vendredi 20 juillet 2018
ISS - Expedition 56 Mission patch.
July 20, 2018
The Expedition 56 crew members continued their work Friday on more fertility research and microbe studies aboard the International Space Station. They also worked on science gear for a study seeking advanced therapies for diseases such as Alzheimer’s and diabetes.
Commander Drew Feustel and Flight Engineer Serena Auñón-Chancellor examined biological samples for the Micro-11 fertility study. They looked at the samples through a microscope which were later stowed in a science freezer. The experiment seeks to determine if human reproduction would be possible off the Earth.
Image above: NASA astronaut Ricky Arnold works on gear inside the International Space Station. Image Credit: NASA.
Feustel also spent some time in the morning working on the Amyloid experiment to help doctors develop advanced treatments for Alzheimer’s disease and diabetes. He collected amyloid fibril samples from the Cell Biology Experiment Facility and stowed them in a science freezer for spectroscopy and microscopic analysis back on Earth.
European astronaut Alexander Gerst and NASA astronaut Ricky Arnold were sampling the station’s atmosphere and surfaces for a pair of microbe investigations today. Gerst collected microbe samples and stowed them in a freezer for molecular analysis on Earth to identify potential pathogens on the station. Arnold processed microbial DNA using the Biomolecule Sequencer, a device that enables DNA sequencing in microgravity, to identify microbes able to survive in microgravity.
Microbe samples: https://www.nasa.gov/mission_pages/station/research/experiments/explorer/Investigation.html?#id=1663
Microbial DNA: https://www.nasa.gov/mission_pages/station/research/experiments/explorer/Investigation.html?#id=7687
Biomolecule Sequencer: https://www.nasa.gov/mission_pages/station/research/experiments/explorer/Investigation.html?#id=1917
Expedition 56: https://cms.nasa.gov/mission_pages/station/expeditions/expedition56/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 14:22
NASA - JUNO Mission logo.
July 20, 2018
This image captures a high-altitude cloud formation surrounded by swirling patterns in the atmosphere of Jupiter's North North Temperate Belt region.
The North North Temperate Belt is one of Jupiter’s many colorful, swirling cloud bands. Scientists have wondered for decades how deep these bands extend. Gravity measurements collected by Juno during its close flybys of the planet have now provided an answer. Juno discovered that these bands of flowing atmosphere actually penetrate deep into the planet, to a depth of about 1,900 miles (3,000 kilometers).
NASA’s Juno spacecraft took this color-enhanced image at 10:11 p.m. PDT on July 15, 2018 (1:11 a.m. EDT on July 16), as the spacecraft performed its 14th close flyby of Jupiter. At the time, Juno was about 3,900 miles (6,200 kilometers) from the planet's cloud tops, above a latitude of 36 degrees.
Citizen scientist Jason Major created this image using data from the spacecraft’s JunoCam imager.
JunoCam's raw images are available for the public to peruse and process into image products at https://missionjuno.swri.edu/junocam/.
More information about Juno is at https://www.nasa.gov/juno and http://missionjuno.swri.edu.
Image, Text, Credits: NASA/Jon Nelson/JPL-Caltech/SwRI/MSSS/Jason Major.
Publié par Orbiter.ch à 14:17
July 20, 2018
Storm chasing takes luck and patience on Earth -- and even more so on Mars.
Image above: Side-by-side movies shows how dust has enveloped the Red Planet, courtesy of the Mars Color Imager (MARCI) wide-angle camera onboard NASA's Mars Reconnaissance Orbiter (MRO). Image Credits:NASA/JPL-Caltech/MSSS.
For scientists watching the Red Planet from data gathered by NASA's orbiters, the past month has been a windfall. "Global" dust storms, where a runaway series of storms creates a dust cloud so large it envelops the planet, only appear every six to eight years (that's three to four Mars years). Scientists still don't understand why or how exactly these storms form and evolve.
Mars Before and After Dust Storm
In June, one of these dust events rapidly engulfed the planet. Scientists first observed a smaller-scale dust storm on May 30. By June 20, it had gone global.
For the Opportunity rover, that meant a sudden drop in visibility from a clear, sunny day to that of an overcast one. Because Opportunity runs on solar energy, scientists had to suspend science activities to preserve the rover's batteries. As of July 18th, no response has been received from the rover.
Luckily, all that dust acts as an atmospheric insulator, keeping nighttime temperatures from dropping down to lower than what Opportunity can handle. But the nearly 15-year-old rover isn't out of the woods yet: it could take weeks, or even months, for the dust to start settling. Based on the longevity of a 2001 global storm, NASA scientists estimate it may be early September before the haze has cleared enough for Opportunity to power up and call home.
When the skies begin to clear, Opportunity's solar panels may be covered by a fine film of dust. That could delay a recovery of the rover as it gathers energy to recharge its batteries. A gust of wind would help, but isn't a requirement for a full recovery.
Mars Before and After Dust Storm. Animation Credits: NASA/JPL-Caltech/MSSS
While the Opportunity team waits in earnest to hear from the rover, scientists on other Mars missions have gotten a rare chance to study this head-scratching phenomenon.
The Mars Reconnaissance Orbiter, Mars Odyssey, and Mars Atmosphere and Volatile EvolutioN (MAVEN) orbiters are all tailoring their observations of the Red Planet to study this global storm and learn more about Mars' weather patterns. Meanwhile, the Curiosity rover is studying the dust storm from the Martian surface.
Here's Here's how each mission is currently studying the dust storm, and what we might learn from it:
With the THEMIS instrument (Thermal Emission Imaging System), scientists can track Mars' surface temperature, atmospheric temperature, and the amount of dust in the atmosphere. This allows them to watch the dust storm grow, evolve, and dissipate over time.
"This is one of the largest weather events that we've seen on Mars," since spacecraft observations began in the 1960s, said Michael Smith, a scientist at NASA's Goddard Spaceflight Center in Greenbelt, Maryland who works on the THEMIS instrument. "Having another example of a dust storm really helps us to understand what's going on."
Since the dust storm began, the THEMIS team has increased the frequency of global atmospheric observations from every 10 days to twice per week, Smith said. One mystery they're still trying to solve: How these dust storms go global. "Every Mars year, during the dusty season, there are a lot of local- or regional-scale storms that cover one area of the planet," Smith said. But scientists aren't yet sure how these smaller storms sometimes grow to end up encircling the entire planet.
Mars Reconnaissance Orbiter (MRO)
Mars Reconnaissance Orbiter has two instruments studying the dust storm. Each day, the Mars Color Imager (MARCI) maps the entire planet in mid-afternoon to track the evolution of the storm. Meanwhile, MRO's Mars Climate Sounder (MCS) instrument measures how the atmosphere's temperature changes with altitude. Since the end of May, the instruments have observed the onset and rapid expansion of a dust storm on Mars.
With these data, scientists are studying how the dust storm changes the planet's atmospheric temperatures. Just as in Earth's atmosphere, changing temperature on Mars can affect wind patterns and even the circulation of the entire atmosphere. This provides a powerful feedback: Solar heating of the dust lofted into the atmosphere changes temperatures, which changes winds, which may amplify the storm by lifting more dust from the surface.
Scientists want to know the details of the storm -- where is the air rising or falling? How do the atmospheric temperatures now compare to a storm-less year? And as with Mars Odyssey, the MRO team wants to know how these dust storms go global.
"The very fact that you can start with something that's a local storm, no bigger than a small [U.S.] state, and then trigger something that raises more dust and produces a haze that covers almost the entire planet is remarkable," said Rich Zurek of NASA's Jet Propulsion Laboratory, Pasadena, California, the project scientist for MRO.
Scientists want to find out why these storms arise every few years, which is hard to do without a long record of such events. It'd be as if aliens were observing Earth and seeing the climate effects of El Niño over many years of observations -- they'd wonder why some regions get extra rainy and some areas get extra dry in a seemingly regular pattern.
Ever since the MAVEN orbiter entered Mars' orbit, "one of the things we've been waiting for is a global dust storm," said Bruce Jakosky, the MAVEN orbiter's principle investigator.
But MAVEN isn't studying the dust storm itself. Rather, the MAVEN team wants to study how the dust storm affects Mars' upper atmosphere, about 62 miles (more than 100 kilometers) above the surface -- where the dust doesn't even reach. MAVEN's mission is to figure out what happened to Mars' early atmosphere. We know that at some point billions of years ago, liquid water pooled and ran along Mars' surface, which means that its atmosphere must have been thicker and more insulating, similar to Earth's. Since MAVEN arrived at Mars in 2014, its investigations have found that this atmosphere may have been stripped away by a torrent of solar wind over several hundred million years, between 3.5 and 4.0 billion years ago.
But there are still nuances to figure out, such as how dust storms like the current one affect how atmospheric molecules escape into space, Jakosky said. For instance, the dust storm acts as an atmospheric insulator, trapping heat from the Sun. Does this heating change the way molecules escape the atmosphere? It is also likely that, as the atmosphere warms, more water vapor rises high enough to be broken down by sunlight, with the solar wind sweeping the hydrogen atoms into space, Jakosky said.
The team won't have answers for a while yet, but each of MAVEN's five orbits per day will continue to provide invaluable data.
Most of NASA's spacecraft are studying the dust storm from above. The Mars Science Laboratory mission's Curiosity rover has a unique perspective: the nuclear-powered science machine is largely immune to the darkened skies, allowing it to collect science from within the beige veil enveloping the planet.
"We're working double-duty right now," said JPL's Ashwin Vasavada, Curiosity's project scientist. "Our newly recommissioned drill is acquiring a fresh rock sample. But we are also using instruments to study how the dust storm evolves."
Curiosity has a number of "eyes" that can determine the abundance and size of dust particles based on how they scatter and absorb light. That includes its Mastcam, ChemCam, and an ultraviolet sensor on REMS, its suite of weather instruments. REMS can also help study atmospheric tides -- shifts in pressure that move as waves across the entire planet's thin air. These tides change drastically based on where the dust is globally, not just inside Gale crater.
The global storm may also reveal secrets about Martian dust devils and winds. Dust devils can occur when the planet's surface is hotter than the air above it. Heating generates whirls of air, some of which pick up dust and become dust devils. During a dust storm, there's less direct sunlight and lower daytime temperatures; this might mean fewer devils swirling across the surface.
Even new drilling can advance dust storm science: watching the small piles of loose material created by Curiosity's drill is the best way of monitoring winds.
Scientists think the dust storm will last at least a couple of months. Every time you spot Mars in the sky in the weeks ahead, remember how much data scientists are gathering to better understand the mysterious weather of the Red Planet.
Martian Dust Storm Grows Global: Curiosity Captures Photos of Thickening Haze
Mars Odyssey: https://mars.nasa.gov/odyssey/
Mars Reconnaissance Orbiter (MRO): https://www.nasa.gov/mission_pages/MRO/main/index.html
Curiosity (Mars Science Laboratory or MSL): https://www.nasa.gov/mission_pages/msl/index.html
Image (mentioned), Animation (mentioned), Video (NASA), Text, Credits: NASA/JoAnna Wendel/JPL/Andrew Good.
Publié par Orbiter.ch à 13:38
Blue Origin logo.
July 20, 2018
New Shepard flew for the ninth time on July 18, 2018. During this mission, known as Mission 9 (M9), the escape motor was fired shortly after booster separation. The Crew Capsule was pushed hard by the escape test and we stressed the rocket to test that astronauts can get away from an anomaly at any time during flight. The mission was a success for both the booster and capsule. Most importantly, astronauts would have had an exhilarating ride and safe landing.
Blue Origin Mission 9 landing
This isn’t the first time we’ve done this type of extreme testing on New Shepard. In October of 2012, we simulated a booster failure on the launch pad and had a successful escape. Then in October of 2016, we simulated a booster failure in-flight at Max Q, which is the most physically strenuous point in the flight for the rocket, and had a completely successful escape of the capsule.
Replay of Mission 9 Webcast
This test on M9 allowed us to finally characterize escape motor performance in the near-vacuum of space and guarantee that we can safely return our astronauts in any phase of flight.
Also on M9, New Shepard carried science and research payloads from commercial companies, universities and space agencies.
Learn more about the payloads on board: https://www.blueorigin.com/news/news/payload-manifest-on-mission-9
For more information about Blue Origin, visit: https://www.blueorigin.com/
Image, Video, Text, Credit: Blue Origin.
Publié par Orbiter.ch à 04:46
mercredi 18 juillet 2018
NASA - Chandra X-ray Observatory patch.
July 18, 2018
Scientists may have observed, for the first time, the destruction of a young planet or planets around a nearby star. Observations from NASA’s Chandra X-ray Observatory indicate that the parent star is now in the process of devouring the planetary debris. This discovery gives insight into the processes affecting the survival of infant planets.
Since 1937, astronomers have puzzled over the curious variability of a young star named RW Aur A, located about 450 light years from Earth. Every few decades, the star’s optical light has faded briefly before brightening again. In recent years, astronomers have observed the star dimming more frequently, and for longer periods.
Image above: This artist’s illustration depicts the destruction of a young planet or planets, which scientists may have witnessed for the first time using data from NASA’s Chandra X-ray Observatory. Image Credits: Illustration: NASA/CXC/M. Weiss; X-ray spectrum: NASA/CXC/MIT/H. M.Günther.
Using Chandra, a team of scientists may have uncovered what caused the star's most recent dimming event: a collision of two infant planetary bodies, including at least one object large enough to be a planet. As the resulting planetary debris fell into the star, it would generate a thick veil of dust and gas, temporarily obscuring the star’s light.
“Computer simulations have long predicted that planets can fall into a young star, but we have never before observed that,” says Hans Moritz Guenther, a research scientist in MIT’s Kavli Institute for Astrophysics and Space Research who led the study. “If our interpretation of the data is correct, this would be the first time that we directly observe a young star devouring a planet or planets.”
The star’s previous dimming events may have been caused by similar smash-ups, of either two planetary bodies or large remnants of past collisions that met head-on and broke apart again.
RW Aur A is located in the Taurus-Auriga Dark Clouds, which host stellar nurseries containing thousands of infant stars. Very young stars, unlike our relatively mature sun, are still surrounded by a rotating disk of gas and clumps of material ranging in size from small dust grains to pebbles, and possibly fledgling planets. These disks last for about 5 million to 10 million years.
RW Aur A is estimated to be several million years old, and is still surrounded by a disk of dust and gas. This star and its binary companion star, RW Aur B, are both about the same mass as the sun.
The noticeable dips in the optical brightness of RW Aur A that occurred every few decades each lasted for about a month. Then, in 2011, the behavior changed. The star dimmed again, this time for about six months. The star eventually brightened, only to fade again in mid-2014. In November 2016, the star returned to its full brightness, and then in January 2017 it dimmed again.
Chandra was used to observe the star during an optically bright period in 2013, and then dim periods in 2015 and 2017, when a decrease in X-rays was also observed.
Because the X-rays come from the hot outer atmosphere of the star, changes in the X-ray spectrum – the intensity of X-rays measured at different wavelengths – over these three observations were used to probe the density and composition of the absorbing material around the star.
The team found that the dips in both optical and X-ray light are caused by dense gas obscuring the star’s light. The observation in 2017 showed strong emission from iron atoms, indicating that the disk contained at least 10 times more iron than in the 2013 observation during a bright period.
Guenther and colleagues suggest the excess iron was created when two planetesimals, or infant planetary bodies, collided. If one or both planetary bodies are made partly of iron, their smash-up could release a large amount of iron into the star’s disk and temporarily obscure its light as the material falls into the star.
Chandra X-ray Observatory. Animation Credits: NASA/CXC
A less favored explanation is that small grains or particles such as iron can become trapped in parts of a disk. If the disk’s structure changes suddenly, such as when the star’s partner star passes close by, the resulting tidal forces might release the trapped particles, creating an excess of iron that can fall into the star.
The scientists hope to make more observations of the star in the future, to see whether the amount of iron surrounding it has changed – a measure that could help researchers determine the size of the iron’s source. For example, if about the same amount of iron appears in a year or two that may indicate it comes from a relatively massive source.
“Much effort currently goes into learning about exoplanets and how they form, so it is obviously very important to see how young planets could be destroyed in interactions with their host stars and other young planets, and what factors determine if they survive,” Guenther says.
Guenther is the lead author of a paper detailing the group’s results, which appears today in the Astronomical Journal. NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra's science and flight operations.
Read more from NASA's Chandra X-ray Observatory: http://chandra.harvard.edu/photo/2018/rwaur/
For more Chandra images, multimedia and related materials, visit: http://www.nasa.gov/chandra
Image (mentioned), Animation (mentioned), Text, Credits: NASA/Lee Mohon/Marshall Space Flight Center/Molly Porter/Chandra X-ray Center/Megan Watzke.
Publié par Orbiter.ch à 15:00
ISS - Expedition 56 Mission patch.
July 18, 2018
Cancer and rodent studies were on the crew’s timeline today to help doctors and scientists improve the health of humans in space and on Earth. The crew also conducted an emergency drill aboard the International Space Station.
Image above: NASA astronauts Serena Auñón-Chancellor and Drew Feustel begin cargo operations shortly after the SpaceX Dragon cargo craft arrived at the International Space Station packed with more than 5,900 pounds of research, crew supplies and hardware. Image Credit: NASA.
Flight Engineer Serena Auñón-Chancellor examined endothelial cells through a microscope for the AngieX Cancer Therapy study. The new cancer research seeks to test a safer, more effective treatment that targets tumor cells and blood vessels. Commander Drew Feustel partnered with astronaut Alexander Gerst and checked on mice being observed for the Rodent Research-7 (RR-7) experiment. RR-7 is exploring how microgravity impacts microbes living inside organisms.
Astronaut Ricky Arnold and Gerst collected and stowed their blood samples for a pair of ongoing human research studies. Arnold went on to work a series of student investigations dubbed NanoRacks Module-9 exploring a variety of topics including botany, biology and physics.
Image above: Flying over South Pacific Ocean, seen by EarthCam on ISS, speed: 27'571 Km/h, altitude: 421,54 Km, image captured by Roland Berga (on Earth in Switzerland) from International Space Station (ISS) using ISS-HD Live application with EarthCam's from ISS on July 18, 2018 at 21:14 UTC. Image Credits: Orbiter.ch Aerospace/Roland Berga.
During the afternoon, all six Expedition 56 crew members joined forces to practice a simulated emergency. The orbital lab residents went over escape routes and safety procedures while coordinating communication and decision-making with mission controllers in Houston and Moscow.
AngieX Cancer Therapy: https://www.nasa.gov/mission_pages/station/research/experiments/explorer/Investigation.html?#id=7502
Rodent Research-7 (RR-7): https://www.nasa.gov/mission_pages/station/research/experiments/explorer/Investigation.html?#id=7425
NanoRacks Module-9: https://www.nasa.gov/mission_pages/station/research/experiments/explorer/search.html?#q=%22module-9%22&i=&p=&c=&g=&s=
Expedition 56: https://www.nasa.gov/mission_pages/station/expeditions/expedition56/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
Images (mentioned), Text, Credits: NASA/Mark Garcia/Orbiter.ch Aerospace/Roland Berga.
Best regards, Orbiter.ch
Publié par Orbiter.ch à 14:22
NASA - STEREO Mission logo.
July 18, 2018
In 1610, Galileo redesigned the telescope and discovered Jupiter’s four largest moons. Nearly 400 years later, NASA’s Hubble Space Telescope used its powerful optics to look deep into space — enabling scientists to pin down the age of the universe.
Suffice it to say that getting a better look at things produces major scientific advances.
In a paper published on July 18 in The Astrophysical Journal, a team of scientists led by Craig DeForest — solar physicist at Southwest Research Institute’s branch in Boulder, Colorado — demonstrate that this historical trend still holds. Using advanced algorithms and data-cleaning techniques, the team discovered never-before-detected, fine-grained structures in the outer corona — the Sun’s million-degree atmosphere — by analyzing images taken by NASA’s STEREO spacecraft. The new results also provide foreshadowing of what might be seen by NASA’s Parker Solar Probe, which after its launch in the summer 2018 will orbit directly through that region.
STEREO spacecrafts. Image Credit: NASA
The outer corona is the source of the solar wind, the stream of charged particles that flow outward from the Sun in all directions. Measured near Earth, the magnetic fields embedded within the solar wind are intertwined and complex, but what causes this complexity remains unclear.
“In deep space, the solar wind is turbulent and gusty,” said DeForest. “But how did it get that way? Did it leave the Sun smooth, and become turbulent as it crossed the solar system, or are the gusts telling us about the Sun itself?”
Answering this question requires observing the outer corona — the source of the solar wind — in extreme detail. If the Sun itself causes the turbulence in the solar wind, then we should be able to see complex structures right from the beginning of the wind’s journey.
But existing data didn’t show such fine-grained structure — at least, until now.
“Previous images of the corona showed the region as a smooth, laminar structure,” said Nicki Viall, solar physicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and coauthor of the study. “It turns out, that apparent smoothness was just due to limitations in our image resolution.”
To understand the corona, DeForest and his colleagues started with coronagraph images — pictures of the Sun’s atmosphere produced by a special telescope that blocks out light from the (much brighter) surface.
How to Read a NASA STEREO Image
Video above: This video shows a coronagraph image taken by the STEREO spacecraft in 2012, highlighting coronal streamers, the solar wind and a coronal mass ejection (CME). Video Credits: NASA's Goddard Space Flight Center/Joy Ng.
These images were generated by the COR2 coronagraph aboard NASA’s Solar and Terrestrial Relations Observatory-A, or STEREO-A, spacecraft, which circles the Sun between Earth and Venus.
In April 2014, STEREO-A would soon be passing behind the Sun, and scientists wanted to get some interesting data before communications were briefly interrupted.
So they ran a special three-day data collection campaign during which COR2 took longer and more frequent exposures of the corona than it usually does. These long exposures allow more time for light from faint sources to strike the instrument’s detector — allowing it to see details it would otherwise miss.
But the scientists didn’t just want longer-exposure images — they wanted them to be higher resolution. Options were limited. The instrument was already in space; unlike Galileo they couldn’t tinker with the hardware itself. Instead, they took a software approach, squeezing out the highest quality data possible by improving COR2’s signal-to-noise ratio.
What is signal-to-noise ratio?
The signal-to-noise ratio is an important concept in all scientific disciplines. It measures how well you can distinguish the thing you care about measuring — the signal — from the things you don’t — the noise.
For example, let’s say that you’re blessed with great hearing. You notice the tiniest of mouse-squeaks late at night; you can eavesdrop on the whispers of huddled schoolchildren twenty feet away. Your hearing is impeccable — when noise is low.
But it’s a whole different ball game when you’re standing in the front row of a rock concert. The other sounds in the environment are just too overpowering; no matter how carefully you listen, mouse-squeaks and whispers (the signal, in this case) can’t cut through the music (the noise).
The problem isn’t your hearing — it’s the poor signal-to-noise ratio.
COR2’s coronagraphs are like your hearing. The instrument is sensitive enough to image the corona in great detail, but in practice its measurements are polluted by noise — from the space environment and even the wiring of the instrument itself. DeForest and his colleagues’ key innovation was in identifying and separating out that noise, boosting the signal-to-noise ratio and revealing the outer corona in unprecedented detail.
The first step towards improving signal-to-noise ratio had already been taken: longer-exposure images. Longer exposures allow more light into the detector and reduce the noise level — the team estimates noise reduction by a factor of 2.4 for each image, and a factor of 10 when combining them over a 20-minute period.
But the remaining steps were up to sophisticated algorithms, designed and tested to extract out the true corona from the noisy measurements.
They filtered out light from background stars (which create bright spots in the image that are not truly part of the corona). They corrected for small (few-millisecond) differences in how long the camera’s shutter was open. They removed the baseline brightness from all the images, and normalized it so brighter regions wouldn’t wash out dimmer ones.
But one of the most challenging obstacles is inherent to the corona: motion blur due to the solar wind. To overcome this source of noise, DeForest and colleagues ran a special algorithm to smooth their images in time.
Animations above: Views of the solar wind from NASA's STEREO spacecraft (left) and after computer processing (right). Scientists used an algorithm to dim the appearance of bright stars and dust in images of the faint solar wind. Animations Credits: NASA’s Goddard Space Flight Center/Craig DeForest, SwRI.
Smoothing in time — with a twist
If you’ve ever done a “double-take,” you know a thing or two about smoothing in time. A double-take — taking a second glance, to verify your first one — is just a low-tech way of combining two “measurements” taken at different times, into one measurement that you can be more confident in.
Smoothing in time turns this idea into an algorithm. The principle is simple: take two (or more) images, overlap them, and average their pixel values together. Random differences between the images will eventually cancel out, leaving behind only what is consistent between them.
But when it comes to the corona, there’s a problem: it’s a dynamic, persistently moving and changing structure. Solar material is always moving away from the Sun to become the solar wind. Smoothing in time would create motion blur — the same kind of blurring you see in photographs of moving objects. That’s a problem if your goal is to see fine detail.
To undo motion blur from the solar wind, the scientists used a novel procedure: while they did their smoothing, they estimated the speed of the solar wind and shifted the images along with it.
To understand how this approach works, think about taking snapshots of the freeway as cars drive past. If you simply overlapped your images, the result would be a big blurry mess — too much has changed between each snapshot.
But if you could figure out the speed of traffic and shift your images to follow along with it, suddenly the details of specific cars would become visible.
For DeForest and his coauthors, the cars were the fine-scale structures of the corona, and the freeway traffic was the solar wind.
Of course there are no speed limit signs in the corona to tell you how fast things are moving. To figure out exactly how much to shift the images before averaging, they scooted the images pixel-by-pixel, correlating them with one another to compute how similar they were. Eventually they found the sweet spot, where the overlapping parts of the images were as similar as possible. The amount of shift corresponded to an average solar wind speed of about 136 miles per second. Shifting each image by that amount, they lined up the images and smoothed, or averaged them together.
“We smoothed, not just in space, not just in time, but in a moving coordinate system,” DeForest said. “That allowed us to create motion blur that was determined not by the speed of the wind, but by how rapidly the features changed in the wind.”
Now DeForest and his collaborators had high-quality images of the corona — and a way to tell how much it was changing over time.
The most surprising finding wasn’t a specific physical structure — it was the simple presence of physical structure in and of itself.
Compared with the dynamic, turbulent inner corona, scientists had considered the outer corona to be smooth and homogenous. But that smoothness was just an artifact of poor signal-to-noise ratio:
“When we removed as much noise as possible, we realized that the corona is structured, all the way down to the optical resolution of the instrument,” DeForest said.
Like the individual blades of grass you see only when you’re up close, the corona’s complex physical structure was revealed in unprecedented detail. And from among that physical detail, three key findings emerged.
The structure of coronal streamers
Coronal streamers — also known as helmet streamers, because they resemble a knight’s pointy helmet — are bright structures that develop over regions of the Sun with enhanced magnetic activity. Readily observed during solar eclipses, magnetic loops on the Sun’s surface are stretched out to pointy tips by the solar wind and can erupt into coronal mass ejections, or CMEs, the large explosions of matter that eject parts of the Sun into surrounding space.
Image above: Coronal streamers observed by the Solar and Heliospheric Observatory (SOHO) spacecraft on Feb. 14, 2002. DeForest and his coauthors’ work indicates that these structures are actually composed of many individual fine strands. Image Credits: NASA/LASCO.
DeForest and his coauthors’ processing of STEREO observations reveals that streamers themselves are far more structured than previously thought.
“What we found is that there is no such thing as a single streamer,” DeForest said. “The streamers themselves are composed of myriad fine strands that together average to produce a brighter feature.”
The Alfvén zone
Where does the corona end and the solar wind begin? One definition points to the Alfvén surface, a theoretical boundary where the solar wind starts moving faster than waves can travel backward through it. At this boundary region, disturbances happening at a point farther away in the traveling solar material can never move backwards fast enough to reach the Sun.
“Material that flows out past the Alfvén surface is lost to the Sun forever,” DeForest said.
Physicists have long believed the Alfvén surface was just that — a surface, or sheet-like layer where the solar wind suddenly reached a critical speed. But that’s not what DeForest and colleagues found.
“What we conclude is that there isn’t a clean Alfvén surface,” DeForest said. “There’s a wide ‘no-man’s land’ or `Alfvén zone’ where the solar wind gradually disconnects from the Sun, rather than a single clear boundary.”
Animation above: A detailed view of the solar corona from the STEREO-A coronagraph after extensive data-cleaning. Animation Credits: Craig DeForest, SwRI.
The observations reveal a patchy framework where, at a given distance from the Sun, some plasma is moving fast enough to stop backward communication, and nearby streams are not. The streams are close enough, and fine enough, to jumble the natural boundary of the Alfvén surface to create a wide, partially-disconnected region between the corona and the solar wind.
Exploring the Unknown with Parker Solar Probe
The newly processed images from STEREO reveal evidence for a new, unsuspected “no-man’s land” between the corona and solar wind: the so-called “Alfvén zone.” This result arrives just in time for Parker Solar Probe, NASA’s mission to touch the Sun, which launches in August 2018. Parker Solar Probe will fly through this newly identified territory and directly explore the environment within it.
A mystery at 10 solar radii
But the close look at coronal structure also raised new questions.
The technique used to estimate the speed of the solar wind pinpointed the altitudes, or distances from the Sun’s surface, where things were changing rapidly. And that’s when the team noticed something funny.
“We found that there’s a correlation minimum around 10 solar radii,” DeForest said.
At a distance of 10 solar radii, even back-to-back images stopped matching up well. But they became more similar again at greater distances — meaning that it’s not just about getting farther away from the Sun. It’s as if things suddenly change once they hit 10 solar radii.
“The fact that the correlation is weaker at 10 solar radii means that some interesting physics is happening around there,” DeForest said. “We don’t know what it is yet, but we do know that it is going to be interesting.”
Where we go from here
The findings create headway in a long-standing debate over the source of the solar wind’s complexity. While the STEREO observations don’t settle the question, the team’s methodology opens up a missing link in the Sun-to-solar-wind chain.
“We see all of this variability in the solar wind just before it hits the Earth’s magnetosphere, and one of our goals was to ask if it was even possible that the variability was formed at the Sun. It turns out the answer is yes,” Viall said.
“It allows us for the first time to really probe the connectivity through the corona and adjust how tangled we think the magnetic field gets in the corona versus the solar wind,” DeForest added.
These first observations also provide key insight into what NASA’s upcoming Parker Solar Probe will find, as the first ever mission to gather measurements from within the outer solar corona. That spacecraft will travel to a distance of 8.86 solar radii, right into the region where interesting things may be found. DeForest and colleagues’ results allow them to make predictions of what Parker Solar Probe may observe in this region.
“We should expect steep fluctuations in density, magnetic fluctuations and reconnection everywhere, and no well-defined Alfvén surface,” DeForest said.
Complemented by Parker Solar Probe’s in situ measurements, long exposure imaging and noise reduction algorithms will become even more valuable to our understanding of our closest star.
The study was supported by a grant from NASA’s Living With a Star - Targeted Research and Technology program.
Solar and Terrestrial Relations Observatory-A (STEREO-A): http://nasa.gov/stereo
Learn more about NASA’s STEREO mission: https://www.nasa.gov/mission_pages/stereo/mission/index.html
Parker Solar Probe: https://www.nasa.gov/content/goddard/parker-solar-probe
Images (mentioned), Animations (mentioned), Video (mentioned), Text, Credits: NASA/Rob Garner/Goddard Space Flight Center, by Miles Hatfield.
Publié par Orbiter.ch à 14:11