vendredi 26 juin 2015
First Instrument Delivered for NASA’s Upcoming Asteroid Sample Return Mission
NASA - OSIRIS-REx Mission patch.
June 26, 2015
The first of five instruments for a spacecraft that will collect a sample from an asteroid and bring it back to Earth has arrived at Lockheed Martin for installation onto NASA’s Origins Spectral Interpretation Resource Identification Security-Regolith Explorer (OSIRIS-REx).
“The next few months will be very busy as we begin integrating the instruments and prepare for the system-level environmental testing program to begin,” said Mike Donnelly, OSIRIS-REx project manager at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
The OSIRIS-REx Thermal Emission Spectrometer (OTES) will conduct surveys to map mineral and chemical abundances and to take the asteroid Bennu’s temperature. OTES is the first such instrument built entirely on the Arizona State University (ASU), Tempe campus.
Image above: Bolted to a cradle in a cleanroom at Arizona State University, the OSIRIS-REx Thermal Emission Spectrometer (OTES) is prepared for one of its final tests: to define precisely the instrument's field of view. A red lens cover nestles within the angular sunshade, keeping the optics clean. Its color is designed as a signal to engineers to remove it before launch. Image Credits: ASU/Charles Leight.
“OTES, the size of a microwave oven, has spent the last several years being designed, built, tested, and calibrated,” said Philip Christensen, OTES instrument scientist at ASU. "Now, OTES is shipping out for the solar system.”
The instrument will be powered on shortly after the OSIRIS-REx spacecraft begins its two-year trip to Bennu. On arrival at Bennu, OTES will provide spectral data for global maps used to assess potential sample sites. It will take thermal infrared spectral data every two seconds and will be able to detect temperatures with an accuracy of 0.2°F. It will also detect the presence of minerals on the asteroid’s surface.
OSIRIS-REx is the first U.S. mission to fly to, study, and retrieve a pristine sample from an asteroid and return it to Earth for study.
Scheduled to launch in September 2016, the spacecraft will reach its asteroid target in 2018 and return a sample to Earth in 2023.
Image above: Origins Spectral Interpretation Resource Identification Security Regolith Explorer (OSIRIS-REx) spacecraft. Image Credit: NASA.
The mission will allow scientists to investigate the composition of material from the very earliest epochs of solar system history, providing information about the source of organic materials and water on Earth.
“It is a significant milestone to have OSIRIS-REx’s first instrument completed and delivered for integration onto the spacecraft,” said Dante Lauretta, principal investigator for OSIRIS-REx at the University of Arizona, Tucson. “The OTES team has done an excellent job on the instrument and I deeply appreciate their scientific contribution to the mission. OTES plays an essential role in characterizing the asteroid in support of sample-site selection.”
NASA's Goddard Space Flight Center in Greenbelt, Maryland provides overall mission management, systems engineering and safety and mission assurance for OSIRIS-REx. Dante Lauretta is the mission's principal investigator at the University of Arizona, Tucson. Lockheed Martin Space Systems in Denver is building the spacecraft. OSIRIS-REx is the third mission in NASA's New Frontiers Program. NASA's Marshall Space Flight Center in Huntsville, Alabama manages New Frontiers for the agency's Science Mission Directorate in Washington.
For more information on OSIRIS-REx visit: http://www.nasa.gov/osiris-rex and http://www.asteroidmission.org
Images (mentioned), Text, Credits: Goddard Space Flight Center/Nancy Neal Jones/Ashley Morrow.
Publié par Orbiter.ch à 17:39
NASA Explains Why June 30 Will Get Extra Second
June 26, 2015
The day will officially be a bit longer than usual on Tuesday, June 30, 2015, because an extra second, or “leap” second, will be added.
“Earth’s rotation is gradually slowing down a bit, so leap seconds are a way to account for that,” said Daniel MacMillan of NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
Strictly speaking, a day lasts 86,400 seconds. That is the case, according to the time standard that people use in their daily lives – Coordinated Universal Time, or UTC. UTC is “atomic time” – the duration of one second is based on extremely predictable electromagnetic transitions in atoms of cesium. These transitions are so reliable that the cesium clock is accurate to one second in 1,400,000 years.
Using Quasars to Measure the Earth: A Brief History of VLBI
Video above: Originally developed to study distant astronomical objects called quasars, the technique called Very Long Baseline Interferometry provides information about the relative locations of observing stations and about Earth’s rotation and orientation in space. Video Credits: NASA Goddard Space Flight Center.
However, the mean solar day – the average length of a day, based on how long it takes Earth to rotate – is about 86,400.002 seconds long. That’s because Earth’s rotation is gradually slowing down a bit, due to a kind of braking force caused by the gravitational tug of war between Earth, the moon and the sun. Scientists estimate that the mean solar day hasn’t been 86,400 seconds long since the year 1820 or so.
This difference of 2 milliseconds, or two thousandths of a second – far less than the blink of an eye – hardly seems noticeable at first. But if this small discrepancy were repeated every day for an entire year, it would add up to almost a second. In reality, that’s not quite what happens. Although Earth’s rotation is slowing down on average, the length of each individual day varies in an unpredictable way.
The length of day is influenced by many factors, mainly the atmosphere over periods less than a year. Our seasonal and daily weather variations can affect the length of day by a few milliseconds over a year. Other contributors to this variation include dynamics of the Earth’s inner core (over long time periods), variations in the atmosphere and oceans, groundwater, and ice storage (over time periods of months to decades), and oceanic and atmospheric tides. Atmospheric variations due to El Niño can cause Earth’s rotation to slow down, increasing the length of day by as much as 1 millisecond, or a thousandth of a second.
Scientists monitor how long it takes Earth to complete a full rotation using an extremely precise technique called Very Long Baseline Interferometry (VLBI). These measurements are conducted by a worldwide network of stations, with Goddard providing essential coordination of VLBI, as well as analyzing and archiving the data collected.
The time standard called Universal Time 1, or UT1, is based on VLBI measurements of Earth’s rotation. UT1 isn’t as uniform as the cesium clock, so UT1 and UTC tend to drift apart. Leap seconds are added, when needed, to keep the two time standards within 0.9 seconds of each other. The decision to add leap seconds is made by a unit within the International Earth Rotation and Reference Systems Service.
Typically, a leap second is inserted either on June 30 or December 31. Normally, the clock would move from 23:59:59 to 00:00:00 the next day. But with the leap second on June 30, UTC will move from 23:59:59 to 23:59:60, and then to 00:00:00 on July 1. In practice, many systems are instead turned off for one second.
Extra second illustration
Previous leap seconds have created challenges for some computer systems and generated some calls to abandon them altogether. One reason is that the need to add a leap second cannot be anticipated far in advance.
“In the short term, leap seconds are not as predictable as everyone would like,” said Chopo Ma, a geophysicist at Goddard and a member of the directing board of the International Earth Rotation and Reference Systems Service. “The modeling of the Earth predicts that more and more leap seconds will be called for in the long-term, but we can’t say that one will be needed every year.”
From 1972, when leap seconds were first implemented, through 1999, leap seconds were added at a rate averaging close to one per year. Since then, leap seconds have become less frequent. This June’s leap second will be only the fourth to be added since 2000. (Before 1972, adjustments were made in a different way.)
Scientists don’t know exactly why fewer leap seconds have been needed lately. Sometimes, sudden geological events, such as earthquakes and volcanic eruptions, can affect Earth’s rotation in the short-term, but the big picture is more complex.
VLBI tracks these short- and long-term variations by using global networks of stations to observe astronomical objects called quasars. The quasars serve as reference points that are essentially motionless because they are located billions of light years from Earth. Because the observing stations are spread out across the globe, the signal from a quasar will take longer to reach some stations than others. Scientists can use the small differences in arrival time to determine detailed information about the exact positions of the observing stations, Earth’s rotation rate, and our planet’s orientation in space.
Current VLBI measurements are accurate to at least 3 microseconds, or 3 millionths of a second. A new system is being developed by NASA’s Space Geodesy Project in coordination with international partners. Through advances in hardware, the participation of more stations, and a different distribution of stations around the globe, future VLBI UT1 measurements are expected to have a precision better than 0.5 microseconds, or 0.5 millionths of a second.
“The next-generation system is designed to meet the needs of the most demanding scientific applications now and in the near future,” says Goddard’s Stephen Merkowitz, the Space Geodesy Project manager.
NASA manages many activities of the International VLBI Service for Geodesy and Astrometry including day-to-day and long-term operations, coordination and performance of the global network of VLBI antennas, and coordination of data analysis. NASA also directly supports the operation of six global VLBI stations.
Proposals have been made to abolish the leap second. No decision about this is expected until late 2015 at the earliest, by the International Telecommunication Union, a specialized agency of the United Nations that addresses issues in information and communication technologies.
For more information about NASA's Space Geodesy Project, including VLBI, visit: http://space-geodesy.nasa.gov/
Image, Video (mentioned), Text, Credits: NASA’s Goddard Space Flight Center/Elizabeth Zubritsky/Lynn Jenner.
Best regards, Orbiter.ch
Publié par Orbiter.ch à 17:10
Hubble View of a Nitrogen-Rich Nebula
NASA - Hubble Space Telescope patch.
June 26, 2015
This NASA/ESA Hubble Space Telescope image shows a planetary nebula named NGC 6153, located about 4,000 light-years away in the southern constellation of Scorpius (The Scorpion). The faint blue haze across the frame shows what remains of a star like the sun after it has depleted most of its fuel. When this happens, the outer layers of the star are ejected, and get excited and ionized by the energetic ultraviolet light emitted by the bright hot core of the star, forming the nebula.
NGC 6153 is a planetary nebula that is elliptical in shape, with an extremely rich network of loops and filaments, shown clearly in this Hubble image. However, this is not what makes this planetary nebula so interesting for astronomers.
Measurements show that NGC 6153 contains large amounts of neon, argon, oxygen, carbon and chlorine — up to three times more than can be found in the solar system. The nebula contains a whopping five times more nitrogen than our sun! Although it may be that the star developed higher levels of these elements as it grew and evolved, it is more likely that the star originally formed from a cloud of material that already contained a lot more of these elements.
Hubble Space Telescope
The Hubble Space Telescope is a project of international cooperation between ESA and NASA.
Hubble Space Telescope: http://www.nasa.gov/mission_pages/hubble/main/index.html
Hubble websites: http://www.spacetelescope.org/ and http://hubblesite.org/
Text, Credit: European Space Agency (ESA)/Images Credits: ESA/Hubble & NASA, Acknowledgement: Matej Novak.
Publié par Orbiter.ch à 16:53
jeudi 25 juin 2015
Chasing clouds in the LHC
CERN - European Organization for Nuclear Research logo.
25 June 2015
It’s time for a big summer clean in the Large Hadron Collider (LHC), but you won't see operators armed with feather dusters sprucing up the 27-km machine. The pipes in which the beams circulate are already ultra-clean and ultra-high vacuum: the pressure in the beam pipes is just 10-10 or even 10-11 millibars – similar to on the Moon.
Image above: Simulation of the electron flux produced when the beam passes through the vacuum chamber. The lines show the electron flux, the colours the density of electrons. The higher the density, the brighter the colours.
However, despite the ultra-high vacuum, residual gas molecules remain trapped on the surface of the walls of the beam pipes, which also contain electrons. When the beams circulate, these electrons are emitted from the walls and accelerated by the beam’s electrical field. The accelerated electrons then hit the walls with enough energy to release the trapped molecules, thereby compromising the vacuum. At the same time, they set off an avalanche of even more electrons, forming electron clouds that can be dense enough to destabilise the beam. The electron-cloud phenomenon is amplified the higher the number of proton bunches in the beam and the more closely spaced they are.
The operators therefore need to dissipate the electron clouds before the LHC can run with more proton bunches. To do that, they've developed a beam scrubbing technique that involves circulating enough protons to release as many trapped gas molecules as possible from the metal and to reduce the rate of production of electrons on the walls of the pipe.
CERN - Large Hadron Collider (LHC)
The operators will thus circulate intense beams (containing many bunches) but at low energies in order to improve the beam pipe surface. After a few days, the LHC will be ready to be ramped up to higher-intensity beams for physics and to restart with 50-nanosecond bunch-spacing. The number of bunches will be gradually increased to 1000 bunches per beam. Another scrubbing run will be performed in the summer to prepare the LHC for operation with more bunches spaced even more closely together later in the year.
CERN, the European Organization for Nuclear Research, is one of the world’s largest and most respected centres for scientific research. Its business is fundamental physics, finding out what the Universe is made of and how it works. At CERN, the world’s largest and most complex scientific instruments are used to study the basic constituents of matter — the fundamental particles. By studying what happens when these particles collide, physicists learn about the laws of Nature.
The instruments used at CERN are particle accelerators and detectors. Accelerators boost beams of particles to high energies before they are made to collide with each other or with stationary targets. Detectors observe and record the results of these collisions.
Founded in 1954, the CERN Laboratory sits astride the Franco–Swiss border near Geneva. It was one of Europe’s first joint ventures and now has 22 Member States.
First technical stop for the LHC: http://orbiterchspacenews.blogspot.ch/2015/06/first-technical-stop-for-lhc.html
Large Hadron Collider (LHC): http://home.web.cern.ch/topics/large-hadron-collider
For more information about the European Organization for Nuclear Research (CERN), visit: http://home.web.cern.ch/
Images, Text, Credits: CERN/Corinne Pralavorio.
Publié par Orbiter.ch à 16:29
New NASA Supercomputer Model Shows Planet Making Waves in Nearby Debris Disk
June 25, 2015
A new NASA supercomputer simulation of the planet and debris disk around the nearby star Beta Pictoris reveals that the planet's motion drives spiral waves throughout the disk, a phenomenon that causes collisions among the orbiting debris. Patterns in the collisions and the resulting dust appear to account for many observed features that previous research has been unable to fully explain.
"We essentially created a virtual Beta Pictoris in the computer and watched it evolve over millions of years," said Erika Nesvold, an astrophysicist at the University of Maryland, Baltimore County, who co-developed the simulation. "This is the first full 3-D model of a debris disk where we can watch the development of asymmetric features formed by planets, like warps and eccentric rings, and also track collisions among the particles at the same time."
In 1984, Beta Pictoris became the second star known to be surrounded by a bright disk of dust and debris. Located only 63 light-years away, Beta Pictoris is an estimated 21 million years old, or less than 1 percent the age of our solar system. It offers astronomers a front-row seat to the evolution of a young planetary system and it remains one of the closest, youngest and best-studied examples today. The disk, which we see edge on, contains rock and ice fragments ranging in size from objects larger than houses to grains as small as smoke particles. It's a younger version of the Kuiper belt at the fringes of our own planetary system.
Nesvold and her colleague Marc Kuchner, an astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, presented the findings Thursday during the "In the Spirit of Lyot 2015" conference in Montreal, which focuses on the direct detection of planets and disks around distant stars. A paper describing the research has been submitted to The Astrophysical Journal.
Supercomputer Shows How an Exoplanet Makes Waves
Video above: Erika Nesvold and Marc Kuchner discuss how their new supercomputer simulation helps astronomers understand Beta Pictoris. Video Credits: NASA's Goddard Space Flight Center.
In 2009, astronomers confirmed the existence of Beta Pictoris b, a planet with an estimated mass of about nine times Jupiter's, in the debris disk around Beta Pictoris. Traveling along a tilted and slightly elongated 20-year orbit, the planet stays about as far away from its star as Saturn does from our sun.
Astronomers have struggled to explain various features seen in the disk, including a warp apparent at submillimeter wavelengths, an X-shaped pattern visible in scattered light, and vast clumps of carbon monoxide gas. A common ingredient in comets, carbon monoxide molecules are destroyed by ultraviolet starlight in a few hundred years. To explain why the gas is clumped, previous researchers suggested the clumps could be evidence of icy debris being corralled by a second as-yet-unseen planet, resulting in an unusually high number of collisions that produce carbon monoxide. Or perhaps the gas was the aftermath of an extraordinary crash of icy worlds as large as Mars.
"Our simulation suggests many of these features can be readily explained by a pair of colliding spiral waves excited in the disk by the motion and gravity of Beta Pictoris b," Kuchner said. "Much like someone doing a cannonball in a swimming pool, the planet drove huge changes in the debris disk once it reached its present orbit."
Images above: These images compare a view of Beta Pictoris in scattered light as seen by the Hubble Space Telescope (top) with a similar view constructed from data in the SMACK simulation (red overlay, bottom). The X pattern in the Hubble image forms as a result of a faint secondary dust disk inclined to the main debris disk. Previous simulations were unable to reproduce this feature, but the SMACK model replicates the overall pattern because it captures the three-dimensional distribution of the collisions responsible for making the dust. Images Credits: Top, NASA/ESA and D. Golimowski (Johns Hopkins Univ.); bottom, NASA Goddard/E. Nesvold and M. Kuchner.
Keeping tabs on thousands of fragmenting particles over millions of years is a computationally difficult task. Existing models either weren't stable over a sufficiently long time or contained approximations that could mask some of the structure Nesvold and Kuchner were looking for.
Working with Margaret Pan and Hanno Rein, both now at the University of Toronto, they developed a method where each particle in the simulation represents a cluster of bodies with a range of sizes and similar motions. By tracking how these "superparticles" interact, they could see how collisions among trillions of fragments produce dust and, combined with other forces in the disk, shape it into the kinds of patterns seen by telescopes. The technique, called the Superparticle-Method Algorithm for Collisions in Kuiper belts (SMACK), also greatly reduces the time required to run such a complex computation.
Using the Discover supercomputer operated by the NASA Center for Climate Simulation at Goddard, the SMACK-driven Beta Pictoris model ran for 11 days and tracked the evolution of 100,000 superparticles over the lifetime of the disk.
As the planet moves along its tilted path, it passes vertically through the disk twice each orbit. Its gravity excites a vertical spiral wave in the disk. Debris concentrates in the crests and troughs of the waves and collides most often there, which explains the X-shaped pattern seen in the dust and may help explain the carbon monoxide clumps.
The planet's orbit also is slightly eccentric, which means its distance from the star varies a little every orbit. This motion stirs up the debris and drives a second spiral wave across the face of the disk. This wave increases collisions in the inner regions of the disk, which removes larger fragments by grinding them away. In the real disk, astronomers report a similar clearing out of large debris close to the star.
"One of the nagging questions about Beta Pictoris is how the planet ended up in such an odd orbit," Nesvold explained. "Our simulation suggests it arrived there about 10 million years ago, possibly after interacting with other planets orbiting the star that we haven't detected yet."
Download high-resolution images and video in HD formats from NASA Goddard's Scientific Visualization Studio: http://svs.gsfc.nasa.gov/goto?11896
Paper: A SMACK Model of Colliding Planetesimals and Dust in the Beta Pictoris Debris Disk: Thermal Radiation and Scattered Light: http://arxiv.org/abs/1506.07187
Disk Detective: Help astronomers find other systems like Beta Pictoris: http://www.diskdetective.org/
Hubble Gets Best View of Circumstellar Debris Disk Distorted by Planet: http://www.nasa.gov/content/goddard/hubble-gets-best-view-of-circumstellar-debris-disk-distorted-by-planet
Nearby Star's Icy Debris Suggests 'Shepherd' Planet: http://www.nasa.gov/content/goddard/nearby-stars-icy-debris-suggests-shepherd-planet
Images (mentioned), Video (mentioned), Text, Credits: NASA's Goddard Space Flight Center/Francis Reddy/Rob Garner.
Publié par Orbiter.ch à 14:57
Can Planets Be Rejuvenated Around Dead Stars?
NASA - Spitzer Space Telescope logo.
June 25, 2015
For a planet, this would be like a day at the spa. After years of growing old, a massive planet could, in theory, brighten up with a radiant, youthful glow. Rejuvenated planets, as they are nicknamed, are only hypothetical. But new research from NASA's Spitzer Space Telescope has identified one such candidate, seemingly looking billions of years younger than its actual age.
"When planets are young, they still glow with infrared light from their formation," said Michael Jura of UCLA, coauthor of a new paper on the results in the June 10 issue of the Astrophysical Journal Letters. "But as they get older and cooler, you can't see them anymore. Rejuvenated planets would be visible again."
Image above: This artist's concept shows a hypothetical "rejuvenated" planet -- a gas giant that has reclaimed its youthful infrared glow. NASA's Spitzer Space Telescope found tentative evidence for one such planet around a dead star, or white dwarf, called PG 0010+280 (depicted as white dot in illustration). Image Credits: NASA/JPL-Caltech.
How might a planet reclaim the essence of its youth? Years ago, astronomers predicted that some massive, Jupiter-like planets might accumulate mass from their dying stars. As stars like our sun age, they puff up into red giants and then gradually lose about half or more of their mass, shrinking into skeletons of stars, called white dwarfs. The dying stars blow winds of material outward that could fall onto giant planets that might be orbiting in the outer reaches of the star system.
Thus, a giant planet might swell in mass, and heat up due to friction felt by the falling material. This older planet, having cooled off over billions of years, would once again radiate a warm, infrared glow.
The new study describes a dead star, or white dwarf, called PG 0010+280. An undergraduate student on the project, Blake Pantoja, then at UCLA, serendipitously discovered unexpected infrared light around this star while searching through data from NASA's Wide-field Infrared Survey Explorer, or WISE. Follow-up research led them to Spitzer observations of the star, taken back in 2006, which also showed the excess of infrared light.
At first, the team thought the extra infrared light was probably coming from a disk of material around the white dwarf. In the last decade or so, more and more disks around these dead stars have been discovered -- around 40 so far. The disks are thought to have formed when asteroids wandered too close to the white dwarfs, becoming chewed up by the white dwarfs' intense, shearing gravitational forces.
Other evidence for white dwarfs shredding asteroids comes from observations of the elements in white dwarfs. White dwarfs should contain only hydrogen and helium in their atmospheres, but researchers have found signs of heavier elements -- such as oxygen, magnesium, silicon and iron -- in about 100 systems to date. The elements are thought to be leftover bits of crushed asteroids, polluting the white dwarf atmospheres.
But the Spitzer data for the white dwarf PG 0010+280 did not fit well with models for asteroid disks, leading the team to look at other possibilities. Perhaps the infrared light is coming from a companion small "failed" star, called a brown dwarf -- or more intriguingly, from a rejuvenated planet.
Spitzer Space Telescope. Image Credit: NASA
"I find the most exciting part of this research is that this infrared excess could potentially come from a giant planet, though we need more work to prove it," said Siyi Xu of UCLA and the European Southern Observatory in Germany. "If confirmed, it would directly tell us that some planets can survive the red giant stage of stars and be present around white dwarfs."
In the future, NASA's upcoming James Webb Space Telescope could possibly help distinguish between a glowing disk or a planet around the dead star, solving the mystery. But for now, the search for rejuvenated planets -- much like humanity's own quest for a fountain of youth -- endures.
JPL manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena. Spacecraft operations are based at Lockheed Martin Space Systems Company, Littleton, Colorado. Data are archived at the Infrared Science Archive housed at the Infrared Processing and Analysis Center at Caltech. Caltech manages JPL for NASA.
For more information on Spitzer, visit: http://spitzer.caltech.edu and http://www.nasa.gov/spitzer
Images (mentioned), Text, Credits: NASA/JLP/Whitney Clavin/Tony Greicius.
Best regards. Orbiter.ch
Publié par Orbiter.ch à 14:46
Giant Galaxy is Still Growing
ESO - European Southern Observatory logo.
25 June 2015
Messier 87 has swallowed an entire galaxy in the last billion years
The halo of galaxy Messier 87
New observations with ESO’s Very Large Telescope have revealed that the giant elliptical galaxy Messier 87 has swallowed an entire medium-sized galaxy over the last billion years. For the first time a team of astronomers has been able to track the motions of 300 glowing planetary nebulae to find clear evidence of this event and also found evidence of excess light coming from the remains of the totally disrupted victim.
Astronomers expect that galaxies grow by swallowing smaller galaxies. But the evidence is usually not easy to see — just as the remains of the water thrown from a glass into a pond will quickly merge with the pond water, the stars in the infalling galaxy merge in with the very similar stars of the bigger galaxy leaving no trace.
But now a team of astronomers led by PhD student Alessia Longobardi at the Max-Planck-Institut für extraterrestrische Physik, Garching, Germany has applied a clever observational trick to clearly show that the nearby giant elliptical galaxy Messier 87 merged with a smaller spiral galaxy in the last billion years.
Planetary nebulae in galaxy Messier 87
"This result shows directly that large, luminous structures in the Universe are still growing in a substantial way — galaxies are not finished yet!" says Alessia Longobardi. "A large sector of Messier 87's outer halo now appears twice as bright as it would if the collision had not taken place."
Messier 87 lies at the centre of the Virgo Cluster of galaxies. It is a vast ball of stars with a total mass more than a million million times that of the Sun, lying about 50 million light-years away.
Rather than try to look at all the stars in Messier 87 — there are literally billions and they are too faint and numerous be studied individually — the team looked at planetary nebulae, the glowing shells around ageing stars . Because these objects shine very brightly in a specific hue of aquamarine green, they can be distinguished from the surrounding stars. Careful observation of the light from the nebulae using a powerful spectrograph can also reveal their motions .
Just as the water from a glass is not visible once thrown into the pond — but may have caused ripples and other disturbances that can be seen if there are particles of mud in the water — the motions of the planetary nebulae, measured using the FLAMES spectrograph on the Very Large Telescope, provide clues to the past merger.
Messier 87 in the constellation of Virgo
"We are witnessing a single recent accretion event where a medium-sized galaxy fell through the centre of Messier 87, and as a consequence of the enormous gravitational tidal forces, its stars are now scattered over a region that is 100 times larger than the original galaxy!" adds Ortwin Gerhard, head of the dynamics group at the Max-Planck-Institut für extraterrestrische Physik, Garching, Germany, and a co-author of the new study.
The team also looked very carefully at the light distribution in the outer parts of Messier 87 and found evidence of extra light coming from the stars in the galaxy that had been pulled in and disrupted. These observations have also shown that the disrupted galaxy has added younger, bluer stars to Messier 87, and so it was probably a star-forming spiral galaxy before its merger.
"It is very exciting to be able to identify stars that have been scattered around hundreds of thousands of light-years in the halo of this galaxy — but still to be able to see from their velocities that they belong to a common structure. The green planetary nebulae are the needles in a haystack of golden stars. But these rare needles hold the clues to what happened to the stars," concludes co-author Magda Arnaboldi (ESO, Garching, Germany).
 Planetary nebulae form as Sun-like stars reach the ends of their lives, and they emit a large fraction of their energy in just a few spectral lines, the brightest of which is in the green part of the spectrum. Because of this, they are the only single stars whose motions can be measured at Messier 87's distance of 50 million light-years from Earth. They behave like beacons of green light and as such they tell us where they are and at what velocity they are travelling.
 These planetary nebulae are still very faint and need the full power of the Very Large Telescope to study them: the light emitted by a typical planetary nebula in the halo of the Messier 87 galaxy is equivalent to two 60-watt light bulbs on Venus as seen from Earth.
The motions of the planetary nebulae along the line of sight towards or away from Earth lead to shifts in the spectral lines, as a result of the Doppler effect. These shifts can be measured accurately using a sensitive spectrograph and the velocity of the nebulae deduced.
This research was presented in a paper entitled “The build-up of the cD halo of M87 — evidence for accretion in the last Gyr”, by A. Longobardi et al., to appear in the journal Astronomy & Astrophysics Letters on 25 June 2015.
This work was also presented at the annual conference of the European Astronomical Society, EWASS 2015, which is being held in La Laguna, Tenerife, at the same time.
The team is composed of A. Longobardi (Max-Planck-Institut für extraterrestrische Physik, Garching, Germany), M. Arnaboldi (ESO, Garching, Germany), O. Gerhard (Max-Planck-Institut für extraterrestrische Physik, Garching, Germany) and J.C. Mihos (Case Western University, Cleveland, Ohio, USA).
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 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. 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 a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre European Extremely Large Telescope, the E-ELT, which will become "the world’s biggest eye on the sky".
European Astronomical Society, EWASS 2015: http://eas.unige.ch/
Research paper in Astronomy & Astrophysics: http://www.aanda.org/articles/aa/pdf/2015/07/aa26282-15.pdf
Photos of the VLT: http://www.eso.org/public/images/archive/category/paranal/
Very Large Telescope (VLT): http://www.eso.org/paranal/
Images, Text. Credits: ESO/Chris Mihos (Case Western Reserve University)/A. Longobardi (Max-Planck-Institut für extraterrestrische Physik)/IAU and Sky & Telescope.
Publié par Orbiter.ch à 14:15
Solar Dynamics Observatory Sees M7.9-Class Solar Flare
NASA - Solar Dynamics Observatory (SDO) patch.
June 25, 2015
Image above: NASA's Solar Dynamics Observatory captured this image of an M7.9-class solar flare on June 25, 2015. This flare originated from the same sunspot group that has been producing minor to mid-level flare since first appearing on the face of the sun. Image Credits: NASA/SDO.
The sun emitted a mid-level solar flare, peaking at 4:16 a.m. EDT on June 25, 2015. NASA’s Solar Dynamics Observatory, which watches the sun constantly, captured an image of the event. Solar flares are powerful bursts of radiation. Harmful radiation from a flare cannot pass through Earth's atmosphere to physically affect humans on the ground, however -- when intense enough -- they can disturb the atmosphere in the layer where GPS and communications signals travel.
Image above: Full image of the Sun. The sun emitted a mid-level solar flare, an M7.9-class, peaking at 4:16 a.m. EDT on June 25, 2015. NASA’s Solar Dynamics Observatory, which watches the sun constantly, captured an image of the event. Image Credit: NASA/SDO.
To see how this event may affect Earth, please visit NOAA's Space Weather Prediction Center at http://spaceweather.gov, the U.S. government's official source for space weather forecasts, alerts, watches and warnings.
This flare is classified as a M7.9 flare. M-class flares are a tenth the size of the most intense flares, the X-class flares. The number provides more information about its strength. An M2 is twice as intense as an M1, an M3 is three times as intense, etc.
What is a solar flare?
For answers to this and other space weather questions, please visit the Spaceweather Frequently Asked Questions page: http://www.nasa.gov/mission_pages/sunearth/spaceweather/index.html
View Past Solar Activity: http://www.nasa.gov/mission_pages/sunearth/solar-events-news/index.html
Solar Dynamics Observatory (SDO): http://www.nasa.gov/mission_pages/sdo/main/index.html
Images (mentioned), Text, Credits: NASA's Goddard Space Flight Center/Genna Duberstein/Holly Zell.
Publié par Orbiter.ch à 14:06
Monster black hole wakes up after 26 years
ESA - Integral Mission patch.
25 June 2015
Over the past week, ESA's Integral satellite has been observing an exceptional outburst of high-energy light produced by a black hole that is devouring material from its stellar companion.
X-rays and gamma rays point to some of the most extreme phenomena in the Universe, such as stellar explosions, powerful outbursts and black holes feasting on their surroundings.
Black hole with stellar companion
In contrast to the peaceful view of the night sky we see with our eyes, the high-energy sky is a dynamic light show, from flickering sources that change their brightness dramatically in a few minutes to others that vary on timescales spanning years or even decades.
On 15 June 2015, a long-time acquaintance of X-ray and gamma ray astronomers made its comeback to the cosmic stage: V404 Cygni, a system comprising a black hole and a star orbiting one another. It is located in our Milky Way galaxy, almost 8000 light-years away in the constellation Cygnus, the Swan.
In this type of binary system, material flows from the star towards the black hole and gathers in a disc, where it is heated up, shining brightly at optical, ultraviolet and X-ray wavelengths before spiralling into the black hole.
First signs of renewed activity in V404 Cygni were spotted by the Burst Alert Telescope on NASA's Swift satellite, detecting a sudden burst of gamma rays, and then triggering observations with its X-ray telescope. Soon after, MAXI (Monitor of All-sky X-ray Image), part of the Japanese Experiment Module on the International Space Station, observed an X-ray flare from the same patch of the sky.
These first detections triggered a massive campaign of observations from ground-based telescopes and from space-based observatories, to monitor V404 Cygni at many different wavelengths across the electromagnetic spectrum. As part of this worldwide effort, ESA's Integral gamma-ray observatory started monitoring the out-bursting black hole on 17 June.
Integral image before and after the outburst
“The behaviour of this source is extraordinary at the moment, with repeated bright flashes of light on time scales shorter than an hour, something rarely seen in other black hole systems,” comments Erik Kuulkers, Integral project scientist at ESA.
“In these moments, it becomes the brightest object in the X-ray sky – up to fifty times brighter than the Crab Nebula, normally one of the brightest sources in the high-energy sky.”
The V404 Cygni black hole system has not been this bright and active since 1989, when it was observed with the Japanese X-ray satellite Ginga and high-energy instruments on board the Mir space station.
“The community couldn't be more thrilled: many of us weren't yet professional astronomers back then, and the instruments and facilities available at the time can’t compare with the fleet of space telescopes and the vast network of ground-based observatories we can use today. It is definitely a 'once in a professional lifetime' opportunity,” adds Kuulkers.
The 1989 outburst of V404 Cygni was crucial in the study of black holes. Until then, astronomers knew only a handful of objects that they thought could be black holes, and V404 Cygni was one of the most convincing candidates.
Integral light curve
A couple of years after the 1989 outburst, once the source had returned to a quieter state, the astronomers were able to see its companion star, which had been outshone by the extreme activity. The star is about half as massive as the Sun, and by studying the relative motion of the two objects in the binary system, it was determined that the companion must be a black hole, about twelve times more massive than the Sun.
At the time, the astronomers also looked back at archival data from optical telescopes over the twentieth century, finding two previous outbursts, one in 1938 and another one in 1956.
These peaks of activity, which occur every two to three decades, are likely caused by material slowly piling up in the disc surrounding the black hole, until eventually reaching a tipping point that dramatically changes the black hole's feeding routine for a short period.
“Now that this extreme object has woken up again, we are all eager to learn more about the engine that powers the outburst we are observing,” says Carlo Ferrigno from the Integral Science Data Centre at the University of Geneva, Switzerland.
“As coordinators of Integral operations, Enrico Bozzo and I received a text message at 01:30 am on 18 June from our burst alert system, which is designed to detect gamma-ray bursts in the Integral data. In this case, it turned out to be 'only' an exceptional flare since Integral was observing this incredible black hole: definitely a good reason to be woken up in the middle of the night!”
Since the first outburst detection on 15 June by the Swift satellite, V404 Cygni has remained very active, keeping astronomers extremely busy. Over the past week, several teams around the world published over twenty Astronomical Telegrams and other official communications, sharing the progress of the observations at different wavelengths.
Integral: gamma-ray observatory
This exciting outburst has also been discussed by astronomers attending the European Week of Astronomy and Space Science conference this week in Tenerife, sharing information on observations that have been made in the past few days.
Integral too has been observing this object continuously since 17 June, except for some short periods when it was not possible for operational reasons. The X-ray data show huge variability, with intense flares lasting only a couple of minutes, as well as longer outbursts over time scales of a few hours. Integral also recorded a huge emission of gamma rays from this frenzied black hole.
Because different components of a black-hole binary system emit radiation at different wavelengths across the spectrum, astronomers are combining high-energy observations with those made at optical and radio wavelengths in order to get a complete view of what is happening in this unique object.
“We have been observing V404 Cygni with the Gran Telescopio Canarias, which has the largest mirror currently available for optical astronomy,” explains Teo Muñoz-Darias from the Instituto de Astrofísica de Canarias in Tenerife, Spain.
Using this 10.4-m telescope located on La Palma, the astronomers can quickly obtain high quality spectra, thus probing what happens around the black hole on short time scales.
“There are many features in our spectra, showing signs of massive outflows of material in the black hole's environment. We are looking forward to testing our current understanding of black holes and their feeding habits with these rich data,” adds Muñoz-Darias.
Radio astronomers all over the world are also joining in this extraordinary observing campaign. The first detection at these long wavelengths was made shortly after the first Swift alert on 15 June with the Arcminute Microkelvin Imager from the Mullard Radio Astronomy Observatory near Cambridge, in the UK, thanks to the robotic mode of this telescope.
Like the data at other wavelengths, these radio observations also exhibit a continuous series of extremely bright flares. Astronomers will exploit them to investigate the mechanisms that give rise to powerful jets of particles, moving away at velocities close to the speed of light, from the black hole's accretion disc.
There are only a handful of black-hole binary systems for which data have been collected simultaneously at many wavelengths, and the current outburst of V404 Cygni offers the rare chance to gather more observations of this kind. Back in space, Integral has a full-time job watching the events unfold.
“We have been devoting all of Integral's time to observe this exciting source for the past week, and we will keep doing so at least until early July,” comments Peter Kretschmar, ESA Integral mission manager.
“The observations will soon be made available publicly, so that astronomers across the world can exploit them to learn more about this unique object. It will also be possible to use Integral data to try and detect polarisation of the X-ray and gamma ray emission, which could reveal more details about the geometry of the black hole accretion process. This is definitely material for the astrophysics textbooks for the coming years.”
Notes for Editors:
The International Gamma-ray Astrophysics Laboratory Integral was launched on 17 October 2002. It is an ESA project with the instruments and a science data centre funded by ESA Member States (especially the Principal Investigator countries: Denmark, France, Germany, Italy, Spain and Switzerland), and with the participation of Russia and the USA. The mission is dedicated to spectroscopy (E/∆E = 500) and imaging (angular resolution: 12 arcmin FWHM) of celestial gamma-ray sources in the energy range 15 keV to 10 MeV with concurrent source monitoring in the X-ray (3–35 keV) and optical (V-band, 550 nm) wavelengths.
For more information about Integral mission, visit: http://www.esa.int/Our_Activities/Space_Science/Integral/
Integral overview: http://www.esa.int/Our_Activities/Space_Science/Integral/Integral_overview
Integral in depth: http://sci.esa.int/science-e/www/area/index.cfm?fareaid=21
Celebrating ten years of Integral science: http://orbiterchspacenews.blogspot.ch/2012/10/celebrating-ten-years-of-integral.html
Related ESA publications:
Integral results leaflet (pdf): http://esamultimedia.esa.int/docs/Integral_2007web.pdf
Integral mission brochure (pdf): http://esamultimedia.esa.int/docs/science/media/integral_brochure.pdf
Integral movies: http://multimedia.esa.int/Missions/INTEGRAL
Images, Text, Credits: ESA/ATG medialab/Integral/IBIS/ISDC.
Publié par Orbiter.ch à 13:52
mercredi 24 juin 2015
Crew Trains for Pair of Supply Ship Arrivals
ISS - Expedition 44 Mission patch.
June 24, 2015
A pair of Expedition 44 crew members are training for next week’s arrival of SpaceX CRS-7. Another crew member is practicing for the rendezvous of an upcoming Russian resupply mission. Meanwhile, science is ongoing aboard the International Space Station.
One-Year crew member Scott Kelly and station Commander Gennady Padalka partnered up for another session of robotics training. Kelly, with assistance from Padalka, will guide the 57.7 foot long Canadarm2 to capture the SpaceX Dragon about 7 a.m. EDT on June 30. Dragon’s launch atop a Falcon 9 rocket is planned for Sunday at 10:21 a.m.
Image above: The SpaceX Dragon craft was pictured May 21, 2015 before it was released from the International Space Station for a splashdown in the Pacific Ocean. Image Credit: NASA.
Kelly’s fellow One-Year crew member Mikhail Kornienko practiced using the telerobotically-operated rendezvous system which would be used to manually dock an approaching Progress cargo craft in case of an emergency. The next Russian resupply mission, ISS Progress 60, is due for launch early July 3rd and dock to the Pirs docking compartment two days later.
The crew was right back at work again today on the Microbiome study researching microgravity’s effect on an astronaut’s immune system. For the Motocard experiment the crew explored astronaut motion in space to potentially improve physical training. The crew also researched acoustic methods to locate micrometeoroid impacts on the station for the Proboy study.
SpaceX CRS-7: http://www.nasa.gov/mission_pages/station/structure/launch/index.html
One-Year crew: http://www.nasa.gov/oneyear/index.html
Microbiome study: http://www.nasa.gov/mission_pages/station/research/experiments/1010.html
Motocard experiment: http://www.energia.ru/en/iss/researches/human/07.html
Proboy study: http://www.energia.ru/en/iss/researches/develop/17.html
International Space Station (ISS): http://www.nasa.gov/mission_pages/station/main/index.html
Image (mentioned), Text, Credit: NASA.
Publié par Orbiter.ch à 16:45
Meteor Investigation Makes a Quick Recovery
ISS - International Space Station logo.
June 24, 2015
Spares are a good idea in many situations. Spare tires, batteries and keys come to mind. Turns out they can be helpful in space-based research as well
Image above: Astronaut Ron Garan, Expedition 28 flight engineer, tweeted this image from the International Space Station in August, 2011 with the following caption: “What a `Shooting Star’ looks like from space, taken yesterday during Perseid Meteor Shower.”. Image Credit: NASA.
When the third Orbital Cygnus mission to the International Space Station suffered a catastrophic anomaly moments after launch on Oct. 28, research and supplies lost included the Meteor investigation. Scientists were sending up a special camera to record meteor showers for two years in order to learn more about the composition and behavior of asteroids and comets that cross paths with Earth. But almost immediately, those scientists were back at work, preparing to send the investigation to the station on the SpaceX-7 launch, currently scheduled for June 28.
“One of the first questions NASA asked was how quickly we thought we could get spares ready for re-launch if we had the opportunity,” says Michael Fortenberry, principal investigator for Meteor and an engineer with Southwest Research Institute. “Within the next month or so, we were tentatively slated for the SpaceX-7 launch, which was a little over 6 months away.”
Image above: The “spare” power box for the Meteor investigation camera system. Image Credit: Southwest Research Institute.
Thanks to the existence of a spare camera and power box, that quick turn-around was possible and preparing for re-flight proved easier than creating a brand-new investigation. Researchers replaced some equipment, such as custom cables and the commercial hard drives used to store images. They also thoroughly tested all equipment, including conducting acoustic checks to ensure none of it made too much noise and vibration checks to make sure equipment will survive the launch. In all, Fortenberry says, the process involved about a quarter of the verifications and proofs done the first time around.
The spare-no-longer camera should be installed in the station’s Window Observational Research Facility (WORF) before the end of July. This window was designed to support the use of high-resolution cameras and produce high-quality images from inside the station rather than outside, where instruments face the vacuum and extreme temperatures of space. Images taken from the station are not affected by weather or interference from Earth’s atmosphere and the camera can observe for longer periods of time and across a broader viewing field than is possible on Earth.
“We’re excited about getting into the WORF in time to watch the Perseids meteor shower in August,” Fortenberry says. “Despite the delay, we haven’t missed any meteor showers that don’t occur every year.”
Image above: The Meteor investigation camera in the WORF window. Image Credit: NASA.
The camera is programmed to record known major meteor showers during its two-year orbit and could spot unpredicted showers as well. Recordings stored on hard drives will be returned to ground on supply vehicles as space allows.
One thing is missing on the re-flight: a shutter actuation system that would allow operators on the ground to open and close the shutter that protects the WORF window. That means that now space station crew will have to open and close the protective cover, an activity that must be scheduled along with the many other tasks the crew perform.
“We might not get as much time to take images as we would have with the window actuator,” Fortenberry explains. “It would be easier with the actuator, especially on the crew. But we will still get really good science.” That science will provide insight on how meteors have affected our planet and help protect spacecraft and Earth from potential collisions with space debris.
All thanks to those spares.
International Space Station (ISS): http://www.nasa.gov/mission_pages/station/main/index.html
Meteor investigation: http://www.nasa.gov/mission_pages/station/research/news/meteors_from_space
Window Observational Research Facility (WORF): http://www.nasa.gov/mission_pages/station/research/experiments/358.html
Southwest Research Institute: http://www.swri.org/
Images (mentioned), Text, Credits: NASA Johnson Space Center/Melissa Gaskill/Kristine Rainey.
Publié par Orbiter.ch à 16:20
Earth Directed CME Lights the Skies
NASA & ESA - SOHO Mission patch.
June 24, 2015
Images above: Two views of the CME on June 20, 2015 from the Solar and Heliospheric Observatory, or SOHO. Earth-directed CMEs like this one are often called halo CMEs, because the material shooting off from the sun looks like a ring around the disk of the sun. This halo can be seen more clearly in the right-hand image called a difference image, which is created by subtracting two consecutive frames to see how the image has changed. Images Credits: ESA&NASA/SOHO.
Earth experienced a geomagnetic storm on June 22, 2015 due to the arrival of an Earth-directed coronal mass ejection, or CME, from June 20.
The CME originated at 10:24 p.m. EDT on June 20, 2015. Coronal material exploded from the sun at about 780 miles per second, arriving at Earth at 1:59 p.m. EDT on June 22.
Image above: Aurora as seen 30 miles west of Philadelphia, PA on June 23, 2015. Image Credit: Courtesy of Jeff Berkes.
NOAA rated the resulting geomagnetic storm as G4, or severe. To see how this event affected Earth, visit NOAA's Space Weather Prediction Center at http://spaceweather.gov, the U.S. government's official source for space weather forecasts, alerts, watches and warnings.
Image above: "My first Aurora! Three brilliant, visible-to-naked-eye, displays of pink-hued Aurora with the last ending around 1:30 a.m. What an unforgettable sight at 38 degrees latitude!" said Michael Charnick of Calhoun County Park, WV. Image Credit: Courtesy of Michael Charnick.
A geomagnetic storm happens when the plasma and magnetic fields in a CME interact with Earth’s magnetic field, disturbing the magnetosphere and allowing stored plasma to flow towards the magnetic poles.
Image above: Aurora as seen in Louisa, Virginia on June 23, 2015. Image Credit: Courtesy of David Murr.
The same active region produced two other CMEs in the past few days, which were pushed along by the faster Earth-directed CME from June 20.
Image above: "The most intense aurora I've ever seen. It started with a wall of light between Lake Preston and DeSmet, South Dakota, while the moon was still out." Image Credit: Courtesy of Christian Begeman.
As a result of the geomagnetic storm, aurora were sighted in several mid-latitude locations, including Virginia in the United States and in the United Kingdom.
High Resolution Media: https://svs.gsfc.nasa.gov/11905
For more information about Solar and Heliospheric Observatory (SOHO), visit: http://www.nasa.gov/mission_pages/soho/index.html and http://sci.esa.int/soho/ and http://soho.esac.esa.int/
Images (mentioned), Text, Credits: NASA’s Goddard Space Flight Center/Sarah Frazier/Susan Hendrix/Holly Zell.
Publié par Orbiter.ch à 15:54
Hubble sees atmosphere being stripped from Neptune-sized exoplanet
ESA - Hubble Space Telescope logo.
24 June 2015
Artist impression of Gliese 436b
Astronomers using the NASA/ESA Hubble Space Telescope have discovered an immense cloud of hydrogen dispersing from a warm, Neptune-sized planet orbiting a nearby star. The enormous gaseous tail of the planet is about 50 times the size of the parent star. The findings will be published in the 24 June issue of the journal Nature.
A phenomenon this large has never before been seen around such a small exoplanet . It may offer clues as to how hot super-Earths — massive, hot versions of Earth — are born around other stars.
"This cloud of hydrogen is very spectacular!" says David Ehrenreich of the Observatory of the University of Geneva in Switzerland, lead author of the study. "Although the evaporation rate doesn't threaten the planet right now, we know that the star, a faint red dwarf, was more active in the past. This means that the planet's atmosphere evaporated faster during its first billion years of existence. Overall, we estimate that it may have lost up to 10 percent of its atmosphere."
Orbit of Gliese 436b around its host star
The planet, named Gliese 436b, is considered to be a "warm Neptune", because it is similar in size to Neptune, but much closer to its star Gliese 436 than Neptune is to the Sun. Although in this case the planet is in no danger of having its atmosphere completely stripped away — leaving just a solid, rocky core — this behaviour could explain the existence of hot super-Earths, which orbit very close to their stars and are typically more massive than Earth, although smaller than the seventeen Earth masses of Neptune.
Hot super-Earths could be the remaining cores of more massive planets that have completely lost their thick, gaseous atmospheres to the same type of evaporation that Hubble observed around Gliese 436b.
As the Earth's atmosphere blocks most ultraviolet light, astronomers needed a space telescope with Hubble's ultraviolet capability and exquisite precision to view the cloud. "You wouldn't be able to see it at visible wavelengths," says Ehrenreich. "But when you turn the ultraviolet eye of Hubble onto the system, it's really quite a transformation — the planet turns into a monstrous thing."
Ehrenreich and his team suggest that such a huge cloud of gas can exist around this planet because the cloud is not rapidly heated and swept away by the radiation from the relatively cool red dwarf star. This allows the cloud to stick around for a longer time.
Artistic impression of Gliese 436b in transit
Evaporation such as this may also have happened in the earlier history of the Solar System, when the Earth had a hydrogen-rich atmosphere that dissipated. It is also possible that it could happen to Earth's atmosphere at the end of our planet's life, when the Sun swells up to become a red giant and boils off our remaining atmosphere, before engulfing our planet completely.
Gliese 436b resides very close to Gliese 436 — just about 4 million kilometres away — and whips around it in just 2.6 Earth days . At the very youngest, this exoplanet is at least 6 billion years old, but astronomers suspect that it is somewhat older. About the size of Neptune, it has a mass of around 23 Earths. At just 30 light-years from Earth, it is one of the closest known exoplanets.
"Finding the cloud around Gliese 436b could be a game-changer for characterising atmospheres of the whole population of Neptunes and Super-Earths in ultraviolet observations ," explains Vincent Bourrier, also of the Observatory of the University of Geneva in Switzerland and co-author of the study. In the coming years, Bourrier expects that astronomers will find thousands of this kind of planet.
 Hubble observed this feature before around more massive exoplanets. The first detection of an evaporating extended atmosphere was around HD 209458b in 2003 (heic0303, heic0403). Heavy elements escaping the hot gas giant WASP-12b were studied in 2010. The lead author of the current paper performed a study on the evaporating atmosphere of the warm gas giant 55 Cancri b in 2012. In 2012 Hubble also observed a powerful burst of evaporation from the planet HD 189733b (heic1209). All observations for these discoveries were performed in the ultraviolet.
 For comparison, the Earth lies just under 150 million kilometres from the Sun and orbits it every 365.24 days, while Mercury, the innermost planet orbits the Sun every 88 days within an average distance to it of only 58 million kilometres.
 The ultraviolet technique may also spot the signatures of oceans evaporating on smaller, more Earth-like planets. It will be extremely challenging for astronomers to directly see water vapour on these worlds, because the vapour would be too low in the atmosphere (and thus shielded from telescopes). However, when stellar radiation breaks water molecules up into hydrogen and oxygen, the relatively light hydrogen atoms can escape the planet. If scientists could spot this hydrogen evaporatingfrom a planet that is a bit more temperate and little less massive than Gliese 436b, it is a good indicator that an ocean may be present on the surface.
Notes for editors:
The Hubble Space Telescope is a project of international cooperation between ESA and NASA.
The study, entitled “A giant comet-like cloud of hydrogen escaping the warm Neptune-mass exoplanet GJ 436b”, will be published in the 24 June issue of the journal Nature.
The international team of astronomers in this study consists of D. Ehrenreich (The Geneva Observatory, Switzerland), V. Bourrier (The Geneva Observatory, Switzerland), P. J. Wheatley (University of Warwick, United Kingdom), A. Lecavelier des Etangs (Institut d’astrophysique de Paris, CNRS; UPMC Univ. Paris 6, France), G. Hébrard (Institut d'astrophysique de Paris, CNRS; UPMC Univ. Paris 6; Observatoire de Haute-Provence, CNRS & OAMP, France), S. Udry (The Geneva Observatory, Switzerland), X. Bonfils (Université Grenoble Alpes; CNRS, Grenoble), X. Delfosse (Université Grenoble Alpes; CNRS, Grenoble), J-M. Désert (University of Colorado, USA), D. K. Sing (University of Exeter, United Kingdom), and A. Vidal-Madjar (Institut d’astrophysique de Paris, CNRS; UPMC Univ. Paris 6, France).
Images of Hubble: http://www.spacetelescope.org/images/archive/category/spacecraft/
Link to hubblesite release: http://hubblesite.org/newscenter/archive/releases/2015/17
Link to science paper: http://www.spacetelescope.org/static/archives/releases/science_papers/heic1515a.pdf
Images, Text, Credits: NASA/ESA/STScI, and G. Bacon/Video: NASA/ESA/STScI, Martin Kornmesser (ESA/Hubble).
Publié par Orbiter.ch à 15:20
Exposed water ice detected on comet’s surface
ESA - Rosetta Mission patch.
24 June 2015
Using the high-resolution science camera on board ESA’s Rosetta spacecraft, scientists have identified more than a hundred patches of water ice a few metres in size on the surface of Comet 67P/Churyumov-Gerasimenko.
Rosetta arrived at the comet in August 2014 at a distance of about 100 km and eventually orbited the comet at 10 km or less, allowing high-resolution images of the surface to be acquired.
A new study just published in the journal Astronomy & Astrophysics focuses on an analysis of bright patches of exposed ice on the comet’s surface.
Ice on Comet 67P/Churyumov-Gerasimenko
Based on observations of the gas emerging from comets, they are known to be rich in ices. As they move closer to the Sun along their orbits, their surfaces are warmed and the ices sublimate into gas, which streams away from the nucleus, dragging along dust particles embedded in the ice to form the coma and tail.
But some of the comet’s dust also remains on the surface as the ice below sublimates, or falls back on to the nucleus elsewhere, coating it with a thin layer of dusty material and leaving very little ice directly exposed on the surface. These processes help to explain why Comet 67P/Churyumov-Gerasimenko and other comets seen in previous flyby missions are so dark.
Despite this, Rosetta’s suite of instruments has already detected a variety of gases, including water vapour, carbon dioxide and carbon monoxide, thought to originate from frozen reservoirs below the surface.
Now, using images taken with Rosetta’s OSIRIS narrow-angle camera last September, scientists have identified 120 regions on the surface of Comet 67P/Churyumov-Gerasimenko that are up to ten times brighter than the average surface brightness.
Some of these bright features are found in clusters, while others appear isolated, and when observed at high resolution, many of them appear to be boulders displaying bright patches on their surfaces.
The clusters of bright features, comprising a few tens of metre-sized boulders spread over several tens of metres, are typically found in debris fields at the base of cliffs. They are most likely the result of recent erosion or collapse of the cliff wall revealing fresher material from below the dust-covered surface.
Icy clusters and individual boulders
By contrast, some of the isolated bright objects are found in regions without any apparent relation to the surrounding terrain. These are thought to be objects lifted up from elsewhere on the comet during a period of cometary activity, but with insufficient velocity to escape the gravitational pull of the comet completely.
In all cases, however, the bright patches were found in areas that receive relatively little solar energy, such as in the shadow of a cliff, and no significant changes were observed between images taken over a period of about a month. Furthermore, they were found to be bluer in colour at visible wavelengths compared with the redder background, consistent with an icy component.
“Water ice is the most plausible explanation for the occurrence and properties of these features,” says Antoine Pommerol of the University of Bern and lead author of the study.
“At the time of our observations, the comet was far enough from the Sun such that the rate at which water ice would sublimate would have been less than 1 mm per hour of incident solar energy. By contrast, if carbon dioxide or carbon monoxide ice had been exposed, it would have rapidly sublimated when illuminated by the same amount of sunlight. Thus we would not expect to see that type of ice stable on the surface at this time.”
The team also turned to laboratory experiments that tested the behaviour of water ice mixed with different minerals under simulated solar illumination in order to gain more insights into the process. They found that after a few hours of sublimation, a dark dust mantle a few millimetres thick was formed. In some places this acted to completely conceal any visible traces of the ice below, but occasionally larger dust grains or chunks would lift from the surface and move elsewhere, exposing bright patches of water ice.
“A 1 mm thick layer of dark dust is sufficient to hide the layers below from optical instruments,” confirms Holger Sierks, OSIRIS principal investigator at the Max Planck Institute for Solar System Research in Göttingen.
“The relatively homogeneous dark surface of the nucleus of Comet 67P/Churyumov-Gerasimenko, only punctuated by some metre-scale bright dots, can be explained by the presence of a thin dust mantle composed of refractory mineral and organic matter, with the bright spots corresponding to areas from which the dust mantle was removed, revealing a water-ice-rich subsurface below.”
Colour composites of icy bright patches on comet
The team also speculates about the timing of the formation of the icy patches. One hypothesis is that they were formed at the time of the last closest approach of the comet to the Sun, 6.5 years ago, with icy blocks ejected into permanently shadowed regions, preserving them for several years below the peak temperature needed for sublimation.
Another idea is that even at relatively large distances from the Sun, carbon dioxide and carbon monoxide driven-activity could eject the icy blocks. In this scenario, it is assumed that the temperature was not yet high enough for water sublimation, such that the water-ice-rich components outlive any exposed carbon dioxide or carbon monoxide ice.
“As the comet continues to approach perihelion, the increase in solar illumination onto the bright patches that were once in shadow should cause changes in their appearance, and we may expect to see new and even larger regions of exposed ice,” says Matt Taylor, ESA’s Rosetta project scientist.
“Combining OSIRIS observations made pre- and post-perihelion with other instruments will provide valuable insight into what drives the formation and evolution of such regions.”
Notes for editors:
“OSIRIS observations of metre-size exposures of H2O ice at the surface of 67P/Churyumov-Gerasimenko and interpretation using laboratory experiments” by A. Pommerol et al. is published in Astronomy & Astrophysics
The scientific imaging system OSIRIS was built by a consortium led by the Max Planck Institute for Solar System Research (Germany) in collaboration with CISAS, University of Padova (Italy), the Laboratoire d'Astrophysique de Marseille (France), the Instituto de Astrofísica de Andalucia, CSIC (Spain), the Scientific Support Office of the European Space Agency (The Netherlands), the Instituto Nacional de Técnica Aeroespacial (Spain), the Universidad Politéchnica de Madrid (Spain), the Department of Physics and Astronomy of Uppsala University (Sweden), and the Institute of Computer and Network Engineering of the TU Braunschweig (Germany). OSIRIS was financially supported by the national funding agencies of Germany (DLR), France (CNES), Italy (ASI), Spain (MEC), and Sweden (SNSB) and the ESA Technical Directorate.
Rosetta is an ESA mission with contributions from its Member States and NASA. Rosetta's Philae lander is contributed by a consortium led by DLR, MPS, CNES and ASI.
For more information about Rosetta mission, visit: http://www.esa.int/Our_Activities/Space_Science/Rosetta
Rosetta overview: http://www.esa.int/Our_Activities/Space_Science/Rosetta_overview
Rosetta factsheet: http://www.esa.int/Our_Activities/Space_Science/Rosetta/Rosetta_factsheet
Frequently asked questions: http://www.esa.int/Our_Activities/Space_Science/Rosetta/Frequently_asked_questions
Rosetta in depth:http://sci.esa.int/rosetta
Rosetta at Astrium: http://www.astrium.eads.net/en/programme/rosetta-1go.html
Rosetta at DLR: http://www.dlr.de/dlr/en/desktopdefault.aspx/tabid-10394/
Ground-based comet observation campaign: http://www.rosetta-campaign.net/home
Rosetta Blog: http://blogs.esa.int/rosetta/
Images, text, Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA.
Best regards, Orbiter.ch
Publié par Orbiter.ch à 14:54
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