samedi 15 octobre 2016
NASA - JUNO Mission logo.
Oct. 15, 2016
Mission managers for NASA’s Juno mission to Jupiter have decided to postpone the upcoming burn of its main rocket motor originally scheduled for Oct. 19. This burn, called the period reduction maneuver (PRM), was to reduce Juno’s orbital period around Jupiter from 53.4 to 14 days. The decision was made in order to further study the performance of a set of valves that are part of the spacecraft’s fuel pressurization system. The period reduction maneuver was the final scheduled burn of Juno’s main engine.
"Telemetry indicates that two helium check valves that play an important role in the firing of the spacecraft’s main engine did not operate as expected during a command sequence that was initiated yesterday,” said Rick Nybakken, Juno project manager at NASA's Jet Propulsion Laboratory in Pasadena, California. “The valves should have opened in a few seconds, but it took several minutes. We need to better understand this issue before moving forward with a burn of the main engine.”
Image above: This artist's rendering shows NASA's Juno spacecraft making one of its close passes over Jupiter. Image Credits: NASA/JPL-Caltech.
After consulting with Lockheed Martin Space Systems of Denver and NASA Headquarters, Washington, the project decided to delay the PRM maneuver at least one orbit. The most efficient time to perform such a burn is when the spacecraft is at the part of its orbit which is closest to the planet. The next opportunity for the burn would be during its close flyby of Jupiter on Dec. 11.
Mission designers had originally planned to limit the number of science instruments on during Juno’s Oct. 19 close flyby of Jupiter. Now, with the period reduction maneuver postponed, all of the spacecraft’s science instruments will be gathering data during the upcoming flyby.
“It is important to note that the orbital period does not affect the quality of the science that takes place during one of Juno’s close flybys of Jupiter,” said Scott Bolton, principal investigator of Juno from the Southwest Research Institute in San Antonio. "The mission is very flexible that way. The data we collected during our first flyby on August 27th was a revelation, and I fully anticipate a similar result from Juno’s October 19th flyby.”
The Juno spacecraft launched on Aug. 5, 2011, from Cape Canaveral, Florida, and arrived at Jupiter on July 4, 2016.
JPL manages the Juno mission for the principal investigator, Scott Bolton, of Southwest Research Institute in San Antonio. Juno is part of NASA's New Frontiers Program, which is managed at NASA's Marshall Space Flight Center in Huntsville, Alabama, for NASA's Science Mission Directorate. Lockheed Martin Space Systems, Denver, built the spacecraft. Caltech in Pasadena, California, manages JPL for NASA.
More information on the Juno mission is available at:
The public can follow the mission on Facebook and Twitter at:
Image (mentioned), Text, Credits: NASA/Dwayne Brown/Laurie Cantillo/Tony Greicius/JPL/DC Agle.
Publié par Orbiter.ch à 13:58
vendredi 14 octobre 2016
NASA - Chandra X-ray Observatory patch.
Oct. 14, 2016
Each year, NASA’s Chandra X-ray Observatory helps celebrate American Archive Month by releasing a collection of images using X-ray data in its archive.
The Chandra Data Archive is a sophisticated digital system that ultimately contains all of the data obtained by the telescope since its launch into space in 1999. Chandra’s archive is a resource that makes these data available to the scientific community and the general public for years after they were originally obtained.
Each of these six new images also includes data from telescopes covering other parts of the electromagnetic spectrum, such as visible and infrared light. This collection of images represents just a small fraction of the treasures that reside in Chandra’s unique X-ray archive.
From left to right, starting on the top row, the objects are:
Westerlund 2: A cluster of young stars – about one to two million years old – located about 20,000 light years from Earth. Data in visible light from the Hubble Space Telescope (green and blue) reveal thick clouds where the stars are forming. High-energy radiation in the form of X-rays, however, can penetrate this cosmic haze, and are detected by Chandra (purple).
3C31: X-rays from the radio galaxy 3C31 (blue), located 240 million light years from Earth, allow astronomers to probe the density, temperature, and pressure of this galaxy, long known to be a powerful emitter of radio waves. The Chandra data also reveal a jet blasting away from one side of the central galaxy, which also is known as NGC 383. Here, the Chandra X-ray image has been combined with Hubble’s visible light data (yellow).
PSR J1509-5850: Pulsars were first discovered in 1967 and today astronomers know of over a thousand such objects. The pulsar, PSR J1509-5850, located about 12,000 light years from Earth and appearing as the bright white spot in the center of this image, has generated a long tail of X-ray emission trailing behind it, as seen in the lower part of the image. This pulsar has also generated an outflow of particles in approximately the opposite direction. In this image, X-rays detected by Chandra (blue) and radio emission (pink) have been overlaid on a visible light image from the Digitized Sky Survey of the field of view.
Abell 665: Merging galaxy clusters can generate enormous shock waves, similar to cold fronts in weather on Earth. This system, known as Abell 665, has an extremely powerful shockwave, second only to the famous Bullet Cluster. Here, X-rays from Chandra (blue) show hot gas in the cluster. The bow wave shape of the shock is shown by the large white region near the center of the image. The Chandra image has been added to radio emission (purple) and visible light data from the Sloan Digital Sky Survey showing galaxies and stars (white).
RX J0603.3+4214: The phenomenon of pareidolia is when people see familiar shapes in images. This galaxy cluster has invoked the nickname of the “Toothbrush Cluster” because of its resemblance to the dental tool. In fact, the stem of the brush is due to radio waves (green) while the diffuse emission where the toothpaste would go is produced by X-rays observed by Chandra (purple). Visible light data from the Subaru telescope show galaxies and stars (white) and a map from gravitational lensing (blue) shows the concentration of the mass, which is mostly (about 80%) dark matter.
CTB 37A: Astronomers estimate that a supernova explosion should occur about every 50 years on average in the Milky Way galaxy. The object known as CTB 37A is a supernova remnant located in our Galaxy about 20,000 light years from Earth. This image shows that the debris field glowing in X-rays (blue) and radio waves (pink) may be expanding into a cooler cloud of gas and dust seen in infrared light (orange).
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.
Chandra X-ray Observatory. Image Credits: NASA/CXC
Read More from NASA's Chandra X-ray Observatory: http://chandra.harvard.edu/photo/2016/archives/
For more Chandra images, multimedia and related materials, visit:
Images (mentioned), Text, Credits: NASA/Lee Mohon/Marshall Space Flight Center/Molly Porter/Chandra X-ray Center/Megan Watzke.
Publié par Orbiter.ch à 13:03
NASA - EOS Terra Mission patch.
Oct. 14, 2016
Nicole (Atlantic Ocean)
Hurricane Nicole made landfall in Bermuda around 11 a.m. EDT on Oct. 13, and NASA's Terra satellite captured an image of the storm within the hour.
On Oct. 13, before landfall in Bermuda, Hurricane Nicole strengthened to a Category 4 storm on the Saffir-Simpson Hurricane Wind Scale with maximum sustained winds of 120 mph. At 11:20 a.m. EDT (15:20 UTC) NASA's Terra satellite captured a visible image of very large Hurricane Nicole about 10 miles east of the island.
Image above: On Oct. 13, 2016, NASA's Terra satellite captured this visible image of very large Hurricane Nicole just east of Bermuda at 11:20 a.m. EDT (15:20 UTC). Image Credits: NASA Goddard MODIS Rapid Response Team.
On Oct. 14 Nicole was racing east-northeastward over the Atlantic, but large ocean swells from the large storm were spreading northward along the U.S. East Coast and into Atlantic Canada.
At 5 a.m. EDT (9:00 UTC), the National Hurricane Center (NHC) said, “The cloud pattern has degraded significantly during the past few hours. The low-level center is difficult to locate, but it appears to be separated and well to the southwest of an area of weakening convection due to southwesterly shear.”
The center of Hurricane Nicole was located near 35.4 degrees north latitude and 59.2 degrees west longitude, about 675 miles (1,090 km) south-southeast of Halifax, Nova Scotia, Canada.
Artist's concept of Terra satellite. Image Credit: NASA
NHC said Nicole is moving toward the east-northeast near 21 mph (33 kph). This general motion is expected to continue today with a decrease in forward speed expected on Saturday, Oct. 15. Maximum sustained winds are near 85 mph (140 kph) with higher gusts. Weakening is forecast during the next 12 to 24 hours, but Nicole is expected to remain a powerful cyclone even when it could become a post-tropical cyclone on Saturday.
Hurricane-force winds extend outward up to 70 miles (110 km) from the center and tropical-storm-force winds extend outward up to 205 miles (335 km).
For updated forecasts on Nicole, visit the NHC website: http://www.nhc.noaa.gov.
For the story about the records Nicole has broken, visit: http://earthobservatory.nasa.gov/NaturalHazards/view.php?id=88918&src=nha
NASA's Terra satellite: http://www.nasa.gov/mission_pages/terra/index.html
Image (mentioned), Text, Credits: NASA's Goddard Space Flight Center, by Rob Gutro.
Publié par Orbiter.ch à 12:49
NASA - Hubble Space Telescope patch.
Oct. 14, 2016
This image, taken by the NASA/ESA Hubble Space Telescope’s Wide Field Planetary Camera 2, shows a spiral galaxy named NGC 278. This cosmic beauty lies some 38 million light-years away in the northern constellation of Cassiopeia (The Seated Queen).
While NGC 278 may look serene, it is anything but. The galaxy is currently undergoing an immense burst of star formation. This flurry of activity is shown by the unmistakable blue-hued knots speckling the galaxy’s spiral arms, each of which marks a clump of hot newborn stars.
However, NGC 278’s star formation is somewhat unusual; it does not extend to the galaxy’s outer edges, but is only taking place within an inner ring some 6500 light-years across. This two-tiered structure is visible in this image — while the galaxy’s center is bright, its extremities are much darker. This odd configuration is thought to have been caused by a merger with a smaller, gas-rich galaxy — while the turbulent event ignited the center of NGC 278, the dusty remains of the small snack then dispersed into the galaxy’s outer regions. Whatever the cause, such a ring of star formation, called a nuclear ring, is extremely unusual in galaxies without a bar at their center, making NGC 278 a very intriguing sight.
Hubble and the sunrise over Earth
Wide Field Planetary Camera 2: https://www.spacetelescope.org/about/general/instruments/wfpc2/
For images and more information about Hubble Space Telescope, visit:
Image Credits: ESA/Hubble & NASA/Text Credits: European Space Agency/NASA/Karl Hille/Video: European Space Agency.
Publié par Orbiter.ch à 08:18
ESA - SMOS Mission logo.
14 October 2016
While ESA’s water mission was built to advance our understanding of Earth, it continues to show how well it’s suited to delivering information for numerous applications that improve everyday life. Taking this a step further, soil moisture data products are now available within three hours of measurement, which is essential for many applications.
SMOS was launched in 2009 to provide global observations of soil moisture and ocean salinity – two important variables in Earth’s water cycle.
Soil moisture processed two ways
The satellite captures images of ‘brightness temperature’, which correspond to radiation emitted from Earth’s surface and can be used to gain information on soil moisture and ocean salinity.
As well as being used to study how Earth works as a system, SMOS’ readings of brightness temperature have proved to be a completely new source of information for tracking hurricanes, measuring thin ice floating in the polar seas, for assessing fire risk, and more.
However, for SMOS to benefit society even more, its data need to be available fast – in what is termed ‘near-real time’, which means within three hours of sensing.
To accommodate this, the process of translating brightness temperature measurements into soil moisture products has been completely redesigned. It involved developing an artificial ‘neural network’, akin to the vast network of neurons in a brain.
After being trained with old soil moisture data, this neural network is now able to compute values of soil moisture from the satellite’s observations within seconds.
Wet soils following extensive rainfall
ESA’s SMOS mission scientist, Matthias Drusch, said, “Short latency and fast access to data products are very important for many applications such as weather prediction and flood forecasting.
“The neural network approach, developed at CESBIO, has allowed us to integrate state-of-the-art science into operational processing, opening the door for operational agencies.”
The operational data processing is being done at the European Centre for Medium-Range Weather Forecasts and the final data products can be obtained through Eumetsat’s Eumetcast system.
The fact that soil moisture data are available within three hours of sensing also makes it easier to combine SMOS data with similar information from other satellites.
In fact, SMOS and NASA’s Soil Moisture Active Passive satellite can provide accurate coarse-resolution soil moisture information. Measurements from the Copernicus Sentinel-1 satellite can then be applied to improve the resolution to ‘field scale’.
By combining measurements from different sensors the spatial resolution is increased from 25 km x 25 km to 100 m x 100 m.
Zooming in on moisture
VanderSat, a Dutch company that focuses on adding value to satellite data products, produces these images regularly, furnishing more than 3000 users with essential information.
VanderSat’s Richard de Jeu said, “The new data fusion method provides cost-effective and information-rich soil moisture information.
“This means that more informed decisions can be made – whether you are monitoring crops, predicting the weather, performing predictive analysis or preventing forest fires.”
SMOS satellite in orbit
Susanne Mecklenburg, SMOS mission manager, said, “A single satellite cannot provide high-accuracy datasets, high spatial resolution and fast global coverage. Therefore, a constellation of satellites with complementary instrumentation is needed to address the needs of agriculture, hydrology, weather forecasting, and climate applications.”
SMOS - Soil Moisture and Ocean Salinity mission: http://www.esa.int/Our_Activities/Observing_the_Earth/SMOS
Access SMOS data: http://earth.esa.int/SMOS/
Images, Text, Credits: ESA/CESBIO/VanderSat/ATG Medialab.
Publié par Orbiter.ch à 07:31
ESA & ROSCOSMOS - ExoMars Mission logo.
14 October 2016
Next week, ESA’s ExoMars has just a single chance to get captured by Mars’ gravity. The spacecraft and the mission controllers who will make it so are ready for arrival.
ExoMars approaching Mars
The ExoMars Trace Gas Orbiter is on a multiyear mission to understand the methane and other gases in Mars’ atmosphere at low levels and could be evidence for possible biological or geological activity.
The 3.7 tonne mothership is carrying the 577 kg Schiaparelli lander that will test key technologies in preparation for ESA's 2020 rover mission.
The pair have almost completed their 496 million km journey, and are now speeding towards a critical stage: releasing the lander on Sunday and the lander’s descent and touchdown next Wednesday, at the same time as the main craft begins circling the planet.
ExoMars at the Red Planet
“They are now on a high-speed collision course with Mars, which is fine for the lander – it will stay on this path to make its controlled landing,” says flight director Michel Denis at mission control in Darmstadt, Germany.
“However, to get the mothership into orbit, we must make a small but vital adjustment on 17 October to ensure it avoids the planet. And on 19 October it must fire its engine at a precise time for 139 minutes to brake into orbit.
“We get just a single chance.”
Realtime mission control
Following months of intensive simulations, the team is now changing to ‘real-time/full-time’ shifts, and will work in the main control room from tomorrow.
Training for ExoMars
The team will oversee separation, set for 14:42 GMT (16:42 CEST) on Sunday, the adjustment 12 hours later to avoid hitting Mars and, finally, the main engine burn starting at 13:05 GMT (15:05 CEST) on Wednesday.
A last pre-arrival correction was made this morning at 08:45 GMT (10:45 CEST) to ensure the craft is perfectly lined up for separation and arrival. The thruster burn delivered a tiny kick of 1.4 cm/s – all that was needed after an earlier series of extremely precise adjustments in July and September (see “Engine burn gives Mars mission a kick” http://www.esa.int/Our_Activities/Operations/Engine_burn_gives_Mars_mission_a_kick).
Mars arrival orbits
“This week, we uploaded the commands to fully charge the lander’s batteries and prepare the orbiter’s data-handling system as well as power- and thruster system for separation and the subsequent trajectory tweak,” says spacecraft operations manager Peter Schmitz.
“Next week, before the big burn, we will place it into a special ‘failop’ mode to minimise any risk that an onboard glitch could interfere with the firing of the engine, which absolutely must happen at the planned time for us to get into orbit.”
Mission controllers have daily, hours-long communication slots with ExoMars booked via ESA and NASA tracking stations, which are providing main and redundant data links, especially during the most critical moments.
Preparing on Earth for missions at Mars
Preparing for Mars arrival has involved years of careful work by teams across ESA in cooperation with experts from European industry.
The mission control team is actually a ‘team of teams’ comprising specialists in operations, flight dynamics, ground stations, and software and systems. They work in tight coordination to operate the current fleet of spacecraft, while developing the systems and procedures to be used for future ESA missions, including BepiColombo, Solar Orbiter and Juice.
The centre is also mission control for ESA’s first Mars mission, Mars Express, which arrived at the Red Planet in 2003. It is playing a crucial role in the arrival of ExoMars, recording signals from the lander during descent (see “A little help from friends” http://orbiterchspacenews.blogspot.ch/2016/06/a-little-help-from-friend.html).
“After many simulations and given the extensive experience our teams have gained through interplanetary missions like Mars Express, Rosetta and Venus Express, I am very confident about orbital insertion,” says Rolf Densing, ESA’s Director of Operations.
“The spacecraft is in great shape, the teams are ready to return to Mars and we’re looking forward to a smooth arrival next week.”
Robotic exploration of Mars: http://exploration.esa.int/
ExoMars at IKI: http://exomars.cosmos.ru/
Thales Alenia Space: https://www.thalesgroup.com/en/worldwide/space/space
NASA In 2016 ExoMars orbiter (Electra radio): http://mars.nasa.gov/programmissions/missions/future/exomarsorbiter2016/
Where on Mars?: http://whereonmars.co/
ExoMars Factsheet: http://www.esa.int/Our_Activities/Space_Science/ExoMars/ExoMars_Factsheet
ExoMars frequently asked questions: http://www.esa.int/Our_Activities/Space_Science/ExoMars/ExoMars_frequently_asked_questions
ExoMars brochure: http://www.esa.int/About_Us/ESA_Publications/ESA_Publications_Brochures/ESA_BR-327_EXOMARS_2016
Images, Videos, Text, Credits: European Space Agency (ESA)/ATG medialab.
Best regards, Orbiter.ch
Publié par Orbiter.ch à 06:56
jeudi 13 octobre 2016
JPL - Jet Propulsion Laboratory logo.
Oct. 13, 2016
Quantum physics is a field that appears to give scientists superpowers. Those who understand the world of extremely small or cold particles can perform amazing feats with them -- including teleportation -- that appear to bend reality.
The science behind these feats is complicated, and until recently, didn’t exist outside of lab settings. But that’s changing: researchers have begun to implement quantum teleportation in real-world contexts. Being able to do so just might revolutionize modern phone and Internet communications, leading to highly secure, encrypted messaging.
Image above: This image shows crystals used for storing entangled photons, which behave as though they are part of the same whole. Scientists use crystals like these in quantum teleportation experiments. Image Credits: Félix Bussières/University of Geneva.
A paper published in Nature Photonics and co-authored by engineers at NASA’s Jet Propulsion Laboratory, Pasadena, California, details the first experiments with quantum teleportation in a metropolitan fiber cable network. For the first time, the phenomenon has been witnessed over long distances in actual city infrastructure. In Canada, University of Calgary researchers teleported the quantum state of a photon more than 3.7 miles (6 kilometers) in “dark” (unused) cables under the city of Calgary. That’s a new record for the longest distance of quantum teleportation in an actual metropolitan network.
While longer distances had been recorded in the past, those were conducted in lab settings, where photons were fired through spools of cable to simulate the loss of signal caused by long distances. This latest series of experiments in Calgary tested quantum teleportation in actual infrastructure, representing a major step forward for the technology.
“Demonstrating quantum effects such as teleportation outside of a lab environment involves a whole new set of challenges. This experiment shows how these challenges can all be overcome and hence it marks an important milestone towards the future quantum Internet,” said Francesco Marsili, one of the JPL co-authors. “Quantum communication unlocks some of the unique properties of quantum mechanics to, for example, exchange information with ultimate security or link together quantum computers.”
Image above: This image shows crystals used for storing entangled photons, which behave as though they are part of the same whole. Scientists use crystals like these in quantum teleportation experiments. Image Credits: Félix Bussières/University of Geneva.
Photon sensors for the experiment were developed by Marsili and Matt Shaw of JPL’s Microdevices Laboratory, along with colleagues at the National Institute of Standards and Technology, Boulder, Colorado. Their expertise was critical to the experiments: quantum networking is done with photons, and requires some of the most sensitive sensors in the world in order to know exactly what’s happening to the particle.
“The superconducting detector platform, which has been pioneered by JPL and NIST researchers, makes it possible to detect single photons at telecommunications wavelengths with nearly perfect efficiency and almost no noise. This was simply not possible with earlier detector types, and so experiments such as ours, using existing fiber-infrastructure, would have been close to impossible without JPL’s detectors,” said Daniel Oblak of the University of Calgary’s Institute for Quantum Science and Technology.
Safer emails using quantum physics
Shrink down to the level of a photon, and physics starts to play by bizarre rules. Scientists who understand those rules can “entangle” two particles so that their properties are linked. Entanglement is a mind-boggling concept in which particles with different characteristics, or states, can be bound together across space. That means whatever affects one particle’s state will affect the other, even if they’re located miles apart from one another.
This is where teleportation comes in. Imagine you have two entangled particles -- let’s call them Photon 1 and Photon 2 -- and Photon 2 is sent to a distant location. There, it meets with Photon 3, and the two interact with each other. Photon 3’s state can be transferred to Photon 2, and automatically “teleported” to the entangled twin, Photon 1. This disembodied transfer happens despite the fact that Photons 1 and 3 never interact.
This property can be used to securely exchange secret messages. If two people share an entangled pair of photons, quantum information can be transmitted in a disembodied fashion, leaving an eavesdropper with nothing to intercept and so unable to read the secret message.
Teleportation Means Going the Distance
This system of highly secure communications is being tested in a number of fields, Marsili said, including financial industries and agencies like NASA that want to protect their space data signals. The superconducting single photon detectors developed by Marsili, Shaw and their NIST colleagues are a key tool in doing this, because sending photons over long distances will inevitably lead to “loss” of the signal. Even when using a laser in space, light diffuses over distance, weakening the power of the signal being transmitted.
The next step is building repeaters that can further teleport the state of a photon from one location to the next. Just as repeaters are used to carry other telecommunication signals across long distances, they could be used to teleport entangled photons. Super-sensitive photon detectors would allow repeaters to send entangled photons across the country. For space-related communications, repeaters wouldn’t even be necessary; photons could eventually be fired into space using lasers, and photon states could be teleported from Earth.
No repeaters were used in the Calgary experiments, which were mainly meant to establish how quantum teleportation can be performed outside the lab. Researchers used the city’s dark fiber -- a single optical cable with no electronics or network equipment flowing through them.
“By using advanced superconducting detectors, we can use individual photons to efficiently communicate both classical and quantum information from space to the ground,” Shaw said. “We are planning to use more advanced versions of these detectors for demonstrations of optical communication from deep space and of quantum teleportation from the International Space Station.”
The study was funded by Alberta Innovates Technology Futures; the National Science and Engineering Research Council of Canada; and the Defense Advanced Research Projects Agency. Part of the detector research was carried out at JPL under a contract with NASA. Caltech in Pasadena manages JPL for NASA.
Paper published in Nature Photonics: http://www.nature.com/nphoton/journal/vaop/ncurrent/full/nphoton.2016.180.html
For more information about JPL’s research on quantum teleportation, visit: http://www.jpl.nasa.gov/news/news.php?feature=4384
Images (mentioned), Text, Credits: NASA/Tony Greicius/JPL/Andrew Good.
Publié par Orbiter.ch à 15:20
NASA - Lunar Reconnaissance Orbiter (LRO) patch.
Oct. 13, 2016
The moon experiences a heavier bombardment by small meteoroids than models had predicted, according to new observations from NASA's Lunar Reconnaissance Orbiter (LRO) spacecraft. The result implies that lunar surface features thought to be young because they have relatively few impact craters may be even younger than previous estimates.
The finding also implies that equipment placed on the moon for long durations -- such as a lunar base -- may have to be made sturdier. While a direct hit from a meteoroid is still unlikely, a more intense rain of secondary debris thrown out by nearby impacts may pose a risk to surface assets.
Gardening Rates on the Moon
Video above: After simulating the distant view of a new impact, the camera zooms up to the surface to show actual before/after images of a new 12-meter crater taken by the Lunar Reconnaissance Orbiter narrow-angle camera. Video Credits: NASA/GSFC/Ernie Wright.
"Before the launch of the Lunar Reconnaissance Orbiter, it was thought that churning of the lunar regolith (soil) from meteoroid impacts typically took millions of years to overturn the surface down to 2 centimeters (about 0.8 inches)," said Emerson Speyerer of Arizona State University, Tempe. "New images from the Lunar Reconnaissance Orbiter Camera (LROC) are revealing small surface changes that are transforming the surface much faster than previously thought." Speyerer is lead author of a paper about this research in the Oct. 13 issue of the journal Nature.
"The newly determined churning rate means that the Apollo astronaut tracks will be gone in tens of thousands of years rather than millions," said Mark Robinson of Arizona State University, a co-author.
Image above: One of the first steps taken on the Moon, this is an image of Buzz Aldrin's bootprint from the Apollo 11 mission. Neil Armstrong and Buzz Aldrin walked on the Moon on July 20, 1969. Image Credit: NASA.
LRO went into lunar orbit in June of 2009 and has acquired an extensive set of high-resolution images of the surface, including pairs of images of the same areas taken at different times. Using these before-and-after images (temporal pairs) acquired by the LROC Narrow Angle Camera (NAC), the team identified over 200 impact craters that formed during the LRO mission, ranging in size from about 10 to 140 feet (approximately 3 to 43 meters) in diameter.
Image above: Temporal ratio image formed from two LROC Narrow Angle Camera images (after image divided by the before image) revealing a new 12 meter (~40 foot) diameter impact crater (Latitude: 36.536°N; Longitude: 12.379°E) formed between 25 October 2012 and 21 April 2013, scene is 1300 meters (~4200 feet) wide. New crater and its continuous ejecta are seen as the small bright area in the center, dark areas are the result of material blasted out of the crater to distances much further than previously thought. Image Credits: NASA/GSFC/Arizona State University.
Since impact craters accumulate over time, a heavily cratered surface is older than a region with fewer craters. Knowing the number of craters that form each year is important when estimating absolute ages of the youngest regions. By analyzing the number, size distribution, and the time between each NAC temporal pair, the team estimated the contemporary cratering rate on the moon. During the search, they identified about 30 percent more new craters than anticipated by previous cratering models.
"With this potentially higher impact rate, features with young model ages derived using crater counts and the standard rate may in fact be even younger than previously thought," said Speyerer. "However, to be certain, we need several more years of observations and new crater discoveries."
In addition to discovering new impact craters, the team observed over 47,000 small surface changes, which they call splotches. They are most likely caused by small impacts, according to Speyerer. There are dense clusters of these splotches around new impact sites suggesting that many splotches may be secondary surface changes caused by material thrown out from the primary impact event.
The team estimated their accumulation over time and from measuring their size they inferred how deeply each splotch dug up the surface and thus how long it takes to effectively churn the upper few centimeters (approximately an inch) of the regolith. The team found that 99 percent of the surface would be overturned by splotch formation after about 81,000 years. This rate is over 100 times faster than previous models that considered overturn from micrometeorite impacts alone, and ignored the effects of secondary impacts.
Lunar Reconnaissance Orbiter (LRO) spacecraft. Image Credit: NASA
"The increased churning rate will be important information for future designers of moon bases, said Speyerer. "Surface assets will have to be designed to withstand impacts from small particles moving at up to 500 meters per second (about 1,600 feet per second or 1,100 miles per hour)."
The team also found that the new impact craters are surrounded by complex reflectance patterns related to material ejected during crater formation. Many of the larger impact craters -- those greater than 10 meters in diameter -- exhibit up to four distinct bright or dark reflectance zones.
The research was funded by the LRO project. The Lunar Reconnaissance Orbiter Camera was developed at Arizona State University in Tempe. LRO is managed by NASA's Goddard Space Flight Center in Greenbelt, Maryland, as a project under NASA's Discovery Program. The Discovery Program is managed by NASA's Marshall Spaceflight Center in Huntsville, Alabama, for the Science Mission Directorate at NASA Headquarters in Washington.
NASA's Lunar Reconnaissance Orbiter (LRO): https://www.nasa.gov/mission_pages/LRO/main/index.html
Lunar Reconnaissance Orbiter Camera (LROC): http://lroc.sese.asu.edu/
Images (mentioned), Video (mentioned), Text, Credits: NASA Goddard Space Flight Center/Nancy Jones/Bill Steigerwald.
Publié par Orbiter.ch à 15:09
NASA - Hubble Space Telescope patch.
Oct. 13, 2016
The universe suddenly looks a lot more crowded, thanks to a deep-sky census assembled from surveys taken by NASA's & ESA's Hubble Space Telescope and other observatories.
Astronomers came to the surprising conclusion that there are at least 10 times more galaxies in the observable universe than previously thought.
Image above: This image covers a portion of a large galaxy census called the Great Observatories Origins Deep Survey (GOODS). Image Credits: NASA, ESA, the GOODS Team, and M. Giavalisco (University of Massachusetts, Amherst).
The results have clear implications for galaxy formation, and also helps shed light on an ancient astronomical paradox - why is the sky dark at night?
Hubblecast 96: How many galaxies are there?
In analyzing the data, a team led by Christopher Conselice of the University of Nottingham, U.K., found that 10 times as many galaxies were packed into a given volume of space in the early universe than found today. Most of these galaxies were relatively small and faint, with masses similar to those of the satellite galaxies surrounding the Milky Way. As they merged to form larger galaxies the population density of galaxies in space dwindled. This means that galaxies are not evenly distributed throughout the universe's history, the research team reports in a paper to be published in The Astrophysical Journal.
"These results are powerful evidence that a significant galaxy evolution has taken place throughout the universe's history, which dramatically reduced the number of galaxies through mergers between them - thus reducing their total number. This gives us a verification of the so-called top-down formation of structure in the universe," explained Conselice.
Zoom on galaxies
One of the most fundamental questions in astronomy is that of just how many galaxies the universe contains. The landmark Hubble Deep Field, taken in the mid-1990s, gave the first real insight into the universe's galaxy population. Subsequent sensitive observations such as Hubble's Ultra Deep Field revealed a myriad of faint galaxies. This led to an estimate that the observable universe contained about 200 billion galaxies.
The new research shows that this estimate is at least 10 times too low.
Conselice and his team reached this conclusion using deep-space images from Hubble and the already published data from other teams. They painstakingly converted the images into 3-D, in order to make accurate measurements of the number of galaxies at different epochs in the universe's history. In addition, they used new mathematical models, which allowed them to infer the existence of galaxies that the current generation of telescopes cannot observe. This led to the surprising conclusion that in order for the numbers of galaxies we now see and their masses to add up, there must be a further 90 percent of galaxies in the observable universe that are too faint and too far away to be seen with present-day telescopes. These myriad small faint galaxies from the early universe merged over time into the larger galaxies we can now observe.
Change in density of galaxies over time
"It boggles the mind that over 90 percent of the galaxies in the universe have yet to be studied. Who knows what interesting properties we will find when we discover these galaxies with future generations of telescopes? In the near future, the James Webb Space Telescope will be able to study these ultra-faint galaxies, said Conselice.
The decreasing number of galaxies as time progresses also contributes to the solution for Olbers' paradox (first formulated in the early 1800s by German astronomer Heinrich Wilhelm Olbers): Why is the sky dark at night if the universe contains an infinity of stars? The team came to the conclusion that indeed there actually is such an abundance of galaxies that, in principle, every patch in the sky contains part of a galaxy.
Pan in time
However, starlight from the galaxies is invisible to the human eye and most modern telescopes due to other known factors that reduce visible and ultraviolet light in the universe. Those factors are the reddening of light due to the expansion of space, the universe's dynamic nature, and the absorption of light by intergalactic dust and gas. All combined, this keeps the night sky dark to our vision.
Pan over GOODS south
The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy in Washington, D.C.
For images and more information about Hubble Space Telescope, visit:
Images, Videos, Text, Credits: NASA/Karl Hille/STSI/Ray Villard/ESA/Mathias Jaeger/University of Nottingham/Christopher Conselice.
Best regards, Orbiter.ch
Publié par Orbiter.ch à 14:38
ESA - Mars Express Mission patch.
13 October 2016
This jumble of eroded blocks lies along the distinctive boundary between the Red Planet’s southern highlands and the northern lowlands, with remnants of ancient glaciers flowing around them.
This boundary is one of the oldest and most prominent features on Mars, marking a height difference of several kilometres.
The scene presented here, captured by the high-resolution camera on ESA’s Mars Express on 29 May, is just one example of the terrain found along this ancient boundary, and focuses on part of the Colles Nili region.
Colles Nili in context
‘Colles’ comes from the Latin word for ‘hill’, and indeed this region hosts a swath of such features. They are likely erosional remnants of a former plateau, as suggested with their similarity in height seen in the topography map.
Zooming in to the main colour image and perspective views shows that some of the mounds are surrounded by smooth, layered deposits gently sloping away from the sides of the hills.
Topography of Colles Nili
An even closer look reveals other finer features on the channel floors around the mounds and inside some of the impact craters: series of ridges and troughs.
Both the layered deposits and the ridges and troughs are thought to be associated with buried ice that has since been covered over by wind-blown dust and local debris from the eroding plateau, perhaps as an underlying ice sheet retreated.
Perspective view in Colles Nili
Similar features are found all along the planet-wide boundary and are thought to represent multiple episodes of glaciation within the past several hundred million years.
Later, volcanic dust has blown in from elsewhere to create the striking streaks of dark material seen in various spots, but particularly dominant in the right-hand side of the main colour image.
Looking inside the large impact crater seen in the top right of the main image, and also in the top left of the perspective view, shows this dark material has been piled up into dunes inside the crater, presumably by prevailing winds.
3D view of Colles Nili
Mars Express has been orbiting the Red Planet since 2003. Next week it will play an important role in listening for signals from Schiaparelli, the ExoMars entry, descent and landing demonstrator, as the lander makes its six-minute descent through the atmosphere to the surface.
Mars Express, Schiaparelli mothership Trace Gas Orbiter and NASA’s Mars Reconnaissance Orbiter will record signals from Schiaparelli to confirm its safe arrival, and they will subsequently act as data relays from the surface.
For more about ExoMars see http://www.esa.int/Our_Activities/Space_Science/ExoMars
Looking at Mars: http://www.esa.int/Our_Activities/Space_Science/Mars_Express
Mars Express overview: http://www.esa.int/Our_Activities/Space_Science/Mars_Express_overview
Mars Express 10 year brochure: http://esamultimedia.esa.int/multimedia/publications/BR-312/
Images, Text, Credits: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO/NASA MGS MOLA Science Team.
Best regards, Orbiter.ch
Publié par Orbiter.ch à 05:21
mercredi 12 octobre 2016
NASA & JAXA - Global Precipitation Measurement (GPM) patch.
Oct. 12, 2016
Matthew (Atlantic Ocean)
A NASA rainfall analysis estimated the amount of rainfall generated by Hurricane Matthew when it moved over the Carolinas.
Hurricane Matthew dropped a lot of rain, caused flooding and deaths in the state of North Carolina. Flooding is still widespread in North Carolina. Some rivers in North Carolina such as the Tar and the Neuse Rivers were still rising on Oct. 12.
Image above: This image shows the amount of rainfall dropped by Hurricane Matthew over the life and track of the storm. IMERG real time data covering the period from Sept. 28 through Oct. 10, 2016 show rainfall from Hurricane Matthew before and after its interaction with a frontal boundary. Matthew caused extreme rainfall in North Carolina resulting in over 20 inches (508 mm) of rain. Image Credits: NASA/JAXA, Hal Pierce.
At NASA's Goddard Space Flight Center in Greenbelt, Maryland a rainfall analysis was accomplished using data from NASA's Integrated Multi-satellitE Retrievals for GPM (IMERG). The GPM or Global Precipitation Measurement mission is a joint mission between NASA and the Japanese space agency JAXA.
Rainfall Totals Over Storm Life of Matthew
Video above: This animation shows the amount of rainfall dropped by Hurricane Matthew over the life and track of the storm/ IMERG real time data covering the period from Sept. 28 through Oct. 10, 2016 show rainfall from Hurricane Matthew before and after its interaction with a frontal boundary. Matthew caused extreme rainfall in North Carolina resulting in over 20 inches (508 mm) of rain. Video Credits: NASA/JAXA, Hal Pierce.
The Integrated Multi-satellitE Retrievals for GPM (IMERG) is a unified U.S. algorithm that provides a multi-satellite precipitation product. IMERG is run twice in near-real time with the “Early” multi-satellite product being created at about 4 hours after observation time and a “Late” multi-satellite product provided at about 12 hours after observation time.
This rainfall analysis was created using IMERG real time data covering the period from Sept. 28 through Oct. 10, 2016. The totals included some rain from a low pressure area that moved through the area near the end of September.
Hurricane Matthew’s interaction with a frontal boundary caused extreme rainfall in North Carolina resulting in over 20 inches (508 mm) of rain being reported in North Carolina. The area was already saturated before Hurricane Matthew arrived. Heavy rainfall from a slow moving low and frontal system moved through during the last week of September. Maximum rainfall total estimates for the real-time IMERG product have been adjusted to reflect observed values.
On Wednesday, Oct. 12 the National Weather Service (NWS) in Wilmington, North Carolina (NC) reported "All major area rivers will remain above flood stage throughout this upcoming week. At 10:59 a.m. EDT on Oct. 12, the North Carolina Department of Transportation reported numerous flooded roads persisting across much the coastal plain of North Carolina. This being the result of heavy rainfall totaling 5 to 12 inches across the region in the last 36 hours. Many roads are impassable, barricaded or washed away. Some neighborhoods are cut off. Swamps, creeks and rivers are still rising flooding even more areas and slowing the recession of high water. People in the warned area should not travel and be prepared for widespread flooding of a magnitude not seen in many years. If asked to evacuate please do so."
Hurricane Matthew's Path Tracked and Rainfall Totals Shown
Video above: In this animation Hurricane Matthew travels up the east coast from Florida to the Carolinas. On October 8, 2016 Matthew (still a category 2 hurricane) dumps massive amounts of rain throughout the southeast dousing North and South Carolina. GPM then flies over the area revealing precipitation rates on the ground. As we zoom in closer, GPM's DPR sensor reveals a curtain of 3D rain rates within the massive weather system. Video Credits: NASA SVS.
Further south, a Flood Warning has been extended for the following rivers: Cape Fear at Elizabethtown affecting Bladen County NC; Cape Fear at Lock and Dam 1 affecting Bladen County NC; Black Creek at Quinby affecting Darlington and Florence Counties South Carolina (SC); Lynches at Effingham affecting Florence County SC.
In addition, a Flood Warning continues for the following rivers: Cape Fear at William O. Huske Lock and Dam 3 affecting Bladen County NC; Northeast Cape Fear near Burgaw affecting Pender County NC; Lumber Near Lumberton affecting Robeson County NC; Little Pee Dee at Galivants Ferry affecting Dillon, Horry and Marion Counties, SC; Waccamaw at Conway affecting Horry County SC; Great Pee Dee at Pee Dee affecting Marion and Florence Counties SC; and Black at Kingstree affecting Williamsburg County SC.
For updated River Forecasts from the NWS, visit: http://water.weather.gov/ahps2/forecasts.php?wfo=ilm
For more information about GPM (Global Precipitation Measurement): http://www.nasa.gov/mission_pages/GPM/main/index.html and http://global.jaxa.jp/projects/sat/gpm/
Image (mentioned), Videos (mentioned), Text, Credits: NASA's Goddard Space Flight Center/Hal Pierce/Rob Gutro.
Publié par Orbiter.ch à 16:43
ISS - International Space Station patch.
Oct. 12, 2016
The old adage of “you are what you eat” has an even greater meaning when preparing for long- duration travel to deep space, where storage is tight and fresh food is limited.
“Understanding the relationship of diet with crew health is critical for future exploration missions, where nutrition will be a key countermeasure in mitigating the negative effects of spaceflight on the body,” said Scott M. Smith, nutritionist at NASA.
The International Space Station Food Intake Tracker (ISS FIT) iPad app, recently delivered to the space station, simplifies the way astronauts track their meals. The ISS FIT app gives astronauts real-time feedback about their dietary habits and offers greater insight for physicians and researchers on Earth looking to keep crews healthy and fit.
Image above: NASA astronaut Michael Hopkins, Expedition 37 flight engineer, holds a spoon containing a piece of food in the Node 2 - Harmony - module of the International Space Station. Image Credit: NASA.
“We’ve recently documented that astronauts can protect their bones with good nutrition and exercise,” said Smith. “This app puts the tools in their hands to track this information in real time.”
While similar to apps available on Earth, the ISS FIT is designed specifically for use in space. With days numbered from one to 365, the food database includes foods available on the space station, including those from international partner agencies. The app does not require internet access to sync with the food database as many of the apps available on Earth require. The app reports nutrients specifically of concern for astronauts (and often terrestrial beings), ensuring adequate calorie consumption, minimizing sodium intake and maintaining hydration to reduce kidney stone risk.
The app, developed through NASA’s Center of Excellence for Collaborative Innovation, used crowdsourcing techniques hosted by TopCoder. Designed for use on the space station, the solution had to meet strict criteria, offer multiple user options and work without internet connectivity. The app allows crew members to record foods available on the space station. It gives astronauts options to record foods from a checklist, search tool, using audio recording, taking photos or scanning barcodes, if available.
Image above: Japan Aerospace Exploration Agency (JAXA) astronaut Koichi Wakata, Expedition 18/19 flight engineer, is pictured near food and drink containers floating freely in the Harmony node of the International Space Station. Image Credit: NASA.
“We’re looking for astronauts to record all of their intake – every food, every meal, every day during their six-month stays on the International Space Station,” said Dr. Sara Zwart, nutritionist at Johnson Space Center in Houston, and lead on the project. “It had to be easy, quick and accurate.”
The app provides real-time information on key nutrients including calories, sodium and fluid, allowing crew members to see at lunch that they need to consume more water later in the day, for example. Fluid intake is important for hydration but specifically for reducing kidney stone risk, which is higher during flight.
The app replaces a weekly computer questionnaire, which provided an estimate of dietary intake over the week. The detailed data not only helps crews in real time each day, but also will allow for more detailed assessments of dietary intake during flight and relating these to other crew health concerns like bone loss and vision changes.
Keep up with the International Space Station, and its research and crews, at: http://www.nasa.gov/station
Learn more about NASA’s Human Research Program at: http://www.nasa.gov/hrp
Information about Human Health and Performance is available at: http://www.nasa.gov/hhp
ISS - Expedition 18: https://www.nasa.gov/mission_pages/station/expeditions/expedition18/index.html
ISS - Expedition 37: https://www.nasa.gov/mission_pages/station/expeditions/expedition37/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.
Publié par Orbiter.ch à 16:23
NASA & ESA - Herschel Observatory patch.
Oct. 12, 2016
Life exists in a myriad of wondrous forms, but if you break any organism down to its most basic parts, it's all the same stuff: carbon atoms connected to hydrogen, oxygen, nitrogen and other elements. But how these fundamental substances are created in space has been a longstanding mystery.
Now, astronomers better understand how molecules form that are necessary for building other chemicals essential for life. Thanks to data from the European Space Agency's Herschel Space Observatory, scientists have found that ultraviolet light from stars plays a key role in creating these molecules, rather than "shock" events that create turbulence, as was previously thought.
Scientists studied the ingredients of carbon chemistry in the Orion Nebula, the closest star-forming region to Earth that forms massive stars. They mapped the amount, temperature and motions of the carbon-hydrogen molecule (CH, or “methylidyne” to chemists), the carbon-hydrogen positive ion (CH+) and their parent: the carbon ion (C+). An ion is an atom or molecule with an imbalance of protons and electrons, resulting in a net charge.
Image above: The dusty side of the Sword of Orion is illuminated in this striking infrared image from ESA’s Hershel Space Observatory. Within the inset image, the emission from ionized carbon atoms (C+) is overlaid in yellow. Image Credits: ESA/NASA/JPL-Caltech.
"On Earth, the sun is the driving source of almost all the life on Earth. Now, we have learned that starlight drives the formation of chemicals that are precursors to chemicals that we need to make life," said Patrick Morris, first author of the paper and researcher at the Infrared Processing and Analysis Center at Caltech in Pasadena.
In the early 1940s, CH and CH+ were two of the first three molecules ever discovered in interstellar space. In examining molecular clouds -- assemblies of gas and dust -- in Orion with Herschel, scientists were surprised to find that CH+ is emitting rather than absorbing light, meaning it is warmer than the background gas. The CH+ molecule needs a lot of energy to form and is extremely reactive, so it gets destroyed when it interacts with the background hydrogen in the cloud. Its warm temperature and high abundance are therefore quite mysterious.
Why, then, is there so much CH+ in molecular clouds such as the Orion Nebula? Many studies have tried to answer this question before, but their observations were limited because few background stars were available for studying. Herschel probes an area of the electromagnetic spectrum -- the far infrared, associated with cold objects -- that no other space telescope has reached before, so it could take into account the entire Orion Nebula instead of individual stars within. The instrument they used to obtain their data, HIFI, is also extremely sensitive to the motion of the gas clouds.
One of the leading theories about the origins of basic hydrocarbons has been that they formed in "shocks," events that create a lot of turbulence, such as exploding supernovae or young stars spitting out material. Areas of molecular clouds that have a lot of turbulence generally create shocks. Like a large wave hitting a boat, shock waves cause vibrations in material they encounter. Those vibrations can knock electrons off atoms, making them ions, which are more likely to combine. But the new study found no correlation between these shocks and CH+ in the Orion Nebula.
Herschel data show that these CH+ molecules were more likely created by the ultraviolet emission of very young stars in the Orion Nebula, which, compared to the sun, are hotter, far more massive and emit much more ultraviolet light. When a molecule absorbs a photon of light, it becomes "excited" and has more energy to react with other particles. In the case of a hydrogen molecule, the hydrogen molecule vibrates, rotates faster or both when hit by an ultraviolet photon.
It has long been known that the Orion Nebula has a lot of hydrogen gas. When ultraviolet light from large stars heats up the surrounding hydrogen molecules, this creates prime conditions for forming hydrocarbons. As the interstellar hydrogen gets warmer, carbon ions that originally formed in stars begin to react with the molecular hydrogen, creating CH+. Eventually the CH+ captures an electron to form the neutral CH molecule.
"This is the initiation of the whole carbon chemistry," said John Pearson, researcher at NASA's Jet Propulsion Laboratory, Pasadena, California, and study co-author. "If you want to form anything more complicated, it goes through that pathway."
Scientists combined Herschel data with models of molecular formation and found that ultraviolet light is the best explanation for how hydrocarbons form in the Orion Nebula.
Herschel Observatory. Image Credit: ESA
The findings have implications for the formation of basic hydrocarbons in other galaxies as well. It is known that other galaxies have shocks, but dense regions in which ultraviolet light dominates heating and chemistry may play the key role in creating fundamental hydrocarbon molecules there, too.
"It's still a mystery how certain molecules get excited in the cores of galaxies," Pearson said. "Our study is a clue that ultraviolet light from massive stars could be driving the excitation of molecules there, too."
Herschel is a European Space Agency mission, with science instruments provided by consortia of European institutes and with important participation by NASA. While the observatory stopped making science observations in April 2013, after running out of liquid coolant as expected, scientists continue to analyze its data. NASA's Herschel Project Office is based at NASA’s Jet Propulsion Laboratory, Pasadena, California. JPL contributed mission-enabling technology for two of Herschel's three science instruments. The NASA Herschel Science Center, part of IPAC, supports the U.S. astronomical community. Caltech manages JPL for NASA.
More information about Herschel is available at:
Images (mentioned), Text, Credits: NASA/Tony Greicius/JPL/Elizabeth Landau.
Publié par Orbiter.ch à 16:06
ESO - European Southern Observatory logo.
12 October 2016
VISTA finds remains of archaic globular star cluster
Variable stars close to the galactic centre
Ancient stars, of a type known as RR Lyrae, have been discovered in the centre of the Milky Way for the first time, using ESO’s infrared VISTA telescope. RR Lyrae stars typically reside in ancient stellar populations over 10 billion years old. Their discovery suggests that the bulging centre of the Milky Way likely grew through the merging of primordial star clusters. These stars may even be the remains of the most massive and oldest surviving star cluster of the entire Milky Way.
A team led by Dante Minniti (Universidad Andrés Bello, Santiago, Chile) and Rodrigo Contreras Ramos (Instituto Milenio de Astrofísica, Santiago, Chile) used observations from the VISTA infrared survey telescope, as part of the Variables in the Via Lactea (VVV) ESO public survey, to carefully search the central part of the Milky Way. By observing infrared light, which is less affected by cosmic dust than visible light, and exploiting the excellent conditions at ESO’s Paranal Observatory, the team was able to get a clearer view of this region than ever before. They found a dozen ancient RR Lyrae stars at the heart of the Milky Way that were previously unknown.
RR Lyrae stars in the constellation of Sagittarius
Our Milky Way has a densely populated centre — a feature common to many galaxies, but unique in that it is close enough to study in depth. This discovery of RR Lyrae stars provides compelling evidence that helps astronomers decide between two main competing theories for how nuclear bulges form .
RR Lyrae stars are typically found in dense globular clusters. They are variable stars, and the brightness of each RR Lyrae star fluctuates regularly. By observing the length of each cycle of brightening and dimming in an RR Lyrae, and also measuring the star’s brightness, astronomers can calculate its distance .
Wide-field view of the Centre of the Milky Way
Unfortunately, these excellent distance-indicator stars are frequently outshone by younger, brighter stars and in some regions they are hidden by dust. Therefore, locating RR Lyrae stars right in the extremely crowded heart of the Milky Way was not possible until the public VVV survey was carried out using infrared light. Even so, the team described the task of locating the RR Lyrae stars in amongst the crowded throng of brighter stars as “daunting”.
Their hard work was rewarded, however, with the identification of a dozen RR Lyrae stars. Their discovery indicate that remnants of ancient globular clusters are scattered within the centre of the Milky Way’s bulge.
Variable RR Lyrae stars
Rodrigo Contreras Ramos elaborates: “This discovery of RR Lyrae Stars in the centre of the Milky Way has important implications for the formation of galactic nuclei. The evidence supports the scenario in which the nuclear bulge was originally made out of a few globular clusters that merged.”
The theory that galactic nuclear bulges form through the merging of globular clusters is contested by the competing hypothesis that these bulges are actually due to the rapid accretion of gas. The unearthing of these RR Lyrae stars — almost always found in globular clusters — is very strong evidence that part of the Milky Way's nuclear bulge did in fact form through merging. By extension, all other similar galactic bulges may have formed the same way.
Zoom on the galactic centre
Not only are these stars powerful evidence for an important theory of galactic evolution, they are also likely to be over 10 billion years old — the dim, but dogged survivors of perhaps the oldest and most massive star cluster within the Milky Way.
Pan across the galactic centre
 The nuclear stellar bulge is the compact component in the innermost regions of the Milky Way (and other galaxies) extending to a size of about 400 light-years.
 RR Lyrae stars, like some other regular variables such as Cepheids, show a simple relationship between how quickly they change in brightness and how luminous they are. Longer periods mean brighter stars. This period-luminosity relationship can be used to deduce the distance of a star from its period of variation and its apparent brightness.
This research was presented in a paper to appear in The Astrophysical Journal Letters.
The team is composed of D. Minniti (Instituto Milenio de Astrofísica, Santiago, Chile; Departamento de Física, Universidad Andrés Bello, Santiago, Chile; Vatican Observatory, Vatican City State; Centro de Astrofisica y Tecnologias Afines - CATA), R. Contreras Ramos (Instituto Milenio de Astrofísica, Santiago, Chile; Pontificia Universidad Católica de Chile, Instituto de Astrofísica, Santiago, Chile), M. Zoccali (Instituto Milenio de Astrofísica, Santiago, Chile; Pontificia Universidad Católica de Chile, Instituto de Astrofísica, Santiago, Chile), M. Rejkuba (European Southern Observatory, Garching bei München, Germany; Excellence Cluster Universe, Garching, Germany), O.A. Gonzalez (UK Astronomy Technology Centre, Royal Observatory, Edinburgh, UK), E. Valenti (European Southern Observatory, Garching bei München, Germany), F. Gran (Instituto Milenio de Astrofísica, Santiago, Chile; Pontificia Universidad Católica de Chile, Instituto de Astrofísica, Santiago, Chile)
ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre European Extremely Large Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.
Research paper: http://www.eso.org/public/archives/releases/sciencepapers/eso1636/eso1636a.pdf
Variables in the Via Lactea (VVV) ESO public survey: https://vvvsurvey.org/
VISTA infrared survey telescope: http://www.eso.org/vista/
ESO’s Paranal Observatory: http://www.eso.org/public/teles-instr/paranal/
Images, Text, Credits: ESO/VVV Survey/D. Minniti/IAU and Sky & Telescope/Digitized Sky Survey 2. Acknowledgment: Davide De Martin and S. Guisard (www.eso.org/~sguisard)/Videos: ESO/VVV Survey/D. Minniti/Digitized Sky Survey 2, N. Risinger (skysurvey.org. Acknowledgment: Davide De Martin and S. Guisard (www.eso.org/~sguisard), Music: Johan B. Monell (www.johanmonell.com)/5th Dimension.
Publié par Orbiter.ch à 09:21