Diamond Worlds Could Exist

Image credit: NASA
Some extrasolar planets may be made substantially from carbon compounds, including diamond, according to a report presented this week at the conference on extrasolar planets in Aspen, Colorado. Earth, Mars and Venus are “silicate planets” consisting mostly of silicon-oxygen compounds. Astrophysicists are proposing that some stars in our galaxy may host “carbon planets” instead.

“Carbon planets could form in much the same way as do certain meteorites in our solar system, the carbonaceous chondrites,” said Dr. Marc J. Kuchner of Princeton University, making the report in Aspen together with Dr. Sara Seager of the Carnegie Institute of Washington. “These meteorites contain large quantities of carbon compounds such as carbides, organics, and graphite, and even the occasional tiny diamond.” Imagine such a meteorite the size of a planet, and you are picturing a carbon planet.

Planets like the Earth are thought to condense from disks of gas orbiting young stars. In gas with extra carbon or too little oxygen, carbon compounds like carbides and graphite condense out instead of silicates, possibly explaining the origin of carbonaceous chondrites and suggesting the possibility of carbon planets. Any condensed graphite would change into diamond under the high pressures inside the carbon planets, potentially forming diamond layers inside the planets many miles thick.

Some of the already known low- and intermediate-mass extrasolar planets may be carbon planets, which should easily survive at high temperatures near a star if they have the mass of Neptune. Carbon planets would probably consist mostly of carbides, thought they may have iron cores and substanial atmospheres. Carbides are a kind of ceramic used to line the cylinders of motorcycle engines among other things.

The planets orbiting the pulsar PSR 1257+12 are good candidates for carbon planets; they may have formed from the disruption of a star that produced carbon as it aged. So are planets located near the center of the Galaxy, where stars are more carbon-rich than the sun, on average. Slowly, the galaxy as a whole is becoming more carbon-rich; in the future, all planets formed may be carbon planets.

“There’s no reason to think that extrasolar planets will be just like the planets in the solar system.” says Kuchner. “The possibilities are startling.”

Kuchner added, “NASA’s future Terrestrial Planet Finder (TPF) mission may be able to spot these planets.” The spectra of these planets should lack water, and instead reveal carbon monoxide, methane, and possibly long-chain carbon compounds synthesized photochemically in their atmospheres. The surfaces of carbon planets may be covered with a layer of long-chain carbon compounds–in other words, something like crude oil or tar.

The first TPF telescope, an optical telescope several times the size of the Hubble Space Telescope is scheduled to launch in 2015. The TPF missions are designed to search for planets like the Earth and determine whether they might be suitable for life.

Original Source: NASA Astrobiology Story

Black Holes Manage Galactic Growth

Using a new computer model of galaxy formation, researchers have shown that growing black holes release a blast of energy that fundamentally regulates galaxy evolution and black hole growth itself. The model explains for the first time observed phenomena and promises to deliver deeper insights into our understanding of galaxy formation and the role of black holes throughout cosmic history, according to its creators. Published in the Feb. 10 issue of Nature, the results were generated by Carnegie Mellon University astrophysicist Tiziana Di Matteo and her colleagues while at the Max Planck Institut fur Astrophysik in Germany. Di Matteo?s collaborators include Volker Springel at Max-Planck Institut for Astrophysics and Lars Hernquist at Harvard University.
“In recent years, scientists have begun to appreciate that the total mass of stars in today?s galaxies corresponds directly to the size of a galaxy?s black hole, but until now, no one could account for this observed relationship,” said Di Matteo, assistant professor of physics at Carnegie Mellon. “Using our simulations has given us a completely new way to explore this problem.”

The key to the researchers? breakthrough was incorporating calculations for black hole dynamics into a computational model of galaxy formation.

As galaxies formed in the early universe, they likely contained small black holes at their centers. In the standard scenario of galaxy formation, galaxies grow by coming together with one another by the pull of gravity. In the process, the black holes at their center merge together and quickly grow to reach their observed masses of a billion times that of the Sun; hence, they are called supermassive black holes. Also at the time of merger, the majority of stars form from available gas. Today?s galaxies and their central black holes must be the result of a series of such events.

Di Matteo and her colleagues simulated the collision of two nascent galaxies and found that when the two galaxies came together, their two supermassive black holes merged and initially consumed the surrounding gas. But this activity was self-limiting. As the remnant galaxy?s supermassive black hole sucked up gas, it powered a luminescent state called a quasar. The quasar energized the surrounding gas to such a level that it was blown away from the vicinity of the supermassive black hole to the outside of the galaxy. Without nearby gas, the galaxy?s supermassive black hole could not “eat” to sustain itself and became dormant. At the same time, gas was no longer available to form any more stars.

“We?ve discovered that the energy released by black holes during a quasar phase powers a strong wind that prevents material from falling into the black hole,” Springel said. “This process inhibits further black hole growth and shuts off the quasar, just as star formation stops inside a galaxy. As a result, the black hole mass and the mass of stars in a galaxy are closely linked. Our results also explain for the first time why the quasar lifetime is such a short phase compared to the life of a galaxy.”

In their simulations, Di Matteo, Springel and Hernquist found that the black holes in small galaxies self-limit their growth more effectively than in those in larger galaxies. A smaller galaxy contains smaller amounts of gas so that a small amount of energy from the black hole can quickly blow this gas away. In a large galaxy, the black hole can reach a greater size before its surrounding gas is energized enough to stop falling in. With their gas quickly spent, smaller galaxies make fewer stars. With a longer-lived pool of gas, larger galaxies make more stars. These findings match the observed relation between black hole size and the total mass of stars in galaxies.

“Our simulations demonstrate that self-regulation can quantitatively account for observed facts associated with black holes and galaxies,” said Hernquist, professor and chair of astronomy in Harvard?s Faculty of Arts and Sciences. “It provides an explanation for the origin of the quasar lifetime and should allow us to understand why quasars were more plentiful in the early universe than they are today.”

“With these computations, we now see that black holes must have an enormous impact on the way galaxies form and evolve,” Di Matteo said. “The successes obtained so far will allow us to implement these models within larger simulated universes, so that we can understand how large populations of black holes and galaxies influence each other in a cosmological context.”

The team ran their simulations with the extensive computing resources of the Center for Parallel Astrophysical Computing at the Harvard-Smithsonian Center for Astrophysics and at the Rechenzentrum der Max-Planck-Gesellschaft in Garching.

Original Source: Max Planck Institute News Release

Death Star Mimas’ Herschel Crater

Saturn’s moon Mimas has many large craters, but its Herschel crater dwarfs all the rest. This large crater 130 kilometers wide (80 miles) has a prominent central peak, seen here almost exactly on the terminator. This crater is the moon’s most prominent feature, and the impact that formed it probably nearly destroyed Mimas. Mimas is 398 kilometers (247 miles) across.

This view is predominantly of the leading hemisphere of Mimas. The image has been rotated so that north on Mimas is up.

This image was taken with the Cassini spacecraft narrow angle camera on Jan. 16, 2005, at a distance of approximately 213,000 kilometers (132,000 miles) from Mimas and at a Sun-Mimas-spacecraft, or phase, angle of 84 degrees. Resolution in the original image was about 1.3 kilometers (0.8 miles) per pixel. A combination of spectral filters sensitive to ultraviolet and polarized light was used to obtain this view. Contrast was enhanced and the image was magnified by a factor of two to aid visibility.

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

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . For images visit the Cassini imaging team home page http://ciclops.org .

Original Source: NASA/JPL/SSI News Release

What Did Galileo See?

A replica of the earliest surviving telescope attributed to Galileo Galilei, on display at the Griffith Observatory. Credit: Wikipedia Commons/Mike Dunn

By the time Galileo took eye to eyepiece in Padua Italy in 1609, he had already begun a life-long quest to understand the natural world around him. At his father’s behest, Gailieo gave up his youthful aspirations to join the Camaldolese Order as a monk and began training in medicine. Before completing his medical studies however, Galileo’s strong interest in the laws of nature (along with a little intercession by one of his teachers in mathematics) overcame his fathers insistence and he embraced mathematics.

Over the next quarter century Galileo made numerous investigations into the mechanics of motion and weight. Early on he was intrigued by Archimedes investigations into specific gravity and published a work entitled: “La Balancitta” (or “The Little Weight”). Galileo’s bent was as scientific as mathematical, he suggested methods of testing the behavior of falling bodies using inclined planes. (Although it is unlikely that he ever dropped objects from the famed “Leaning Tower of Pisa”.)

By the year 1609 Galileo had spent nearly two decades ensconced as a lecturer on mathematics and physical sciences at the University of Padua. He is said to have described this period as one of the most personally fulfilling years of his life. But the quiet joys of teaching and raising a family of three children were poised for change. And that change came in the form of a fateful letter describing a spyglass demonstrated by a Dutchman visiting Venice (located some 40 kms west of the university).

Based on a scant description of the spyglass workings, Galileo concluded that its main principle was that of refraction. Obtaining “off-the-shelf” lenses normally for spectacle use, he soon possessed a 4x instrument and it wasn’t long thereafter that he had personally ground a lens set and crafted a telescope of twice that magnification. By the Spring of 1610, Galileo had published the first telescopic “observing reports” describing denizens of the night sky. And in that report (Sidereus Nuncius – The Starry Messenger) Galileo himself lists a few of his most startling discoveries:

“With the aid of this new instrument one looks upon the face of the Moon, the expanse of the Milky Way, innumerable fixed stars, faint nebulosities and asterisms, and the four wandering stars attending Jupiter never before seen.”-1

Recognizing the significance of these discoveries Galileo goes on to say:

“Great things embodying the spirit of truth based on observation and contemplation of nature do I propose in this short treatise. Large, I say, and for the clarification of truth, based on an innovation never heard throughout the centuries, and finally I extoll the instrument by which means these same things have been revealed to our perception.”

There can be no doubt that Galileo’s early adoption of the recently invented spyglass for astronomical purposes marked a major departure toward the way we now view the world. For before Galileo’s era the heavens and the Earth were not in accord. The bulk of the thinking going on prior to Galileo was scholastic in nature. Truth depended on the words of the ancients – words which carried greater weight of authority than natural law and behavior. It was the era of faith – not science – that Galileo was born into. But his observations built a bridge between Terrum et Coelum. Earth and sky became part of a single natural order. The telescope could demonstrate to anyone with an open mind that there was more to all things than could be conceived of by the great minds of the past. Nature had begun to instruct the hearts and minds of humanity…

But let us speak no more of Earth-shaking events. What did Galileo actually see in the early months of the year 1610?

Lacking a background in Latin is no hindrance to furthering our investigation, for “the Starry Messenger” himself left many fine sketches (a few which are seen in the above composite image).

Of course, any amateur astronomer of the today can do no better than to begin with the Moon. Using a telescope is no easy matter. Sweeping the sky unsteadily at high magnifications to find anything in the heavens can be very frustrating to the neophyte to our High Art and Science. Of course, Galileo’s first telescope was very low power and this simplified things. But his later instruments always included a second smaller “finder scope” to simplify astro-navigation. Here are some of Galileo’s descriptions of the Moon:

“Most beautiful and admirable is it to see the Moon’s luminous form,… At nearly thirty diameters – some 900 times greater in region – anyone can perceive that the Moon is not covered with a smooth and uniform surface but in fact reveals great mountainous shelves, deep cavities, and gorges just like those of the Earth.”

Even during the winter the Milky Way can be seen – a faint gossamer of light attending Cassiopeia and Perseus to the north then plummeting south east of Orion – the Hunter, into Monoceros – the Unicorn. Again The Starry Messenger speaks:

“Moreover let us not underestimate the questions surrounding the Milky Way. For it has revealed to the senses its essence (through the turning of our instrument upon it). And in so doing out of its cloudy substance numerous stars are called forth.”

But in terms of Galileo’s own estimation his observations of the four Jupiterean satellites evoked the greatest of significances:

“By far and exceeding every other wonder, and mainly promoted for the contemplation of all astronomers and philosophers, is the discovery of four wandering stars. For I propose that they – like Venus and Mercury around the Sun – have revolutions around a conspicuous star among the known wanderers. And in their lesser wanderings they may precede the greater – sometimes before it and sometimes after – never going beyond some pre-determined limits.”

Galileo also went on to detect sun spots and the phases of Venus. The Venusian phases, in particular conclusively demonstrated the heliocentrism conceived by Copernicus and mathematically described by Johan Kepler of Galileo’s own time and correspondence.

Of course Galileo was large enough in his perception to realize that these few initial discoveries were but only the beginnings of a beginning for the telescope as an instrument and astronomy as a whole for he goes on to say:

“Perhaps other miraculous things from both myself and others will be discovered in the future aided by this instrument…”

Galileo was wrong – there was no “perhaps” about it…

-1 This and later quotations ascribed to Galileo are re-interpretations of an Italian to English Babelfish translation of Siderius Nuncius by the author.

About The Author:
Inspired by the early 1900’s masterpiece: “The Sky Through Three, Four, and Five Inch Telescopes”, Jeff Barbour got a start in astronomy and space science at the age of seven. Currently Jeff devotes much of his time observing the heavens and maintaining the website Astro.Geekjoy.

Huygens Wind Data Released

Image credit: ESA
Using a global network of radio telescopes, scientists have measured the speed of the winds faced by Huygens during its descent through the atmosphere of Titan.

This measurement could not be done from space because of a configuration problem with one of Cassini?s receivers. The winds are weak near the surface and increase slowly with altitude up to about 60 km, becoming much rougher higher up where significant vertical wind shear may be present.

Preliminary estimates of the wind variations with altitude on Titan have been obtained from measurements of the frequency of radio signals from Huygens, recorded during the probe?s descent on 14 January 2005. These ?Doppler? measurements, obtained by a global network of radio telescopes, reflect the relative speed between the transmitter on Huygens and the receiver on the Earth.

Winds in the atmosphere affected the horizontal speed of the probe?s descent and produced a change in the frequency of the signal received on Earth. This phenomenon is similar to the commonly heard change in pitch of a siren on a speeding police car.

Leading the list of large radio antennas involved in the programme were the NRAO Robert C. Byrd Green Bank Telescope (GBT) in West Virginia, USA, and the CSIRO Parkes Radio Telescope in Australia. Special instrumentation designed for detection of weak signals was used to measure the ?carrier? frequency of the Huygens radio signal during this unique opportunity.

The initial detection, made with the ?Radio Science Receivers? on loan from NASA?s Deep Space Network, provided the first unequivocal proof that Huygens had survived the entry phase and had begun its radio relay transmission to Cassini.

The very successful signal detection on Earth provided a surprising turnabout for the Cassini-Huygens Doppler Wind Experiment (DWE), whose data could not be recorded on the Cassini spacecraft due to a commanding error needed to properly configure the receiver.

?Our team has now taken a significant first step to recovering the data needed to fulfil our original scientific goal, an accurate profile of Titan’s winds along the descent trajectory of Huygens,? said DWE?s Principal Investigator Dr Michael Bird (University of Bonn, Germany).

The ground-based Doppler measurements were carried out and processed jointly by scientists from the NASA Jet Propulsion Laboratory (JPL, USA) and the Joint Institute for VLBI in Europe (JIVE, The Netherlands) working within the DWE team.

Winds on Titan are found to be flowing in the direction of Titan’s rotation (from west to east) at nearly all altitudes. The maximum speed of roughly 120 metres per second (430 km/h) was measured about ten minutes after the start of the descent, at an altitude of about 120 km. The winds are weak near the surface and increase slowly with altitude up to about 60 km.

This pattern does not continue at altitudes above 60 km, where large variations in the Doppler measurements are observed. Scientists believe that these variations may arise from significant vertical wind shear. That Huygens had a rough ride in this region was already known from the science and engineering data recorded on board Huygens.

?Major mission events, such as the parachute exchange about 15 minutes into the atmospheric flight and impact on Titan at 13:45 CET, produced Doppler signatures that we can clearly identify in the data,? Bird said.

At present, there exists an approximately 20-minute interval with no data between the measurements at GBT and Parkes. This gap in Doppler coverage will eventually be closed by data from other radio telescopes which are presently being analysed. In addition, the entire global set of radio telescopes performed Very Long Baseline Interferometry (VLBI) recordings of the Huygens signal to determine the probe?s precise position during the descent.

?This is a stupendous example of the effectiveness of truly global scientific co-operation,? said Jean-Pierre Lebreton, ESA Huygens Project Scientist. ?By combining the Doppler and VLBI data we will eventually obtain an extremely accurate three-dimensional record of the motion of Huygens during its mission at Titan,? he concluded.

Original Source: ESA News Release

Northern Saturn is a Little Blue

Colorful new images from the Cassini spacecraft show that Saturn’s northern hemisphere has a case of the blues.

In the first image, the icy moon Mimas is set against a dazzling and dramatic portrait of Saturn’s azure northern hemisphere and the shadows of its rings. A second image shows Saturn’s northern polar region is a dim blue.

The new images are available at http://www.nasa.gov/cassini, http://saturn.jpl.nasa.gov and http://ciclops.org.

The blue color of Saturn’s northern latitudes may to be linked to the apparently cloud-free nature of the upper atmosphere there. A precise understanding of the phenomenon may come from further study by Cassini imaging scientists.

In the first of these colorful views, Mimas moves in its orbit against the blue backdrop of Saturn’s atmosphere, which is draped by sweeping shadows cast by the rings. A few large craters are visible on Mimas, giving the icy moon a dimpled appearance.

The second view shows Saturn’s northern polar region, where shadows cast by the rings surrounding the pole appear as dark bands. The ring shadows at higher latitudes correspond to locations on the ring plane that are farther from the planet – in other words, the northernmost ring shadow in this view is cast by the outer edge of Saturn’s A ring. Spots of bright clouds also are visible throughout the region.

The view of Saturn and Mimas was taken by the Cassini spacecraft’s narrow angle camera on Jan. 18, 2005, at a distance of approximately 1.4 million kilometers (870,000 miles) from Saturn. The view of Saturn’s northern polar region was taken with Cassini’s wide angle camera on Dec. 14, 2004, at a distance of 719,200 kilometers (446,900 miles) from Saturn.

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 imaging team is based at the Space Science Institute, Boulder, Colo.

Original Source: NASA/JPL News Release

Mini Solar System Around a Brown Dwarf

Moons circle planets, and planets circle stars. Now, astronomers have learned that planets may also circle celestial bodies almost as small as planets.

NASA’s Spitzer Space Telescope has spotted a dusty disk of planet-building material around an extraordinarily low-mass brown dwarf, or “failed star.” The brown dwarf, called OTS 44, is only 15 times the mass of Jupiter. Previously, the smallest brown dwarf known to host a planet-forming disk was 25 to 30 times more massive than Jupiter.

The finding will ultimately help astronomers better understand how and where planets — including rocky ones resembling our own — form.

“There may be a host of miniature solar systems out there, in which planets orbit brown dwarfs,” said Dr. Kevin Luhman, lead author of the new study from the Harvard-Smithsonian Center for Astrophysics, Cambridge, Mass. “This leads to all sorts of new questions, like ‘Could life exist on such planets?’ or ‘What do you call a planet circling a planet-sized body? A moon or a planet?'”

Brown dwarfs are something of misfits in the astronomy world. These cool orbs of gas have been called both failed stars and super planets. Like planets, they lack the mass to ignite and produce starlight. Like stars, they are often found alone in space, with no parent body to orbit.

“In this case, we are seeing the ingredients for planets around a brown dwarf near the dividing line between planets and stars. This raises the tantalizing possibility of planet formation around objects that themselves have planetary masses,” said Dr. Giovanni Fazio, an astronomer at the Harvard Smithsonian Center for Astrophysics and a co-author of the new study.

The results were presented today at the Planet Formation and Detection meeting at the Aspen Center for Physics, Aspen, Colo., and will be published in the Feb. 10th issue of The Astrophysical Journal Letters.

Planet-forming, or protoplanetary, disks are the precursors to planets. Astronomers speculate that the disk circling OTS 44 has enough mass to make a small gas giant planet and a few Earth-sized, rocky ones. This begs the question: Could a habitable planet like Earth sustain life around a brown dwarf?

“If life did exist in this system, it would have to constantly adjust to the dwindling temperatures of a brown dwarf,” said Luhman. “For liquid water to be present, the planet would have to be much closer to the brown dwarf than Earth is to our Sun.”

“It’s exciting to speculate about the possibilities for life in such as system, of course at this point we are only beginning to understand the unusual circumstances under which planets arise,” he added.

Brown dwarfs are rare and difficult to study due to their dim light. Though astronomers recently reported what may be the first-ever image of a planet around a brown dwarf called 2M1207, not much is understood about the planet-formation process around these odd balls of gas. Less is understood about low-mass brown dwarfs, of which only a handful are known.

OTS 44 was first discovered about six months ago by Luhman and his colleagues using the Gemini Observatory in Chile. The object is located 500 light-years away in the Chamaeleon constellation. Later, the team used Spitzer’s highly sensitive infrared eyes to see the dim glow of OTS 44’s dusty disk. These observations took only 20 seconds. Longer searches with Spitzer could reveal disks around brown dwarfs below 10 Jupiter masses.

Other authors of this study include Dr. Paola D’Alessia of the Universidad Nacional Autonoma de Mexico; and Drs. Nuria Calvet, Lori Allen, Lee Hartmann, Thomas Megeath and Philip Myers of the Harvard-Smithsonian Center for Astrophysics.

NASA’s Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer Space Telescope mission for NASA’s Science Mission Directorate, Washington, D.C. Science operations are conducted at the Spitzer Science Center, Pasadena, Calif. JPL is a division of Caltech. The infrared array camera, which spotted the protoplanetary disk around OTS 44, was built by NASA Goddard Space Flight Center, Greenbelt, Md.; its development was led by Fazio.

Original Source: Spitzer News Release

Smallest Extrasolar Planet Found

Penn State’s Alex Wolszczan, the discoverer in 1992 of the first planets ever found outside our solar system, now has discovered with Caltech’s Maciej Konacki the smallest planet yet detected,in that same far-away planetary system. Immersed in an extended cloud of ionized gas, the new planet orbits a rapidly spinning neutron star called a pulsar. The discovery, to be announced during a press conference at a meeting concerning planetary formation and detection in Aspen, Colorado, on 7 February, yields an astonishingly complete description of the pulsar planetary system and confirms that it is remarkably like a half-size version of our own solar system ? even though the star these planets orbit is quite different from our Sun.

“Despite the extreme conditions that must have existed at the time these planets were forming, Nature has managed to create a planetary system that looks like a scaled-down copy of our own inner solar system,” Wolszczan reports. The star at the center of this system is a pulsar named PSR B1257+12 ? the extremely dense and compact neutron star left over from a massive star that died in a violent explosion 1,500 light years away in the constellation Virgo.

Wolszczan and his colleagues earlier had discovered three terrestrial planets around the pulsar, with their orbits in an almost exact proportion to the spacings between Mercury, Venus, and Earth. The newly discovered fourth planet has an orbit approximately six times larger than that of the third planet in the system, which Konacki says is amazingly close to the average distance from our Sun to our solar system’s asteroid belt, located between the orbits of Mars and Jupiter.

“Because our observations practically rule out a possible presence of an even more distant, massive planet or planets around the pulsar, it is quite possible that the tiny fourth planet is the largest member of a cloud of interplanetary debris at the outer edge of the pulsar’s planetary system, a remnant of the original protoplanetary disk that created the three inner planets,” Wolszczan explains. The small planet, about one-fifth of the mass of Pluto, may occupy the same outer-boundary position in its planetary system as Pluto does in our solar system. “Surprisingly, the planetary system around this pulsar resembles our own solar system more than any extrasolar planetary system discovered around a Sun-like star,” Konacki says.

Fifteen years ago, before Wolszczan’s discovery of the first extrasolar planets, astronomers did not seriously entertain the idea that planets could survive around pulsars because they would have been blasted with the unimaginable force of the radiation and remnants of their exploding parent star. Since then, Wolszczan, Konacki, and colleagues have gradually been unraveling the mysteries of this system of pulsar planets, using the Arecibo radio telescope in Puerto Rico to collect and analyze pulsar-timing data. “We feel now, with this discovery, that the basic inventory of this planetary system has been completed,” Wolszczan says.

These discoveries have been possible because pulsars, especially those with the fastest spin, behave like very accurate clocks. “The stability of the repetition rate of the pulsar pulses compares favorably with the precision of the best atomic clocks constructed by humans,” Konacki explains. Measurements of the pulse arrival times, called pulsar timing, give astronomers an extremely precise method for studying the physics of pulsars and for detecting the phenomena that occur in a pulsar’s environment.

“A pulsar wobble due to orbiting planets manifests itself by variations in the pulse arrival times, just like a stellar wobble is detectable with the well-known Doppler effect so successfully used by optical astronomers to identify planets around nearby stars by the shifts of their spectral lines,” Wolszczan explains. “An important advantage of the fantastic stability of the pulsar clocks, which achieve precisions better than one millionth of a second, is that this method allows us to detect planets with masses all the way down to those of large asteroids.”

The very existence of the pulsar planets may represent convincing evidence that Earth-mass planets form just as easily as do the gas giants that are known to exist around more than 5 percent of the nearby Sun-like stars. However, Wolszczan says, “the message carried by the pulsar planets may equally well be that the formation of Earth-like planets requires special conditions, making such planets a rarity. For example, there is growing evidence that a nearby supernova explosion may have played an important role in our solar system’s formation.” Future space observatories, including the Kepler and the Space Interferometry Missions, and the Terrestrial Planet Finder, will play a decisive role in making a distinction between these fundamental alternatives.

ESA Will Risk Deploying MARSIS

The European Space Agency has given the green light for the MARSIS radar on board its Mars Express spacecraft to be deployed during the first week of May. Assuming that this operation is successful, the radar will finally start the search for subsurface water reservoirs and studies of the Martian ionosphere.

ESA’s decision to deploy MARSIS follows eight months of intensive computer simulations and technical investigations on both sides of the Atlantic. These were to assess possible harmful boom configurations during deployment and to determine any effects on the spacecraft and its scientific instruments.

The three radar booms of MARSIS were initially to have been deployed in April 2004, towards the end of the Mars Express instrument commissioning phase. They consist of a pair of 20-metre hollow cylinders, each 2.5 centimetres in diameter, and a 7-metre boom. No satisfactory ground test of deployment in flight conditions was possible, so that verification of the booms’ performance had to rely on computer simulation. Just prior to their scheduled release, improved computer simulations carried out by the manufacturer, Astro Aerospace (California), revealed the possibility of a whiplash effect before they locked in their final outstretched positions, so that they might hit the spacecraft.

Following advice from NASA?s Jet Propulsion Laboratory (JPL), which contributed the boom system to the Italian-led MARSIS radar instrument, and the Mars Express science team, ESA put an immediate hold on deployment until a complete understanding of the dynamics was obtained. JPL led a comprehensive investigation, including simulations, theoretical studies and tests on representative booms, the latter to assess potential aging of the boom material. European experts, from ESA and the former spacecraft prime contractor, Astrium SAS, France, worked closely with JPL throughout the entire investigation. An independent engineering review board, composed of ESA and industry experts, met in January to evaluate the findings and advise on ?if and when? to proceed with deployment.

The ESA review board, at its final meeting on 25 January, recommended deployment of the MARSIS booms. The rationale for the decision was based on the results of the analyses, which showed the possible impact scenarios, the amount of energy involved, the nature of the materials, and the physical conditions in space. The board concluded that the risk of an impact on the spacecraft could not be ruled out, but that the impact energy would be low and the probability of a severe failure was very small.

One credible failure case is that an antenna boom could become blocked during deployment, either by itself or by the spacecraft. Although means are available to unblock a deployment, in the worst case MARSIS would have to be considered partially or completely lost. However, the analyses have shown that the Mars Express control systems would be able to cope with such a configuration and minimise the consequences for the other scientific instruments.

The ESA board recommended planning the deployment for the week beginning 2 May. However, should the remaining preparations proceed faster than planned, it might be feasible to start deployment during the week beginning 25 April. An early deployment is scientifically desirable, as the evolution of the Mars Express orbit will allow radar measurements of the most interesting scientific regions on Mars to start in May 2005.

If, as expected, the deployment is successful, MARSIS will probe the secrets of Mars?s subsurface at least until 30 November 2005, the nominal end date of Mars Express operations, and beyond if the mission is further extended.

Original Source: ESA News Release

This Star is Leaving Our Galaxy

Using the MMT Observatory in Tucson, AZ, astronomers at the Harvard-Smithsonian Center for Astrophysics (CfA) are the first to report the discovery of a star leaving our galaxy, speeding along at over 1.5 million miles per hour. This incredible speed likely resulted from a close encounter with the Milky Way’s central black hole, which flung the star outward like a stone from a slingshot. So strong was the event that the speedy star eventually will be lost altogether, traveling alone in the blackness of intergalactic space.

“We have never before seen a star moving fast enough to completely escape the confines of our galaxy,” said co-discoverer Warren Brown (CfA). “We’re tempted to call it the outcast star because it was forcefully tossed from its home.”

The star, catalogued as SDSS J090745.0+24507, once had a companion star. However, a close pass by the supermassive black hole at the galaxy’s center trapped the companion into orbit while the speedster was violently flung out. Astronomer Jack Hills proposed this scenario in 1998, and the discovery of the first expelled star seems to confirm it.

“Only the powerful gravity of a very massive black hole could propel a star with enough force to exit our galaxy,” explained Brown.

While the star’s speed offers one clue to its origin, its path offers another. By measuring its line-of-sight velocity, it suggests that the star is moving almost directly away from the galactic center. “It’s like standing curbside watching a baseball fly out of the park,” said Brown.

Its composition and age provide additional proof of the star’s history. The fastest star contains many elements heavier than hydrogen and helium, which astronomers collectively call metals. “Because this is a metal-rich star, we believe that it recently came from a star-forming region like that in the galactic center,” said Brown. Less than 80 million years were needed for the star to reach its current location, which is consistent with its estimated age.

The star is traveling twice as fast as galactic escape velocity, meaning that the Milky Way’s gravity will not be able to hold onto it. Like a space probe launched from Earth, this star was launched from the galactic center onto a never-ending outward journey. It faces a lonely future as it leaves our galaxy, never to return.

Brown’s co-authors on the paper announcing this find are Margaret J. Geller, Scott J. Kenyon and Michael J. Kurtz (Smithsonian Astrophysical Observatory). This study will be published in an upcoming issue of The Astrophysical Journal.

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