vendredi 26 août 2011
Cassini Closes in on Saturn's Tumbling Moon Hyperion
NASA - ESA Cassini "Insider's" Mission logo.
August 26, 2011
NASA's Cassini spacecraft captured new views of Saturn's oddly shaped moon Hyperion during its encounter with this cratered body on Thursday, Aug. 25. Raw images were acquired as the spacecraft flew past the moon at a distance of about 15,500 miles (25,000 kilometers), making this the second closest encounter.
Image above: NASA's Cassini spacecraft obtained this unprocessed image of Saturn's moon Hyperion on Aug. 25, 2011. Image credit: NASA / JPL-Caltech / Space Science Institute.
Hyperion is a small moon -- just 168 miles (270 kilometers) across. It has an irregular shape and surface appearance, and it rotates chaotically as it tumbles along in orbit. This odd rotation prevented scientists from predicting exactly what terrain the spacecraft's cameras would image during this flyby.
Image above: Side view taken by NASA's Cassini spacecraft of Saturn's moon Hyperion. Image credit: NASA / JPL-Caltech / Space Science Institute.
However, this flyby's closeness has likely allowed Cassini's cameras to map new territory. At the very least, it will help scientists improve color measurements of the moon. It will also help them determine how the moon's brightness changes as lighting and viewing conditions change, which can provide insight into the texture of the surface. The color measurements provide additional information about different materials on the moon's deeply pitted surface.
Image above: Closeup view of Hyperion taken by NASA's Cassini spacecraft. Image credit: NASA / JPL-Caltech / Space Science Institute.
The latest raw images of Hyperion are online at: http://saturn.jpl.nasa.gov/photos/raw/
Cassini's closest encounter with Hyperion was on September 26, 2005, when the spacecraft flew approximately 310 miles (500 kilometers) above the moon's surface.
Cassini's next flyby of Hyperion will be on Sept. 16, 2011, when it passes the tumbling moon at a distance of about 36,000 miles (58,000 kilometers).
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.
For more information about the Cassini-Huygens mission, visit http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov
Images (mentioned), Text, Credits: NASA / JPL / Rosemary Sullivant.
Greetings, Orbiter.ch
ATV Edoardo Amaldi arrives in Kourou
ESA - ATV-3 Edoardo Amaldi Mission patch.
26 August 2011
cargo carrier to the International Space Station, has completed its first long voyage – sailing across the Atlantic. It is now at Europe’s Spaceport in Kourou, French Guiana to be prepared for launch early next year.
With only a few months since the end of the ATV-2 mission, the ESA teams in Europe and Kourou are getting into high gear with the next craft: ATV Edoardo Amaldi.
Unloading in Kourou harbour
Involving some 2000 highly skilled engineers across Europe, ATV-3 was reviewed and qualified in July by the ESA and EADS teams in Bremen, Germany for shipping to Kourou.
The review is of importance because, once the ATV is in Kourou, any major changes may affect the schedule.
ATV-3 interior during review
MN Toucan, a French cargo ship used normally by Arianespace to transport Ariane rocket elements, steamed from Bremerhaven on 6 August.
After sailing across the Atlantic for 13 days, it arrived early this week to hold position near Devil’s Island off the coast of French Guiana to wait for a favourable tide.
Yesterday, the ship docked in Kourou harbour and unloading began.
Image above: ATV-3 containers on the cargo deck of the French cargo ship MN Toucan during the 13-day voyage from Bremerhaven to Kourou.
Shipped in sections in several hermetically sealed containers, ATV-3 will be reassembled and tested before cargo will be inserted and it is fuelled for its mission.
The launch campaign is scripted in great detail and spans 180 working days.
MN Toucan leaving Bremen harbour
According to current planning, Edoardo Amaldi will carry about two tonnes of dry cargo, 285 kg of water and more than three tonnes of propellants.
ATV is the biggest cargo carrier servicing the Space Station and a vital element of ISS logistics.
ATV approaching Space Station
Related links:
ATV - Automated Transfer Vehicle: http://www.esa.int/SPECIALS/ATV/index.html
ATV blog: http://blogs.esa.int/atv
ATV Factsheet: http://esamultimedia.esa.int/docs/ATV/Fact_ATV_cropmarks_EN.pdf
Space pioneers: Edoardo Amaldi: http://www.esa.int/SPECIALS/Space_Year_2007/SEMT5D0P0WF_0.html
Images, Text, Credits: ESA / D.Ducros.
Best regards, Orbiter.ch
jeudi 25 août 2011
Proba-2 fuel tank refilled from ‘solid gas’
ESA - PROBA-2 Mission logo.
25 August 2011
Sometimes all it takes is fresh air to get a new lease of life. ESA’s Proba-2 microsatellite is a good example: an influx of nitrogen has replenished its fuel tank, in the process demonstrating a whole new space technology.
On 16 August a telecommand was sent from ESA’s Redu ground station in Belgium to boost the gases in Proba-2’s unusual ‘resistojet’ engine.
Used to maintain the microsatellite’s orbit at 600 km altitude, this experimental engine runs on xenon gas heated before ejection to provide added thrust.
Proba-2
The command added nitrogen gas to the fuel tank, bringing its pressure close to its launch level.
“What makes this repressurisation unique is that the added gas was not stored in a pressurised state but produced from a solid material at room temperature, the first of four ‘cool-gas generators’ on Proba-2,” explained Laurens van Vliet of Dutch research organisation TNO, which developed the technology.
“Nitrogen, like xenon, is an inert, non-reactive gas, so the resistojet can work just as well with a xenon–nitrogen mixture.”
Cool-gas generators
The bottle-shaped cool-gas generators are filled with a rigid solid material that, once triggered, produces more than 250 times its own volume in pure nitrogen gas.
“The generators are a huge step forward because they can be stored without pressure with no danger of leaking, and require no maintenance,” added Berry Sanders of TNO. “Proba’s generators had not been touched in six years.
“This is very different to standard systems with gas under pressure, which are much more complex and need regular checking and maintenance.”
The other three generators will be used later in Proba-2’s orbital lifetime.
Integrating the cool-gas generators
TNO designed the Proba-2 cool-gas experiment in close cooperation with Netherlands-based Bradford Engineering, responsible for constructing it. The resistojet design came from UK company Surrey Satellite Technology Ltd while the experiment was integrated with the satellite by Belgium's QinetiQ Space.
The technology had been fast-tracked for space by the Dutch National Space Office as part of ESA’s General Support Technology Programme, supporting the development of promising prototypes into flight-ready hardware.
Proba-2 fuel tank telemetry
“With this test the technology has been ‘space-proven’, such demonstrations being one of the main goals of the Proba-2 mission,” concluded Mr Sanders.
It now has many other potential uses in space, including propulsion systems, oxygen production for astronauts and inflatable structures such as antennas, booms, landing airbags and full-sized habitat modules.
TNO team celebrate success
About Proba-2
Proba-2 is the latest in ESA’s Project for Onboard Autonomy series of satellites, dedicated to the in-orbit demonstration of innovative technologies.
Proba-2
Proba-2 was launched on 2 November 2009. Less than a cubic metre in volume, it carries a total of 17 new technologies and four science payloads focused on the Sun and space weather.
More information:
Proba-2: science payloads: http://www.esa.int/SPECIALS/Proba/SEMSD5ZVNUF_0.html
Proba-2: technology demonstrations: http://www.esa.int/SPECIALS/Proba/SEMZC5ZVNUF_0.html
About the General Support Technology Programme (GSTP): http://www.esa.int/SPECIALS/Technology/SEMEU4WPXPF_0.html
Related links:
TNO website: http://www.tno.nl/groep.cfm?context=overtno&content=magazines&laag1=37&item_id=70&Taal=2
Bradford Engineering: http://www.bradford-space.com/cms/
Surrey Satellite Technolgy Limited: http://www.sstl.co.uk/
Qinetiq Space (B): http://www.qinetiq.com/home_qinetiq_space_nv.html
Images, Text, Credits: ESA / Pierre Carril / TNO.
Cheers, Orbiter.ch
mercredi 24 août 2011
Launch vehicle "Soyuz-U" failed to transport cargo vehicle "Progress M-12M"
ROSCOSMOS logo.
24/08/2011
Mission Control Moscow reported an abnormal situation from the Progress 44 cargo craft that launched on time at 9 a.m. EDT today.
The Progress-M-12M blasts off from the launch pad at the Baikonour cosmodrome
Progress 44 launched from the Baikonur Cosmodrome into a cloudless sky at 7 p.m. Kazakhstan time bound for the International Space Station and a docking on Friday. At the time of launch, the space station was flying 230 miles over Equatorial Guinea on the west coast of Africa. The spacecraft is carrying 2.9 tons of food, fuel and supplies for the space station.
Progress M-12M 44P Launch - Failure
But, 5 minutes and 50 seconds after launch, Mission Control Houston received a report of an "off-nominal situation" during the rocket's third and final stage.
The unmanned Russian cargo spacecraft Progress has crashed in eastern Siberia after failing to reach its target orbit.
Progress M cargo spacecraft
Emergency with the carrier rocket "Soyuz-U" and not removal of cargo vehicle "Progress M-12M" on the target orbit will not affect the life support crews 28/29 International Space Station expeditions. Availability of food, water and life support systems allow for the functioning of the crew for a long period.
To investigate the reasons for this situation, a commission from among the Russian Space Agency and the organizations of the rocket-space industry.
Images, Video, Text, Credit: Press Service of the Russian Space Agency (Roscosmo PAO) / AFP, Getty / Orbiter.ch.
Greetings, Orbiter.ch
NASA'S Swift Satellite Spots Black Hole Devouring A Star
NASA - SWIFT Mission patch.
Aug. 24, 2011
Two studies appearing in the Aug. 25 issue of the journal Nature provide new insights into a cosmic accident that has been streaming X-rays toward Earth since late March. NASA's Swift satellite first alerted astronomers to intense and unusual high-energy flares from the new source in the constellation Draco.
"Incredibly, this source is still producing X-rays and may remain bright enough for Swift to observe into next year," said David Burrows, professor of astronomy at Penn State University and lead scientist for the mission's X-Ray Telescope instrument. "It behaves unlike anything we've seen before."
Astronomers soon realized the source, known as Swift J1644+57, was the result of a truly extraordinary event -- the awakening of a distant galaxy's dormant black hole as it shredded and consumed a star. The galaxy is so far away, it took the light from the event approximately 3.9 billion years to reach Earth.
Burrows' study included NASA scientists. It highlights the X- and gamma-ray observations from Swift and other detectors, including the Japan-led Monitor of All-sky X-ray Image (MAXI) instrument aboard the International Space Station.
Image above: Positions from Swift's XRT constrained the source to a small patch of sky that contains a faint galaxy known to be 3.9 billion light-years away. But to link the Swift event to the galaxy required observations at radio wavelengths, which showed that the galaxy's center contained a brightening radio source. Analysis of that source using the Expanded Very Large Array and Very Long Baseline Interferometry (VLBI) shows that it is still expanding at more than half the speed of light. Credit: NRAO / CfA / Zauderer et al.
The second study was led by Ashley Zauderer, a post-doctoral fellow at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. It examines the unprecedented outburst through observations from numerous ground-based radio observatories, including the National Radio Astronomy Observatory's Expanded Very Large Array (EVLA) near Socorro, N.M.
Most galaxies, including our own, possess a central supersized black hole weighing millions of times the sun's mass. According to the new studies, the black hole in the galaxy hosting Swift J1644+57 may be twice the mass of the four-million-solar-mass black hole in the center of the Milky Way galaxy. As a star falls toward a black hole, it is ripped apart by intense tides. The gas is corralled into a disk that swirls around the black hole and becomes rapidly heated to temperatures of millions of degrees.
Image above: Swift's X-Ray Telescope continues to record high-energy flares from Swift J1644+57 more than three months after the source's first appearance. Astronomers believe that this behavior represents the slow depletion of gas in an accretion disk around a supermassive black hole. The first flares from the source likely coincided with the disk's creation, thought to have occurred when a star wandering too close to the black hole was torn apart. Credit: NASA / Swift / Penn State.
The innermost gas in the disk spirals toward the black hole, where rapid motion and magnetism create dual, oppositely directed "funnels" through which some particles may escape. Jets driving matter at velocities greater than 90 percent the speed of light form along the black hole's spin axis. In the case of Swift J1644+57, one of these jets happened to point straight at Earth.
"The radio emission occurs when the outgoing jet slams into the interstellar environment," Zauderer explained. "By contrast, the X-rays arise much closer to the black hole, likely near the base of the jet."
Images from Swift's Ultraviolet/Optical (white, purple) and X-Ray telescopes (yellow and red) were combined to make this view of Swift J1644+57. Evidence of the flares is seen only in the X-ray image, which is a 3.4-hour exposure taken on March 28, 2011. Credit: NASA / Swift / Stefan Immler.
Theoretical studies of tidally disrupted stars suggested they would appear as flares at optical and ultraviolet energies. The brightness and energy of a black hole's jet is greatly enhanced when viewed head-on. The phenomenon, called relativistic beaming, explains why Swift J1644+57 was seen at X-ray energies and appeared so strikingly luminous.
When first detected March 28, the flares were initially assumed to signal a gamma-ray burst, one of the nearly daily short blasts of high-energy radiation often associated with the death of a massive star and the birth of a black hole in the distant universe. But as the emission continued to brighten and flare, astronomers realized that the most plausible explanation was the tidal disruption of a sun-like star seen as beamed emission.
By March 30, EVLA observations by Zauderer's team showed a brightening radio source centered on a faint galaxy near Swift's position for the X-ray flares. These data provided the first conclusive evidence that the galaxy, the radio source and the Swift event were linked.
This illustration steps through the events that scientists think likely resulted in Swift J1644+57. Credit: NASA / Goddard Space Flight Center / Swift.
"Our observations show that the radio-emitting region is still expanding at more than half the speed of light," said Edo Berger, an associate professor of astrophysics at Harvard and a coauthor of the radio paper. "By tracking this expansion backward in time, we can confirm that the outflow formed at the same time as the Swift X-ray source."
Swift, launched in November 2004, is managed by NASA's Goddard Space Flight Center in Greenbelt, Md. It is operated in collaboration with Penn State, the Los Alamos National Laboratory in N.M. and Orbital Sciences Corp., in Dulles, Va., with international collaborators in the U.K., Italy, Germany and Japan. MAXI is operated by the Japan Aerospace Exploration Agency as an external experiment attached to the Kibo module of the space station. For images and animations related to the studies, visit: http://www.nasa.gov/swift
Images (mentioned), Video (mentioned), Text, Credit: NASA / Trent J. Perrotto / Lynn Chandler / Goddard Space Flight Center / Francis Reddy.
Greetings, Orbiter.ch
VLT Looks into The Eyes of the Virgin
ESO - European Southern Observatory logo.
24 August 2011
VLT looks into The Eyes of the Virgin
ESO’s Very Large Telescope has taken a striking image of a beautiful yet peculiar pair of galaxies nicknamed The Eyes. The larger of these, NGC 4438, was once a spiral galaxy but has become badly deformed by collisions with other galaxies in the last few hundred million years. This picture is the first to come out of ESO’s Cosmic Gems programme, an initiative in which ESO has granted dedicated observing time for outreach purposes.
The Eyes are about 50 million light-years away in the constellation of Virgo (The Virgin) and are some 100 000 light-years apart. The nickname comes from the apparent similarity between the cores of this pair of galaxies — two white ovals that resemble a pair of eyes glowing in the dark when seen in a moderate-sized telescope.
But although the centres of these two galaxies look similar, their outskirts could not be more different. The galaxy in the lower right, known as NGC 4435, is compact and seems to be almost devoid of gas and dust. In contrast, in the large galaxy in the upper left (NGC 4438) a lane of obscuring dust is visible just below its nucleus, young stars can be seen left of its centre, and gas extends at least up to the edges of the image.
The Eyes in the constellation of Virgo
The contents of NGC 4438 have been stripped out by a violent process: a collision with another galaxy. This clash has distorted the galaxy’s spiral shape, much as could happen to the Milky Way when it collides with its neighbouring galaxy Andromeda in three or four billion years.
NGC 4435 could be the culprit. Some astronomers believe that the damage caused to NGC 4438 resulted from an approach between the two galaxies to within about 16 000 light-years that happened some 100 million years ago. But while the larger galaxy was damaged, the smaller one was significantly more affected by the collision. Gravitational tides from this clash are probably responsible for ripping away the contents of NGC 4438, and for reducing NGC 4435’s mass and removing most of its gas and dust.
Another possibility is that the giant elliptical galaxy Messier 86, further away from The Eyes and not visible in this image, was responsible for the damage caused to NGC 4438. Recent observations have found filaments of ionised hydrogen gas connecting the two large galaxies, indicating that they may have collided in the past.
The elliptical galaxy Messier 86 and The Eyes belong to the Virgo Cluster, a very rich grouping of galaxies. In such close quarters, galaxy collisions are fairly frequent, so perhaps NGC 4438 suffered from encounters with both NGC 4435 and Messier 86.
This picture is the first to be produced as part of the ESO Cosmic Gems programme. This is a new initiative to produce astronomical images for educational and public outreach purposes. The programme mainly makes use of time when the sky conditions are not suitable for science observations to take pictures of interesting, intriguing or visually attractive objects. The data are also made available to professional astronomers through ESO’s science archive.
Zooming in on The Eyes
In this case, although there were some clouds, the atmosphere was exceptionally stable, which allowed very sharp details to be revealed in this image taken using the VLT’s FORS2 [1] instrument. Light passing through two different filters was used: red (coloured red) and green-yellow (coloured blue), and the exposure times were 1800 seconds and 1980 seconds, respectively.
Notes:
[1] FORS2 is the visual and near ultraviolet FOcal Reducer and low dispersion Spectrograph for the VLT. It is installed on the VLT’s Unit Telescope 1.
More information:
ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive astronomical observatory. 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 a 40-metre-class European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.
Links:
ESO’s Cosmic Gems Programme: http://www.eso.org/public/outreach/gems.html
Photos of the VLT: http://www.eso.org/public/images/archive/category/paranal/
Images, Text, Credits: ESO / Gems project / IAU and Sky & Telescope / Richard Hook / Olivier R. Hainaut / Lars Lindberg Christensen / Video: ESO / A. Fujii and Digitized Sky Survey 2. Music: John Dyson (from the album Moonwind).
Best regards, Orbiter.ch
mardi 23 août 2011
NASA's Wise Mission Discovers Coolest Class of Stars
NASA - WISE Mission patch labeled.
Aug. 23, 2011
Scientists using data from NASA's Wide-field Infrared Survey Explorer (WISE) have discovered the coldest class of star-like bodies, with temperatures as cool as the human body.
Astronomers hunted these dark orbs, termed Y dwarfs, for more than a decade without success. When viewed with a visible-light telescope, they are nearly impossible to see. WISE's infrared vision allowed the telescope to finally spot the faint glow of six Y dwarfs relatively close to our sun, within a distance of about 40 light-years.
This artist's conception illustrates what a "Y dwarf" might look like. Y dwarfs are the coldest star-like bodies known, with temperatures that can be even cooler than the human body. Image credit: NASA / JPL-Caltech.
"WISE scanned the entire sky for these and other objects, and was able to spot their feeble light with its highly sensitive infrared vision," said Jon Morse, Astrophysics Division director at NASA Headquarters in Washington. "They are 5,000 times brighter at the longer infrared wavelengths WISE observed from space than those observable from the ground."
The Y's are the coldest members of the brown dwarf family. Brown dwarfs are sometimes referred to as "failed" stars. They are too low in mass to fuse atoms at their cores and thus don't burn with the fires that keep stars like our sun shining steadily for billions of years. Instead, these objects cool and fade with time, until what little light they do emit is at infrared wavelengths.
Astronomers study brown dwarfs to better understand how stars form and understand the atmospheres of planets beyond our solar system. The atmospheres of brown dwarfs are similar to those of gas giant planets like Jupiter, but they are easier to observe because they are alone in space, away from the blinding light of a parent star.
NASA's Wide-field Infrared Survey Explorer, or WISE, has uncovered the coldest brown dwarf known so far (green dot in very center of this infrared image). Image credit: NASA / JPL-Caltech / UCLA.
So far, WISE data have revealed 100 new brown dwarfs. More discoveries are expected as scientists continue to examine the enormous quantity of data from WISE.
The telescope performed the most advanced survey of the sky at infrared wavelengths to date, from Jan. 2010 to Feb. 2011, scanning the entire sky about 1.5 times.
Of the 100 brown dwarfs, six are classified as cool Y's. One of the Y dwarfs, called WISE 1828+2650, is the record holder for the coldest brown dwarf with an estimated atmospheric temperature cooler than room temperature, or less than 80 degrees Fahrenheit (25 degrees Celsius).
"The brown dwarfs we were turning up before this discovery were more like the temperature of your oven," said Davy Kirkpatrick, a WISE science team member at the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena, Calif. "With the discovery of Y dwarfs, we've moved out of the kitchen and into the cooler parts of the house."
Kirkpatrick is lead author of a paper appearing in the Astrophysical Journal Supplement Series, describing the 100 confirmed brown dwarfs. Michael Cushing, a WISE team member at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif., is lead author of a paper describing the Y dwarfs in the Astrophysical Journal.
The Y dwarfs are in our sun's neighborhood, from approximately nine to 40 light-years away. The Y dwarf approximately nine light-years away, WISE 1541-2250, may become the seventh closest star system, bumping Ross 154 back to eighth. By comparison, the star closest to our solar system, Proxima Centauri, is about four light-years away.
This artist's conception illustrates what brown dwarfs of different types might look like to a hypothetical interstellar traveler who has flown a spaceship to each one. Image credit: NASA / JPL-Caltech.
"Finding brown dwarfs near our sun is like discovering there's a hidden house on your block that you didn't know about," Cushing said. "It's thrilling to me to know we've got neighbors out there yet to be discovered. With WISE, we may even find a brown dwarf closer to us than our closest known star."
Once the WISE team identified brown dwarf candidates, they turned to NASA's Spitzer Space Telescope to narrow their list. To definitively confirm them, the WISE team used some of the most powerful telescopes on Earth to split apart the objects' light and look for telltale molecular signatures of water, methane and possibly ammonia. For the very coldest of the new Y dwarfs, the team used NASA's Hubble Space Telescope. The Y dwarfs were identified based on a change in these spectral features compared to other brown dwarfs, indicating they have a lower atmospheric temperature.
JPL manages WISE for NASA's Science Mission Directorate. The principal investigator is Edward Wright at UCLA. The WISE satellite was decommissioned in 2011 after completing its sky survey observations. The mission was selected under NASA's Explorers Program managed by the Goddard Space Flight Center in Greenbelt, Md. The science instrument was built by the Space Dynamics Laboratory in Logan, Utah, and the spacecraft by Ball Aerospace and Technologies Corp., in Boulder, Colo. Science operations and data processing are at the Infrared Processing and Analysis Center at the California Institute of Technology. For more information about WISE, visit: http://www.nasa.gov/wise and http://wise.astro.ucla.edu
Images (mentioned) Text, Credit: NASA / JPL / Whitney Clavin / Trent J. Perrotto.
Greetings, Orbiter.ch
Inscription à :
Articles (Atom)

























