it is possible that new stars are still forming, while others were ejected by gravitation. Known as “runaway” stars, we’ll look at these strange members later in detail. A tremendous X-ray source (2U0525-06) is quite near the Trapezium and hints at the possibility of a black hole present within M42!

Sunday, January 22 – With tonight’s dark skies let’s have a look at another “cloud in space” – M78. It is easily located around two finger-widths north-northeast of Alnitak. Despite being 8th magnitude, you’ll probably need a telescope to see it. M78 is actually a bright outcropping of an extended region of nebulosity (the Orion Complex) including M42, 43, NGC 1975-77-79, the Flame Nebula, and the Horsehead. There’s plenty of material for future starbirth here! Nicknamed “Casper the Friendly Ghost Nebula,” M78 was discovered by Pierre Mechain in 1780. It shines almost purely by reflection and is the brightest non-emission nebula observable by amateurs. For larger scopes, look at nearby nebula NGC 2071. Unlike M78, NGC 2071 is associated with a single 10th magnitude star instead of the pair that gives “Casper” his glowing eyes.

Thank you again to all the kind folks who have responded to “365 Days of SkyWatching”! May all your journeys be at light speed… ~Tammy Plotner.

Posted on by Fraser Cain

Huygens Celebrates a Year on Titan

An artist’s impression of Huygens at its landing site on Titan. Image credit: ESA Click to enlarge
One year ago this week, on January 14, 2005, the European Space Agency’s (ESA) Huygens probe reached the upper layer of Titan’s atmosphere and landed on the surface after a parachute descent 2 hours and 28 minutes later.

As part of the joint NASA/ESA/ASI mission to Saturn and its moons, the Huygens probe was sent from the Cassini spacecraft to explore Titan, Saturn’s largest moon. Titan’s organic chemistry may be like that of the primitive Earth around 4000 million years ago, and it may hold clues about how life began on our planet.

The Huygens mission has been an outstanding engineering and scientific success, one of the most complex and scientifically rewarding space missions to date.

The touchdown on the surface of Titan marked the farthest a man-made spacecraft has successfully landed away from Earth.

Clear images of the surface of Titan were obtained below an altitude of 40 kilometers (25 miles) — revealing an extraordinary world that resembled Earth in many respects, especially in meteorology, geomorphology and fluvial activity, but with different ingredients. The images show strong evidence for erosion due to liquid flows, possibly methane.

Huygens enabled studies of the atmosphere and surface, including the first in-situ sampling of the organic chemistry and the aerosols below 150 kilometers (93 miles). These confirmed the presence of a complex organic chemistry, which reinforces the idea that Titan is a promising place to observe the molecules that may have been the precursors of the building blocks of life on Earth.

Around 260 scientists and up to 10,000 engineers and other professionals from 19 countries overcame cross-cultural and multi-disciplinary differences to achieve an astonishing co-operation. ESA’s Huygens project scientist, Jean-Pierre Lebreton said, “This mission took two decades to accomplish and pushed the limits of our capabilities, whether scientific, technological or organisational. But the scientists and engineers used their skills and intelligence to overcome technical, political and celestial barriers to their goals.

“In the end, they triumphed spectacularly and, apart from the amazing scientific return, the mission should be an inspiration and a lesson for organisations of all kinds, in all sectors, of how people can work together.”

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA’s Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The Descent Imager/Spectral team is based at the University of Arizona, Tucson, Ariz.

Original Source: NASA/JPL/SSI News Release

Posted on by Fraser Cain

Dark Matter Galaxy?

Neutral hydrogen gas streams between NGC 4254 and VIRGOH1 21. Image credit: Arecibo Observatory. Click to enlarge
New evidence that VIRGOHI 21, a mysterious cloud of hydrogen in the Virgo Cluster 50 million light-years from the Earth, is a Dark Galaxy, emitting no star light, was presented today at the American Astronomical Society meeting in Washington, D. C. by an international team led by astronomers from the National Science Foundation’s Arecibo Observatory and from Cardiff University in the United Kingdom. Their results not only indicate the presence of a dark galaxy but also explain the long-standing mystery of its strangely stretched neighbour.

The new observations, made with the Westerbork Synthesis Radio Telescope in the Netherlands, show that the hydrogen gas in VIRGOHI 21 appears to be rotating, implying a dark galaxy with over ten billion times the mass of the Sun. Only one percent of this mass has been detected as neutral hydrogen – the rest appears to be dark matter.

But this is not all that the new data reveal. The results may also solve a long-standing puzzle about another nearby galaxy. NGC 4254 is lopsided, with one spiral arm much larger than the rest. This is usually caused by the influence of a companion galaxy, but none could be found until now – the team thinks VIRGOHI 21 is the culprit. Dr. Robert Minchin of Arecibo Observatory says; “The Dark Galaxy theory explains both the observations of VIRGOHI 21 and the mystery of NGC 4254.”

Gas from NGC 4254 is being torn away by the dark galaxy, forming a temporary link between the two and stretching the arm of the spiral galaxy. As the VIRGOH1 21 moves on, the two will separate and NGC 4254’s unusual arm will relax back to match its partner.

The team have looked at many other possible explanations, but have found that only the Dark Galaxy theory can explain all of the observations. As Professor Mike Disney of Cardiff University puts it, “The new observations make it even harder to escape the conclusion that VIRGOHI 21 is a Dark Galaxy.”

The team hope that this will be the first of many such finds. “We’re going to be searching for more Dark Galaxies with the new ALFA instrument at Arecibo Observatory,” explains Dr. Jon Davies of Cardiff University. “We hope to find many more over the next few years – this is a very exciting time!”

Original Source: PPARC News Release

Posted on by Fraser Cain

Black Holes Churn Up Interstellar Dust

NGC 0507 galaxy. Image credit: NASA Click to enlarge
Chandra images of 56 elliptical galaxies have revealed evidence for unsuspected turmoil. As this sample gallery of X-ray (blue & white) and optical (gray & white) images shows, the shapes of the massive clouds of hot gas that produce X-ray light in these galaxies differ markedly from the distribution of stars that produce the optical light.

Except for rare cases, most violent activity in isolated elliptical galaxies was thought to have stopped long ago. Elliptical galaxies contain very little cool gas and dust, and far fewer massive young stars which explode as supernovas. Thus it was expected that the hot interstellar gas would have settled into an equilibrium shape similar to, but rounder than that of the stars.

Surprisingly, this study of elliptical galaxies shows that the distribution of hot gas has no correlation with the optical shape. A powerful source of energy must be pushing the hot gas around and stirring it up every hundred million years or so.

Although supernovas are a possible energy source, a more probable cause has been identified. The scientists detected a correlation between the shape of the hot gas clouds and the power produced at radio wavelengths by high-energy electrons. This power source can be traced back to the supermassive black hole in the galaxies’ central regions.

Repetitive explosive activity fueled by the infall of gas into the central supermassive black hole is known to occur in giant elliptical galaxies located in galaxy clusters. Scientists’ analysis of the Chandra data indicates that the same phenomena are occurring in isolated elliptical galaxies as well.

Original Source: Chandra X-Ray Observatory

Posted on by Fraser Cain

Magnetic Slinky in Space

Helical magnetic field wrapping around molecular cloud in Orion. Image credit: NRAO/AUI/NSF Click to enlarge
Astronomers announced today (Thursday, Jan. 12) what may be the first discovery of a helical magnetic field in interstellar space, coiled like a snake around a gas cloud in the constellation of Orion.

“You can think of this structure as a giant, magnetic Slinky wrapped around a long, finger-like interstellar cloud,” said Timothy Robishaw, a graduate student in astronomy at the University of California, Berkeley. “The magnetic field lines are like stretched rubber bands; the tension squeezes the cloud into its filamentary shape.”

Astronomers have long hoped to find specific cases in which magnetic forces directly influence the shape of interstellar clouds, but according to Robishaw, “telescopes just haven’t been up to the task … until now.”

The findings provide the first evidence of the magnetic field structure around a filamentary-shaped interstellar cloud known as the Orion Molecular Cloud.

Today’s announcement by Robishaw and Carl Heiles, UC Berkeley professor of astronomy, was made during a presentation at the American Astronomical Society meeting in Washington, D.C.

Interstellar molecular clouds are the birthplaces of stars, and the Orion Molecular Cloud contains two such stellar nurseries – one in the belt and another in the sword of the Orion constellation. Interstellar clouds are dense regions embedded in a much lower-density external medium, but the “dense” interstellar clouds are, by Earth standards, a perfect vacuum. In combination with magnetic forces, it’s the large size of these clouds that makes enough gravity to pull them together to make stars.

Astronomers have known for some time that many molecular clouds are filamentary structures whose shapes are suspected to be sculpted by a balance between the force of gravity and magnetic fields. In making theoretical models of these clouds, most astrophysicists have treated them as spheres rather than finger-like filaments. However, a theoretical treatment published in 2000 by Drs. Jason Fiege and Ralph Pudritz of McMaster University suggested that when treated properly, filamentary molecular clouds should exhibit a helical magnetic field around the long axis of the cloud. This is the first observational confirmation of this theory.

“Measuring magnetic fields in space is a very difficult task,” Robishaw said, “because the field in interstellar space is very weak and because there are systematic measurement effects that can produce erroneous results.”

The signature of a magnetic field pointing towards or away from the Earth is known as the Zeeman effect and is observed as the splitting of a radio frequency line.

“An analogy would be when you’re scanning the radio dial and you get the same station separated by a small blank space,” Robishaw explained. “The size of the blank space is directly proportional to the strength of the magnetic field at the location in space where the station is being broadcast.”

The signal, in this case, is being broadcast at 1420 MHz on the radio dial by interstellar hydrogen – the simplest and most abundant atom in the universe. The transmitter is located 1750 light years away in the Orion constellation.

The antenna that received these radio transmissions is the National Science Foundation’s Green Bank Telescope (GBT), operated by the National Radio Astronomy Observatory. The telescope, 148 meters (485 feet) tall and with a dish 100 meters (300 feet) in diameter, is located in West Virginia where 13,000 square miles have been set aside as the National Radio Quiet Zone. This allows radio astronomers to observe radio waves coming from space without interference from manmade signals.

Using the GBT, Robishaw and Heiles observed radio waves along slices across the Orion Molecular Cloud and found that the magnetic field reversed its direction, pointing towards the Earth on the upper side of the cloud and away from it on the bottom. They used previous observations of starlight to inspect how the magnetic field in front of the cloud is oriented. (There is no way to gain information about what’s happening behind the cloud since the cloud is so dense that neither optical light nor radio waves can penetrate it.) When they combined all available measurements, the picture emerged of a corkscrew pattern wrapping around the cloud.

“These results were incredibly exciting to me for a number of reasons,” Robishaw said. “There’s the scientific result of a helical field structure. Then, there’s the successful measurement: This type of observation is very difficult, and it took dozens of hours on the telescope just to understand how this enormous dish responds to the polarized radio waves that are the signature of a magnetic field.”

The results of these investigations suggested to Robishaw and Heiles that the GBT is not only unparalleled among large radio telescopes for measuring magnetic fields, but it is the only one that can reliably detect weak magnetic fields.

Heiles cautioned that there is one possible alternative explanation for the observed magnetic field structure: The field might be wrapped around the front of the cloud.

“It’s a very dense object,” Heiles said. “It also happens to lie inside the hollowed-out shell of a very large shock wave that was formed when many stars exploded in the neighboring constellation of Eridanus.”

That shock wave would have carried the magnetic field along with it, he said, “until it reached the molecular cloud! The magnetic field lines would get stretched across the face of the cloud and wrapped around the sides. The signature of such a configuration would be very similar to what we see now. What really convinces us that this is a helical field is that there seems to be a constant pitch angle to the field lines across the face of the cloud.”

However, the situation can be clarified by further research. Robishaw and Heiles plan to extend their measurements in this cloud and others using the GBT. They will also collaborate with Canadian colleagues to use starlight to measure the field across the face of this and other clouds.

“The hope is to provide enough evidence to understand what the true structure of this magnetic field is,” said Heiles. “A clear understanding is essential in order to truly understand the processes by which molecular clouds form stars in the Milky Way galaxy.”

The research was supported by the National Science Foundation.

UC Berkeley News Release

Posted on by Fraser Cain

The Next Orion Nebula

Future astronomers will see this nebula in the sky. Image credit: David A. Aguilar. Click to enlarge.
Astronomers announced today that they have found the next Orion Nebula. Known as W3, this glowing gas cloud in the constellation Cassiopeia has just begun to shine with newborn stars. Shrouds of dust currently hide its light, but this is only a temporary state. In 100,000 years – a blink of the eye in astronomical terms – it may blaze forth, delighting stargazers around the world and becoming the Grand Nebula in Cassiopeia..

“The Grand Nebula in Cassiopeia will appear in our sky just as the Great Nebula in Orion fades away,” said Smithsonian astronomer Tom Megeath (Harvard-Smithsonian Center for Astrophysics), who made the announcement in a press conference at the 207th meeting of the American Astronomical Society. “Even better, its home constellation is visible year-round from much of the northern hemisphere.”

The Orion Nebula is one of the most famous and easily viewed deep-sky sights. It holds special significance for researchers as the nearest region of massive star formation.

The star formation process begins in a dark cloud of cold gas, where small lumps of material begin to contract. Gravity draws the gas into hot condensations that ignite and become stars. The most massive stars produce hot winds and intense light that blast away the surrounding cloud. But during the process of destruction, stellar radiation lights up the cloud, creating a bright nebula for stargazers to admire.

“Orion may seem very peaceful on a cold winter night, but in reality it holds very massive, luminous stars that are destroying the dusty gas cloud from which they formed,” said Megeath. “Eventually, the cloud of material will disperse and the Orion Nebula will fade from our sky.”

Orion’s Trapezium
Of special interest to Megeath is a system of four bright, massive stars at the center of Orion known as the Trapezium. These stars bathe the entire nebula with powerful ultraviolet radiation, lighting up nearby gas. Even a modest telescope reveals the Trapezium surrounded by billowing ripples of matter gleaming eerily across the vastness of space. Yet the Trapezium is only the tip of the iceberg, surrounded by more than 1000 faint, low-mass stars similar to the Sun.

“The question we want to answer is: why are these massive stars sitting in the center of the cluster?” said Megeath.

There are two competing theories to explain the Trapezium’s location. One holds that the Trapezium stars formed apart from each other but descended to the center of the cluster, ejecting a spray of low-mass stars in the process. The other leading theory is that the Trapezium stars formed together in the center of the cluster and have not moved from their birthplace.

“Obviously, we can’t go back in time and look at the Trapezium when it was still forming, so we try to find younger examples in the sky,” explained Megeath.

Such proto-Trapeziums would still be buried in their birth cocoons, hidden to visible-light telescopes but detectable by radio and infrared telescopes. Searches at those longer wavelengths have identified many regions where massive stars are forming, but could not determine whether the protostars were alone or in collections of four or more stars that could be considered Trapeziums.

Cassiopeia’s Trapezium
Megeath and his colleagues examined one such protostellar clump in W3 using the NICMOS instrument on NASA’s Hubble Space Telescope and the National Science Foundation’s Very Large Array. They discovered that the object, which was thought to be a binary star, actually contained four or five young, massive protostars, making it a likely proto-Trapezium.

These protostars are so young that they appear to be still growing by accreting gas from the surrounding cloud. All of the stars crowd into a small area only about 500 billion miles across (just under one-tenth of a light-year), making this cluster more than 100,000 times denser than stars in the Sun’s neighborhood. This suggests that the massive stars in Orion’s Trapezium formed together in the center of the cluster.

The same physical processes that have carved the Orion Nebula now are molding the W3 nebula. The massive stars in this compact group are starting to eat away at the surrounding gas with ultraviolet radiation and fast stellar outflows. Eventually, they will destroy their dense cocoon and emerge to form a new Trapezium in the center of W3. However, the final form of the nebula and the time that it will reach maximum brilliance are uncertain.

“Who knows, in 100,000 years the emerging Grand Nebula in Cassiopeia may replace the fading Orion Nebula as a favorite object for amateur astronomers,” said Megeath. “In the meantime, I think it will be a favorite target for professional astronomers trying to solve the riddle of massive star formation.”

Megeath’s colleagues on this work were Thomas Wilson (European Southern Observatory) and Michael Corbin (Arizona State University).

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

Original Source: CfA News Release