mardi 21 novembre 2017
Nov. 21, 2017
When comet 45P zipped past Earth early in 2017, researchers observing from NASA’s Infrared Telescope Facility, or IRTF, in Hawai’i gave the long-time trekker a thorough astronomical checkup. The results help fill in crucial details about ices in Jupiter-family comets and reveal that quirky 45P doesn’t quite match any comet studied so far.
Like a doctor recording vital signs, the team measured the levels of nine gases released from the icy nucleus into the comet’s thin atmosphere, or coma. Several of these gases supply building blocks for amino acids, sugars and other biologically relevant molecules. Of particular interest were carbon monoxide and methane, which are so hard to detect in Jupiter-family comets that they’ve only been studied a few times before.
Image above: Comet 45P/Honda-Mrkos-Pajdušáková is captured using a telescope on December 22 from Farm Tivoli in Namibia, Africa. Image Credit: Gerald Rhemann.
The gases all originate from the hodgepodge of ices, rock and dust that make up the nucleus. These native ices are thought to hold clues to the comet’s history and how it has been aging.
“Comets retain a record of conditions from the early solar system, but astronomers think some comets might preserve that history more completely than others,” said Michael DiSanti, an astronomer at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and lead author of the new study in the Astronomical Journal.
The comet—officially named 45P/Honda-Mrkos-Pajdušáková—belongs to the Jupiter family of comets, frequent orbiters that loop around the Sun about every five to seven years. Much less is known about native ices in this group than in the long-haul comets from the Oort Cloud.
To identify native ices, astronomers look for chemical fingerprints in the infrared part of the spectrum, beyond visible light. DiSanti and colleagues conducted their studies using the iSHELL high-resolution spectrograph recently installed at IRTF on the summit of Maunakea. With iSHELL, researchers can observe many comets that used to be considered too faint.
The spectral range of the instrument makes it possible to detect many vaporized ices at once, which reduces the uncertainty when comparing the amounts of different ices. The instrument covers wavelengths starting at 1.1 micrometers in the near-infrared (the range of night-vision goggles) up to 5.3 micrometers in the mid-infrared region.
iSHELL also has high enough resolving power to separate infrared fingerprints that fall close together in wavelength. This is particularly necessary in the cases of carbon monoxide and methane, because their fingerprints in comets tend to overlap with the same molecules in Earth’s atmosphere.
“The combination of iSHELL’s high resolution and the ability to observe in the daytime at IRTF is ideal for studying comets, especially short-period comets,” said John Rayner, director of the IRTF, which is managed for NASA by the University of Hawai’i.
While observing for two days in early January 2017—shortly after 45P’s closest approach to the Sun—the team made robust measurements of water, carbon monoxide, methane and six other native ices. For five ices, including carbon monoxide and methane, the researchers compared levels on the sun-drenched side of the comet to the shaded side. The findings helped fill in some gaps but also raised new questions.
The results reveal that 45P is running so low on frozen carbon monoxide, that it is officially considered depleted. By itself, this wouldn’t be too surprising, because carbon monoxide escapes into space easily when the Sun warms a comet. But methane is almost as likely to escape, so an object lacking carbon monoxide should have little methane. 45P, however, is rich in methane and is one of the rare comets that contains more methane than carbon monoxide ice.
It’s possible that the methane is trapped inside other ice, making it more likely to stick around. But the researchers think the carbon monoxide might have reacted with hydrogen to form methanol. The team found that 45P has a larger-than-average share of frozen methanol.
When this reaction took place is another question—one that gets to the heart of comet science. If the methanol was produced on grains of primordial ice before 45P formed, then the comet has always been this way. On the other hand, the levels of carbon monoxide and methanol in the coma might have changed over time, especially because Jupiter-family comets spend more time near the Sun than Oort Cloud comets do.
“Comet scientists are like archaeologists, studying old samples to understand the past,” said Boncho Bonev, an astronomer at American University and the second author on the paper. “We want to distinguish comets as they formed from the processing they might have experienced, like separating historical relics from later contamination.”
The team is now on the case to figure out how typical their results might be among similar comets. 45P was the first of five such short-period comets that are available for study in 2017 and 2018. On the heels of 45P were comets 2P/Encke and 41P/Tuttle-Giacobini-Kresak. Due next summer and fall is 21P/Giacobini–Zinner, and later will come 46P/Wirtanen, which is expected to remain within 10 million miles (16 million kilometers) of Earth throughout most of December 2018.
“This research is groundbreaking,” said Faith Vilas, the solar and planetary research program director at the National Science Foundation, or NSF, which helped support the study. “This broadens our knowledge of the mix of molecular species coexisting in the nuclei of Jovian-family comets, and the differences that exist after many trips around the Sun.”
“We’re excited to see this first publication from iSHELL, which was built through a partnership between NSF, the University of Hawai’i, and NASA,” said Kelly Fast, IRTF program scientist at NASA Headquarters. “This is just the first of many iSHELL results to come.”
More information about NASA’s IRTF: http://irtfweb.ifa.hawaii.edu/
More information about comets: https://www.nasa.gov/comets
Image (mentioned), Text, Credits: NASA/Karl Hille/Goddard Space Flight Center, by Elizabeth Zubritsky.
Publié par Orbiter.ch à 15:03
lundi 20 novembre 2017
ISS - Expedition 53 Mission patch.
November 20, 2017
An experimental module attached to the International Space Station is being prepared for upcoming cargo operations. Tiny research satellites were also ejected from the orbital lab while a pair of Expedition 53 crew members scanned their leg muscles today.
BEAM, officially called the Bigelow Expandable Activity Module, is being outfitted this week for future stowage operations. Excess gear, including inflation tanks and dynamic sensors, used during its initial expansion back in May of 2016 is being removed to make room for new cargo. BEAM’s old gear and trash will now be stowed in the Cygnus resupply craft for disposal early next month.
Image above: A deployer mechanism attached to the outside of the Japanese Kibo lab module ejects a CubeSat into Earth orbit. Image Credit: NASA.
The Kibo lab module from the Japan Aerospace Exploration Agency was the site for the deployment of several CubeSats Monday morning. A mechanism attached to the outside of Kibo ejected the CubeSats that will orbit Earth and provide insights into antibiotic resistance, astrophysics and “space weather.” More CubeSats will be deployed Tuesday.
Flight Engineers Paolo Nespoli and Sergey Ryazanskiy spent Monday exploring how the lack of gravity affects leg muscles. Nespoli strapped himself into a specialized exercise chair and attached electrodes to his leg with assistance from Ryazanskiy. The Sarcolab-3 experiment uses measurements from an ultrasound device and magnetic resonance imaging to observe impacts to the muscles and tendons of a crew member.
Bigelow Expandable Activity Module (BEAM): https://www.nasa.gov/content/bigelow-expandable-activity-module
Cygnus resupply craft: http://orbiterchspacenews.blogspot.ch/2017/11/robotic-arm-reaches-out-and-grapples.html
Antibiotic resistance: https://www.nasa.gov/centers/ames/engineering/projects/ecamsat
Space weather: https://www.nasa.gov/mission_pages/station/research/experiments/2518.html
Expedition 53: https://www.nasa.gov/mission_pages/station/expeditions/expedition53/index.html
Space Station Research and Technology: https://www.nasa.gov/mission_pages/station/research/index.html
International Space Station (ISS): https://www.nasa.gov/mission_pages/station/main/index.html
Image (mentioned), Text, Credits: NASA/Mark Garcia.
Best regards, Orbiter.ch
Publié par Orbiter.ch à 15:42
NASA - Solar Dynamics Observatory (SDO) patch.
Nov. 20, 2017
A broad hole in the corona was the Sun's dominant feature November 7-9, 2017, as shown in this image from NASA's Solar Dynamics Observatory. The hole is easily recognizable as the dark expanse across the top of the Sun and extending down in each side. Coronal holes are magnetically open areas on the Sun that allow high-speed solar wind to gush out into space. They always appear darker in extreme ultraviolet. This one was likely the source of bright aurora that shimmered for numerous observers, with some reaching down even to Nebraska.
SDO (Solar Dynamics Observatory): http://www.nasa.gov/mission_pages/sdo/main/index.html
Image, Text, Credits:NASA/Yvette Smith/GSFC/Solar Dynamics Observatory.
Publié par Orbiter.ch à 15:36
ESO - European Southern Observatory logo.
20 November 2017
VLT reveals dark, reddish and highly-elongated object
Artist’s impression of the interstellar asteroid `Oumuamua
For the first time ever astronomers have studied an asteroid that has entered the Solar System from interstellar space. Observations from ESO’s Very Large Telescope in Chile and other observatories around the world show that this unique object was traveling through space for millions of years before its chance encounter with our star system. It appears to be a dark, reddish, highly-elongated rocky or high-metal-content object. The new results appear in the journal Nature on 20 November 2017.
Combined deep image of `Oumuamua from the VLT and other telescopes (annotated)
The Orbit of ‘Oumuamua
“We had to act quickly,” explains team member Olivier Hainaut from ESO in Garching, Germany. “`Oumuamua had already passed its closest point to the Sun and was heading back into interstellar space.”
ESO’s Very Large Telescope was immediately called into action to measure the object’s orbit, brightness and colour more accurately than smaller telescopes could achieve. Speed was vital as `Oumuamua was rapidly fading as it headed away from the Sun and past the Earth’s orbit, on its way out of the Solar System. There were more surprises to come.
Combined deep image of ‘Oumuamua from the VLT and other telescopes (unannotated)
Combining the images from the FORS instrument on the VLT using four different filters with those of other large telescopes, the team of astronomers led by Karen Meech (Institute for Astronomy, Hawai`i, USA) found that `Oumuamua varies dramatically in brightness by a factor of ten as it spins on its axis every 7.3 hours.
Artist’s impression of the interstellar asteroid `Oumuamua
Karen Meech explains the significance: “This unusually large variation in brightness means that the object is highly elongated: about ten times as long as it is wide, with a complex, convoluted shape. We also found that it has a dark red colour, similar to objects in the outer Solar System, and confirmed that it is completely inert, without the faintest hint of dust around it.”
Light curve of interstellar asteroid `Oumuamua
These properties suggest that `Oumuamua is dense, possibly rocky or with high metal content, lacks significant amounts of water or ice, and that its surface is now dark and reddened due to the effects of irradiation from cosmic rays over millions of years. It is estimated to be at least 400 metres long.
Animation of `Oumuamua passing through the Solar System
Preliminary orbital calculations suggested that the object had come from the approximate direction of the bright star Vega, in the northern constellation of Lyra. However, even travelling at a breakneck speed of about 95 000 kilometres/hour, it took so long for the interstellar object to make the journey to our Solar System that Vega was not near that position when the asteroid was there about 300 000 years ago. `Oumuamua may well have been wandering through the Milky Way, unattached to any star system, for hundreds of millions of years before its chance encounter with the Solar System.
Animation of `Oumuamua passing through the Solar System (annotated)
Astronomers estimate that an interstellar asteroid similar to `Oumuamua passes through the inner Solar System about once per year, but they are faint and hard to spot so have been missed until now. It is only recently that survey telescopes, such as Pan-STARRS, are powerful enough to have a chance to discover them.
“We are continuing to observe this unique object,” concludes Olivier Hainaut, “and we hope to more accurately pin down where it came from and where it is going next on its tour of the galaxy. And now that we have found the first interstellar rock, we are getting ready for the next ones!”
Animation of artist's concept of `Oumuamua
 The Pan-STARRS team’s proposal to name the interstellar objet was accepted by the International Astronomical Union, which is responsible for granting official names to bodies in the Solar System and beyond. The name is Hawaiian and more details are given here http://www.minorplanetcenter.org/mpec/K17/K17V17.html. The IAU also created a new class of objects for interstellar asteroids, with this object being the first to receive this designation. The correct forms for referring to this object are now: 1I, 1I/2017 U1, 1I/`Oumuamua and 1I/2017 U1 (`Oumuamua). Note that the character before the O is an okina. So, the name should sound like H O u mu a mu a. Before the introduction of the new scheme, the object was referred to as A/2017 U1.
This research was presented in a paper entitled “A brief visit from a red and extremely elongated interstellar asteroid”, by K. Meech et al., to appear in the journal Nature on 20 November 2017.
The team is composed of Karen J. Meech (Institute for Astronomy, Honolulu, Hawai`i, USA [IfA]) Robert Weryk (IfA), Marco Micheli (ESA SSA-NEO Coordination Centre, Frascati, Italy; INAF–Osservatorio Astronomico di Roma, Monte Porzio Catone, Italy), Jan T. Kleyna (IfA) Olivier Hainaut (ESO, Garching, Germany), Robert Jedicke (IfA) Richard J. Wainscoat (IfA) Kenneth C. Chambers (IfA) Jacqueline V. Keane (IfA), Andreea Petric (IfA), Larry Denneau (IfA), Eugene Magnier (IfA), Mark E. Huber (IfA), Heather Flewelling (IfA), Chris Waters (IfA), Eva Schunova-Lilly (IfA) and Serge Chastel (IfA).
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 and by Australia as a strategic partner. 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 and its world-leading Very Large Telescope Interferometer as well as two survey telescopes, VISTA working in the infrared and the visible-light VLT Survey Telescope. ESO is also a major partner in two facilities on Chajnantor, APEX and ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre Extremely Large Telescope, the ELT, which will become “the world’s biggest eye on the sky”.
Research paper in Nature: https://www.eso.org/public/archives/releases/sciencepapers/eso1737/eso1737a.pdf
Photos of the VLT: http://www.eso.org/public/images/archive/category/paranal/
ESO’s Very Large Telescope (VLT): http://www.eso.org/public/teles-instr/paranal-observatory/vlt/
FORS instrument: http://www.eso.org/instruments/fors1/
International Astronomical Union: https://www.iau.org/
Pan-STARRS 1 telescope in Hawai: https://en.wikipedia.org/wiki/Pan-STARRS
Images, Text, Credits: ESO/Richard Hook/Olivier Hainaut/M. Kornmesser/Institute for Astronomy
Honolulu/Karen Meech et al./Videos: ESO, M. Kornmesser, L.Calcada. Music: Azul Cobalto.
Best regards, Orbiter.ch
Publié par Orbiter.ch à 15:00
Asteroid Watch logo.
Nov. 20, 2017
Astronomers recently scrambled to observe an intriguing asteroid that zipped through the solar system on a steep trajectory from interstellar space—the first confirmed object from another star.
Image above: Artist’s concept of interstellar asteroid 1I/2017 U1 (‘Oumuamua) as it passed through the solar system after its discovery in October 2017. The aspect ratio of up to 10:1 is unlike that of any object seen in our own solar system. Image Credits: European Southern Observatory/M. Kornmesser.
Now, new data reveal the interstellar interloper to be a rocky, cigar-shaped object with a somewhat reddish hue. The asteroid, named ‘Oumuamua by its discoverers, is up to one-quarter mile (400 meters) long and highly-elongated—perhaps 10 times as long as it is wide. That aspect ratio is greater than that of any asteroid or comet observed in our solar system to date. While its elongated shape is quite surprising, and unlike asteroids seen in our solar system, it may provide new clues into how other solar systems formed.
The observations and analyses were funded in part by NASA and appear in the Nov. 20 issue of the journal Nature. They suggest this unusual object had been wandering through the Milky Way, unattached to any star system, for hundreds of millions of years before its chance encounter with our star system.
“For decades we’ve theorized that such interstellar objects are out there, and now – for the first time – we have direct evidence they exist,” said Thomas Zurbuchen, associate administrator for NASA’s Science Mission Directorate in Washington. “This history-making discovery is opening a new window to study formation of solar systems beyond our own.”
Immediately after its discovery, telescopes around the world, including ESO’s Very Large Telescope in Chile and other observatories around the world were called into action to measure the object’s orbit, brightness and color. Urgency for viewing from ground-based telescopes was vital to get the best data.
Combining the images from the FORS instrument on the ESO telescope using four different filters with those of other large telescopes, a team of astronomers led by Karen Meech of the Institute for Astronomy in Hawaii found that ‘Oumuamua varies in brightness by a factor of ten as it spins on its axis every 7.3 hours. No known asteroid or comet from our solar system varies so widely in brightness, with such a large ratio between length and width. The most elongated objects we have seen to date are no more than three times longer than they are wide.
“This unusually big variation in brightness means that the object is highly elongated: about ten times as long as it is wide, with a complex, convoluted shape,” said Meech. We also found that it had a reddish color, similar to objects in the outer solar system, and confirmed that it is completely inert, without the faintest hint of dust around it.”
These properties suggest that ‘Oumuamua is dense, comprised of rock and possibly metals, has no water or ice, and that its surface was reddened due to the effects of irradiation from cosmic rays over hundreds of millions of years.
A few large ground-based telescopes continue to track the asteroid, though it’s rapidly fading as it recedes from our planet. Two of NASA’s space telescopes (Hubble and Spitzer) are tracking the object the week of Nov. 20. As of Nov. 20, ‘Oumuamua is travelling about 85,700 miles per hour (38.3 kilometers per second) relative to the Sun. Its location is approximately 124 million miles (200 million kilometers) from Earth -- the distance between Mars and Jupiter – though its outbound path is about 20 degrees above the plane of planets that orbit the Sun. The object passed Mars’s orbit around Nov. 1 and will pass Jupiter’s orbit in May of 2018. It will travel beyond Saturn’s orbit in January 2019; as it leaves our solar system, ‘Oumuamua will head for the constellation Pegasus.
Hubble Space Telescope (HST). Animation Credits: NASA/ESA
Observations from large ground-based telescopes will continue until the object becomes too faint to be detected, sometime after mid-December. NASA’s Center for Near-Earth Object Studies (CNEOS) continues to take all available tracking measurements to refine the trajectory of 1I/2017 U1 as it exits our solar system.
This remarkable object was discovered Oct. 19 by the University of Hawaii’s Pan-STARRS1 telescope, funded by NASA’s Near-Earth Object Observations (NEOO) Program, which finds and tracks asteroids and comets in Earth’s neighborhood. NASA Planetary Defense Officer Lindley Johnson said, “We are fortunate that our sky survey telescope was looking in the right place at the right time to capture this historic moment. This serendipitous discovery is bonus science enabled by NASA’s efforts to find, track and characterize near-Earth objects that could potentially pose a threat to our planet.”
Preliminary orbital calculations suggest that the object came from the approximate direction of the bright star Vega, in the northern constellation of Lyra. However, it took so long for the interstellar object to make the journey – even at the speed of about 59,000 miles per hour (26.4 kilometers per second) -- that Vega was not near that position when the asteroid was there about 300,000 years ago.
While originally classified as a comet, observations from ESO and elsewhere revealed no signs of cometary activity after it slingshotted past the Sun on Sept. 9 at a blistering speed of 196,000 miles per hour (87.3 kilometers per second).
The object has since been reclassified as interstellar asteroid 1I/2017 U1 by the International Astronomical Union (IAU), which is responsible for granting official names to bodies in the solar system and beyond. In addition to the technical name, the Pan-STARRS team dubbed it ‘Oumuamua (pronounced oh MOO-uh MOO-uh), which is Hawaiian for “a messenger from afar arriving first.”
Astronomers estimate that an interstellar asteroid similar to ‘Oumuamua passes through the inner solar system about once per year, but they are faint and hard to spot and have been missed until now. It is only recently that survey telescopes, such as Pan-STARRS, are powerful enough to have a chance to discover them.
“What a fascinating discovery this is!” said Paul Chodas, manager of the Center for Near-Earth Object Studies at NASA’s Jet Propulsion Laboratory, Pasadena, California. “It’s a strange visitor from a faraway star system, shaped like nothing we’ve ever seen in our own solar system neighborhood.”
For more on NASA’s Planetary Defense Coordination Office:
To watch a NASA Planetary Defense video on International Asteroid Day:
Click here for interstellar asteroid FAQs:
ESO’s Very Large Telescope: http://www.eso.org/public/teles-instr/paranal-observatory/vlt/
NASA’s Center for Near-Earth Object Studies (CNEOS): https://cneos.jpl.nasa.gov/
NASA’s Near-Earth Object Observations (NEOO): https://cneos.jpl.nasa.gov/about/search_program.html
Image (mentioned), Animation (mentioned), Text, Credits: NASA/Tricia Talbert.
Publié par Orbiter.ch à 09:05
NASA - Mars Reconnaissance Orbiter (MRO) patch.
Nov. 20, 2017
Image above: This inner slope of a Martian crater has several of the seasonal dark streaks called "recurrent slope lineae," or RSL, that a November 2017 report interprets as granular flows, rather than darkening due to flowing water. The image is from the HiRISE camera on NASA's Mars Reconnaissance Orbiter. Image Credits: NASA/JPL-Caltech/UA/USGS.
Dark features on Mars previously considered evidence for subsurface flowing of water are interpreted by new research as granular flows, where grains of sand and dust slip downhill to make dark streaks, rather than the ground being darkened by seeping water.
Continuing examination of these still-perplexing seasonal dark streaks with a powerful camera on NASA's Mars Reconnaissance Orbiter (MRO) shows they exist only on slopes steep enough for dry grains to descend the way they do on faces of active dunes.
The findings published today in Nature Geoscience argue against the presence of enough liquid water for microbial life to thrive at these sites. However, exactly how these numerous flows begin and gradually grow has not yet been explained. Authors of the report propose possibilities that include involvement of small amounts of water, indicated by detection of hydrated salts observed at some of the flow sites.
These features have evoked fascination and controversy since their 2011 discovery, as possible markers for unexpected liquid water or brine on an otherwise dry planet. They are dark streaks that extend gradually downhill in warm seasons, then fade away in winter and reappear the next year. On Earth, only seeping water is known to have these behaviors, but how they form in the dry Martian environment remains unclear.
Many thousands of these Martian features, collectively called "recurring slope lineae" or RSL, have been identified in more than 50 rocky-slope areas, from the equator to about halfway to the poles.
"We've thought of RSL as possible liquid water flows, but the slopes are more like what we expect for dry sand," said Colin Dundas of the U.S. Geological Survey's Astrogeology Science Center in Flagstaff, Arizona. "This new understanding of RSL supports other evidence that shows that Mars today is very dry."
Dundas is lead author of the report, which is based on observations with the High Resolution Imaging Science Experiment (HiRISE) camera on MRO. The data include 3-D models of slope steepness using pairs of images for stereo information. Dundas and co-authors examined 151 RSL features at 10 sites.
The RSL are almost all restricted to slopes steeper than 27 degrees. Each flow ends on a slope that matches the dynamic "angle of repose" seen in the slumping dry sand of dunes on Mars and Earth. A flow due to liquid water should readily extend to less steep slopes.
"The RSL don't flow onto shallower slopes, and the lengths of these are so closely correlated with the dynamic angle of repose, it can't be a coincidence," said HiRISE Principal Investigator Alfred McEwen at the University of Arizona, Tucson, a co-author of the new report.
The seasonal dark streaks have been thought of as possible evidence for biologically significant liquid water -- sufficient water for microbial life -- though explaining how so much liquid water could exist on the surface in Mars' modern environment would be challenging. A granular-flow explanation for RSL fits with the earlier understanding that the surface of modern Mars, exposed to a cold, thin atmosphere, lacks flowing water. A 2016 report also cast doubt on possible sources of underground water at RSL sites. Liquid water on today's Mars may be limited to traces of dissolved moisture from the atmosphere and thin films, which are challenging environments for life as we know it.
However, RSL remain puzzling. Traits with uncertain explanations include their gradual growth, their seasonal reappearance, their rapid fading when inactive, and the presence of hydrated salts, which have water molecules bound into their crystal stucture.
Mars Reconnaissance Orbiter (MRO). Image Credits: NASA/JPL-Caltech
The new report describes possible connections between these traits and how RSL form. For example, salts can become hydrated by pulling water vapor from the atmosphere, and this process can form drops of salty water. Seasonal changes in hydration of salt-containing grains might result in some trigger mechanism for RSL grainflows, such as expansion, contraction, or release of some water. Darkening and fading might result from changes in hydration. If atmospheric water vapor is a trigger, then a question is why the RSL appear on some slopes but not others.
"RSL probably form by some mechanism that is unique to the environment of Mars," McEwen said, "so they represent an opportunity to learn about how Mars behaves, which is important for future surface exploration."
"Full understanding of RSL is likely to depend upon on-site investigation of these features," said MRO Project Scientist Rich Zurek of NASA's Jet Propulsion Laboratory, Pasadena, California. "While the new report suggests that RSL are not wet enough to favor microbial life, it is likely that on-site investigation of these sites will still require special procedures to guard against introducing microbes from Earth, at least until they are definitively characterized. In particular, a full explanation of how these enigmatic features darken and fade still eludes us. Remote sensing at different times of day could provide important clues."
The University of Arizona operates HiRISE, which was built by Ball Aerospace & Technologies Corp., Boulder, Colorado. JPL, a division of Caltech in Pasadena, California, manages the MRO Project for the NASA Science Mission Directorate in Washington. Lockheed Martin Space Systems of Denver built the orbiter and supports its operations.
NASA's Mars Reconnaissance Orbiter (MRO): https://mars.nasa.gov/mro/
Images (mentioned), Text, Credits: NASA/Laurie Cantillo/Dwayne Brown/JPL/Guy Webster/U.S. Geological Survey/Jennifer LaVista.
Publié par Orbiter.ch à 08:58
samedi 18 novembre 2017
NASA - Solar Dynamics Observatory (SDO) patch.
Nov. 18, 2017
When our Sun erupts with giant explosions — such as bursts of radiation called solar flares — we know they can affect space throughout the solar system as well as near Earth. But monitoring their effects requires having observatories in many places with many perspectives, much the way weather sensors all over Earth can help us monitor what’s happening with a terrestrial storm.
By using multiple observatories, two recent studies show how solar flares exhibit pulses or oscillations in the amount of energy being sent out. Such research provides new insights on the origins of these massive solar flares as well as the space weather they produce, which is key information as humans and robotic missions venture out into the solar system, farther and farther from home.
The first study spotted oscillations during a flare — unexpectedly — in measurements of the Sun’s total output of extreme ultraviolet energy, a type of light invisible to human eyes. On Feb. 15, 2011, the Sun emitted an X-class solar flare, the most powerful kind of these intense bursts of radiation. Because scientists had multiple instruments observing the event, they were able to track oscillations in the flare’s radiation, happening simultaneously in several different sets of observations.
Animation above: NASA’s Solar Dynamics Observatory captured these images of an X-class flare on Feb. 15, 2011. Animation Credits: NASA's Goddard Space Flight Center/SDO.
“Any type of oscillation on the Sun can tell us a lot about the environment the oscillations are taking place in, or about the physical mechanism responsible for driving changes in emission,” said Ryan Milligan, lead author of this first study and solar physicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and the University of Glasgow in Scotland. In this case, the regular pulses of extreme ultraviolet light indicated disturbances — akin to earthquakes — were rippling through the chromosphere, the base of the Sun’s outer atmosphere, during the flare.
What surprised Milligan about the oscillations was the fact that they were first observed in extreme ultraviolet data from NOAA’s GOES — short for Geostationary Operation Environmental Satellite, which resides in near-Earth space. The mission studies the Sun from Earth’s perspective, collecting X-ray and extreme ultraviolet irradiance data — the total amount of the Sun’s energy that reaches Earth’s atmosphere over time.
This wasn’t a typical data set for Milligan. While GOES helps monitor the effects of solar eruptions in Earth’s space environment — known collectively as space weather — the satellite wasn’t initially designed to detect fine details like these oscillations.
When studying solar flares, Milligan more commonly uses high-resolution data on a specific active region in the Sun’s atmosphere to study the physical processes underlying flares. This is often necessary in order to zoom in on events in a particular area — otherwise they can easily be lost against the backdrop of the Sun’s constant, intense radiation.
“Flares themselves are very localized, so for the oscillations to be detected above the background noise of the Sun’s regular emissions and show up in the irradiance data was very striking,” Milligan said.
There have been previous reports of oscillations in GOES X-ray data coming from the Sun’s upper atmosphere, called the corona, during solar flares. What’s unique in this case is that the pulses were observed in extreme ultraviolet emission at frequencies that show they originated lower, in the chromosphere, providing more information about how a flare’s energy travels throughout through the Sun’s atmosphere.
To be sure the oscillations were real, Milligan and his colleagues checked corresponding data from other Sun-observing instruments on board NASA’s Solar Dynamics Observatory or SDO, for short: one that also collects extreme ultraviolet irradiance data and another that images the corona in different wavelengths of light. They found the exact same pulses in those data sets, confirming they were a phenomenon with its source at the Sun. Their findings are summarized in a paper published in The Astrophysical Journal Letters on Oct. 9, 2017.
These oscillations interest the scientists because they may be the result of a mechanism by which flares emit energy into space — a process we don’t yet fully understand. Additionally, the fact that the oscillations appeared in data sets typically used to monitor larger space patterns suggests they could play a role in driving space weather effects.
In the second study, scientists investigated a connection between solar flares and activity in Earth’s atmosphere. The team discovered that pulses in the electrified layer of the atmosphere — called the ionosphere — mirrored X-ray oscillations during a July 24, 2016, C-class flare. C-class flares are of mid-to-low intensity, and about 100 times weaker than X-flares.
How Solar Flares Affect Earth
Video above: A team of scientists investigated a connection between solar flares and Earth’s atmosphere. They discovered pulses in the electrified layer of the atmosphere — called the ionosphere — mirrored X-ray oscillations during a July 24, 2016, flare. Video Credits: NASA’s Goddard Space Flight Center/Genna Duberstein.
Stretching from roughly 30 to 600 miles above Earth’s surface, the ionosphere is an ever-changing region of the atmosphere that reacts to changes from both Earth below and space above. It swells in response to incoming solar radiation, which ionizes atmospheric gases, and relaxes at night as the charged particles gradually recombine.
In particular, the team of scientists — led by Laura Hayes, a solar physicist who splits her time between NASA Goddard and Trinity College in Dublin, Ireland, and her thesis adviser Peter Gallagher — looked at how the lowest layer of the ionosphere, called the D-region, responded to pulsations in a solar flare.
“This is the region of the ionosphere that affects high-frequency communications and navigation signals,” Hayes said. “Signals travel through the D-region, and changes in the electron density affect whether the signal is absorbed, or degraded.”
The scientists used data from very low frequency, or VLF, radio signals to probe the flare’s effects on the D-region. These were standard communication signals transmitted from Maine and received in Ireland. The denser the ionosphere, the more likely these signals are to run into charged particles along their way from a signal transmitter to its receiver. By monitoring how the VLF signals propagate from one end to the other, scientists can map out changes in electron density.
Pooling together the VLF data and X-ray and extreme ultraviolet observations from GOES and SDO, the team found the D-region’s electron density was pulsing in concert with X-ray pulses on the Sun. They published their results in the Journal of Geophysical Research on Oct. 17, 2017.
“X-rays impinge on the ionosphere and because the amount of X-ray radiation coming in is changing, the amount of ionization in the ionosphere changes too,” said Jack Ireland, a co-author on both studies and Goddard solar physicist. “We’ve seen X-ray oscillations before, but the oscillating ionosphere response hasn’t been detected in the past.”
Solar Dynamics Observatory (SDO). Image Credit: NASA
Hayes and her colleagues used a model to determine just how much the electron density changed during the flare. In response to incoming radiation, they found the density increased as much as 100 times in just 20 minutes during the pulses — an exciting observation for the scientists who didn’t expect oscillating signals in a flare would have such a noticeable effect in the ionosphere. With further study, the team hopes to understand how the ionosphere responds to X-ray oscillations at different timescales, and whether other solar flares induce this response.
“This is an exciting result, showing Earth’s atmosphere is more closely linked to solar X-ray variability than previously thought,” Hayes said. “Now we plan to further explore this dynamic relationship between the Sun and Earth’s atmosphere.”
Both of these studies took advantage of the fact that we are increasingly able to track solar activity and space weather from a number of vantage points. Understanding the space weather that affects us at Earth requires understanding a dynamic system that stretches from the Sun all the way to our upper atmosphere — a system that can only be understood by tapping into a wide range of missions scattered throughout space.
September 2017’s Intense Solar Activity Viewed from Space: https://www.nasa.gov/feature/goddard/2017/september-2017s-intense-solar-activity-viewed-from-space
NASA’s ICON Explores the Boundary Between Earth and Space: https://www.nasa.gov/feature/goddard/2017/nasa-s-icon-explores-the-boundary-between-earth-and-space/
Journal of Geophysical Research:
On Oct. 9, 2017:
On Oct. 17, 2017:
NOAA’s GOES: https://www.nasa.gov/content/goes/
NASA’s Solar Dynamics Observatory or SDO: http://nasa.gov/sdo
Animation (mentioned), Image (mentioned), Video (mentioned), Text, Credits: NASA/Rob Garner.
Publié par Orbiter.ch à 18:12