samedi 20 juillet 2013

Atlas 5 Launches MUOS-2 Satellite into Orbit












ULA - MUOS-2 Mission patch.

July 20, 2013

A United Launch Alliance Atlas 5 rocket launched the second of the U.S. Navy’s new generation of mobile communications satellites July 19 from Cape Canaveral Air Force Station, Fla.

video
Launch of MUOS-2 on Largest Atlas V 551 Rocket

Upper level winds delayed liftoff of the Mobile User Objective System (MUOS)-2 satellite until 9 a.m. EDT.  By 9:30 a.m., the Atlas 5 rocket’s Centaur upper stage had completed two of three scheduled burns. The final burn, which will deploy MUOS-2 into a geostationary transfer orbit, is scheduled to occur at approximately 12 p.m. EDT. The satellite is expected to take eight days to maneuver into its geostationary orbit some 36,000 kilometers above the equator, Capt. Paul Ghyzel, the Navy’s MUOS program manager, said in a prelaunch conference call with reporters July 15. The Navy expects to declare MUOS-2 operational after a six-month check-out period.

Weighing more than 6,800 kilograms, MUOS-2 is also the heaviest satellite launched aboard an Atlas 5, said Jim Sponnick, United Launch Alliance’s vice president of Atlas and Delta programs.

MUOS-2 Satellite

The satellite is equipped with a UHF-band narrow band payload to provide links to ships at sea and to mobile ground forces operating in hard-to-reach areas such as beneath dense forest canopies.

The first of the MUOS satellites was launched in February 2012.

The third MUOS satellite is expected to launch in 2014 and the program is expected to achieve full operational capability in 2015. The satellites are expected to provide service through 2025.

For more information about United Launch Alliance (ULA), visit: http://www.ulalaunch.com/site/default.shtml

Image, Video, Text, Credits: ULA / ATS / Gunter.

Greetings, Orbiter.ch

vendredi 19 juillet 2013

MAVEN Spectrometer Opens Window to Red Planet’s Past






NASA - MAVEN Mission logo.

July 19, 2013

When NASA’s MAVEN mission begins its journey to the Red Planet later this year, it will be equipped with a special instrument to take the planet back in time.

That instrument is the Neutral Gas and Ion Mass Spectrometer, a network of electrically charged rods that will measure the charged gas particles—or ions—making up Mars’ upper atmosphere.

video
Searching for Mars Missing Atmosphere

Video above: MAVEN will use its Neutral Gas and Ion Mass Spectrometer to study the interaction of neutral gases and ions in the Martian atmosphere with the solar wind, helping scientists to understand how Mars has lost its atmosphere over time. Video Credit: NASA's Goddard Space Flight Center.

Designed and developed at NASA’s Goddard Space Flight Center in Greenbelt, Md., the state-of-the-art instrument will launch aboard MAVEN, short for Mars Atmosphere and Volatile Evolution, in November. Once at Mars, the spectrometer will collect data on the ions above the Red Planet.

"The data could be used to build models showing how Mars has lost the majority of its atmosphere, a phenomenon that continues to be one of the planet’s greatest mysteries," said Paul Mahaffy, the spectrometer’s principal investigator from Goddard.

Once the MAVEN spacecraft launches, the team would apply radio frequency and electrical voltages to the instrument’s four metal cylinders, or quadrupole rods.

Each specific voltage isolates ions based on their specific mass. This allows the instrument to build a profile, known as a mass spectrum, of all the different gas particles present in the Martian atmosphere.

“We’re basically sorting ions by mass,” Mahaffy said.

Artist concept of MAVEN spacecraft. Image Credit: NASA's Goddard Space Flight Center

Besides measuring the ions already present in the atmosphere, the instrument could also create ions from neutral gas molecules. An electron gun will fire a beam of electrons, breaking the gas molecules into smaller, charged particles. By doing this, the instrument can collect information on all of the gas particles, both neutral and charged, in the upper atmosphere.

“Our part of the overall mission is to measure the neutral and ion composition of the atmosphere,” Mahaffy said. “We’re measuring ions that are already there and those that are created.”

The instrument will measure the composition of the current atmosphere and how variables like time of day change the gas particles over time. This critical information can then be used to build simulations of both the current Martian atmosphere and the atmosphere billions of years ago.

“What we’re doing is measuring the composition of the atmosphere as a measure of latitude, longitude, time of day and solar activities,” Mahaffy said. “We’re trying to understand over billions of years how the atmosphere has been lost.”

While it’s unknown why Mars has lost most of its atmosphere, scientists point to solar wind for stripping it. The planet itself lacks a global magnetic field, which typically protects planets like Earth from solar wind, maintaining the atmosphere.

If the models can accurately portray the Martian atmosphere billions of years ago, scientists might be able to answer critical questions like whether the atmosphere was once substantial enough to sustain liquid water on its surface and support life. Currently, the planet is barren and below freezing, with much of its water seen near the surface as ice.

“The big question is can the models help us understand the atmosphere back in time,” Mahaffy said. “This is another part of the puzzle in understanding what [the] atmosphere is like that’s intended to be solved by the MAVEN mission.”

The spectrometer instrument, known by the acronym “NGIMS,” will be located on a platform below the spacecraft, keeping it away from its own gases and allowing it to face different directions. It will collect data when MAVEN is between about 93 and 311 miles (150 and 500 kilometers) above the planet, storing it in the spacecraft’s memory bank for several days before it’s transmitted to NASA’s Deep Space Network satellites around the globe.

In addition to providing important information on its own, NGIMS would complement other instruments aboard, specifically the Imaging Ultraviolet Spectrometer, which would also measure gas composition.

“Both instruments get composition of the atmosphere and how it changes based on variables,” Mahaffy said. “Not only do the different instruments get different species, but we measure at different locations, and that’s really helpful for understanding what the atmosphere is doing.”

NGIMS electrical lead Florence Tan said the information the instrument is trying to find supports mankind’s desire to determine if Earth is the only planet supporting life.

“The question of why only Earth to me is the big science question,” Tan said. “Mars is a close neighbor, so we look at it from the point of view of finding organisms on Earth living in extreme conditions.”

The instrument promises to collect a lot of exciting data.

“It is one step in getting to a really big question, which is, ‘Are we alone in the universe?” Mahaffy said. “MAVEN is one step in that program for understanding life on early Mars, and we’ll try to do everything we can to understand it.”

Related Link:

NASA's MAVEN website: http://www.nasa.gov/mission_pages/maven/main/index.html

Image (mentioned), Video (mentioned), Text, Credits: NASA’s Goddard Space Flight Center / Claire Saravia.

Best regards, Orbiter.ch

Reports Detail Mars Rover Clues to Atmosphere's Past












NASA - Mars Science Laboratory (MSL) patch.

July 19, 2013

A pair of new papers report measurements of the Martian atmosphere's composition by NASA's Curiosity rover, providing evidence about loss of much of Mars' original atmosphere.

Curiosity's Sample Analysis at Mars (SAM) suite of laboratory instruments inside the rover has measured the abundances of different gases and different isotopes in several samples of Martian atmosphere. Isotopes are variants of the same chemical element with different atomic weights due to having different numbers of neutrons, such as the most common carbon isotope, carbon-12, and a heavier stable isotope, carbon-13.


Image above: This picture shows a lab demonstration of the measurement chamber inside the Tunable Laser Spectrometer, an instrument that is part of the Sample Analysis at Mars investigation on NASA's Curiosity rover. Image Credit: NASA/JPL-Caltech.

SAM checked ratios of heavier to lighter isotopes of carbon and oxygen in the carbon dioxide that makes up most of the planet's atmosphere. Heavy isotopes of carbon and oxygen are both enriched in today's thin Martian atmosphere compared with the proportions in the raw material that formed Mars, as deduced from proportions in the sun and other parts of the solar system. This provides not only supportive evidence for the loss of much of the planet's original atmosphere, but also a clue to how the loss occurred.

"As atmosphere was lost, the signature of the process was embedded in the isotopic ratio," said Paul Mahaffy of NASA Goddard Space Flight Center, Greenbelt, Md.  He is the principal investigator for SAM and lead author of one of the two papers about Curiosity results in the July 19 issue of the journal Science.

Other factors also suggest Mars once had a much thicker atmosphere, such as evidence of persistent presence of liquid water on the planet's surface long ago even though the atmosphere is too scant for liquid water to persist on the surface now. The enrichment of heavier isotopes measured in the dominant carbon-dioxide gas points to a process of loss from the top of the atmosphere -- favoring loss of lighter isotopes -- rather than a process of the lower atmosphere interacting with the ground.

Curiosity measured the same pattern in isotopes of hydrogen, as well as carbon and oxygen, consistent with a loss of a substantial fraction of Mars' original atmosphere. Enrichment in heavier isotopes in the Martian atmosphere has previously been measured on Mars and in gas bubbles inside meteorites from Mars. Meteorite measurements indicate much of the atmospheric loss may have occurred during the first billion years of the planet's 4.6-billion-year history. The Curiosity measurements reported this week provide more precise measurements to compare with meteorite studies and with models of atmospheric loss.

Mars Science Laboratory (MSL) "Curiosity" rover description. Image Credit: NASA/JPL-Caltech

The Curiosity measurements do not directly measure the current rate of atmospheric escape, but NASA's next mission to Mars, the Mars Atmosphere and Volatile Evolution Mission (MAVEN), will do so. "The current pace of the loss is exactly what the MAVEN mission now scheduled to launch in November of this year is designed to determine," Mahaffy said.

The new reports describe analysis of Martian atmosphere samples with two different SAM instruments during the initial 16 weeks of the rover's mission on Mars, which is now in its 50th week. SAM's mass spectrometer and tunable laser spectrometer independently measured virtually identical ratios of carbon-13 to carbon-12. SAM also includes a gas chromatograph and uses all three instruments to analyze rocks and soil, as well as atmosphere.

"Getting the same result with two very different techniques increased our confidence that there's no unknown systematic error underlying the measurements," said Chris Webster of NASA's Jet Propulsion Laboratory, Pasadena, Calif. He is the lead scientist for the tunable laser spectrometer and the lead author for one of the two papers. "The accuracy in these new measurements improves the basis for understanding the atmosphere's history."

Curiosity landed inside Mars' Gale Crater on Aug. 6, 2012 Universal Time (on Aug. 5 PDT). The rover this month began a drive of many months from an area where it found evidence for a past environment favorable for microbial life, toward a layered mound, Mount Sharp, where researchers will seek evidence about how the environment changed.  

More information about Curiosity is online at: http://www.nasa.gov/msl and http://mars.jpl.nasa.gov/msl/ .

You can follow the mission on Facebook at: http://www.facebook.com/marscuriosity and on Twitter at http://www.twitter.com/marscuriosity .

Images (mentioned), Text, Credits: NASA / JPL / Guy Webster / Goddard Space Flight Center / Nancy Neal Jones.

Greetings, Orbiter.ch

Telescope Door on IRIS Opens










NASA - Interface Region Imaging Spectrograph (IRIS) patch.

July 19, 2013

Wednesday at 11:14 pm PDT (2:14 pm EDT) the IRIS Lockheed Martin instrument team successfully opened the door on NASA’s Interface Region Imaging Spectrograph, which launched June 27, 2013, aboard a Pegasus XL rocket from Vandenberg Air Force Base, Calif.


Image above: In its first major milestone since launch, the IRIS team opened the telescope door on July 17, 2013. The telescope door is the circular white object on the far left of this graphic. Image Credit: NASA Goddard.

A 60-day check out period began at launch. The first 30 days, which ends July 27, consists of tests and spacecraft system checks. The team will use the remaining 30 days for initial observing runs to fine tune instrument observations. If all is nominal, the team plans to begin normal science mode by August 26.

All data will be available to scientists and the public as soon as the mission begins science operations. The team is looking forward to receiving high-resolution images and spectra soon after first light.

Additional mission updates will be provided as warranted.

For more information about Interface Region Imaging Spectrograph (IRIS), visit: http://www.nasa.gov/mission_pages/iris/index.html

Image (mentioned), Text, Credits: NASA's Goddard Space Flight Center/Susan Hendrix.

Cheers, Orbiter.ch

ESA / NASA Hubble Sees a Stranger in the Crowd














NASA - Hubble Space Telescope patch / ESA - Hubble Space Telescope patch.

July 19, 2013


The constellation of Virgo (The Virgin) is the largest of the Zodiac constellations, and the second largest overall after Hydra (The Water Snake). Its most appealing feature, however, is the sheer number of galaxies that lie within it. In this picture, among a crowd of face- and edge-on spiral, elliptical, and irregular galaxies, lies NGC 4866, a lenticular galaxy situated about 80 million light-years from Earth.

Lenticular galaxies are somewhere between spirals and ellipticals in terms of shape and properties. From the picture, we can appreciate the bright central bulge of NGC 4866, which contains primarily old stars, but no spiral arms are visible. The galaxy is seen from Earth as almost edge-on, meaning that the disc structure — a feature not present in elliptical galaxies — is clearly visible. Faint dust lanes trace across NGC 4866 in this image, obscuring part of the galaxy’s light.

To the right of the galaxy is a very bright star that appears to lie within NGC 4866’s halo. However, this star actually lies much closer to us; in front of the galaxy, along our line of sight. These kinds of perspective tricks are common when observing, and can initially deceive astronomers as to the true nature and position of objects such as galaxies, stars, and clusters.

This sharp image of NGC 4866 was captured by the Advanced Camera for Surveys, an instrument on the NASA / ESA Hubble Space Telescope.

The Hubble Space Telescope is a cooperative project between NASA and the European Space Agency. NASA's Goddard Space Flight Center in Greenbelt, Md., manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Md., conducts Hubble science operations. STScI is operated by the Association of Universities for Research in Astronomy Inc., in Washington.

For more information about NASA / ESA Hubble Space Telescope: http://www.nasa.gov/hubble and http://www.spacetelescope.org/

Image Credit: European Space Agency, Text, Credit: NASA.

Greetings, Orbiter.ch

jeudi 18 juillet 2013

Wobbly magnetic reconnection speeds up electrons












ESA - Cluster II Mission patch.

18 July 2013

Scientists have discovered a missing piece in the puzzle of where high-energy particles in Earth's magnetosphere come from. Using data from ESA's Cluster mission, they found that magnetic reconnection can accelerate electrons to very high energies - as long as reconnection happens at a variable pace rather than steadily. The result will improve predictions of space weather, studies of fusion plasma, and the understanding of astrophysical environments affected by magnetic fields.

Unsteady magnetic reconnection in Earth's magnetosphere. Credit: ESA/ATG medialab

From the magnetosphere of Earth and the atmosphere of stars to the interstellar medium, plasma pervades space. Studying this state of matter consisting of charged particles – electrons, protons, and heavier ions – is vital to our understanding of a range of natural and artificial phenomena.

The properties of plasma are strongly shaped by the presence of magnetic fields. In some cases, this interaction can accelerate particles – mainly electrons – to very high energies. In Earth's magnetosphere, high-energy electrons can disrupt GPS transmissions and even endanger the health of astronauts involved in spacewalks.

A team of scientists, led by Huishan Fu from the Swedish Institute of Space Physics in Uppsala, Sweden and Beihang University in Beijing, China, used ESA's Cluster mission to investigate how particles are accelerated by directly probing plasma in Earth's magnetosphere.

Their study, which is published in Nature Physics, examines how particles are energised by a phenomenon that is known to take place in plasma – magnetic reconnection. They show that as long as the reconnection is unsteady, it can accelerate electrons to very high energies.

"Magnetic reconnection happens at the collision of two flows of plasma with magnetic fields that are oriented in opposite directions," explains Fu.

"In the process, the magnetic field lines are broken and immediately rearranged in a new configuration; at the same time, two jets of high-speed plasma are launched from the site of magnetic reconnection into opposite directions."

Magnetic reconnection is an efficient mechanism to transfer the energy stored in the magnetic field to the kinetic energy of particles in the plasma.

In the Solar System, magnetic reconnection may take place in the solar wind as it travels through interplanetary space, as well as in the magnetosphere of planets that possess a magnetic field.

Scientists know that magnetic reconnection can accelerate particles and produce high-energy electrons. Whether acceleration happens every time as a result of reconnection, however, was still an open issue.

"We know that electrons are accelerated up to 100 keV, and even more, after magnetic reconnection in the magnetotail, the tail of Earth's magnetosphere which points away from the Sun," says co-author Mats André from the Swedish Institute of Space Physics in Uppsala, Sweden. "But for some reason the same thing doesn't seem to happen during reconnection in the interplanetary solar wind."

"This was clearly a signature of something more fundamental underneath, but we didn't know what that was," he adds.

So the scientists browsed the Cluster archive looking for magnetic reconnection events in the tail of the magnetosphere.

Acceleration of electrons caused by unsteady magnetic reconnection. Credit: ESA/ATG medialab

"The data we analysed were taken as the Cluster spacecraft were in the trajectory of the jet launched from the site of magnetic reconnection and directed to Earth, so we could directly sample the plasma particles in situ and probe the properties of the jet."

The scientists noticed an interesting structure in this jet as it travelled towards Earth: it turned out not to be a single jet but two distinct ones, launched with a time difference of about 25 seconds. And, each of the two Earthward jets showed a finer structure, with the bulk velocity of plasma increasing in the leading part of the jet and decreasing in the following part.

"This is a textbook recipe for particle acceleration: in the part of the jet where velocity is rising, the magnetic field is compressed by the high-speed flow, and the magnetic field lines get close to one another," explains André.

"This boosts the magnetic field and 'traps' the particles, forcing them to interact repeatedly with the magnetic field: eventually, this turns out to be a very efficient accelerator of electrons," he adds.

The study by Fu and his collaborators shows that, like in artificial accelerators, the acceleration of electrons in the magnetotail advances via a sequence of mechanisms. First, unsteady magnetic reconnection speeds up plasma particles in the jets. Then the magnetic field lines are compressed, accelerating the electrons via the betatron or Fermi acceleration mechanisms.

While in artificial accelerators the first steps of the process must be induced by external electric and magnetic fields, in space the acceleration process is triggered by naturally occurring electric and magnetic fields within the plasma.

"In the tail of Earth's magnetosphere, the origin of the acceleration appears to be in the fine structure of the jets. We think that this structure arises because the magnetic reconnection is happening at an unsteady rate," says Fu.

Such an erratic rate of reconnection can be caused by temporal variability in the speed of the inflowing plasma that triggers the process, or by turbulence that develops directly in the magnetic reconnection site.

"Unsteady magnetic reconnection is a well-known phenomenon, but up until now nobody had studied it in relation to high-energy electrons," comments Fu.

"For the first time, our study proved that the two processes are intimately linked."

The scientists compared these data with observations of magnetic reconnection taking place at a uniform pace in the interplanetary solar wind, and confirmed that, without the unsteady rate of reconnection, electrons are not accelerated to high energies.

"We have finally grasped how exactly magnetic reconnection gives rise to high-energy electrons," comments Philippe Escoubet, Cluster Project Scientist at ESA.

"This will deepen our understanding of the behaviour of energetic particles in a variety of environments where unsteady reconnection takes place, from fusion plasma to places like the centre of our Galaxy or the chromosphere of stars.

"It will also improve our ability to predict space weather, since the electrons that are accelerated by unsteady reconnection feed the population of energetic particles in the Van Allen radiation belts."

Notes for editors

The study presented here is based on data gathered by one of the spacecraft (C1) of ESA's Cluster mission on 23 August 2006.

The data were collected during and after a magnetic reconnection event in the tail of Earth's magnetosphere. Data analysis revealed that the reconnection, which proceeded at an unsteady rate, eventually resulted in accelerating electrons in the plasma to very high energies via two mechanisms: betatron and Fermi acceleration.

The betatron mechanism, in which a time-varying magnetic field is responsible for increasing the energy of the electrons, was originally described by Norwegian physicist Rolf Widerøe in 1928. This mechanism was also applied to artificial particle accelerators by American physicist Donald Kerst, who constructed one of the first machines to produce high-energy electrons on the ground.

Fermi acceleration, which was first suggested by Italian-American physicist Enrico Fermi in 1949, is a mechanism whereby particles are energised by repeatedly bouncing off the turbulent magnetic field, which results in a net and substantial gain of energy. This may take place in the turbulent plasma associated with magnetic reconnection in the magnetotail.

Cluster is a constellation of four spacecraft flying in formation around Earth. It is the first space mission able to study, in three dimensions, the natural physical processes occurring within and in the near vicinity of the Earth's magnetosphere. Launched in 2000, it is composed of four identical spacecraft orbiting the Earth in a pyramidal configuration, along a nominal polar orbit of 4 × 19.6 Earth radii (1 Earth radius = 6380 km). Cluster's payload consists of state-of-the-art plasma instrumentation to measure electric and magnetic fields over wide frequency ranges, and key physical parameters characterising electrons and ions from energies of near 0 eV to a few MeV. The science operations are coordinated by the Joint Science Operations Centre (JSOC) at the Rutherford Appleton Laboratory, United Kingdom, and implemented by ESA's European Space Operations Centre (ESOC), in Darmstadt, Germany.

Related publications:

H. S. Fu, Yu. V. Khotyaintsev, A. Vaivads, A. Retinò & M. André, "Energetic electron acceleration by unsteady magnetic reconnection", 2013, Nature Physics, published online 23 June 2013. DOI: 10.1038/nphys2664

For more information about Cluster Mission, visit: http://sci.esa.int/cluster/

Images (mentioned), Text, Credit: ESA.

Cheers, Orbiter.ch

Snow in an Infant Planetary System












ESO - European Southern Observatory logo.

18 July 2013

A frosty landmark for planet and comet formation

Artist’s impression of snow lines around TW Hydrae

A snow line has been imaged in a far-off infant planetary system for the very first time. The snow line, located in the disc around the Sun-like star TW Hydrae, promises to tell us more about the formation of planets and comets, the factors that decide their composition, and the history of the Solar System. The results are published today in Science Express.

Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) have taken the first ever image of the snow line in an infant planetary system. On Earth, snow lines form at high altitudes where falling temperatures turn the moisture in the air into snow. This line is clearly visible on a mountain, where the snow-capped summit ends and the rocky face begins.

The snow lines around young stars form in a similar way, in the distant, colder reaches of the dusty discs from which planetary systems form. Starting from the star and moving outwards, water (H2O) is the first to freeze, forming the first snow line. Further out from the star, as temperatures drop, more exotic molecules can freeze and turn to snow, such as carbon dioxide (CO2), methane (CH4), and carbon monoxide (CO). These different snows give the dust grains a sticky outer coating and play an essential role in helping the grains to overcome their usual tendency to break up in collisions, allowing them to become the crucial building blocks of planets and comets. The snow also increases how much solid matter is available and may dramatically speed up the planetary formation process.

ALMA image of the carbon monoxide snow line

Each of these different snow lines — for water, carbon dioxide, methane and carbon monoxide — may be linked to the formation of particular kinds of planets [1]. Around a Sun-like star in a planetary system like our own, the water snow line would correspond to a distance between the orbits of Mars and Jupiter, and the carbon monoxide snow line would correspond to the orbit of Neptune.

The snow line spotted by ALMA is the first glimpse of the carbon monoxide snow line, around TW Hydrae, a young star 175 light-years away from Earth. Astronomers believe this budding planetary system shares many of the same characteristics of the Solar System when it was just a few million years old.

“ALMA has given us the first real picture of a snow line around a young star, which is extremely exciting because of what it tells us about the very early period in the history of the Solar System,” said Chunhua “Charlie” Qi (Harvard-Smithsonian Center for Astrophysics, Cambridge, USA) one of the two lead authors of the paper. “We can now see previously hidden details about the frozen outer reaches of another planetary system similar to our own.”

But the presence of a carbon monoxide snow line could have greater consequences than just the formation of planets. Carbon monoxide ice is needed to form methanol, which is a building block of the more complex organic molecules that are essential for life. If comets ferried these molecules to newly forming Earth-like planets, these planets would then be equipped with the ingredients necessary for life.

Snow line distance compared to the Solar System

Before now, snow lines had never been imaged directly because they always form in the relatively narrow central plane of a protoplanetary disc, so their precise location and extent could not be determined. Above and below the narrow region where snow lines exist, the star’s radiation prevents ice formation. The dust and gas concentration in the central plane is necessary to insulate the area from the radiation so that carbon monoxide and other gases can cool and freeze.

This team of astronomers succeeded in peering inside this disc to where the snow has formed with the help of a clever trick. Instead of looking for the snow — as it cannot be observed directly — they searched for a molecule known as diazenylium (N2H+), which shines brightly in the millimetre portion of the spectrum, and so is a perfect target for a telescope such as ALMA. The fragile molecule is easily destroyed in the presence of carbon monoxide gas, so would only appear in detectable amounts in regions where carbon monoxide had become snow and could no longer destroy it. In essence, the key to finding carbon monoxide snow lies in finding diazenylium.

ALMA's unique sensitivity and resolution has allowed the astronomers to trace the presence and distribution of diazenylium and find a clearly defined boundary approximately 30 astronomical units from the star (30 times the distance between the Earth and the Sun). This gives, in effect, a negative image of the carbon monoxide snow in the disc surrounding TW Hydrae, which can be used to see the carbon monoxide snow line precisely where theory predicts it should be — the inner rim of the diazenylium ring.

"For these observations we used only 26 of ALMA's eventual full complement of 66 antennas. Indications of snow lines around other stars are already showing up in other ALMA observations, and we are convinced that future observations with the full array will reveal many more of these and provide further, exciting insights into the formation and evolution of planets. Just wait and see,” concludes Michiel Hogerheijde from Leiden Observatory, the Netherlands.

Notes:

[1] For instance dry rocky planets form on the inner side of the water snow line (nearest the star), where only dust can exist. At the other extreme are the icy giant planets which form beyond the carbon monoxide snow line.

More information:

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of Europe, North America and East Asia in cooperation with the Republic of Chile. ALMA is funded in Europe by the European Southern Observatory (ESO), in North America by the U.S. National Science Foundation (NSF) in cooperation with the National Research Council of Canada (NRC) and the National Science Council of Taiwan (NSC) and in East Asia by the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Academia Sinica (AS) in Taiwan. ALMA construction and operations are led on behalf of Europe by ESO, on behalf of North America by the National Radio Astronomy Observatory (NRAO), which is managed by Associated Universities, Inc. (AUI) and on behalf of East Asia by the National Astronomical Observatory of Japan (NAOJ). The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

This research was presented in a paper appearing in the 18 July 2013 issue of Science Express.

The team is composed of C. Qi (Harvard-Smithsonian Center for Astrophysics, USA), K. I. Öberg (Departments of Chemistry and Astronomy, University of Virginia, USA), D. J. Wilner (Harvard-Smithsonian Center for Astrophysics, USA), P. d’Alessio (Centro de Radioastronomía y Astrofisica, Universidad Nacional Autónoma de Mexico, Mexico), E. Bergin (Department of Astronomy, University of Michigan, USA), S. M. Andrews (Harvard-Smithsonian Center for Astrophysics, USA), G. A. Blake (Division of Geological and Planetary Sciences, California Institute of Technology, USA), M. R. Hogerheijde (Leiden Observatory, Leiden University, Netherlands) and E. F. van Dishoeck (Max Planck Institute for Extraterrestrial Physics, Germany).

Qi and Öberg were joint lead authors of this work.

ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning the 39-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

Links:

More about ALMA: http://www.eso.org/public/teles-instr/alma.html

Photos of ALMA: http://www.eso.org/public/images/archive/category/alma/

Press release at NRAO: http://www.nrao.edu/pr/2013/snowline/

Images, Text, Credits: ESO / B. Saxton & A. Angelich / NRAO / AUI / NSF /ALMA (ESO / NAOJ / NRAO).

Greetings, Orbiter.ch

Hubble Shows Link Between Stars' Ages and Their Orbits in Dense Cluster











NASA - Hubble Space Telescope patch.

July 18, 2013

 Globular Cluster 47 Tucanae

Astronomers using NASA's Hubble Space Telescope have for the first time linked two distinct populations of stars in an ancient globular star cluster to their unique orbital dynamics, offering proof that the stars do not share the same birth date.

The analysis of the globular cluster 47 Tucanae shows that the two populations differ in age by less than 100 million years. The cluster resides roughly 16,700 light-years away in the southern constellation Tucana.

47 Tucanae — Hubble

Researchers, led by Harvey Richer of the University of British Columbia in Vancouver, combined recent Hubble observations with eight years' worth of data from the telescope's archive to determine the motions of the stars in this cluster.

Previous spectroscopic studies revealed that many globular clusters contain stars of varying chemical compositions, suggesting multiple episodes of star birth. This Hubble analysis, however, goes a step further, adding the stars' orbital motion to the analysis.

"When analyzing the motions of stars, the longer the time baseline for observations, the more accurately we can measure their motion," Richer explained. "These data are so good, we can actually see for the first time the individual motions of the stars in the cluster. The data offer detailed evidence to help us understand how various stellar populations formed in such clusters."

47 Tucanae — Digitized Sky Survey (DSS)

The Milky Way's globular clusters are the surviving relics from our galaxy's formation. They offer insights into the early history of our galaxy. 47 Tucanae is 10.5 billion years old and one of the brightest of our galaxy's more than 150 globular clusters. The cluster measures about 120 light-years wide.

Richer and his team used Hubble's Advanced Camera for Surveys in 2010 to observe the cluster. They combined those observations with 754 archival images to accurately measure the changes in positions of more than 30,000 stars. Using these data, they could discern how fast the stars are moving. The team also measured the stellar luminosities as well as temperatures.

This stellar archaeology identified the two distinct populations of stars. The first consists of redder stars, which are older, less chemically enriched, and in random, circularized orbits. The second population comprises bluer stars, which are younger, more chemically enhanced, and in more elliptical orbits.

Compass and Scale Image for 47 Tucanae

"The redder generation, which is deficient in heavier elements, reflects the initial motion of the gas that formed the cluster," Richer said. "These stars have retained a memory of their original motion."

After the most massive of these stars completed their stellar evolution, they expelled gas enriched with heavier elements back into the cluster. This gas collided with other gas and formed a second, more chemically enriched generation of stars that was concentrated towards the cluster center. Slowly over time these stars have been moving outwards, putting them on more radial orbits.

Evolution of 47 Tuc Stellar Populations

This discovery is not the first for Hubble in revealing multiple generations of stars in globular clusters. In 2007 Hubble researchers found three generations of stars in the massive globular cluster NGC 2808. Richer's team, however, linked stellar dynamics to separate populations for the first time. Finding multiple stellar populations in globular clusters has deep cosmological implications. Astronomers need to solve future enigmas of these multiple generations to better understand how stars formed in distant galaxies in the early universe.

The team's results are published in the July 1 issue of The Astrophysical Journal Letters.

The Hubble Space Telescope is a cooperative project between NASA and the European Space Agency. NASA's Goddard Space Flight Center in Greenbelt, Md., manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Md., conducts Hubble science operations. STScI is operated by the Association of Universities for Research in Astronomy Inc., in Washington.

For more information about NASA / ESA Hubble Space Telescope: http://www.nasa.gov/hubble and http://www.spacetelescope.org/

Images, Text, Credits: NASA, ESA, Digitized Sky Survey (DSS; STScI/AURA/UKSTU/AAO), H. Richer and J. Heyl (University of British Columbia), and J. Anderson and J. Kalirai (STScI).

Best regards, Orbiter.ch

Target asteroid tracked by European teams











Asteroid Watch.

18 July 2013

In a recent close-ish flyby, asteroid 2002 GT was studied in detail for the first time by a network of European astronomers. The observations were coordinated by ESA’s asteroid centre in Italy, and should prove crucial for a future spacecraft rendezvous.

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Asteroid 2002GT passes Earth 26 June 2013

Asteroid 2002 GT, a relatively large object a few hundred metres across, made a somewhat close flyby of Earth on 26 June, passing us at almost 50 times the distance of the Moon.

The encounter sparked intensive worldwide observations because the asteroid is the target of NASA’s Epoxi mission in January 2020.

Last month’s flyby was the last chance before then to study the object’s diameter, rotation, composition and other physical characteristics.

Ideal opportunity to coordinate response

“The flyby presented an ideal opportunity to exercise the unique ‘coordinating function’ of ESA’s new Near-Earth Object Coordination Centre,” says Ettore Perozzi, project leader for NEO services at Deimos Space.

“By alerting and then collating observations from diverse European teams, the Centre was able to provide a comprehensive set of results back to the scientific and space exploration communities, a cycle that wasn’t happening before. This is really a first for Europe.”

Asteroid in infrared

Deimos Space leads a project team that operates the Centre at the Agency’s ESRIN site near Rome.

The gathered information will enable a very good characterisation of the asteroid’s surface composition, thermal properties, shape and rotation. All of these features are crucial for any spacecraft visit.

Moreover, analysis of its changing brightness indicates the possible presence of a small moon. 

Focal point: ESA's NEO Coordination Centre

Gerhard Drolshagen, co-manager of the NEO segment at ESA’s Space Situational Awareness programme office, says the 2002 GT event highlighted the potential coordination role that the Centre can play in addition to its primary function of providing information on all known NEOs, including their orbits, impact risk and close approaches to Earth.

Asteroid 2002 GT

“Traditionally, Europe’s asteroid community reliably delivered world-class observations and has been credited with many significant discoveries and findings. What was lacking, however, was a central point to coordinate and synthesise data that could function across national and organisational boundaries.

“Our Centre has proven it can act as a driving force and a focal point for the European and international community involved in asteroid science, impact monitoring and mitigation.”

Asteroid type (click for enlarge)

Ettore adds: “We now know 2002 GT is a rocky body, belonging to a peculiar transition class that astronomers refer to as ‘Sq-type’.

“It’s also a potentially hazardous object, as its orbit crosses that of Earth, so it’s certainly a very interesting object, well worth watching.”

More about the NEO Coordination Centre, SSA and contact information: http://www.esa.int/Our_Activities/Operations/Space_Situational_Awareness/About_SSA-NEO_Coordination_Centre

About 2002GT observations
ESA’s Near-Earth Object Coordination Centre (NEO-CC) received well-documented observations of 2002GT as follows:

- Photometry and light-curve data from the 1 m-diameter C2PU   telescope at the Observatoire de la Cote d’Azur, which allows   calculation of the rotation period (3.77 hours). The shape of   the light curve is also compatible with the presence of a   satellite.
- Spectra and photometric data from Asiago Observatory (University   of Padova and Observatory of Padova) which allows determination   of the asteroid type (Sq), in agreement with other observations.
- Infrared observations from the Campo Imperatore Station of the   INAF Rome Astronomical Observatory. Even under bad weather   conditions, teams there were able to spot the asteroid 20 days   before Earth flyby.
- Astrometry from Gaia-FUN-SSO. Six telescopes observed 2002 GT   providing more than 1000 astrometric measurements. These were   sent to the Minor Planet Centre and processed at the Institut de   Mécanique Céléste et de Calcul des Ephémérides for computing   orbital elements.

Related kinks:

Observatoire de la Cote d’Azur: https://www.oca.eu/?lang=en

Asiago Observatory (University of Padova and Observatory of Padova): http://archive.oapd.inaf.it/asiago/

Campo Imperatore Station of the INAF Rome Astronomical Observatory: http://www.oa-roma.inaf.it/cimperatore/

Gaia-FUN-SSO: http://www.imcce.fr/hosted_sites/gaiafun2012/index.php

Minor Planet Centre: http://www.minorplanetcenter.org/iau/mpc.html

Institut de Mécanique Céléste et de Calcul des Ephémérides: http://www.imcce.fr/langues/en/

Images, Graphic, Video, Text, Credits: ESA / Observatoire de la Côte d'Azur & Université de Liège/M. Devogèle, J-P. Rivet, P. Tanga, Ph. Bendjoya, L. Abe, O. Suarez / Campo Imperatore Observatory / C2PU project / Asiago Oservatory.

Best regards, Orbiter.ch

mercredi 17 juillet 2013

A Timeline Of Comet ISON’s Dangerous Journey















NASA - STEREO Mission patch / NASA / ESA - Hubble Space Telescope patch.

July 17, 2013

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Video above: Comet ISON, which will round the sun on Nov. 28, 2013, at a distance of just 730,000 miles from the sun, is what's known as a sungrazing comet, due to its close approach. Video Credit: NASA/Goddard Space Flight Center.

A comet’s journey through the solar system is perilous and violent. A giant ejection of solar material from the sun could rip its tail off. Before it reaches Mars -- at some 230 million miles away from the sun -- the radiation of the sun begins to boil its water, the first step toward breaking apart. And, if it survives all this, the intense radiation and pressure as it flies near the surface of the sun could destroy it altogether.

Right now, Comet ISON is making that journey. It began its trip from the Oort cloud region of our solar system and is now travelling toward the sun. The comet will reach its closest approach to the sun on Thanksgiving Day -- Nov. 28, 2013 -- skimming just 730,000 miles above the sun’s surface. If it comes around the sun without breaking up, the comet will be visible in the Northern Hemisphere with the naked eye, and from what we see now, ISON is predicted to be a particularly bright and beautiful comet.


Image above: Predicted hour-by-hour position of Comet ISON in various instruments on one of NASA’s Solar Terrestrial Relations Observatory spacecraft between 1 a.m. EST on Nov. 26, 2013, and 7 p.m. EST on Nov. 29, 2013. The blue field of view is from the outer coronagraph and green from the inner coronagraph. Image Credit: NASA/STEREO/Goddard Space Flight Center.

Cataloged as C/2012 S1, Comet ISON was first spotted 585 million miles away in September 2012. This is its very first trip around the sun, which means it is still made of pristine matter from the earliest days of the solar system’s formation, its top layers never having been lost by a trip near the sun. Scientists will point as many ground-based observatories as they can and at least 15 space-based assets towards the comet along the way, in order to learn more about this time capsule from when the solar system first formed.

Even if the comet does not survive, tracking its journey will help scientists understand what the comet is made of, how it reacts to its environment, and what this explains about the origins of the solar system. Closer to the sun, watching how the comet and its tail interact with the vast solar atmosphere can teach scientists more about the sun itself.


Image above: Hubble's view of Comet ISON (C/2012 S1) on April 10, 2013. This image was taken in visible light. The blue false color was added to bring out details in the comet structure. Image Credit: NASA, ESA, J.-Y. Li (Planetary Science Institute).

NASA has initiated a Comet ISON Observing Campaign to facilitate a massive global observation campaign incorporating both space-based and ground-based telescopes and encouraging citizen scientists and both professional and amateur astronomers to participate.

Read on for a timeline of observations expected of Comet ISON on its perilous journey.


Related Links:

More on the Comet ISON Observing Campaign: http://www.isoncampaign.org/

NASA’s Comet ISON Toolkit: http://solarsystem.nasa.gov/ison/

Images (mentioned), Video (mentioned), Text, Credits: NASA's Goddard Space Flight Center / Karen C. Fox.

Best regards, Orbiter.ch

In the Zone: How Scientists Search for Habitable Planets












NASA - Kepler Mission patch.

July 17, 2013

 Toxic Wasteland or Lush Paradise

Image above: This artist's concept shows a Super Venus planet on the left, and a Super Earth on the right. Image credit: NASA/JPL-Caltech/Ames.

There is only one planet we know of, so far, that is drenched with life. That planet is Earth, as you may have guessed, and it has all the right conditions for critters to thrive on its surface. Do other planets beyond our solar system, called exoplanets, also host life forms?

Astronomers still don't know the answer, but they search for potentially habitable planets using a handful of criteria. Ideally, they want to find planets just like Earth, since we know without a doubt that life took root here. The hunt is on for planets about the size of Earth that orbit at just the right distance from their star – in a region termed the habitable zone.

NASA's Kepler mission is helping scientists in the quest to find these worlds, sometimes called Goldilocks planets after the fairy tale because they orbit where conditions are "just right" for life. Kepler and other telescopes have confirmed a handful so far, all of which are a bit larger than Earth -- the Super Earths. The search for Earth's twin, a habitable-zone planet as small as Earth, is ongoing.

An important part of this research is the continuing investigation into exactly where a star's habitable zone starts and stops.

The habitable zone is the belt around a star where temperatures are ideal for liquid water -- an essential ingredient for life as we know it -- to pool on a planet's surface. Earth lies within the habitable zone of our star, the sun. Beyond this zone, a planet would probably be too cold and frozen for life (though it's possible life could be buried underneath a moon's surface). A planet lying between a star and the habitable zone would likely be too hot and steamy.

That perfect Goldilocks planet within the zone wouldn't necessarily be home to any furry creatures. But it would have the potential for some type of life to abound, if even microbes.

In one new study, researchers based at NASA's Exoplanet Science Institute at the California Institute of Technology, in Pasadena, Calif., carefully analyzed the location of both a planet called Kepler-69c and its habitable zone. Their analysis shows that this planet, which is 1.7 times the size of Earth, lies just outside the inner edge of the zone, making it more of a Super Venus than a Super Earth, as previous estimates indicated.

"On the way to finding Earths, Kepler is telling us a lot about the frequency of Venus-like planets in our galaxy," said Stephen Kane, lead author of the new paper on Kepler-69c appearing in the Astrophysical Journal Letters.

To determine the location of a star’s habitable zone, one must first learn how much total radiation it emits. Stars more massive than our sun are hotter, and blaze with radiation, so their habitable zones are farther out. Similarly, stars that are smaller and cooler sport tighter belts of habitability than our sun. For example, the Super Earth planet called Kepler-62f, discovered by Kepler to orbit in the middle of a habitable zone around a cool star, orbits closer to its star than Earth. The planet takes just 267 days to complete an orbit, as compared to 365 days for Earth.

Knowing precisely how far away a habitable zone needs to be from a star also depends on chemistry. For example, molecules in a planet's atmosphere will absorb a certain amount of energy from starlight and radiate the rest back out. How much of this energy is trapped can mean the difference between a turquoise sea and erupting volcanoes.

Researchers led by Ravi kumar Kopparapu of Penn State University, University Park, Pa., used this type of chemical information to nudge the habitable zone out a bit farther than previously thought. The team's 2013 Astrophysical Journal study is the current gold standard in determining how a star's total radiation output relates to the location of its habitable zone. Kane and his colleagues used this information to fine-tune the boundaries of Kepler-69c's habitable zone, in addition to careful measurements of the star's total energy output and the orbit of the planet.

"Understanding the properties of the star is critical to determining planetary properties and calculating the extent of the habitable zone in that system," said Kane.

But before you purchase real estate in a habitable zone, keep in mind there are other factors that dictate whether a world develops lush greenery and beaches. Eruptions from the surfaces of stars called flares, for example, can wreak havoc on planets.

NASA's Kepler, the search for Earth size planet. Image credit: NASA/JPL-Caltech

"There are a lot of unanswered questions about habitability," said Lucianne Walkowicz, a Kepler science team member based at Princeton University, N.J., who studies flaring stars. "If the planet gets zapped with radiation all the time by flares from its parent star, the surface might not be a very pleasant place to live. But on the other hand, if there's liquid water around, that makes a really good shield from high-energy radiation, so maybe life could thrive in the oceans."

Flares can also scrape off the atmospheres of planets, complicating the picture further. This is particularly true for the smaller, cooler stars, which tend to be more hyperactive than stars like our sun.

Ideally, astronomers would like to know more about the atmosphere of potentially habitable planets. That way they could look at the planet's molecular makeup for signs of runaway greenhouse gases that could indicate an inhospitable Venus-like planet. Or, future space telescopes might even be able to pick up signatures of oxygen, water, carbon dioxide and methane -- indicators that the planet might be somebody's home.

NASA's upcoming James Webb Space Telescope will bring us closer to this goal, by probing the atmospheres of planets, some of which may lie in habitable zones. The mission won't be able to examine the atmospheres of planets as small as Earth, so we'll have to wait for another future telescope to separate out the Venuses from the Earths.

NASA Ames manages Kepler's ground system development, mission operations and science data analysis. NASA's Jet Propulsion Laboratory in Pasadena, Calif., managed Kepler mission development. Ball Aerospace & Technologies Corp. in Boulder, Colo., developed the Kepler flight system and supports mission operations with JPL at the Laboratory for Atmospheric and Space Physics at the University of Colorado in Boulder. The Space Telescope Science Institute in Baltimore archives, hosts and distributes the Kepler science data. Kepler is NASA's 10th Discovery Mission and is funded by NASA's Science Mission Directorate at the agency's headquarters in Washington.

More information about the Kepler mission is at http://www.nasa.gov/kepler .

More information about exoplanets and NASA's planet-finding program is at http://planetquest.jpl.nasa.gov .

Images (mentioned), Text, Credits:  NASA / JPL / Whitney Clavin / Ames Research Center / Michele Johnson.

Greetings, Orbiter.ch

Curiosity Mars Rover Passes Kilometer of Driving












NASA - Mars Science Laboratory (MSL) patch.

July 17, 2013


Image above: NASA's Curiosity Mars rover captured this image with its left front Hazard-Avoidance Camera (Hazcam) just after completing a drive that took the mission's total driving distance past the 1 kilometer (0.62 mile) mark. Image credit: NASA/JPL-Caltech.

The latest drive by NASA's Curiosity Mars rover brought the total distance that the rover has driven on Mars to more than 1 kilometer. One kilometer is about 0.62 mile.

The drive covered about 38 meters (125 feet) and brought the mission's odometry to about 1.029 kilometers (3,376 feet). The drive was completed in the early afternoon of the rover's 335th Martian day, or sol, of work on Mars (July 17). It continued progress in a multi-month trek begun this month toward a mountain destination.

"When I saw that the drive had gone well and passed the kilometer mark, I was really pleased and proud," said rover driver Frank Hartman of NASA's Jet Propulsion Laboratory, Pasadena, Calif. "Hopefully, this is just the first of many kilometers to come."

Yesterday was is halfway through the mission's prime mission of one Martian year. Two weeks ago, Curiosity finished investigating science targets in the Glenelg area, about half a kilometer (500 yards) east of where the one-ton rover landed on Aug. 5, 2012, PDT (Aug. 6, Universal Time). The mission's next major destination is at the lower layers of Mount Sharp, about 8 kilometers (5 miles) southwest of Glenelg.

NASA's Curiosity Mars rover or Mars Science Laboratory (MSL). Image credit: NASA/JPL-Caltech

Mount Sharp, in the middle of Gale Crater, exposes many layers where scientists anticipate finding evidence about how the ancient Martian environment changed and evolved. At targets in the Glenelg area, the rover already accomplished the mission's main science objective by finding evidence for an ancient wet environment that had conditions favorable for microbial life.

JPL, a division of the California Institute of Technology, Pasadena, manages the Mars Science Laboratory Project for NASA's Science Mission Directorate, Washington. JPL designed and built the project's Curiosity rover.

More information about Curiosity is online at http://www.nasa.gov/msl and http://mars.jpl.nasa.gov/msl/ . You can follow the mission on Facebook at http://www.facebook.com/marscuriosity and on Twitter at http://www.twitter.com/marscuriosity .

Images (mentioned), Text, Credits: NASA / JPL / Guy Webster.

Cheers, Orbiter.ch

Ripped Apart by a Black Hole












ESO - European Southern Observatory logo.

17 July 2013

 Images of gas cloud being ripped apart by the black hole at the centre of the Milky Way

VLT watches in real time as gas cloud makes closest approach to the monster at the centre of the Milky Way

New observations from ESO’s Very Large Telescope show for the first time a gas cloud being ripped apart by the supermassive black hole at the centre of the galaxy. The cloud is now so stretched that its front part has passed the closest point and is travelling away from the black hole at more than 10 million km/h, whilst the tail is still falling towards it.

Simulation of gas cloud being ripped apart by the black hole at the centre of the Milky Way

In 2011 ESO's Very Large Telescope (VLT) discovered a gas cloud with several times the mass of the Earth accelerating towards the black hole at the centre of the Milky Way (eso1151) [1]. This cloud is now making its closest approach and new VLT observations show that it is being grossly stretched by the black hole’s extreme gravitational field.

Gas cloud being ripped apart by the black hole at the centre of the Milky Way

"The gas at the head of the cloud is now stretched over more than 160 billion kilometres around the closest point of the orbit to the black hole. And the closest approach is only a bit more than 25 billion kilometres from the black hole itself — barely escaping falling right in," explains Stefan Gillessen (Max Planck Institute for Extraterrestrial Physics, Garching, Germany) who led the observing team [2]. "The cloud is so stretched that the close approach is not a single event but rather a process that extends over a period of at least one year."

As the gas cloud is stretched its light gets harder to see. But by staring at the region close to the black hole for more than 20 hours of total exposure time with the SINFONI instrument on the VLT — the deepest exposure of this region ever with an integral field spectrometer [3] — the team was able to measure the velocities of different parts of the cloud as it streaks past the central black hole [4].

Gas cloud being ripped apart by the black hole at the centre of the Milky Way (annotated)

"The most exciting thing we now see in the new observations is the head of the cloud coming back towards us at more than 10 million km/h along the orbit — about 1% of the speed of light," adds Reinhard Genzel, leader of the research group that has been studied this region for nearly twenty years. "This means that the front end of the cloud has already made its closest approach to the black hole."

Images of gas cloud being ripped apart by the black hole at the centre of the galaxy (click for enlarge)

The origin of the gas cloud remains mysterious, although there is no shortage of ideas [5]. The new observations narrow down the possibilities.

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Simulation of gas cloud being ripped apart by the black hole at the centre of the Milky Way

"Like an unfortunate astronaut in a science fiction film, we see that the cloud is now being stretched so much that it resembles spaghetti. This means that it probably doesn’t have a star in it," concludes Gillessen. "At the moment we think that the gas probably came from the stars we see orbiting the black hole."

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Gas cloud being ripped apart by the black hole at the centre of the Milky Way

The climax of this unique event at the centre of the galaxy is now unfolding and being closely watched by astronomers around the world. This intense observing campaign will provide a wealth of data, not only revealing more about the gas cloud [6], but also probing the regions close to the black hole that have not been previously studied and the effects of super-strong gravity.

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Gas cloud falling in towards the black hole at the centre of the Milky Way

Notes:
[1] The black hole at the centre of the Milky Way is estimated to have a mass of about four million times that of the Sun and is formally known as Sgr A* (pronounced Sagittarius A star). It is the closest supermassive black hole known by far and hence is the best place to study black holes in detail. The study of the supermassive black hole at the centre of the galaxy and its environment is rated number one in the list of ESO's top ten astronomical discoveries.

[2] The distance of closest approach is about five times the distance of the planet Neptune from the Sun. This is much too close for comfort to a black hole with a mass four million times that of the Sun!

[3] In an integral field spectrometer the light recorded in each pixel is separately spread out into its component colours and so spectra are recorded for each pixel. The spectra can then be analysed individually and used to create maps of the velocities and the chemical properties of each part of the object, for example.

[4] The team is also hoping to see evidence of how the rapidly moving cloud interacts with any ambient gas around the black hole. So far nothing has been found, but further observations are planned to look for such effects.

[5] Astronomers thought that the gas cloud might have been created by stellar winds from the stars orbiting the black hole. Or possibly even be the result of a jet from the galactic centre. Another option was that a star was at the centre of the cloud. In this case the gas would come either from a wind from the star, or from a planet-forming disc of gas and dust around the star.

[6] As this event at the centre of the galaxy unfolds, astronomers expect to see that the evolution of the cloud switches from purely gravitational and tidal to complex, turbulent hydrodynamics.

More information:

This research was presented in a paper "Pericenter passage of the gas cloud G2 in the Galactic Center", by S. Gillessen et al, to appear in the Astrophysical Journal.

The team is composed of S. Gillessen (Max Planck Institute for Extraterrestrial Physics, Garching, Germany [MPE]), R. Genzel (MPE; Departments of Physics and Astronomy, University of California, Berkeley, USA), T. K. Fritz (MPE), F. Eisenhauer (MPE), O. Pfuhl (MPE), T. Ott (MPE), M. Schartmann (Universitätssternwarte der Ludwig-Maximilians-Universität, Munich, Germany [USM]; MPE), A. Ballone (USM; MPE) and A. Burkert (USM; MPE).

ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world's largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning the 39-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become "the world's biggest eye on the sky".

Links:

Research paper: http://www.eso.org/public/archives/releases/sciencepapers/eso1332/eso1332a.pdf

Photos of the VLT: http://www.eso.org/public/images/archive/category/paranal/

MPE web page on the Galactic Centre: http://www.mpe.mpg.de/ir/GC

Press release from MPE:
(English): http://www.mpe.mpg.de/2189104/News_20130717
(German): http://www.mpe.mpg.de/2188727/News_20130717

Images, Videos, Text, Credits: ESO / S. Gillessen / MPE / Marc Schartmann.

Greetings, Orbiter.ch