Stellar Family Portrait Takes Imaging Technique to New Extremes

picture: Zoom in onto Trumpler 14
picture: Trumpler 14 in the Carina Nebula



picture: Widest adaptive optics view of the open star cluster Trumpler 14

The young star cluster Trumpler 14 is revealed in another stunning ESO image. The amount of exquisite detail seen in this portrait, which beautifully reveals the life of a large family of stars, is due to the Multi-conjugate Adaptive optics Demonstrator (MAD) on ESO’s Very Large Telescope. Never before has such a large patch of sky been imaged using adaptive optics [1], a technique by which astronomers are able to remove most of the atmosphere's blurring effects.

Noted for harbouring Eta Carinae — one of the wildest and most massive stars in our galaxy — the impressive Carina Nebula also houses a handful of massive clusters of young stars. The youngest of these stellar families is the Trumpler 14 star cluster, which is less than one million years old — a blink of an eye in the Universe’s history. This large open cluster is located some 8000 light-years away towards the constellation of Carina (the Keel).

A team of astronomers, led by Hugues Sana, acquired astounding images of the central part of Trumpler 14 using the Multi-conjugate Adaptive optics Demonstrator (MAD, [2]) mounted on ESO’s Very Large Telescope (VLT). Thanks to MAD, astronomers were able to remove most of the blurring effects of the atmosphere and thus obtain very sharp images. MAD performs this correction over a much larger patch of the sky than any other current adaptive optics instrument, allowing astronomers to make wider, crystal-clear images.

Thanks to the high quality of the MAD images, the team of astronomers could obtain a very nice family portrait. They found that Trumpler 14 is not only the youngest — with a refined, newly estimated age of just 500 000 years — but also one of the most populous star clusters within the nebula. The astronomers counted about 2000 stars in their image, spanning the whole range from less than one tenth up to a factor of several tens of times the mass of our own Sun. And this in a region which is only about six light-years across, that is, less than twice the distance between the Sun and its closest stellar neighbour!

The most prominent star is the supergiant HD 93129A, one of the most luminous stars in the Galaxy. This titan has an estimated mass of about 80 times that of the Sun and is approximately two and a half million times brighter! It makes a stellar couple — a binary star — with another bright, massive star. The astronomers found that massive stars tend to pair up more often than less massive stars, and preferably with other more massive stars.

The Trumpler 14 cluster is undoubtedly a remarkable sight to observe: this dazzling patch of sky contains several white-blue, hot, massive stars, whose fierce ultraviolet light and stellar winds are blazing and heating up the surrounding dust and gas. Such massive stars rapidly burn their vast hydrogen supplies — the more massive the star, the shorter its lifespan. These giants will end their brief lives dramatically in convulsive explosions called supernovae, just a few million years from now.

A few orange stars are apparently scattered through Trumpler 14, in charming contrast to their bluish neighbours. These orange stars are in fact stars located behind Trumpler 14. Their reddened colour is due to absorption of blue light in the vast veils of dust and gas in the cloud.

The technology used in MAD to correct for the effect of the Earth’s atmosphere over large areas of sky will play a crucial role in the success of the next generation European Extremely Large Telescope (E-ELT).

Notes

[1] Telescopes on the ground suffer from a blurring effect introduced by atmospheric turbulence. This turbulence causes the stars to twinkle in a way that delights poets but frustrates astronomers, since it smears out the fine details of the images. However, with adaptive optics techniques, this major drawback can be overcome so that the telescope produces images that are as sharp as theoretically possible, i.e. approaching conditions in space. Adaptive optics systems work by means of a computer-controlled deformable mirror that counteracts the image distortion introduced by atmospheric turbulence. It is based on real-time optical corrections computed at very high speed (several hundreds of times each second) from image data obtained by a wavefront sensor (a special camera) that monitors light from a reference star.

[2] Present adaptive optics systems can only correct the effect of atmospheric turbulence in a very small region of the sky — typically 15 arcseconds or less — the correction degrading very quickly when moving away from the reference star. Engineers have therefore developed new techniques to overcome this limitation, one of which is multi-conjugate adaptive optics. MAD uses up to three stars instead of one as references to remove the blur caused by atmospheric turbulence over a field of view thirty times larger than that available to existing techniques.

Date: Thursday, December 03, 2009

Key Terms: Adaptive optics,open cluster,young star cluster,ESO, Trumpler 14,Very Large Telescope,MAD,HD 93129A,Binary Star,Stellar Winds,E-ELT,Arcsecond,Carina Constellation(the keel).

Revised and Edited By: Imran Khan.
year: 2009

A Superbright Supernova That’s the First of Its Kind

picture: In this schematic illustration of the material ejected from SN 2007bi, the radioactive nickel core (white) decays to cobalt, emitting gamma rays and positrons that excite surrounding layers (textured yellow) rich in heavy elements like iron. The outer layers (dark shadow) are lighter elements such as oxygen and carbon, where any helium must reside, which remain unilluminated and do not contribute to the visible spectrum.

But not the last, now that astronomers know where to look

Berkeley, CA – An extraordinarily bright, extraordinarily long-lasting supernova named SN 2007bi, snagged in a search by a robotic telescope, turns out to be the first example of the kind of stars that first populated the Universe. The superbright supernova occurred in a nearby dwarf galaxy, a kind of galaxy that’s common but has been little studied until now, and the unusual supernova could be the first of many such events soon to be discovered.

SN 2007bi was found early in 2007 by the international Nearby Supernova Factory (SNfactory) based at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory. The supernova’s spectrum was unusual, and astronomers at the University of California at Berkeley subsequently obtained a more detailed spectrum. Over the next year and a half the Berkeley scientists participated in a collaboration led by Avishay Gal-Yam of Israel’s Weizmann Institute of Science to collect and analyze much more data as the supernova slowly faded away.

The analysis indicated that the supernova’s precursor star could only have been a giant weighing at least 200 times the mass of our Sun and initially containing few elements besides hydrogen and helium – a star like the very first stars in the early Universe.

“Because the core alone was some 100 solar masses, the long-hypothesized phenomenon called pair instability must have occurred,” says astrophysicist Peter Nugent. A member of the SNfactory, Nugent is the co-leader of the Computational Cosmology Center (C3), a collaboration between Berkeley Lab’s Physics Division and Computational Research Division (CRD), where Nugent is a staff scientist. “In the extreme heat of the star’s interior, energetic gamma rays created pairs of electrons and positrons, which bled off the pressure that sustained the core against collapse.”

“SN 2007bi was the explosion of an exceedingly massive star,” says Alex Filippenko, a professor in the Astronomy Department at UC Berkeley whose team helped obtain, analyze, and interpret the data. “But instead of turning into a black hole like many other heavyweight stars, its core went through a nuclear runaway that blew it to shreds. This type of behavior was predicted several decades ago by theorists, but never convincingly observed until now.”

SN 2007bi is the first confirmed observation of a pair-instability supernova. The researchers describe their results in the 3 December 2009 issue of Nature.

On the trail of a strange beast

SN 2007bi was recorded on images taken as part of the Palomar-QUEST Survey, an automated search with the wide-field Oschin Telescope at the California Institute of Technology’s Palomar Observatory, and was quickly detected and categorized as an unusual supernova by the SNfactory. The SNfactory has so far discovered nearly a thousand supernovae of all types and amassed thousands of spectra, but has focused on those designated Type Ia, the “standard candles” used to study the expansion history of the Universe. SN 2007bi, however, turned out not to be a Type Ia. For one thing, it was at least ten times as bright.

“The thermonuclear runaway experienced by the core of SN 2007bi is reminiscent of that seen in the explosions of white dwarfs as Type Ia supernovae,” says Filippenko, “but on a much larger scale and with a far greater amount of power.”

“The discovery is a great example of how we can get all the science, in addition to cosmology, out of the SNfactory search,” says Greg Aldering, SNfactory project leader, who was not an author of the Nature paper. “Berkeley Lab and Caltech’s Astronomy Department agreed that we would split the work, the Lab handling the Type Ia’s and Caltech all the other types.”

Nugent contacted Gal-Yam, then a Caltech postdoctoral fellow, the lead investigator for the all-other category. “I asked, are you interested? He said, sure!” Nugent then contacted Filippenko, who was about to conduct a night of observation with the 10-meter Keck I telescope on the summit of Mauna Kea in Hawaii. Filippenko immediately set out to obtain an optical spectrum of the unusual supernova.

Caltech researchers subsequently acquired additional spectra with the Keck telescope, as did Paolo Mazzali’s team from the Max Planck Institute for Astrophysics in Garching, Germany, using the Very Large Telescope (VLT) in Chile.

Says Mazzali, “The Keck and VLT spectra clearly indicated that an extremely large amount of material was ejected by the explosion, including a record amount of radioactive nickel, which caused the expanding gases to glow very brightly.”

Rollin Thomas of CRD, a member of C3 and the SNfactory, aided the early analysis, using the Franklin supercomputer at the National Energy Research Scientific Computing Center (NERSC) to run a code he developed to generate numerous synthetic spectra for comparison with the real spectrum.

“The code uses hundreds of cores to systematically test a large number of simplified model supernovae, searching through the candidates by adjusting parameters until it finds a good fit,” says Thomas. “This kind of data-driven approach is key to helping us understand new types of transients for which no reliable theoretical predictions yet exist.” The model fit was unambiguous: SN 2007bi was a pair-instability supernova.

“The central part of the huge star had fused to oxygen near the end of its life, and was very hot,” Filippenko explains. “Then the most energetic photons of light turned into electron-positron pairs, robbing the core of pressure and causing it to collapse. This led to a nuclear runaway explosion that created a large amount of radioactive nickel, whose decay energized the ejected gas and kept the supernova visible for a long time.”

Gal-Yam organized a team of collaborators from many institutions to continue to observe SN 2007bi and obtain data as it slowly faded over a span of 555 days. Says Gal-Yam, “As our follow-up observations started to roll in, I immediately realized this must be something new. And indeed it turned out to be a fantastic example of how we are finding new types of stellar explosions.”

Because it had no hydrogen or helium lines, the usual classification scheme would have labeled the supernova a Type Ic. But it was so much brighter than an ordinary Type Ic that it reminded Nugent of only one prior event, a supernova designated SN 1999as, found by the international Supernova Cosmology Project but unfortunately three weeks after its peak brightness.

Understanding a supernova requires a good record of its rise and fall in brightness, or light curve. Although SN 2007bi was detected more than a week after its peak, Nugent delved into years of data compiled by NERSC from the SNfactory and other surveys. He found that the Catalina Sky Survey had recorded SN 2007bi before its peak brightness and could provide enough data to calculate the duration of the rising curve, an extraordinarily long 70 days – more evidence for the pair-instability identification.

A fossil laboratory of the early Universe

“It’s significant that the first unambiguous example of a pair-instability supernova was found in a dwarf galaxy,” says Nugent. “These are incredibly small, very dim galaxies that contain few elements heavier than hydrogen and helium, so they are models of the early Universe.”
Dwarf galaxies are ubiquitous but so faint and dim – “they take only a few pixels on a camera,” says Nugent, “and until recently, with the development of wide-field projects like the SNfactory, astronomers had wanted to fill the chip with galaxies” – that they’ve rarely been studied. SN 2007bi is expected to focus attention on what Gal-Yam and his collaborators call “fossil laboratories to study the early Universe.”

Says Filippenko, “In the future, we might end up detecting the very first generation of stars, early in the history of the Universe, through explosions such as that of SN 2007bi – long before we have the capability of directly seeing the pre-explosion stars.”

With the advent of the multi-institutional Palomar Transient Factory, a fully automated, wide-field survey to find transients, led by Caltech’s Shri Kulkarni, and with the aid of the Deep Sky Survey established by Nugent at NERSC to compile historical data from Palomar-QUEST, the SNfactory, the Near Earth Asteroid Team, and other surveys, the collaborators expect they will soon find many more ultrabright, ultramassive supernovae, revealing the role of these supernovae in creating the Universe as we know it today.


Edited By : Imran Khan
Key Terms: Pair Instability Supernova,SN 2007bi,light curve
Year:2009
Wednesday, December 02, 2009

Blushing Dusty Nebula

This close-up of an area in the northwest region of the large Iris Nebula seems to be clogged with cosmic dust. With bright light from the nearby star HD 200775 illuminating it from above, the dust resembles thick mounds of billowing cotton. It is actually made up of tiny particles of solid matter, with sizes from ten to a hundred times smaller than those of the dust grains we find at home. Both background and foreground stars are dotted throughout the image. Researchers studying the object are particularly interested in the region to the left and slightly above centre in the image, where dusty filaments appear redder than is expected.

North is down, East is right. The field of view is 3.3 arcminutes. The image is a composite of four images obtained through blue, green, near-infrared and H-alpha filters.Credit: NASA & ESA

Tuesday, December 01, 2009

A recent NASA/ESA Hubble Space Telescope image of part of NGC 7023, or the Iris Nebula, highlights a perfect dust laboratory in the sky.

On Earth, we tend to find dust nothing more than a nuisance that blankets our furniture and causes us to sneeze. Cosmic dust can also be a hindrance to astronomers because cameras using visible light cannot see through it. However, studying cosmic dust in detail helps astronomers to pin down the ingredients of the raw mixture that eventually gives birth to stars.

This close-up of an area in the northwest region of the large Iris Nebula seems to be clogged with cosmic dust. With bright light from the nearby star HD 200775 [1] illuminating it from above, the dust resembles thick mounds of billowing cotton. It is actually made up of tiny particles of solid matter, with sizes from ten to a hundred times smaller than those of the dust grains we find at home [2]. Both background and foreground stars are dotted throughout the image.

NGC 7023 is a reflection nebula, which means it scatters light from a massive nearby star, in this case, HD 200775. Reflection nebulae are different from emission nebulae, which are clouds of gas that are hot enough to emit light themselves. Reflection nebulae tend to appear blue because of the way light scatters, but parts of the Iris Nebula appear unusually red.

Researchers studying the object are particularly interested in the region to the left and slightly above centre in the image, where they find dusty filaments to be redder than expected. An unknown chemical compound, most likely based on hydrocarbons, is responsible for the red tinge. The high resolution and sensitivity of Hubble’s instruments allow astronomers to study the area in detail. Images and spectra are only part of the analysis. On Earth, scientists are performing additional laboratory tests to assess better the exact chemical composition of the nebula.

NGC 7023 was discovered by Sir William Herschel in 1794; the nebula is in the constellation of Cepheus, the King, in the northern sky. NGC 7023 is approximately 1400 light–years from Earth and about six light-years across. This aethereal image was taken by Hubble's Advanced Camera for Surveys. Astronomers also used Hubble’s Near Infrared Camera and Multi-Object Spectrometer (NICMOS) instrument to try to determine which chemical elements are present in the nebula.

Notes for you:

North is down, East is right. The field of view is 3.3 arcminutes. The image is a composite of four images obtained through blue, green, near-infrared and H-alpha filters.

[1] HD 200775 is about ten times the mass of the Sun.

[2] The typical sizes of cosmic dust grains range between a few hundredths of a micron and several microns.

The Hubble Space Telescope is a project of international cooperation between ESA and NASA.

These observations were obtained by a team led by Karl Gordon from the Space Telescope Science Institute in Baltimore, Maryland, USA.

Vampires and collisions rejuvenate stars

Image credit: NASA, ESA and Francesco Ferraro (University of Bologna)

Wednesday, December 23, 2009

Using the NASA/ESA Hubble Space Telescope, astronomers have uncovered two distinct kinds of "rejuvenated" stars in the globular cluster Messier 30. A new study shows that both stellar collisions and a process sometimes called vampirism are behind this cosmic "face lift". The scientists also uncover evidence that both sorts of blue stragglers were produced during a critical dynamical event (known as "core collapse") that occurred in Messier 30 a few billion years ago.

Stars in globular clusters [1] are generally extremely old, with ages of 12-13 billion years. However, a small fraction of them appear to be significantly younger than the average population and, because they seem to have been left behind by the stars that followed the normal path of stellar evolution and became red giants, have been dubbed blue stragglers [2]. Blue stragglers appear to regress from "old age" back to a hotter and brighter "youth", gaining a new lease on life in the process. A team of astronomers used Hubble to study the blue straggler star content in Messier 30, which formed 13 billion years ago and was discovered in 1764 by Charles Messier. Located about 28 000 light-years away from Earth, this globular cluster — a swarm of several hundred thousand stars — is about 90 light-years across.

Although blue stragglers have been known since the early 1950s, their formation process is still an unsolved puzzle in astrophysics. "It’s like seeing a few kids in the group picture of a rest-home for retired people. It is natural to wonder why they are there," says Francesco Ferraro from the University of Bologna in Italy, lead author of the study that will be published this week in Nature [3]. Researchers have been studying these stars for many years and knew that blue stragglers are indeed old. They were thought to have arisen in a tight binary system [4]. In such a pair, the less massive star acts as a "vampire", siphoning fresh hydrogen from its more massive companion star. The new fuel supply allows the smaller star to heat up, growing bluer and hotter — behaving like a star at an earlier stage in its evolution.

The new study shows that some of the blue stragglers have instead been rejuvenated by a sort of "cosmic facelift", courtesy of cosmic collisions. These stellar encounters are nearly head-on collisions in which the stars might actually merge, mixing their nuclear fuel and re-stoking the fires of nuclear fusion. Merged stars and binary systems would both be about twice the typical mass of individual stars in the cluster.

"Our observations demonstrate that blue stragglers formed by collisions have slightly different properties from those formed by vampirism. This provides a direct demonstration that the two formation scenarios are valid and that they are both operating simultaneously in this cluster," says team member Giacomo Beccari from ESA.
Using data from the now-retired Wide Field Planetary Camera 2 (WFPC2) aboard Hubble, astronomers found that these "straggling" stars are much more concentrated towards the centre of the cluster than the average star. "This indicates that blue stragglers are more massive than the average star in this cluster," says Ferraro. "More massive stars tend to sink deep into the cluster the way a billiard ball would sink in a bucket of honey."

The central regions of high density globular clusters are crowded neighbourhoods where interactions between stars are nearly inevitable. Researchers conjecture that one or two billion years ago, Messier 30 underwent a major "core collapse" that started to throw stars towards the centre of the cluster, leading to a rapid increase in the density of stars. This event significantly increased the number of collisions among stars, and favoured the formation of one of the families of blue stragglers. On the other hand, the increase of stellar crowding due to the collapse of the core also perturbed the twin systems, encouraging the vampirism phenomenon and thus forming the other family of blue stragglers. "Almost ten percent of galactic globular clusters have experienced core collapse, but this is the first time that we see the effect of the core collapse imprinted on a stellar population," says Barbara Lanzoni, University of Bologna.

"The two distinct populations of blue stragglers discovered in Messier 30 are the relics of the collapse of the core that occurred two billion years ago. In a broad context our discovery is direct evidence of the impact of star cluster dynamics on stellar evolution. We should now try to see if other globular clusters present this double population of blue stragglers," concludes Ferraro.


Notes for you:

[1] Globular clusters are dense agglomerations of several hundred thousand stars. Present among the earliest inhabitants of our Milky Way, they formed in the vast halo of our galaxy before it flattened to form a pancake-shaped spiral disc. Star formation essentially stopped in globular clusters 13 billion years ago, so astronomers expect to find only old stars and they use globular cluster ages as a benchmark for estimating the age of the Universe.

[2] In 1953, astronomer Allan Sandage found a puzzling new population of stars that seemed to go against the rules of stellar evolution in globular clusters. Sandage detected hot young blue stars in the globular cluster Messier 3, and subsequently in other globular clusters. He dubbed them stragglers because they looked like they were trailing or left behind by other blue stars in the cluster that had long ago evolved to the red giant stage.

[3] This research was presented in a paper that appears in the 24 December 2009 issue of Nature, “Two distinct sequences of blue straggler stars in the globular cluster M30”, by F. R. Ferraro et al.

[4] In 1964 astronomers Fred Hoyle and W.H. McCrea independently suggested that blue stragglers result when two stars capture each other and form a tight binary system.

Scientific Research on ISS (International Space Station)

A comparison between fire on Earth (left) and fire in a microgravity environment (right), such as that found on the ISS.

One of the main goals of the ISS is to provide a place to conduct experiments that require one or more of the unusual conditions present on the station. The primary fields of research include biology, physics, astronomy, and meteorology.The 2005 NASA Authorization Act designated the US segment of the International Space Station as a national laboratory with a goal to increase the use of the ISS by other Federal entities and the private sector.

One research goal is to improve the understanding of long-term space exposure on the human body. Subjects currently under study include muscle atrophy, bone loss, and fluid shift. The data will be used to determine whether space colonisation and lengthy human spaceflight are feasible. As of 2006, data on bone loss and muscular atrophy suggest that there would be a significant risk of fractures and movement problems if astronauts landed on a planet following a lengthy space cruise.

Researchers are investigating the relation of the near-weightless environment on the ISS to the evolution, development and growth, and the internal processes of plants and animals. In response to some of this data, NASA wants to investigate microgravity's effects on the growth of three-dimensional, human-like tissues, and the unusual protein crystals that can be formed in space.

The physics of fluids in microgravity is being investigated, enabling researchers to better model the behaviour of fluids in the future. Because of the ability to almost completely combine fluids in microgravity, physicists are interested in investigating the combinations of fluids that will not normally mix well on Earth. In addition, by examining reactions that are slowed down by low gravity and temperatures, scientists hope to gain new insight regarding superconductivity.

Materials science is an important part of the research activity aboard the station, with the goal of reaping economic benefits by improving techniques used on the ground. Experiments are intended to provide a better understanding of the relationship between processing, structure, and properties so the conditions required on Earth to achieve desired materials properties can be reliably predicted.

Other areas of interest include the effect of the low gravity environment on combustion, studying the efficiency of burning and control of emissions and pollutants. These findings may improve our understanding of energy production, and in turn have an economic and environmental impact. There are also plans to use the ISS to examine aerosols, ozone, water vapour, and oxides in Earth's atmosphere, as well as cosmic rays, cosmic dust, antimatter, and dark matter in the universe.

One component assisting in these various studies is the ExPRESS Logistics Carrier (ELC). Developed by NASA, four of these units are set to be launched to the ISS. As currently envisioned, the ELCs will be delivered on three separate Space Shuttle missions. They will allow experiments to be deployed and conducted in the vacuum of space, and will provide the necessary electricity and computing to process experimental data locally. Delivery is currently scheduled for STS-129 in November 2009, STS-133 in May 2010 and STS-134 in September 2010.

The Alpha Magnetic Spectrometer (AMS), a particle physics experiment, is scheduled to be added to the station. This device will be launched on STS-134 in 2010, and will be mounted externally on the Integrated Truss Structure. The AMS will search for various types of unusual matter by measuring cosmic rays. The experiments conducted will help researchers study the formation of the universe, and search for evidence of dark matter and antimatter.

Keck Interferometer Nuller Spots Double Dust Cloud

Credit: NASA/GSFC/Marc Kuchner and Francis Reddy
This graphic compares the inner and outer disk of the 51 Oph system to the location of the planets and asteroid belt of the Solar System.


KAMUELA, Hawaii (Sept. 24, 2009) — Linking the twin, 10-meter telescopes in Hawaii, astronomers at the W. M. Keck Observatory discovered an extended, double-layered dust disk orbiting 51 Ophiuchi, a star that is 410 light-years from Earth. It is the first time the Keck Interferometer Nuller instrument has identified such a compact cloud around a star so far away.

The new data suggest that 51 Ophiuchi is a protoplanetary system with a dust cloud that orbits extremely close to its parent star, said University of Maryland astronomer Christopher Stark, who led the research team.

Keck Observatory operates one of the largest optical interferometers in the United States. The interferometer provides high precision resolution measurements equal to a telescope as large as the distance that separates the telescope’s primary mirrors—85 meters in the case of the Keck twins. In April 2007, the team simultaneously pointed both Keck telescopes at the star 51 Ophiuchi, or 51 Oph, and used the Interferometer’s Nuller, a technique to combine the incoming light in a particular way, to block the unwanted starlight of 51 Oph and measure faint adjacent signals from the dust cloud surrounding the star.

According to the observations, excess material orbited 51 Oph. Stark and his collaborators repeated the nulling measurements at several different wavelengths of light and combined this data with information from other telescopes to determine the shape and orientation of the material as well as the sizes of the dust grains.

The data suggest that two debris disks orbit 51 Oph. The inner disk has larger grains, roughly 10 micrometers or larger in diameter, and extends out to four astronomical units, or AUs, beyond the star. The second disk comprised of mainly 0.1 micrometer grains extends from roughly seven AU to 1200 AU. One AU is the distance between Earth and the Sun or roughly 93 million miles. The new results appear in the Oct. 1 Astrophysical Journal.

If these debris disks orbited the Sun, the inner cloud of larger grains would extend roughly from the position of Mercury’s orbit to just past the edge of the asteroid belt. The outer disk of smaller grains would originate just before Saturn’s orbit and extend to a distance ten times farther than the edge of the Kuiper belt.

51 Oph’s inner, compact dust disk is one of the most compact dust clouds ever detected, and the new Keck Interferometer Nuller observations demonstrate the instrument’s ability to detect dust clouds a hundred times smaller than a conventional telescope can observe, Stark said.

The instrument was also essential to solving the mystery of what made 51 Oph’s dust disk appear so compact while its spectra, or chemical fingerprints, suggested that the dust orbited at much larger distances, added Marc Kuchner, an astronomer at NASA’s Goddard Space Flight Center in Greenbelt, Md. who was part of the research team. The answer was simply that the star had two debris disks.

Because of the power of the Keck Nuller, Stark and his team were able to resolve inner and outer dust disks, which together form 51 Oph’s exozodiacal cloud. In similar star systems, the outer cloud of dust seems to be a distinct outer belt, probably analogous to the Kuiper belt or a second system of asteroids. But 51 Oph appears to be different, Kuchner said. The observations suggest that the star’s outer cloud is comprised of smaller grains and is connected to the inner cloud so that the system has only one underlying belt of asteroids.

This system most likely represents a rare, nearby example of a young planetary system just entering the late stages of planet formation. Terrestrial planets may be forming, although none have been detected within the system yet, Stark said.

His team’s data also indicates that the cloud around 51 Oph is 100,000 times more dense than the dust cloud circling the Solar System. In most planet-forming systems, as asteroid and comet collisions produce dust, the larger grains spiral toward the star while its outward pressure pushes smaller particles to the edge or even out of the system. 51 Ophiuchi, a star 260 times more luminous than the Sun, likely pushes the smaller dust grains from the inner disk to the outer disk, Kuchner explained.

Keck’s Nuller, which was funded by NASA and built by the Jet Propulsion Laboratory in Pasadena, Calif., will be used to help astronomers further understand how and when these asteroid belts form and how dust from the star’s debris disk might interfere with direct imaging of planets orbiting another star, he said.

Radical New Theory: Black Holes Attack and Devour Stars from the Inside

As if they weren't considered beastly enough, black holes can dive into nearby stars and devour them from the inside out, scientists now suggest. Such invasions by such black holes could help explain the most powerful explosions in the universe, gamma-ray bursts, whose origins remain elusive.

The idea needs support from further theoretical work, and observations would help, too. Meanwhile, here's what spawned the notion:

Gamma-ray bursts are narrow beams of intense radiation that can unleash as much energy as our sun will during its entire 10-billion-year lifetime — all in anywhere from milliseconds to a minute or more. The processes that can generate that much energy in that short a time are among the biggest mysteries in astronomy today.

The majority of gamma-ray bursts last two seconds or more. These cosmic flashes, dubbed long gamma-ray bursts, are linked to jets of plasma from massive dying stars. Scientists currently suggest this plasma is heated up by the energy released from neutrinos as they meet and annihilate their antimatter counterparts. Both kinds of particles are emitted by the dense, hot disk of matter that accretes or builds up around a black hole as it rips apart a dying star.

Now researchers have come up with a different, radical explanation — the plasma jets come directly from black holes when they invade stars.

Powerful forces

Their concept is based on recent observations by the Swift satellite that indicates the central engine driving these plasma jets can operate for up to 10,000 seconds, much longer than the neutrino model can explain.

Scientists at the University of Leeds in England instead suggest the matter that falls into black holes can generate extremely powerful magnetic forces that focus and drive the plasma jets linked with long gamma-ray bursts. The matter has to whirl very rapidly, with the centrifugal forces caused by this spin opposing the powerful gravitational pull of the black hole, for the prolonged blast seen in long gamma-ray bursts.

The researchers found one way such whirling matter could result is if a black hole plunged into a star and began eating it from the inside. As the black hole ripped the star apart, its remains could twirl apart in precisely the right way needed for a long gamma-ray burst.

"This 'invader variant' provides a natural explanation of the very fast rotation," researcher Serguei Komissarov, a mathematician and astrophysicist at the University of Leeds in England, told.

Other ideas

Another way such rapid spinning might have occurred is if the dying star was initially born rotating very quickly and retained this rate of spin during its entire life. Also, the dying star in question might have orbited very close to another star, and the resulting tidal forces — the tug of one object that distorts the shape of another, just as the sun and moon cause tides in Earth's ocean and even in its rocky crust — could have spun it up, Komissarov explained.

"The magnetic model has been proposed by other scientists, say 10 years ago or so, but was never popular," Komissarov said. "During the last few years we have been studying the true potential of this model and now we argue that some observational data, including the latest data from Swift, speak in favor of it."

Komissarov did caution that no direct observations linked with long gamma-ray bursts have revealed the extremely strong magnetic fields required by their model so far.

"Further research, both theoretical and observational, is needed to clarify this issue," he said.

Komissarov and his colleague Maxim Barkov detailed their findings in the Monthly Notices of the Royal Astronomical Society.

The Planet that will die soon

Picture: The camera which has found Planet WASP-18b

WASP-18b is an extrasolar planet that is notable for having an orbital period of less than one day. It has a mass equal to 10 Jupiter masses,just below the boundary line between planets and brown dwarfs, about 13 Jupiter masses. Due to tidal deceleration, it is expected to spiral towards and eventually merge with its host star, WASP-18, in less than a million years.The planet is approximately 1.9 million miles from its star, which is about 325 light years from Earth. It was discovered by Coel Hellier, a professor of astrophysics at Keele University in England.

Scientists at Keele and at the University of Maryland are working to understand whether the discovery of this planet so shortly before its expected demise (with less than 0.1% of its lifetime remaining) was fortuitous, or whether tidal dissipation by WASP-18 is actually much less efficient than astrophysicists typically assume.Observations made over the next decade should yield a measurement of the rate at which WASP-18b's orbit is decaying.

The closest example of a similar situation in our own solar system is Mars' moon, Phobos. Phobos orbits Mars at a distance of only about 5,600 miles, 40 times closer than our moon is to the Earth,and is expected to be destroyed in about eleven million years.

Orbital chaos may destroy Earth

Image: possible orbital chaos collision between Venus and Earth

A force known as orbital chaos may cause our solar system to go haywire, leading to a possible collision between earth and Venus or Mars, according to a study released today.The good news is that the likelihood of such a smash-up is small, around one-in-2500.And even if the planets did careen into one another, it would not happen before another 3.5 billion years.

Indeed, there is a 99 per cent chance that the sun's posse of planets will continue to circle in an orderly pattern throughout the expected life span of our life-giving star, another five billion years, the study found.After that, the sun will likely expand into a red giant, engulfing earth and its other inner planets - Mercury, Venus and Mars - in the process.Astronomers have long been able to calculate the movement of planets with great accuracy hundreds, even thousands of years in advance. This is how eclipses have been predicted. But peering further into the future of celestial mechanics with exactitude is still beyond our reach, said Jacques Laskar, a researcher at the Observatoire de Paris and lead author of the study.

"The most precise long-term solutions for the orbital motion of the solar system are not valid over more than a few tens of millions of years," he said.

Using powerful computers, Mr Laskar and colleague Mickael Gastineau generated numerical simulations of orbital instability over the next five billion years.
Unlike previous models, they took into account Albert Einstein's theory of general relativity. Over a short time span, this made little difference, but over the long haul it resulted in dramatically different orbital paths.The researchers looked at 2501 possible scenarios, 25 of which ended with a severely disrupted solar system.

"There is one scenario in which Mars passes very close to earth," 794 kilometres to be exact, said Mr Laskar."When you come that close, it is almost the same as a collision because the planets get torn apart."

Life on earth, if there still were any, would almost certainly cease to exist.To get a more fine-grained view of how this might unfold, Mr Laskar and Mr Gastineau ran an additional 200 computer models, slightly changing the path of Mars each time.All but five of them ended in a two-way collision involving the sun, earth, Mercury, Venus or Mars. A quarter of them saw earth smashed to pieces.The key to all the scenarios of extreme orbital chaos was the rock closest to the sun, found the study, published in the British journal Nature."Mercury is the trigger, and would be be the first planet to be destabilised because it has the smallest mass," said Mr Laskar.At some point Mercury's orbit would get into resonance with that of Jupiter, throwing the smaller orb even more out of kilter, he said.Once this happens, the so-called "angular momentum" from the much larger Jupiter would wreak havoc on the other inner planets' orbits too.

"The simulations indicate that Mercury, in spite of its diminutive size, poses the greatest risk to our present order," said University of California scientist Gregory Laughlin in a commentary, also published in Nature.

Edited By: Imran Khan
Key Terms: Observatorie de paris,Angular momentum,computer simulations and models
Year: 2009

Spitzer sees the cosmos through "warm" infrared eyes

Fig:Cygnus region. NASA/JPL-Caltech

NASA's Spitzer Space Telescope is starting a second career and taking its first shots of the cosmos since warming up. The infrared telescope ran out of coolant May 15, 2009, more than 5.5 years after launch. It has since warmed to a still-frosty -406° Fahrenheit (-208° Celsius).

New images taken with two of Spitzer's infrared detector channels — two that work at the new warmer temperature — demonstrate the observatory remains a powerful tool for probing the dusty universe. The images show a bustling star-forming region, the remains of a star similar to the Sun, and a swirling galaxy lined with stars.

"The performance of the two short-wavelength channels of Spitzer's Infrared Array Camera is essentially unchanged from what it was before the observatory's liquid helium was exhausted," said Doug Hudgins, the Spitzer program scientist at NASA headquarters in Washington. "To put that in perspective, that means Spitzer's sensitivity at those wavelengths is still roughly the same as a 30-meter ground-based telescope. This breathtaking image demonstrates Spitzer will continue to deliver world-class imagery and science during its warm mission."

The first of three images shows a cloud bursting with stars in the Cygnus region of our Milky Way galaxy. Spitzer's infrared eyes peer through and see dust, revealing young stars tucked in dusty nests. A second image shows a nearby dying star — a planetary nebula called NGC 4361 — which has outer layers that expand outward in the rare form of four jets. The last picture is of a classic spiral galaxy called NGC 4145, located approximately 68 million light-years from Earth.

"With Spitzer's remaining shorter-wavelength bands, we can continue to see through the dust in galaxies and get a better look at the overall populations of stars," said Robert Hurt, imaging specialist for Spitzer at NASA's Spitzer Science Center at the California Institute of Technology in Pasadena. "All stars are equal in the infrared."

Since its launch from Cape Canaveral, Florida, August 25, 2003, Spitzer has made many discoveries. They include planet-forming disks around stars, the composition of the material making up comets, hidden black holes, galaxies billions of light-years away, and more.

Perhaps the most revolutionary and surprising Spitzer finds involve planets around other stars, called exoplanets. In 2005, Spitzer detected the first photons of light from an exoplanet. In a clever technique, now referred to as the secondary-eclipse method, Spitzer was able to collect the light of a hot, gaseous exoplanet and learn about its temperature. Later detailed studies revealed more about the composition and structure of the atmospheres of these exotic worlds.

Warm Spitzer will address many of the same science questions as before. It also will tackle new projects, such as refining estimates of Hubble's constant, or the rate at which our universe is stretching apart; searching for galaxies at the edge of the universe; characterizing more than 700 near-Earth objects, or asteroids and comets with orbits that pass close to our planet; and studying the atmospheres of giant gas planets expected to be discovered soon by NASA's Kepler mission.

August 5, 2009

Mars orbiter shows angled view of martian crater

Oblique view of Victoria Crater. NASA/JPL-caltech/University of Arizona

August 12, 2009

The high-resolution camera on NASA's Mars Reconnaissance Orbiter has returned a dramatic oblique view of the martian crater that a rover explored for two years.

The new view of Victoria Crater shows layers on steep crater walls, difficult to see from straight overhead, plus wheel tracks left by NASA's Mars Exploration Rover Opportunity between September 2005 and August 2007. The orbiter's High Resolution Imaging Science Experiment camera shot it at an angle comparable to looking at landscape from an airplane window. Some of the camera's earlier, less angled images of Victoria Crater aided the rover team in choosing safe routes for Opportunity and contributed to joint scientific studies.



Martian dust devil with track and shadow. NASA/JPL-Caltech/University of Arizona

Another new image from the same camera catches an active dust devil leaving a trail and casting a shadow. These whirlwinds have been a subject of investigation by Opportunity's twin rover, Spirit.

The Mars Reconnaissance Orbiter has been studying Mars with an advanced set of instruments since 2006. It has returned more data about the planet than all other past and current missions to Mars combined.

Provided by JPL, Pasadena, California

Scientists discover storms in the tropics of Titan

This image of Titan is a product of observations taken with the Palomar 200-inch telescope, JPL adaptive optics system, and Cornell-built PHARO near-infrared camera. A. Bouchez

August 13, 2009

For all its similarities to Earth-clouds that pour rain — albeit liquid methane not liquid water — onto the surface producing lakes and rivers, vast dune fields in desert-like regions, plus a smoggy orange atmosphere, Saturn's largest moon, Titan, is generally "a very bland place," according to Mike Brown of the California Institute of Technology (Caltech).

"We can watch for years and see almost nothing happen," said Brown. "This is bad news for people trying to understand Titan's meteorological cycle. Not only do things happen infrequently, but we tend to miss them when they do happen because nobody wants to waste time on big telescopes."

However, just because weather occurs infrequently, it doesn't mean it never occurs, nor does it mean that astronomers can't catch it in the act.

In April 2008, that's just what Emily Schaller, now at the University of Arizona, and her colleagues accomplished when they observed a large system of storm clouds appear in the apparently dry mid-latitudes and spread in a southeastward direction across the moon. Eventually, the storm generated a number of bright but transient clouds over Titan's tropical latitudes, a region where clouds had never been seen and where it was thought they were extremely unlikely to form.

"A couple of years ago, we set up a highly efficient system on a smaller telescope to figure out when to use the biggest telescopes," Brown said. The first telescope, NASA's Infrared Telescope Facility, on Mauna Kea, Hawaii, takes a spectrum of Titan almost every single night. "From that we can't tell much, but we can say 'no clouds,' 'a few clouds,' or, if we get lucky, 'monster clouds,'" he said.

"The period during which I was collecting data for my thesis corresponded entirely to an extended period of essentially no clouds, so we never really got to show the full power of the combined telescopes," Schaller said. "But then, after finishing my thesis, I walked back across campus to my office to look at the data from the previous night to find that Titan suddenly had the biggest clouds ever."

The day after the telescope's big find, Schaller, Brown, and Roe began tracking the clouds with the large Gemini telescope on Mauna Kea and watched this system evolve for a month. "And what a cool show it was," Brown said.

"The first cloud was seen near the tropics and was caused by a still-mysterious process, but it behaved almost like an explosion in the atmosphere, setting off waves that traveled around the planet, triggering their own clouds," Brown said. "Within days a huge cloud system had covered the south pole, and sporadic clouds were seen all the way up to the equator."

Schneider, an expert on atmospheric circulations, was instrumental in helping to sort out the complicated chain of events that followed the initial outburst of cloud activity.

"The month-long event has many important implications for understanding the hydrological cycle on Titan," said Brown, "but one of the reasons I am most excited about it is that it shows clouds near the equator — where the European Space Agency's Huygens probe landed — for the first time. For a while now, people have speculated that the equatorial regions are simply too dry to ever have significant clouds."

And yet, the images snapped by the Huygens probe in January 2005 revealed small-scale channels and streams that looked just like features created by fluids — by water here on Earth and probably by liquid methane on Titan.

Experts had speculated for years on how there could be streams and channels in a region with no rain. The new results suggest those speculations may prove unnecessary. "No one considered how storms in one location can trigger them in many other locations," said Brown.

Caltech, Pasadena, California

Tiny flares responsible for outsized heat of Sun's atmosphere

This false-color temperature map shows solar active region AR 10923, observed close to center of the Sun's disk. Blue regions indicate plasma near 10 million degrees K. Reale, et al.

August 17, 2009

Solar physicists at NASA have confirmed that small, sudden bursts of heat and energy — called nanoflares — cause temperatures in the thin, translucent gas of the Sun's atmosphere to reach millions of degrees.

The Sun's outer atmosphere, or corona, is made up of loops of hot gas that arch high above the surface. These loops are comprised of bundles of smaller, individual magnetic tubes or strands that can have temperatures reaching several million degrees Kelvin (K), even though the Sun's surface is only 5,700 degrees K.

Nanoflares are small, sudden bursts of energy that happen within these thin magnetic tubes in the corona. Unlike solar flares that can be viewed through satellites and ground-based telescopes, nanoflares are too small to be resolved individually. We only see the combined effect of many of them occurring at about the same time.

"Coronal loops are the fundamental building blocks of the corona," said James Klimchuk, an astrophysicist at the Goddard Space Flight Center in Greenbelt, Maryland. "Their shape is defined by the magnetic field, which guides the hot flowing gases called plasma. The magnetic field is also the source of the nanoflare energy. We believe that stresses in the field are released when thin sheets of electric current become unstable."

Klimchuk and colleagues have constructed a theoretical model to explain how nanoflares occur and how plasma within the tubes responds to the skyrocketing temperatures. "We simulate bursts of heating and predict what the loop should look like when observed with a variety of instruments," said Klimchuk.

To test their model, the team observed gas emissions in the solar corona using the NASA-funded X-Ray Telescope and Extreme Ultraviolet Imaging Spectrometer on Japan's Hinode spacecraft.

"The 10 million degree temperatures we detected in the corona can only be produced by the impulsive energy bursts," said Klimchuk. The ultra-hot plasma cools very quickly, however, which explains why it is so faint and has been so difficult to detect until now. The energy lost from the cooling conducts down to the relatively cold solar surface. The gas there is heated to about 1 million degrees K and expands upward to become the 1 million degree component of the corona that has been observed for many years.

NASA's upcoming mission to study the Sun, the Solar Dynamics Observatory, will help scientists answer the outstanding questions of coronal heating by observing the coronal plasma at different temperatures with an unprecedented combination of close-up detail and rapid sequences.

Goddard Space Center, Greenbelt, MD

Star clusters point to black holes ejected from host galaxies

This artist's conception shows a rogue black hole that has been kicked out from the center of two merging galaxies. The black hole is surrounded by a cluster of stars that were ripped from the galaxies. STScI

The tight cluster of stars surrounding a supermassive black hole after it has been violently kicked out of a galaxy represents a new kind of astronomical object and a fossil record of the kick.

A paper in The Astrophysical Journal discusses the theoretical properties of "hypercompact stellar systems" and suggests that hundreds of these faint star clusters might be detected at optical wavelengths in our immediate cosmic environment. Some of these objects may already have been picked up in astronomical surveys, reports David Merritt, from Rochester Institute of Technology (RIT), Jeremy Schnittman, from Johns Hopkins University, and Stefanie Komossa, from the Max-Planck-Institute for Extraterrestrial Physics in Germany.

Hypercompact stellar systems result when a supermassive black hole is violently ejected from a galaxy, following a merger with another supermassive black hole. The evicted black hole rips stars from the galaxy as it is thrown out. The stars closest to the black hole move in tandem with the massive object and become a permanent record of the velocity at which the kick occurred.

"You can measure how big the kick was by measuring how fast the stars are moving around the black hole," said Merritt, professor of physics at RIT. "Only stars orbiting faster than the kick velocity remain attached to the black hole after the kick."

These stars carry with them a kind of fossil record of the kick, even after the black hole has slowed down. In principle, you can reconstruct the properties of the kick, which is nice because there would be no other way to do it."

"Finding these objects would be like discovering DNA from a long-extinct species," said Komossa.

The best place to find hypercompact stellar systems, the authors said, is in cluster of galaxies like the nearby Coma and Virgo clusters. These dense regions of space contain thousands of galaxies that have been merging for a long time. Merging galaxies result in merging black holes, which is a prerequisite for the kicks.

"Even if the black hole gets kicked out of one galaxy, it's still going to be gravitationally bound to the whole cluster of galaxies," Merritt said. "The total gravity of all the galaxies is acting on that black hole. If it was ever produced, it's still going to be there somewhere in that cluster."

Merritt and his co-authors think that scientists may have already seen hypercompact stellar systems and not realized it. These objects would be easy to mistake for common star systems like globular clusters. The key signature making hypercompact stellar systems unique is a high internal velocity. This is detectable only by measuring the velocities of stars moving around the black hole, a difficult measurement that would require a long time exposure on a large telescope.

From time to time, a hypercompact stellar system will make its presence known in a much more dramatic way, when one of the stars is tidally disrupted by the supermassive black hole. In this case, gravity stretches the star and sucks it into the black hole. The star is torn apart, causing a beacon-like flare that signals a black hole.

"The only contact of these floating black holes with the rest of the universe is through their armada of stars with an occasional display of stellar fireworks to signal 'here we are,'" Merritt said.

July 10, 2009

Turbulence from large black holes halts star formation

Snapshot of gas temperatures in a three-dimensional computer simulation of a cool-core cluster. The blue ring shows the cool gas accreting onto the central black hole disk; the red and yellow jets show the hot gas ejected by this disk. Older bubbles from an earlier outburst are visible on the far left and right sides of the image. Turbulence generated by the jets mixes the hot and cool material together, which stabilizes further accretion and allows the cluster to perform its remarkable balancing act. E. Scannapieco/ M. Brueggen / ASU Fulton High Performance Computing Initiative

New simulations reveal that turbulence created by jets of material ejected from the disks of the universe's largest black holes is responsible for halting star formation. Evan Scannapieco, an assistant professor in the School of Earth and Space Exploration at Arizona State University (ASU) and Marcus Brueggen, professor of Jacobs University in Bremen, Germany, presented the new model.

We live in a hierarchical universe where small structures join larger ones. Earth is a planet in our solar system, the solar system resides in the Milky Way Galaxy, and galaxies combine into groups and clusters. Clusters are the largest structures in the universe. Researchers have long known that the gas in the centers of some galaxy clusters cools and condenses rapidly, but were puzzled why this condensed gas did not form into stars. Until recently, no model existed that successfully explained how this was possible.

Scannapieco has spent much of his career studying the evolution of galaxies and clusters. "There are two types of clusters — cool-core clusters and non-cool core clusters," he said. "Non-cool core clusters haven't been around long enough to cool, whereas cool-core clusters are rapidly cooling, although by our standards they are still very hot."

X-ray telescopes have revolutionized our understanding of the activity occurring within cool-core clusters. Although these clusters can contain hundreds or thousands of galaxies, they are mostly made up of a diffuse, but very hot gas known as the intracluster medium. This intergalactic gas is only visible to X-ray telescopes, which are able to map out its temperature and structure. These observations show that the diffuse gas is rapidly cooling into the centers of cool-core clusters.

At the core of each of these clusters is a black hole, billions of times more massive than the Sun. Some of the cooling medium makes its way down to a dense disk surrounding the black hole, some of it goes into the black hole itself, and some of it is shot outward. X-ray images clearly show jet-like bursts of ejected material, occurring in regular cycles.

But why were these outbursts so regular, and why did the cooling gas never drop to colder temperatures that lead to the formation of stars? Some unknown mechanism was creating an impressive balancing act.

"It looked like the jets coming from black holes were somehow responsible for stopping the cooling," said Scannapieco, "but until now no one was able to determine how exactly."

Scannapieco and Brueggen used the enormous supercomputers at ASU to develop their own three-dimensional simulation of the galaxy cluster surrounding one of the universe's biggest black holes. By adapting an approach developed by Guy Dimonte at Los Alamos National Laboratory and Robert Tipton at Lawrence Livermore National Laboratory, Scannapieco and Brueggen added the component of turbulence to the simulations, which was never accounted for in the past.

And that was the key ingredient.

Turbulence works in partnership with the black hole to maintain the balance. Without turbulence, jets coming from around the black hole would grow stronger and stronger, and the gas would cool catastrophically into a swarm of new stars. When turbulence is accounted for, the black hole not only balances the cooling, but also goes through regular cycles of activity.

"When you have turbulent flow, you have random motions on all scales," said Scannapieco. "Each jet of material ejected from the disk creates turbulence that mixes everything together."

Scannapieco and Brueggen's results reveal that turbulence acts to effectively mix the heated region with its surroundings so that the cool gas can't make it down to the black hole, thus preventing star formation.

Every time some cool gas reaches the black hole, it is shot out in a jet. This generates turbulence that mixes the hot gas with the cold gas. This mixture becomes so hot that it doesn't accrete onto the black hole. The jet stops and there is nothing to drive the turbulence so it fades away. At that point, the hot gas no longer mixes with the cold gas, so the center of the cluster cools, and more gas makes its way down to the black hole.

Before long, another jet forms and the gas once again is mixed together.

"We improved our simulations so that they could capture those tiny turbulent motions," said Scannapieco. "Even though we can't see them, we can estimate what they would do. The time it takes for the turbulence to decay away is exactly the same amount of time observed between the outbursts."

July 14, 2009

Study aims to maximize scientific return from Moon rovers

South Pole-Aitken Basin, the largest and deepest impact basin in the solar system, is likely to be one of the primary targets for lunar rovers. This view, which is centered on the basin, consists of color-coded topography overlaid on a shaded relief representation of the Moon. Purple and blue are low, and orange and red are high. The basin is up to 8 miles (13 kilometers) deep, with an average depth of about 6 miles (10 kilometers). Rovers may find volcanic evidence in the basin that could help unravel the Moon's thermal evolution. Clementine Science Group, Lunar and Planetary Institute

NASA and other national space agencies are again focused on lunar exploration, which raises the question of how to best use semi-autonomous rovers to explore the Moon's surface.

R. Aileen Yingst, a senior scientist at the Tucson-based Planetary Science Institute, is leading a group of Mars-rover veterans who are conducting field studies to answer that question.

The scientists are evaluating operational strategies to maximize the scientific return from rover activities. This includes determining the types of instruments the rover should carry and how they should be used to recognize surface features that speak to the Moon's volcanic history, possible ice formation at its poles, and other geologic questions.

"We've done 5 years of semi-autonomous rover operations on Mars, and we have a good day-to-day operational understanding of how that works," said Yingst, a participating scientist on the Mars Exploration Rover (MER) mission. "But there will be some significant changes in those strategies when we have rovers on the Moon, just because of the difference in time lag, among other things."

Because it takes 40 minutes to radio a martian rover and receive an answer, continuous communication is not possible. This has led scientists to upload the operational sequences for up to three days of rover activities in a single message. The rover then operates independently for that time period.

But the Moon is much closer than Mars, and the round-trip message time from Earth is only about 3 seconds, not much longer than the time lag a cable TV newsroom experiences when contacting a reporter in Baghdad. The short time lag will change how scientists direct the rover and how they will use its instruments.

Lunar geology also is different from martian geology, so the rover will be looking for different things, Yingst said. For instance, lunar rovers could search for a variety of basaltic lava types that will help explain the Moon's thermal evolution. They also may search for ice at the poles, which might occur as permafrost or coatings of ice on rocky grains, she said.

Scientists also want to date portions of the lunar surface to field check their current estimates of the age of lunar formations. This is important because the ages of many other planetary surfaces in the solar system are keyed to the age of lunar landforms and the number of craters found on them.

Yingst's team will be studying volcanic areas in New Mexico and permafrost in Alaska as Earth analogs of similar surfaces on the Moon. One field team will pretend to be an autonomous rover and will use a camera, spectrometer, and other instruments — and only the data from those instruments — to make decisions about where to go and what kind of data to collect.

A team of scientists that will use traditional field methods to study the geology will follow the rover team.

"Human geologists certainly will be able to figure out a lot more about the geology than an autonomous rover can," Yingst said. "We already know that. But then the questions are: What can they figure out that the rover can't? How do they do that? And how can we use that information to make the rover smarter and more efficient?"

She emphasized that this method is a low-cost way to explore these questions because it doesn't require building and testing costly rover prototypes. "We're mimicking the methodology, without incurring the time or expense involved in dealing with rovers and space-qualified instruments in the field," she said.

The results from this study will help scientists design more intelligent rovers and operate them more efficiently once they land on the Moon, she said.

July 27, 2009

Unveiling the true face of a mammoth star

Artist's impression showing how a vast amount of material is flung out from Betelgeuse into space. ESO/L. Calcada

An international team of astronomers, led by Keiichi Ohnaka at the Max Planck Institute for Radio Astronomy (MPIfR) in Bonn, Germany, has taken the sharpest view yet of a dying mammoth star. The image shows how gas moves in different areas over the surface of a distant star. This view was made possible by combining three 1.8-meter telescopes as an interferometer, giving the astronomers the resolving power of a gigantic 48-meter telescope.

Using the European Southern Observatory's (ESO) Very Large Telescope Interferometer (VLTI) in Chile, the group discovered that the gas in the dying star's atmosphere is vigorously moving up and down, but the size of such "bubbles" is as large as the star itself. These colossal bubbles are a key for pushing material out of the star's atmosphere into space before the star explodes as a supernova.

In a clear winter night sky, it is easy to spot a bright, orange star on the shoulder of the constellation Orion the Hunter, even in light-flooded big cities. That is Betelgeuse. It is a mammoth star big enough that, if it were in our solar system, it would reach the orbit of Jupiter, swallowing the inner planets Mercury, Venus, Earth, and Mars. It is also glaringly bright, emitting 100,000 times more light than the Sun. Betelgeuse is a red supergiant, and it is approaching the end of its short life of several million years. Red supergiants shed a large amount of material made of various molecules and dust, which are recycled for the next generation of stars and planets, possibly like Earth. Betelgeuse loses material equivalent to Earth's mass every year.

How these mammoth stars can lose mass, which would normally be bound to the star by the gravitational pull, is a long-standing mystery. The best way to tackle this issue is to observe the scene where the material is ejected from a star's surface. Although Betelgeuse is such a huge star, it looks like a mere reddish dot even with today's largest telescopes because the star is 640 light-years away.

Astronomers use a special technique to overcome this problem. By combining two or more telescopes as an interferometer, astronomers can achieve a much higher resolution than individual telescopes provide. The VLTI is one of the world's largest interferometers. The astronomers observed Betelgeuse with the telescope's AMBER instrument operating at near-infrared wavelengths.

"Our AMBER observations mark the sharpest view ever made on Betelgeuse," said Keiichi Ohnaka at the MPIfR. "And for the first time, we have spatially resolved the gas motion in the atmosphere of a star other than the Sun. Thus, we could observe how the gas is moving in different areas over the star's surface."

The AMBER observations have revealed that the gas in Betelgeuse's atmosphere is moving vigorously up and down. The size of these "bubbles" is also gigantic, as large as the supergiant star. While the origin of these bubbles is not yet entirely clear, the AMBER observations have shed new light on the question about how red supergiant stars lose mass. It also means that the material is not spilling out in a quiet, ordered way, but is flung out more violently in arcs or clumps.

Cosmic fireworks known as a supernova, like the famous SN1987A, will accompany the death of the mammoth star, which is expected in the next few thousand to hundred thousand years. However, as Betelgeuse is much closer to Earth than SN1987A, the supernova can be clearly seen with the unaided eye, even in daylight.

July,2009

Jupiter impact continues to impress

An infrared image of Jupiter, taken by the Keck II Telescope shows how the diameter of the impact site compares with the size of Earth. P. Kalas (UCB), M. Fitzgerald (LLNL/UCLA), F. Marchis (SETI Institute/UCB), J. Graham (UCB)

New pictures of Jupiter and its recent impact site keep pouring in, showing the rapidly growing atmospheric aftermath in increasingly greater detail. First discovered by Australian amateur astronomer Anthony Wesley on July 19, the Pacific Ocean-sized black spot is likely the result of a collision with an asteroid or comet.

The W. M. Keck Observatory, located on Hawaii's Mauna Kea volcano, confirmed the impact last week with a set of infrared images. Astronomers there plan to test theories developed 15 years ago during Comet Shoemaker-Levy 9's impact with the gas giant, the only other planetary collision ever witnessed.Later in the week, the Hubble Space Telescope's newest camera captured the sharpest visible-light picture to date of Jupiter's latest feature. Not only did the image provide greater detail on the impact itself, but also it proved astronauts successfully serviced the telescope in May.

Operators of the Keck and Hubble telescopes originally scheduled other work for the week but decided to postpone their plans to better study the unfolding events on Jupiter. They join a multitude of amateur and professional astronomers across the world now training their eyepieces on the planet's constantly changing spot.

NASA scientists estimate the colliding object was several hundreds of yards across and the force of its impact to have been thousands of times greater than the explosion in 1908 over the Siberian Tunguska River Valley.

July 27, 2009

Mars, methane and mysteries

Artist's impression of Mars Express

Mars may not be as dormant as scientists once thought. The 2004 discovery of methane means that either there is life on Mars, or that volcanic activity continues to generate heat below the martian surface. ESA plans to find out which it is. Either outcome is big news for a planet once thought to be biologically and geologically inactive.

The methane mystery started soon after December 2003, when ESA’s Mars Express arrived in orbit around the red planet. As the Planetary Fourier Spectrometer (PFS) began taking data, Vittorio Formisano, Istituto di Fisica dello Spazio Interplanetario CNR, Rome, and the rest of the instrument team saw a puzzling signal. As well as the atmospheric gases they were anticipating, such as carbon monoxide and water vapour, they also saw methane. “Methane was a surprise, we were not expecting that,” says Agustin Chicarro, ESA Mars Lead Scientist. The reason is that on Earth much of the methane in our atmosphere is released by evolved life forms, such as cattle digesting food. While there are ways to produce methane without life, such as by volcanic activity, it is the possible biological route that has focused attention on the discovery.

The Mars Express detection of methane is not an isolated case. While the spacecraft was en route, two independent teams of astronomers using ground-based telescopes started to see traces of methane. After five years of intensive study, the suite of observations all confirmed the discovery and presented planetary scientists with a big puzzle.

Methane is thought to be stable in the martian atmosphere for around 300 years. So, whatever is generating the methane up there, it is a recent occurrence. In January 2009, a team led by Michael Mumma of NASA’s Goddard Space Flight Center published results that the methane they saw in 2003 was concentrated in three regions of the planet. This showed that the methane was being released at the present time and was being observed before it had time to distribute itself around the planet.

Things then took a strange turn. Instead of taking 300 years to disappear, the methane had almost entirely vanished by early 2006. Clearly something unusual is going on at Mars. “We thought we understood how methane behaved on Mars but if the measurements are correct then we must be missing something big,” says Franck Lefèvre, Université Pierre et Marie Curie, CNRS, Paris and a member of Mars Express’s SPICAM instrument team.

Together with his colleague François Forget, Mars Express Interdisciplinary Scientist in charge of atmospheric studies and also of Université Pierre et Marie Curie, CNRS, Paris, Lefèvre has investigated the disappearance using a computer model of Mars’ climate. “We have tackled the problem as atmospheric physicists, without worrying about the nature of the source of the methane,” he says.

In results published last week they found that, while their computer model can reproduce atmospheric species such as carbon monoxide and ozone, it is unable to reproduce the behaviour of the methane. “Something is removing the methane from the atmosphere 600 times faster than the models can account for,” says Lefèvre. “Consequently, the source must be 600 times more intense than originally assumed, which is considerable even by Earth’s geological standards.”


To remove methane at such a rate, suspicion falls on the surface of the planet. Either the methane is being trapped in the dust there or highly reactive chemicals such as hydrogen peroxide are destroying it, as was hinted by the Viking missions in the 1970s. If the latter, then the surface is much more hostile to organic molecules (those containing carbon) than previously thought. This will make searching for traces of past or present life much tougher and future rovers will have to drill below the martian surface to look for signs of life.

To help get to the bottom of the methane mystery, ESA and the Italian space agency (ASI) are to hold a three-day international workshop in November. The assembled scientists will discuss the results and plan strategies for the future study of methane. At the workshop, the Mars Express PFS team hopes to present a global map of martian methane. “We have made the PFS mapping a priority over the last few months,” says Olivier Witasse, ESA Project Scientist for Mars Express.

In July, ESA agreed with NASA to launch joint missions to Mars. The topic of methane is of such importance that it will be most likely addressed in these future missions. “Understanding the methane on Mars is one of our top priorities,” says Witasse.

However the methane is eventually explained, it makes Mars a more fascinating place than even planetary scientists dreamed.

10 August 2009

Astronomers Find Hyperactive Galaxies in the Early Universe

Looking almost 11 billion years into the past, astronomers have measured the motions of stars for the first time in a very distant galaxy and clocked speeds upwards of one million miles per hour, about twice the speed of our Sun through the Milky Way.

The fast-moving stars shed new light on how these distant galaxies, which are a fraction the size of our Milky Way, may have evolved into the full-grown galaxies seen around us today. The results will be published in the August 6, 2009 issue of the journal Nature, with a companion paper in the Astrophysical Journal.

"This galaxy is very small, but the stars are whizzing around as if they were in a giant galaxy that we would find closer to us and not so far back in time," says Pieter van Dokkum, professor of astronomy and physics at Yale University in New Haven, Conn., who led the study. It is still not understood how galaxies like these, with so much mass in such a small volume, can form in the early universe and then evolve into the galaxies we see in the more contemporary, nearby universe, which is about 13.7 billion years old.

The work by the international team combined data collected using NASA's Hubble Space Telescope with observations taken by the 8-meter Gemini South telescope in Chile. According to van Dokkum, "The Hubble data, taken in 2007, confirmed that this galaxy was a fraction the size of most galaxies we see today in the more evolved, older universe. The giant, 8-meter mirror of the Gemini telescope then allowed us to collect enough light to determine the overall motions of the stars using a technique not very different from the way police use laser light to catch speeding cars." The Gemini near-infrared spectroscopic observations required an extensive 29 hours on the sky to collect the extremely faint light from the distant galaxy, which goes by the designation 1255-0.

"By looking at this galaxy we are able to look back in time and see what galaxies looked like in the distant past when the universe was very young," says team member Mariska Kriek of Princeton University in Princeton, N.J. 1255-0 is so far away that the universe was only about 3 billion years old when its light was emitted.

Astronomers confess that it is a difficult riddle to explain how such compact, massive galaxies form, and why they are not seen in the current, local universe. "One possibility is that we are looking at what will eventually be the dense central region of a very large galaxy," explains team member Marijn Franx of Leiden University in the Netherlands. "The centers of big galaxies may have formed first, presumably together with the giant black holes that we know exist in today's large galaxies that we see nearby."

To witness the formation of these extreme galaxies astronomers plan to observe galaxies even farther back in time in great detail. By using the Wide Field Camera 3, which was recently installed on the Hubble Space Telescope, such objects should be detectable. "The ancestors of these extreme galaxies should have quite spectacular properties as they probably formed a huge amount of stars, in addition to a massive black hole, in a relatively short amount of time," says van Dokkum.

This research follows recent studies revealing that the oldest, most luminous galaxies in the early universe are very compact yet surprisingly have stellar masses similar to those of present-day elliptical galaxies. The most massive galaxies we see in the local universe (where we don't look back in time significantly) that have a mass similar to 1255-0 are typically five times larger than the young compact galaxy. How galaxies grew so much in the past 10 billion years is an active area of research, and understanding the dynamics in these young compact galaxies is a key piece of evidence in eventually solving this puzzle.

The Hubble Space Telescope observations were made with the Near Infrared Camera and Multi-Object Spectrometer (NICMOS).

The Gemini observations were made using the Gemini Near Infrared Spectrograph (GNIRS), which is currently undergoing upgrades and will be reinstalled on the Gemini North telescope on Mauna Kea in 2010.

August 5, 2009