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
ISS - Expedition 53 Mission patch.
Nov. 18, 2017
Expedition 53 checked out a specialized microscope and worked on the International Space Station’s toilet today. More supplies and hardware are also being offloaded from the newly-arrived Cygnus cargo craft.
Commander Randy Bresnik opened up the Fluids Integrated Rack this morning to take a look at its Light Microscopy Module (LMM), an advanced space microscope. He was troubleshooting the device and swapping out its cables. The LMM provides a facility to examine the microscopic properties of different types of fluids in microgravity.
Image above: The six-member Expedition 53 crew poses for a portrait inside the Japanese Kibo laboratory module with the VICTORY art spacesuit that was hand-painted by cancer patients in Russia and the United States. On the right (from top to bottom) are European Space Agency astronaut Paolo Nespoli, cosmonaut Sergey Ryazanskiy of Roscosmos and Expedition 53 Commander Randy Bresnik of NASA.
European Space Agency Paolo Nespoli worked on space plumbing throughout the day in the station’s restroom, the Waste and Hygiene Compartment (WHC). The veteran station resident removed and replaced valves and sensors in the WHC as part regular preventative maintenance.
More crew supplies and research gear are being unloaded from Cygnus today to outfit the crew and continue ongoing space science experiments. NASA astronaut Joe Acaba was unpacking food, batteries and computer gear for stowage throughout the station. The second-time station resident was also removing Genes in Space gear and blood sample kits for upcoming science work.
Light Microscopy Module (LMM): https://www.nasa.gov/mission_pages/station/research/experiments/541.html
Genes in Space: https://www.nasa.gov/mission_pages/station/research/experiments/2524.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, Text, Credits: NASA/Mark Garcia.
Best regards, Orbiter.ch
Publié par Orbiter.ch à 07:27
ULA - Delta II / JPSS-1 Mission poater.
Nov. 18, 2017
Image above: At Vandenberg Air Force Base's Space Launch Complex 2, the Delta II rocket engines roar to life. The 1:47 a.m. PST (4:47 a.m. EST), liftoff begins the Joint Polar Satellite System-1, or JPSS-1, mission. JPSS is the first in a series four next-generation environmental satellites in a collaborative program between NOAA and NASA.
NASA has successfully launched for the National Oceanic and Atmospheric Administration (NOAA) the first in a series of four highly advanced polar-orbiting satellites, equipped with next-generation technology and designed to improve the accuracy of U.S. weather forecasts out to seven days.
The Joint Polar Satellite System-1 (JPSS-1) lifted off on a United Launch Alliance Delta II rocket from Vandenberg Air Force Base, California, at 1:47 a.m. PST Saturday.
Approximately 63 minutes after launch the solar arrays on JPSS-1 deployed and the spacecraft was operating on its own power. JPSS-1 will be renamed NOAA-20 when it reaches its final orbit. Following a three-month checkout and validation of its five advanced instruments, the satellite will become operational.
NASA Launches NOAA Weather Satellite to Improve Forecasts
“Launching JPSS-1 underscores NOAA’s commitment to putting the best possible satellites into orbit, giving our forecasters -- and the public -- greater confidence in weather forecasts up to seven days in advance, including the potential for severe, or impactful weather,” said Stephen Volz, director of NOAA’s Satellite and Information Service.
JPSS-1 will join the joint NOAA/NASA Suomi National Polar-orbiting Partnership satellite in the same orbit and provide meteorologists with observations of atmospheric temperature and moisture, clouds, sea-surface temperature, ocean color, sea ice cover, volcanic ash, and fire detection. The data will improve weather forecasting, such as predicting a hurricane’s track, and will help agencies involved with post-storm recovery by visualizing storm damage and the geographic extent of power outages.
“Emergency managers increasingly rely on our forecasts to make critical decisions and take appropriate action before a storm hits,” said Louis W. Uccellini, director of NOAA’s National Weather Service. “Polar satellite observations not only help us monitor and collect information about current weather systems, but they provide data to feed into our weather forecast models.”
JPSS-1 has five instruments, each of which is significantly upgraded from the instruments on NOAA’s previous polar-orbiting satellites. The more-detailed observations from JPSS will allow forecasters to make more accurate predictions. JPSS-1 data will also improve recognition of climate patterns that influence the weather, such as El Nino and La Nina.
The JPSS program is a partnership between NOAA and NASA through which they will oversee the development, launch, testing and operation all the satellites in the series. NOAA funds and manages the program, operations and data products. NASA develops and builds the instruments, spacecraft and ground system and launches the satellites for NOAA. JPSS-1 launch management was provided by NASA’s Launch Services Program based at the agency's Kennedy Space Center in Florida.
“Today’s launch is the latest example of the strong relationship between NASA and NOAA, contributing to the advancement of scientific discovery and the improvement of the U.S. weather forecasting capability by leveraging the unique vantage point of space to benefit and protect humankind,” said Sandra Smalley, director of NASA’s Joint Agency Satellite Division.
Ball Aerospace designed and built the JPSS-1 satellite bus and Ozone Mapping and Profiler Suite instrument, integrated all five of the spacecraft’s instruments and performed satellite-level testing and launch support. Raytheon Corporation built the Visible Infrared Imaging Radiometer Suite and the Common Ground System. Harris Corporation built the Cross-track Infrared Sounder. Northrop Grumman Aerospace Systems built the Advanced Technology Microwave Sounder and the Clouds and the Earth's Radiant Energy System instrument.
To learn more about the JPSS-1 mission, visit:
http://www.jpss.noaa.gov/ and https://www.nesdis.noaa.gov/jpss-1
Images, Video, Text, Credits: NASA/Sean Potter.
Publié par Orbiter.ch à 07:23
vendredi 17 novembre 2017
NASA - Magnetospheric Multiscale Mission (MMS) patch.
Nov. 17, 2017
Interplanetary space is hardly tranquil. High-energy charged particles from the Sun, as well as from beyond our solar system, constantly whizz by. These can damage satellites and endanger astronaut health — though, luckily for life on Earth, the planet is blanketed by a protective magnetic bubble created by its magnetic field. This bubble, called the magnetosphere, deflects most of the harmful high-energy particles.
Nevertheless, some sneak through — and at the forefront of figuring out just how this happens is NASA’s Magnetospheric Multiscale mission, or MMS. New results show that tornado-like swirls of space plasma create a boundary tumultuous enough to let particles slip into near Earth space.
Animation above: This simulation of the boundary shows how areas of low density plasma, shown by blue, mix with areas of higher density plasma, red, forming turbulent tornadoes of plasma. Animation Credits: NASA/Takuma Nakamura.
MMS, launched in 2015, uses four identical spacecraft flying in a pyramid formation to take a three-dimensional look at the magnetic environment around Earth. The mission studies how particles transfer into the magnetosphere by focusing on the causes and effects of magnetic reconnection — an explosive event where magnetic field lines cross, launching electrons and ions from the solar wind into the magnetosphere.
By combining observations from MMS with new 3-D computer simulations, scientists have been able to investigate the small-scale physics of what’s happening at our magnetosphere’s borders for the first time. The results, recently published in a paper in Nature Communications, are key for understanding how the solar wind sometimes enters Earth’s magnetosphere, where it can interfere with satellites and GPS communications.
Inside the magnetosphere, the density of the space plasma — charged particles, like electrons and ions — is much lower than the plasma outside, where the solar wind prevails. The boundary, called the
magnetopause, becomes unstable when the two different density regions move at different rates. Giant swirls, called Kelvin Helmholtz waves, form along the edge like crashing ocean waves. The once-smooth boundary becomes tangled and squeezed, forming plasma tornadoes, which act as portholes for the transportation of charged particles from the solar wind into the magnetosphere.
Image above: Kelvin-Helmholtz waves, with their classic surfer's wave shape, are found in nature wherever two fluids meet, such as in these clouds. Image Credits: Danny Ratcliffe.
Kelvin Helmholtz waves are found across the universe wherever two materials of different density move past one another. They can be seen in cloud formations around Earth and have even been observed in other planetary atmospheres in our solar system.
Using large-scale computer simulations of this mixing, performed at the Oak Ridge National Laboratory in Oak Ridge, Tennessee, on the Titan supercomputer, and comparing them to observations MMS took while passing through such a region in space, scientists were able to show that the tornadoes were extremely efficient at transporting charged particles — much more so than previously thought. The comparisons between the simulations and observations allowed the scientists to measure the exact dimensions of the tornadoes. They found these tornadoes to be both large and small — ones reaching 9,300 miles spawned smaller tornadoes 60 to 90 miles wide and over 125 miles long.
MMS recently moved into a new orbit, flying on the far side of Earth, away from the Sun. Here too, it will continue to study magnetic reconnection, but focus instead on how energy and particles interact within Earth’s magnetosphere, in the long trailing magnetotail. Understanding such fundamental processes in Earth’s neighborhood helps improve our situational awareness of the space that surrounds us — crucial information as it becomes ever more filled with satellites and communications systems we depend on.
Learn more about the Magnetospheric Multiscale Mission: https://www.nasa.gov/mission_pages/mms/index.html
Learn more about NASA’s research on the Sun-Earth environment: https://www.nasa.gov/mission_pages/sunearth/index.html
Animation (mentioned9, Image (mentioned), Text, Credits: NASA/Rob Garner.
Publié par Orbiter.ch à 14:30
NASA - JUNO Mission logo.
Nov. 17, 2017
This color-enhanced image of a massive, raging storm in Jupiter’s northern hemisphere was captured by NASA’s Juno spacecraft during its ninth close flyby of the gas giant planet.
The image was taken on Oct. 24, 2017 at 10:32 a.m. PDT (1:32 p.m. EDT). At the time the image was taken, the spacecraft was about 6,281 miles (10,108 kilometers) from the tops of the clouds of Jupiter at a latitude of 41.84 degrees. The spatial scale in this image is 4.2 miles/pixel (6.7 kilometers/pixel).
The storm is rotating counter-clockwise with a wide range of cloud altitudes. The darker clouds are expected to be deeper in the atmosphere than the brightest clouds. Within some of the bright “arms” of this storm, smaller clouds and banks of clouds can be seen, some of which are casting shadows to the right side of this picture (sunlight is coming from the left). The bright clouds and their shadows range from approximately 4 to 8 miles (7 to 12 kilometers) in both widths and lengths. These appear similar to the small clouds in other bright regions Juno has detected and are expected to be updrafts of ammonia ice crystals possibly mixed with water ice.
Juno spacecraft orbiting Jupiter
Citizen scientists Gerald Eichstädt and Seán Doran processed this image using data from the JunoCam imager.
JunoCam's raw images are available for the public to peruse and process into image products at: http://www.missionjuno.swri.edu/junocam
More information about Juno is at:
https://www.nasa.gov/juno and http://missionjuno.swri.edu
Image, Animation, Text, Credits: NASA/JPL-Caltech/SwRI/MSSS/Gerald Eichstädt/Seán Doran.
Publié par Orbiter.ch à 14:18
NASA - Hubble Space Telescope patch.
Nov. 17, 2017
This new picture of the week, taken by the NASA/ESA Hubble Space Telescope, shows the dwarf galaxy NGC 4625, located about 30 million light-years away in the constellation of Canes Venatici (The Hunting Dogs). The image, acquired with the Advanced Camera for Surveys (ACS), reveals the single major spiral arm of the galaxy, which gives it an asymmetric appearance. But why is there only one such spiral arm, when spiral galaxies normally have at least two?
Astronomers looked at NGC 4625 in different wavelengths in the hope of solving this cosmic mystery. Observations in the ultraviolet provided the first hint: in ultraviolet light the disk of the galaxy appears four times larger than on the image depicted here. An indication that there are a large number of very young and hot — hence mainly visible in the ultraviolet — stars forming in the outer regions of the galaxy. These young stars are only around one billion years old, about 10 times younger than the stars seen in the optical center. At first astronomers assumed that this high star formation rate was being triggered by the interaction with another, nearby dwarf galaxy called NGC 4618.
They speculated that NGC 4618 may be the culprit “harassing” NGC 4625, causing it to lose all but one spiral arm. In 2004 astronomers found proof for this claim. The gas in the outermost regions of the dwarf galaxy NGC 4618 has been strongly affected by NGC 4625.
Hubble Space Telescope (HST)
For images and more information about Hubble, visit:
Image, Animation, Text, Credits: ESA/Hubble & NASA/Text Credits: European Space Agency/NASA/Karl Hille.
Best regards, Orbiter.ch
Publié par Orbiter.ch à 14:11
jeudi 16 novembre 2017
NASA - Spitzer Space Telescope patch.
November 16, 2017
Image above: The super-Earth exoplanet 55 Cancri e, depicted with its star in this artist's concept, likely has an atmosphere thicker than Earth's but with ingredients that could be similar to those of Earth's atmosphere. Image Credits: NASA/JPL.
Twice as big as Earth, the super-Earth 55 Cancri e was thought to have lava flows on its surface. The planet is so close to its star, the same side of the planet always faces the star, such that the planet has permanent day and night sides. Based on a 2016 study using data from NASA's Spitzer Space Telescope, scientists speculated that lava would flow freely in lakes on the starlit side and become hardened on the face of perpetual darkness. The lava on the dayside would reflect radiation from the star, contributing to the overall observed temperature of the planet.
Now, a deeper analysis of the same Spitzer data finds this planet likely has an atmosphere whose ingredients could be similar to those of Earth's atmosphere, but thicker. Lava lakes directly exposed to space without an atmosphere would create local hot spots of high temperatures, so they are not the best explanation for the Spitzer observations, scientists said.
"If there is lava on this planet, it would need to cover the entire surface," said Renyu Hu, astronomer at NASA's Jet Propulsion Laboratory, Pasadena, California, and co-author of a study published in The Astronomical Journal. "But the lava would be hidden from our view by the thick atmosphere."
Using an improved model of how energy would flow throughout the planet and radiate back into space, researchers find that the night side of the planet is not as cool as previously thought. The "cold" side is still quite toasty by Earthly standards, with an average of 2,400 to 2,600 degrees Fahrenheit (1,300 to 1,400 Celsius), and the hot side averages 4,200 degrees Fahrenheit (2,300 Celsius). The difference between the hot and cold sides would need to be more extreme if there were no atmosphere.
"Scientists have been debating whether this planet has an atmosphere like Earth and Venus, or just a rocky core and no atmosphere, like Mercury. The case for an atmosphere is now stronger than ever," Hu said.
Researchers say the atmosphere of this mysterious planet could contain nitrogen, water and even oxygen -- molecules found in our atmosphere, too -- but with much higher temperatures throughout. The density of the planet is also similar to Earth, suggesting that it, too, is rocky. The intense heat from the host star would be far too great to support life, however, and could not maintain liquid water.
Spitzer Space Telescope. Image Credits: NASA/JPL
Hu developed a method of studying exoplanet atmospheres and surfaces, and had previously only applied it to sizzling, giant gaseous planets called hot Jupiters. Isabel Angelo, first author of the study and a senior at the University of California, Berkeley, worked on the study as part of her internship at JPL and adapted Hu's model to 55 Cancri e.
In a seminar, she heard about 55 Cancri e as a potentially carbon-rich planet, so high in temperature and pressure that its interior could contain a large amount of diamond.
"It's an exoplanet whose nature is pretty contested, which I thought was exciting," Angelo said.
Spitzer observed 55 Cancri e between June 15 and July 15, 2013, using a camera specially designed for viewing infrared light, which is invisible to human eyes. Infrared light is an indicator of heat energy. By comparing changes in brightness Spitzer observed to the energy flow models, researchers realized an atmosphere with volatile materials could best explain the temperatures.
There are many open questions about 55 Cancri e, especially: Why has the atmosphere not been stripped away from the planet, given the perilous radiation environment of the star?
"Understanding this planet will help us address larger questions about the evolution of rocky planets," Hu said.
NASA's Jet Propulsion Laboratory, Pasadena, California, manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at Caltech in Pasadena. Spacecraft operations are based at Lockheed Martin Space Systems Company, Littleton, Colorado. Data are archived at the Infrared Science Archive housed at IPAC at Caltech. Caltech manages JPL for NASA. For more information about Spitzer, visit:
Images (mentioned), Text, Credits: NASA/JPL/Elizabeth Landau.
Publié par Orbiter.ch à 18:37
ESA - Gaia Mission patch.
16 November 2017
It's the perfect meeting of old and new. Astronomers have combined the latest data from ESA's Gaia mission with a simple analysis technique from the 18th century to discover a massive star cluster that had previously escaped detection. Now, subsequent investigations are helping reveal the star-forming history of our Galaxy, the Milky Way.
Gaia: How to find a star cluster
Video above: Video explainer: How to find a star cluster. Video Credit: ESA.
In the latter years of the 18th century, astronomers William and Caroline Herschel began to count stars. William called the technique "star gauging" and his aim was to determine the shape of our Galaxy.
Ever since 1609, when Galileo lifted his telescope to the misty patch of light known as the Milky Way and saw that it was composed of myriad faint stars whose light all blurred together, we have known that there are different numbers of stars in different directions throughout space. This means that our local collection of stars, the Galaxy, must have a shape to it. Herschel set out to find out what that shape was.
He used a large telescope, twenty feet (610 cm) in length, mounted between tall wooden frames to sweep out a large circle in the sky that passed through the Milky Way at right angles. He then split this circle into more than 600 regions and counted or estimated the number of stars in each.
With this simple technique the Herschels produced the first shape estimate for the Galaxy. Fast-forward to the 21st century and now researchers use star counts to search for hidden star clusters and satellite galaxies. They look for regions where the density of stars rises higher than expected. These patches are called stellar over-densities.
Image above: Gaia's first sky map. Image Credits: ESA/Gaia/DPAC. Acknowledgement: A. Moitinho & M. Barros (CENTRA – University of Lisbon), on behalf of DPAC.
Back in 1785, Herschel's circular track passed close to the brightest star in the night sky Sirius. Now, scientists mining the first data released from the ESA spacecraft Gaia have revisited that particular area of the sky and made a remarkable discovery.
They have revealed a large star cluster that could have been discovered more than a century and a half ago had it not been so close to Sirius.
The cluster was spotted by Sergey E. Koposov, then at the University of Cambridge (UK) and now at Carnegie Mellon University Pennsylvania (USA), and his colleagues. They have been looking for star clusters and satellite galaxies in various surveys for the past decade. It was natural for them to do this with the Gaia mission's first data release.
Gaia is the European Space Agency's astrometric mission. Collecting positions, brightnesses and additional information for more than a billion sources of light, its data allows nothing less than the most precise 'star gauging' ever.
Gaia scanning the sky
Video above: Gaia scanning the sky. Video Credits: ESA/Gaia/DPAC. Acknowledgement: B. Holl (University of Geneva, Switzerland), A. Moitinho & M. Barros (CENTRA – University of Lisbon), on behalf of DPAC.
These days the laborious task of counting the stars is done by computers but the results still have to be scrutinised by humans. Koposov was combing the list of over-densities when he saw the massive cluster. At first it seemed too good to be true.
"I thought it must be an artefact related to Sirius," he says. Bright stars can create false signals, termed artefacts, that astronomers must be careful not to mistake for stars. An early paper from the Gaia team had even discussed artefacts around Sirius using a nearby patch of sky to the one Koposov was looking at.
Although he moved on and found another over-density that looked promising, his mind kept wanting to return to the first one. "I thought, 'That's strange, we shouldn't have that many artefacts from Sirius.' So I went and looked at it again. And I realised that it too was a genuine object," he says.
These two objects were named: Gaia 1 for the object located near Sirius, and Gaia 2, which is close to the plane of our Galaxy, and both were duly published. Gaia 1 in particular contains enough mass to make a few thousand stars like the Sun, is located 15 thousand light years away, and spread across 30 light years. This means it is a massive star cluster.
Image above: The brightest star in this WISE image is Sirius. To the left of Sirius, and centred on this image, is Gaia 1, a massive star cluster discovered by scientists mining Gaia data. Image Credits: Sergey Koposov; NASA/JPL; D. Lang, 2014; A.M. Meisner et al. 2017.
Collections of stars like Gaia 1 are called open clusters. They are families of stars that all form together and then gradually disperse around the Galaxy. Our own Sun very likely formed in an open cluster. Such assemblies can tell us about the star formation history of our Galaxy. Finding a new one that can be easily studied is already paying dividends.
"The age is of great interest," says Jeffrey Simpson, Australian Astronomical Observatory, who conducted follow-up observations with colleagues using the 4-metre-class Anglo-Australian telescope at Siding Springs Observatory, Australia.
Identifying 41 members of the cluster, Simpson and colleagues found that Gaia 1 is unusual in at least two ways. Firstly, it is about 3 billion years old. This is odd because there are not many clusters with this age in the Milky Way.
Typically clusters are either younger than a few hundred million years – these are the open clusters – or older than 10 billion years – these are a distinct class called globular clusters, which are found beyond the main bulk of stars in our Galaxy. Being of intermediate age, Gaia 1 might represent an important bridge in our understanding between the two populations.
Images above: Star cluster Westerlund 2. Image Credits: NASA, ESA, the Hubble Heritage Team (STScI/AURA), A. Nota (ESA/STScI), and the Westerlund 2 Science Team.
Images above: Globular cluster 47 Tucanae. Image Credits: NASA, ESA, and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration. Acknowledgment: J. Mack (STScI) and G. Piotto (University of Padova, Italy).
Secondly, its orbit through the galaxy is unusual. Most open clusters lie close to the plane of the Galaxy but Simpson found that Gaia 1 flies high above it before ducking down and passing underneath. "It might go as much as a kiloparsec (more than 3000 light years) above and below the plane," he says. About 90% of clusters never go more than a third of this distance.
Simulations of clusters with orbits like Gaia 1 find that they are stripped of stars and dispersed by these high velocity 'plane passages'. That puts it at odds with the age estimate.
"Our finding that Gaia 1 is three billion years old is curious as the models would have it not surviving anywhere near as long. More research is required to try and reconcile this," says Simpson.
To test a possible explanation, Alessio Mucciarelli, Universita' degli Studi di Bologna, Italy and colleagues investigated the chemical composition of Gaia 1. Such a study has the ability to see if the cluster formed outside of the Galaxy and has been caught in the act of falling in.
"The chemical composition of the stars can be considered a 'genetic' signature of their origin. If a stellar cluster formed in another galaxy, its chemical composition will be different with respect to that of our Galaxy," says Mucciarelli.
They found that the compositions were practically identical to those expected if Gaia 1 formed in the Milky Way – so the puzzle remains.
Now Mucciarelli hopes that the discrepancy might go away when Gaia releases more data. "Even if the orbital parameters seem to suggest a peculiar orbit, their uncertainties are large enough to prevent any firm conclusion. More accurate orbital parameters will be obtained with the second Gaia data release and we will better understand whether the orbit of Gaia 1 is peculiar or not," he says.
As well as finding new clusters, the Gaia data are proving useful for checking out the reality of previously reported associations of stars. "Using Gaia data I can see stars that share the same motion. So I can confirm which ones form real open clusters," says Andrés E. Piatti, Consejo Nacional de Investigaciones Científicas y Técnicas, Argentina.
He recently published a study that showed ten out of fifteen previously published open clusters were not really star clusters at all, they were just statistical flukes where a lot of unrelated stars happened to be passing in different directions through the same region of space.
It is laborious but vital work. "No one wants to spend their life doing this," says Piatti, "but it is necessary. If we can determine the real size of the cluster population we can learn a lot about the processes that the Galaxy has suffered during its lifetime."
In astronomy, the most famous list of star clusters, nebulae and galaxies was compiled by astronomer and comet hunter, Charles Messier, in the 18th century. Unaware of the importance of these objects, he designed his catalogue to stop the frustration felt by him and other astronomers in mistaking one of these 'deep-sky objects' for a nearby comet.
That original catalogue ran to 110 objects. If it hadn't been for the glare from Sirius obscuring the view, Gaia 1 would have been bright and obvious enough to have made it onto that list too. And there is every reason to think that there are more to come, thanks to Gaia.
The next data release will give accurate proper motions and distances to an unprecedented number of stars, which can be used to more efficiently find star clusters that were buried too deep in the stellar field or were too diffuse or too distant to be seen before.
There is always the possibility to find something totally new too. "I hope with the next data release we can find some new classes of objects too," says Simpson.
For the astronomers ready to explore the Gaia data, the adventure has only just begun. Gaia's second data release is scheduled for April 2018. Subsequent data releases are scheduled for 2020 and 2022.
A large pan-European team of expert scientists and software developers known as DPAC (Data Processing and Analysis Consortium), located in and funded by many ESA member states, is responsible for the processing and validation of Gaia's data with the final objective of producing the Gaia Catalogue.
"Gaia 1 and 2. A pair of new Galactic star clusters," by S. E. Koposov, V. Belokurov and G. Torrealba, is published in Monthly Notices of the Royal Astronomical Society, Volume 470, Issue 3, 21 September 2017, Pages 2702–2709, https://doi.org/10.1093/mnras/stx1182
"Siriusly, a newly identified intermediate-age Milky Way stellar cluster: A spectroscopic study of Gaia 1," by J. D. Simpson, G. M. De Silva, S. L. Martell, D. B. Zucker, A. M. N. Ferguson, E. J. Bernard, M. Irwin, J. Penarrubia and E. Tolstoy is accepted for publication in Monthly Notices of the Royal Astronomical Society, stx1892, https://doi.org/10.1093/mnras/stx1892
"Chemical composition of the stellar cluster Gaia1: no surprise behind Sirius," by A. Mucciarelli, L. Monaco, P. Bonifacio and I. Saviane, is published in Astronomy & Astrophysics, 603 (2017) L7, https://doi.org/10.1051/0004-6361/201731009
"On the physical reality of overlooked open clusters," by A. E. Piatti is published in Monthly Notices of the Royal Astronomical Society, Volume 466, Issue 4, 1 May 2017, Pages 4960–4973, https://doi.org/10.1093/mnras/stx081
First Gaia release (Gaia DR1): http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=58272
Second Gaia data release: https://www.cosmos.esa.int/web/gaia/release
Anglo-Australian telescope: https://www.aao.gov.au/about-us/AAT
ESA's Gaia mission: http://www.esa.int/Our_Activities/Space_Science/Gaia
Images (mentioned), Videos (mentioned), text, Credit: European Space Agency (ESA.
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Publié par Orbiter.ch à 18:22