mercredi 14 octobre 2015
Coronal Hole Front and Center
NASA - Solar Dynamics Observatory (SDO) patch.
Oct. 14, 2015
The dark area across the top of the sun in this image is a coronal hole, a region on the sun where the magnetic field is open to interplanetary space, sending coronal material speeding out in what is called a high-speed solar wind stream. The high-speed solar wind originating from this coronal hole, imaged here on Oct. 10, 2015, by NASA's Solar Dynamics Observatory, created a geomagnetic storm near Earth that resulted in several nights of auroras. This image was taken in wavelengths of 193 Angstroms, which is invisible to our eyes and is typically colorized in bronze.
Related article:
- Fast Solar Wind Causes Aurora Light Shows: http://www.nasa.gov/image-feature/goddard/fast-solar-wind-causes-aurora-light-shows
For more information about Solar Dynamics Observatory (SDO), visit: http://www.nasa.gov/mission_pages/sdo/main/index.html
Image, Text, Credits: NASA/SDO/Ashley Morrow.
Greetings, Orbiter.ch
A Cosmic Sackful of Black Coal
ESO - European Southern Observatory logo.
14 October 2015
Part of the Coalsack Nebula in close-up
Part of the Coalsack Nebula
Dark smudges almost block out a rich star field in this new image captured by the Wide Field Imager camera, installed on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile. The inky areas are small parts of a huge dark nebula known as the Coalsack, one of the most prominent objects of its kind visible to the unaided eye. Millions of years from now, chunks of the Coalsack will ignite, rather like its fossil fuel namesake, with the glow of many young stars.
The Coalsack Nebula in the constellation of Crux
The Coalsack Nebula is located about 600 light-years away in the constellation of Crux (The Southern Cross). This huge, dusky object forms a conspicuous silhouette against the bright, starry band of the Milky Way and for this reason the nebula has been known to people in the southern hemisphere for as long as our species has existed.
Wide-field view of part of the Coalsack Nebula
The Spanish explorer Vicente Yáñez Pinzón first reported the existence of the Coalsack Nebula to Europe in 1499. The Coalsack later garnered the nickname of the Black Magellanic Cloud, a play on its dark appearance compared to the bright glow of the two Magellanic Clouds, which are in fact satellite galaxies of the Milky Way. These two bright galaxies are clearly visible in the southern sky and came to the attention of Europeans during Ferdinand Magellan’s explorations in the 16th century. However, the Coalsack is not a galaxy. Like other dark nebulae, it is actually an interstellar cloud of dust so thick that it prevents most of the background starlight from reaching observers.
Zooming in on the dark and dusty Coalsack Nebula
A significant number of the dust particles in dark nebulae have coats of frozen water, nitrogen, carbon monoxide and other simple organic molecules. The resulting grains largely prevent visible light from passing through the cosmic cloud. To get a sense of how truly dark the Coalsack is, back in 1970, the Finnish astronomer Kalevi Mattila published a study estimating that the Coalsack has only about 10 percent of the brightness of the encompassing Milky Way. A little bit of background starlight, however, still manages to get through the Coalsack, as is evident in the new ESO image and in other observations made by modern telescopes.
A close look at part of the Coalsack Nebula
The little light that does make it through the nebula does not come out the other side unchanged. The light we see in this image looks redder than it ordinarily would. This is because the dust in dark nebulae absorbs and scatters blue light from stars more than red light, tinting the stars several shades more crimson than they would otherwise be.
Millions of years in the future the Coalsack’s dark days will come to an end. Thick interstellar clouds like the Coalsack contain lots of dust and gas — the fuel for new stars. As the stray material in the Coalsack coalesces under the mutual attraction of gravity, stars will eventually light up, and the coal “nuggets” in the Coalsack will "combust", almost as if touched by a flame.
More information:
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”.
Links:
Photos of ESO’s La Silla Observatory: https://www.eso.org/public/images/archive/category/lasilla/
Photos of the MPG/ESO.2.2-metre telescope: http://www.eso.org/public/images/archive/search/?adv=&subject_name=mpg
Photos taken with the MPG/ESO.2.2-metre telescope: http://www.eso.org/public/images/archive/search/?adv=&facility=15
Images, Text, Credits: ESO/IAU and Sky & Telescope/videos: ESO, N. Risinger (skysurvey.org), Digitized Sky Survey 2. Music: Johan Monell (www.johanmonell.com).
Greetings, Orbiter.ch
AIMing a light across millions of kilometres
ESA - Asteroid Impact & Deflection Assessment Mission (AIDA) logo.
14 October 2015
Imagine beaming a light across millions of kilometres of empty space, all the way back to Earth. ESA’s proposed Asteroid Impact Mission is intended to do just that: demonstrate laser communications across an unprecedented void.
Laser communication with Earth
The Asteroid Impact Mission, or AIM, undergoing detailed design ahead of a final go/no-go decision by ESA’s Ministerial Council in December 2016, is a deep-space technology-demonstration mission that would also be humanity’s first probe to a double asteroid.
Among its innovative technologies, laser communications would return results to scientists several times faster than standard radio signals.
“Optical communications in general is not yet a well-established technology for space and ESA’s European Data Relay System (EDRS) will be the first commercial application,” explains ESA optics engineer Zoran Sodnik.
ESA’s laser station
“In principle it works something like Morse code, with encoded rapid flashes on and off. ERDS with satellites in high orbits will use laser links to return environmental data from Europe’s low-orbiting Sentinel satellites on a realtime basis, a technique previously demonstrated using ESA’s Alphasat and Artemis telecom missions.
“In 2013 ESA’s Optical Ground Station in Tenerife participated in a two-way contact with NASA’s LADEE lunar orbiter, across 400 000 km.
“But AIM will need to operate much further: we are benchmarking a maximum span of 75 million kilometres, or half the distance between Earth and the Sun. That might sound like a lot, but operating around Mars one day will involve much further distances still.”
Transmitter telescope
A laser beam shone back from AIM’s 13.5 cm-diameter laser telescope at such a distance would have a ground footprint of about 1100 km – further than from London to Berlin. Also a lot but the equivalent radio beam radiating out across space would end up wider than our whole planet.
“The much higher frequency of laser light is what gives us higher directivity and as a result increased bandwidth,” adds ESA laser engineer Clemens Heese.
“At the same time, many photons will get lost on the way, so we need to use sophisticated photon counting methods to detect the signal reliably using our receiver telescope of around 1 m diameter.
AIM laser
“While radio communications is a very mature technology and close to optimum efficiency, there’s still lots of room for development with optical communications. So this is the way we need to go to really boost the quantity and speed of data we can deliver to scientists.”
To meet the challenge, ESA’s AIM team this month issued technology pre-development contracts to industry to tackle key issues including telescope design, detector electronics and coarse and fine-pointing systems. To give an idea of the kind of pointing required, AIM will need to align with the signal from Earth to within the diameter of planet Mars seen in our terrestrial sky.
Laser for altimetry
“At 39.3 kg, AIM’s laser system will be one of the single largest payload items,” explains Andres Galvez, heading ESA’s General Studies Programme.
“We intend to gain maximum utility from it, by also using it for scientific purposes: the laser can also serve as an altimeter to chart the asteroid.”
Earth defense test
The system design is led by RUAG Space in Switzerland, building on its existing family of Optel laser communication terminals, the latest of which is tailored for direct-to-Earth downlinks from minisatellites.
For more information about Asteroid Impact Mission (AIM), visit: http://www.esa.int/Our_Activities/Space_Engineering_Technology/Asteroid_Impact_Mission
Images, Video, Text, Credits: ESA/RUAG/ScienceOffice.org.
Best regards, Orbiter.ch
mardi 13 octobre 2015
Cassini Begins Series of Flybys with Close-up of Saturn Moon Enceladus
NASA - Cassini International logo.
Oct. 13, 2015
Image above: Artist's view of the Cassini flyby on Enceladus. Image Credits: NASA/JPL-Caltech.
NASA's Cassini spacecraft will wrap up its time in the region of Saturn's large, icy moons with a series of three close encounters with Enceladus starting Wednesday, Oct. 14. Images are expected to begin arriving one to two days after the flyby, which will provide the first opportunity for a close-up look at the north polar region of Enceladus.
Wednesday’s flyby is considered a moderately close approach for Cassini, which will pass at an altitude of 1,142 miles (1,839 kilometers) above the moon's surface. Closest approach to Enceladus will occur at 6:41 a.m. EDT (3:41 a.m. PDT). The spacecraft’s final two approaches will take place in late October and mid-December.
During Cassini’s early-mission encounters with the moon, the northern terrain of Enceladus was masked by wintry darkness. Now that the summer sun is shining on the high northern latitudes, scientists will be looking for signs of ancient geological activity similar to the geyser-spouting, tiger-stripe fractures in the moon's south polar region. Features observed during the flyby could help them understand whether the north also was geologically active at some time in the past.
Image above: Earlier in Cassini's mission at Saturn, northern terrains on the ocean-bearing icy moon Enceladus were in the shadow of winter. Image Credits: NASA/JPL-Caltech.
"We've been following a trail of clues on Enceladus for 10 years now," said Bonnie Buratti, a Cassini science team member and icy moons expert at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California. "The amount of activity on and beneath this moon's surface has been a huge surprise to us. We're still trying to figure out what its history has been, and how it came to be this way."
Since Cassini's 2005 discovery of continually-erupting fountains of icy material on Enceladus, the Saturn moon has become one of the most promising places in the solar system to search for present-day habitable environments. Mission scientists announced evidence in March that hydrothermal activity may be occurring on the seafloor of the moon's underground ocean. In September they broke news that its ocean -- previously thought to be only a regional sea -- was, in fact, global.
Animation of Cassini "E20" Enceladus Flyby - Oct. 14, 2015
Animation above: This animation shows NASA's Cassini spacecraft during its Oct. 14, 2015, flyby of Enceladus, which will focus on the Saturnian moon's northern polar region. Animation Credit: NASA.
"The global nature of Enceladus' ocean and the inference that hydrothermal systems might exist at the ocean's base strengthen the case that this small moon of Saturn may have environments similar to those at the bottom of our own ocean," said Jonathan Lunine, an interdisciplinary scientist on the Cassini mission at Cornell University in Ithaca, New York. "It is therefore very tempting to imagine that life could exist in such a habitable realm, a billion miles from our home."
The Oct. 14 encounter will serve as a prelude to the main event, a flyby of Enceladus on Wednesday, Oct. 28, during which Cassini will come dizzyingly close to the icy moon, passing a mere 30 miles (49 kilometers) above the moon's south polar region. During this encounter, Cassini will make its deepest-ever dive through the moon's plume of icy spray, collecting images and valuable data about what's going on beneath the frozen surface. Cassini scientists are hopeful data from that flyby will provide evidence of how much hydrothermal activity is occurring in the moon's ocean, and how the amount of activity impacts the habitability of Enceladus’ ocean.
Cassini's final close flyby on Dec. 19 will examine how much heat is coming from the moon's interior from an altitude of 3,106 miles (4,999 kilometers).
An online toolkit for all three final Enceladus flybys is available at:
http://solarsystem.nasa.gov/finalflybys
Cassini arrived at Saturn in 2004 and still has about two years left on its mission. Beginning in November, mission controllers will begin to slowly raise Cassini's orbit out of the space around the Saturn’s equator, where flybys of the large moons are more common. Coming up are a number of closest-ever brushes with the small moons that huddle near the planet's rings.
"We'll continue observing Enceladus and its remarkable activity for the remainder of our precious time at Saturn," said Linda Spilker, Cassini project scientist at JPL. "But these three encounters will be our last chance to see this fascinating world up close for many years to come."
The Cassini-Huygens mission is a cooperative project of NASA, ESA (European Space Agency) and the Italian Space Agency. JPL manages the mission for NASA's Science Mission Directorate in Washington.
For more information about Cassini, visit: http://www.nasa.gov/cassini or http://saturn.jpl.nasa.gov and http://www.esa.int/Our_Activities/Space_Science/Cassini-Huygens
NASA/Dwayne Brown/Laurie Cantillo/JPL/Preston Dyches/Karen Northon.
Best regards, Orbiter.ch
Pluto: The Impact of Craters
NASA - New Horizons Mission logo.
October 13, 2015
There are many ways scientists investigate a planet they’re seeing for the first time, and this is one example. With a flyby mission you can’t probe the ice on the surface or analyze samples, so you have other methods to determine a planet’s makeup and age – and gain insight into how it involved into the world it is today. Analyzing craters can help us understand the age of a planet’s surface.
Image above: This portrait of Pluto is in enhanced color, to illustrate differences in the composition and texture of Pluto’s surface. Image Credit: NASA/JHUAPL/SwRI.
A surface with more craters indicates that it’s older, geologically, than a less-cratered surface. Pluto displays many good examples of this concept. Any guesses as to which parts of Pluto mission scientists think are younger?
If you went with the informally named Sputnik Planum – the left half of Pluto’s “heart” feature – as a young geologic unit, then you are on the right track. So far we have not identified any obvious craters on Sputnik Planum. We can also try to put an actual date on a surface (e.g., that a given surface is 1 billion years old), but this is more difficult because it requires some knowledge of how often impactors (chunks of space debris) of a certain size hit the surface to make craters.
Image above: These close-up images of Pluto and Charon illustrate the effect of lighting geometry on the appearance of craters. Image Credits: SwRI/Kelsi Singer.
Age-dating based on craters is complicated by a number of other factors as well. I will highlight one big issue here: How one “sees” craters is affected by lighting over the planet’s surface. Just like on Earth, the lighting on Pluto and Charon changes both with latitude and over the course of the day. When the sun is directly overhead, there are very few shadows cast and it is hard to see topography, but that overhead lighting makes it much easier to see dark or bright markings. The opposite is true when the sun hits the surface at a shallow angle near sunrise or sunset: topography is easy to see, but bright and dark colorations are often washed out.
Because New Horizons flew by Pluto so quickly (in just a few hours out of Pluto’s day, which is 6.4 Earth days), our highest-resolution pictures were all taken under the same lighting conditions. The northern latitudes of Pluto and Charon have the sun mostly overhead, while near the equator the sun hits the surface at an angle. This gives the effect that craters in the north look flatter and have stronger dark/bright contrasts, while craters near the equator look more 3-D.
Image above: Kelsi Singer, NASA's blogger from the New Horizons science team, writer of this article.
There are many other complicating factors, such as variable image resolutions and variable surface erosion or degradation. Even fragments of surface material ejected while creating a “primary” crater can pose a problem because they may litter the surface and make smaller, so-called “secondary craters” that influence crater statistics. We are taking all of these factors into account as we map Pluto and Charon’s craters and mine this data to learn more about the history and evolution of these amazing, mysterious worlds.
For more information about New Horizons, visit: http://www.nasa.gov/mission_pages/newhorizons/main/index.html
Images (mentioned), Text, Credits: NASA/Kelsi Singer.
Greetings, Orbiter.ch
Hubble’s Planetary Portrait Captures New Changes in Jupiter’s Great Red Spot
NASA - Hubble Space Telescope patch.
Oct. 13, 2015
Scientists using NASA’s Hubble Space Telescope have produced new maps of Jupiter – the first in a series of annual portraits of the solar system’s outer planets.
Jupiter in 4k Ultra HD
Video above: This new portrait of Jupiter was produced from observations made using NASA’s Hubble Space Telescope. Video Credits: NASA/ESA/Goddard/UCBerkeley/JPL-Caltech/STScI.
Collecting these yearly images – essentially the planetary version of annual school picture days for children – will help current and future scientists see how these giant worlds change over time. The observations are designed to capture a broad range of features, including winds, clouds, storms and atmospheric chemistry.
Already, the Jupiter images have revealed a rare wave just north of the planet’s equator and a unique filamentary feature in the core of the Great Red Spot not seen previously.
“Every time we look at Jupiter, we get tantalizing hints that something really exciting is going on,” said Amy Simon, a planetary scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “This time is no exception.”
Simon and her colleagues produced two global maps of Jupiter from observations made using Hubble’s high-performance Wide Field Camera 3. The two maps represent nearly back-to-back rotations of the planet, making it possible to determine the speeds of Jupiter’s winds. The findings are described in an Astrophysical Journal paper, available online.
Image above: Jupiter at a glance. Image Credits: NASA, ESA, A. Simon (GSFC), M. Wong (UC Berkeley), and G. Orton (JPL-Caltech).
The new images confirm that the Great Red Spot continues to shrink and become more circular, as it has been doing for years. The long axis of this characteristic storm is about 150 miles (240 kilometers) shorter now than it was in 2014. Recently, the storm had been shrinking at a faster-than-usual rate, but the latest change is consistent with the long-term trend.
The Great Red Spot remains more orange than red these days, and its core, which typically has more intense color, is less distinct than it used to be. An unusual wispy filament is seen, spanning almost the entire width of the vortex. This filamentary streamer rotates and twists throughout the 10-hour span of the Great Red Spot image sequence, getting distorted by winds blowing at 330 miles per hour (150 meters per second) or even greater speeds.
In Jupiter’s North Equatorial Belt, the researchers found an elusive wave that had been spotted on the planet only once before, decades earlier, by Voyager 2. In those images, the wave is barely visible, and nothing like it was seen again, until the current wave was found traveling at about 16 degrees north latitude, in a region dotted with cyclones and anticyclones. Similar waves – called baroclinic waves – sometimes appear in Earth’s atmosphere where cyclones are forming.
(Click on the image for enlarge)
Image above: In Jupiter’s North Equatorial Belt, scientists spotted a rare wave that had been seen there only once before. It is similar to a wave that sometimes occurs in Earth’s atmosphere when cyclones are forming. This false-color close-up of Jupiter shows cyclones (arrows) and the wave (vertical lines). Image Credits: NASA/ESA/Goddard/UCBerkeley/JPL-Caltech/STScI.
“Until now, we thought the wave seen by Voyager 2 might have been a fluke,” said co-author Glenn Orton of NASA’s Jet Propulsion Laboratory in Pasadena, California. “As it turns out, it’s just rare!”
The wave may originate in a clear layer beneath the clouds, only becoming visible when it propagates up into the cloud deck, according to the researchers. That idea is supported by the spacing between the wave crests.
In addition to Jupiter, the researchers have observed Neptune and Uranus, and maps of those planets also will be placed in the public archive. Saturn will be added to the series later. Hubble will dedicate time each year to this special set of observations, called the Outer Planet Atmospheres Legacy program.
Image above: The movement of Jupiter’s clouds can be seen by comparing the first map to the second one. Zooming in on the Great Red Spot at blue (left) and red (right) wavelengths reveals a unique filamentary feature not previously seen. Image Credits: NASA/ESA/Goddard/UCBerkeley/JPL-Caltech/STScI.
“The long-term value of the Outer Planet Atmospheres Legacy program is really exciting,” said co-author Michael H. Wong of the University of California, Berkeley. “The collection of maps that we will build up over time will not only help scientists understand the atmospheres of our giant planets, but also the atmospheres of planets being discovered around other stars, and Earth’s atmosphere and oceans, too.”
The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, in Washington.
To access the Outer Planet Atmospheres Legacy program images and data, visit: https://archive.stsci.edu/prepds/opal/
For images and more information about Hubble, visit: http://www.nasa.gov/hubble and http://hubblesite.org/ and http://www.spacetelescope.org/
Related multimedia is available at: http://svs.gsfc.nasa.gov/goto?12021
Images (mentioned), Video (mentioned), Text, Credits: NASA/Nancy Neal-Jones/Elizabeth Zubritsky/JPL/Preston Dyches/Space Telescope Science Institute/Ray Villard.
Best regards, Orbiter.ch
Worlds Apart
NASA - Cassini Mission to Saturn patch.
Oct. 13, 2015
Although Mimas and Pandora, shown here, both orbit Saturn, they are very different moons. Pandora, "small" by moon standards (50 miles or 81 kilometers across) is elongated and irregular in shape. Mimas (246 miles or 396 kilometers across), a "medium-sized" moon, formed into a sphere due to self-gravity imposed by its higher mass.
The shapes of moons can teach us much about their history. For example, one explanation for Pandora's elongated shape and low density is that it may have formed by gathering ring particles onto a dense core.
This view looks toward the unilluminated side of the rings from 0.26 degrees below the ring plane. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on July 26, 2015.
The view was obtained at a distance of approximately 485,000 miles (781,000 kilometers) from Pandora. Image scale is 3 miles (5 kilometers) per pixel. Mimas is 904,000 miles (1.4 million kilometers) from the spacecraft in this image. The scale on Mimas is 5.4 miles (8.4 kilometers) per pixel.
The Cassini mission is a cooperative project of NASA, ESA (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, Colorado.
For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov or http://www.nasa.gov/cassini . The Cassini imaging team homepage is at http://ciclops.org and http://www.esa.int/Our_Activities/Space_Science/Cassini-Huygens
Image, Text, Credits: NASA/JPL-Caltech/Space Science Institute/Tony Greicius.
Greetings, Orbiter.ch
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