mardi 19 septembre 2017

Astronomy Gear Work and Muscle Scans on Tuesday’s Schedule












ISS - Expedition 53 Mission patch.

September 19, 2017

Auroras seen from International Space Station. Animation Credit: NASA

The Expedition 53 crew worked on a variety of astronomy gear today that looks at meteors in Earth orbit and harmful radiation from deep space. The crew also explored how microgravity affects human bones and muscles.

Flight Engineer Mark Vande Hei worked on a camera for the Meteor experiment, ongoing since March 2016, which peers out of a specialized window in the Destiny laboratory module. The camera observes meteors and meteor showers and analyzes the imagery to determine their physical and chemical composition.


Image above: The spectacular aurora borealis, or the “northern lights,” over Canada is sighted from the space station near the highest point of its orbital path. The station’s main solar arrays are seen in the left foreground. Image Credit: NASA.

Flight Engineer Joe Acaba installed the Fast Neutron Spectrometer in the Unity module today to explore a new technique that measures deep space radiation. The new technology may be used to provide a more accurate assessment of the mixed radiation future crews and spacecraft may be exposed to.

Cosmonaut Sergey Ryazanskiy strapped himself into the Muscle Atrophy Research and Exercise System (MARES) chair today for a look at his calf muscle and tendons. Flight Engineer Paolo Nespoli assisted Ryazanskiy into the MARES chair and Commander Randy Bresnik collected ultrasound imagery of his leg. The data is being collected for the Sarcolab-3 experiment that is observing space-induced chemical and structural changes in muscle fibers.

Related links:

Meteor: https://www.nasa.gov/mission_pages/station/research/experiments/1323.html

Fast Neutron Spectrometer: https://www.nasa.gov/mission_pages/station/research/experiments/2103.html

Sarcolab-3: https://www.nasa.gov/mission_pages/station/research/experiments/738.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), Animation (mentioned), Text, Credits: NASA/Mark Garcia.

P.S:: 6000 th article since the creation of this blog (2010).

Best regards, Orbiter.ch

NASA Small Satellite Promises Big Discoveries












NASA Goddard Space Flight Center logo.

Sept. 19, 2017

Small satellites provide a cheap, responsive alternative to larger, more expensive satellites. As demand grows, engineers must adapt these “nanosatellites” to provide greater data returns. NASA, in collaboration with educational partners, targets 2021 for the launch of an innovative CubeSat that addresses these challenges.

CubeSats consist of standardized cubed units, or U’s, typically up to 12U. A 1U CubeSat is 10 cubic centimeters and can weigh as little as three pounds. They launch as auxiliary payloads on existing missions, providing a cost-effective opportunity for small-scale research projects. The satellites spend an average 90 days in orbit before falling to Earth and burning up in the atmosphere. Since their inception, CubeSats have been a boon to small satellite research and development.

video
UF-Radsat's Orbit

Video above: UF-Radsat, in a highly elliptical orbit, will communicate with the Tracking and Data Relay Satellite (TDRS) constellation and the Near Earth Network. Video Credits: NASA's Goddard Space Flight Center.

Typically, NASA’s Near Earth Network (NEN) provides direct-to-ground communication for CubeSats. Communication only occurs when a satellite passes over one of the NEN antennas, located around the globe. A team of engineers and scientists from NASA's Goddard Space Flight Center in Greenbelt, Maryland, NASA’s Kennedy Space Center in Florida and the University of Florida are collaborating on a 12U CubeSat that will be the first to interface with NASA’s Space Network, which provides continuous communications services. The University of Florida RadSat (UF-RadSat) is a collaborative design effort of NASA interns from several universities across the country, who have filed multiple invention disclosures for its technologies. The satellite will circle Earth in a geosynchronous transfer orbit, communicating with three Tracking and Data Relay Satellites (TDRS) and NEN ground stations. This methodology provides almost constant data coverage — an innovation that could be useful to many future CubeSat missions.

“The purpose of our mission is to simultaneously provide critical engineering data to strengthen NASA missions while demonstrating the operational advantages of near-continuous communications between CubeSats and the TDRS constellation,” said Harry Shaw, a NASA co-investigator on the project. “The work we execute for our CubeSat mission will enable this communications option for other CubeSats.”


Image above: Dr. Reyhan Baktur, a co-investigator from Utah State University, poses with a glass component of UF-Radsat’s solar array. Image Credits: Utah State University.

UF-RadSat is more than just a communications demonstration. NASA will also run two radiation experiments aboard the CubeSat. The first experiment was created by a team at the University of Florida under the direction of Michele Manuel, department chair of Materials Science and Engineering. The team developed a magnesium and gadolinium alloy with radiation mitigating properties. The alloy, stronger and lighter than steel or aluminum, will be tested for its on-orbit effectiveness in trapping thermal neutrons, a radiation health hazard. The experiment will determine the metal’s usefulness in mitigating the risks posed by radiation to future human spaceflight endeavors.

The second experiment aboard UF-RadSat originates at Goddard. Ray Ladbury and Jean-Marie Lauenstein, scientists from Goddard’s Radiation Effects Group, will assess the reliability of power metal-oxide-semiconductor field-effect transistors (MOSFETs) under the harsh radiation conditions of space. Spacecraft power systems use MOSFETs to amplify or switch electronic signals. They can be damaged or destroyed by the radiation environment in space. The experiment will contribute to assessing and improving MOSFETs on-orbit reliability and provide valuable insight into single-event gate rupture, a primary radiation-induced failure in MOSFETs.

“Since its beginnings in the late 1950s, NASA has played a key and influential role in advancing space capabilities,” said Pat Patterson, the Small Satellite Conference committee chair. “The same can be said for NASA’s influence on the rise of small satellites, as NASA is now using these technologies to continue to advance scientific and human exploration, reduce the cost of new space missions, and expand access to space.”


Animation above: UF-Radsat will deploy its parabolic mesh high-gain antenna once placed in orbit. Animation Credits: NASA's Goddard Space Flight Center.

The research aboard UF-RadSat continues NASA’s legacy in the small satellite community. Nanosatellites like UF-RadSat reflect NASA’s dedication to cost-effective research at the cutting edge of communications technology.

NASA interns from University of Maryland, College Park; Morgan State University; University of Puerto Rico; University of Maryland, Baltimore County; University of Colorado; and University of Florida collaborated on UF-Radsat.

CubeSats. Image Credit: NASA

Small satellites, including CubeSats, are playing an increasingly larger role in exploration, technology demonstration, scientific research and educational investigations at NASA, including: planetary space exploration; Earth observations; fundamental Earth and space science; and developing precursor science instruments like cutting-edge laser communications, satellite-to-satellite communications and autonomous movement capabilities.

To learn more about NASA’s CubeSats, visit http://www.nasa.gov/mission_pages/cubesats/index.html

Related links:

SCaN (Space Communications and Navigation): https://www.nasa.gov/directorates/heo/scan/index.html

Small Satellite Missions: http://www.nasa.gov/mission_pages/smallsats

TDRS (Tracking and Data Relay Satellite): https://www.nasa.gov/mission_pages/tdrs/home/index.html

CubeSats: http://www.nasa.gov/cubesats/

Near Earth Network (NEN): https://www.nasa.gov/directorates/heo/scan/services/networks/txt_nen.html

Space Network: https://www.nasa.gov/directorates/heo/scan/services/networks/txt_sn.html

NASA's Goddard Space Flight Center: https://www.nasa.gov/goddard

NASA’s Kennedy Space Center: https://www.nasa.gov/centers/kennedy/home/index.html

Images (mentioned), Animation (mentioned), Video (mentioned), Text, Credits: NASA/Rob Garner/Goddard Space Flight Center, by Danny Baird.

Greetings, Orbiter.ch

NASA Looks Within Category 5 Hurricane Maria Before and After First Landfall














NOAA & NASA - GOES Mission logo / NASA - EOS Aqua Mission logo / NASA & JAXA - GPM Mission patch.

Sept. 19, 2017

Maria (Atlantic Ocean)

Satellite data is enabling forecasters to look inside and outside of powerful Hurricane Maria. A NASA animation of satellite imagery shows Hurricane Maria's first landfall on the island of Dominica. NASA's GPM satellite provided a 3-D look at the storms within that gave forecasters a clue to Maria strengthening into a Category 5 storm, and NASA's Aqua satellite gathered temperature data on the frigid cloud tops of the storm.


Image above: This image of Category 5 Hurricane Maria moving through the eastern Caribbean Sea was taken on Sept. 19 at 11 a.m. EDT from NOAA's GOES East satellite. Image Credits: NASA/NOAA GOES Project.

Maria's First Landfall

On Monday, Sept. 18 at 9:35 p.m. AST/EDT the National Hurricane Center reported that Maria made landfall on Dominica as a category 5 hurricane. Radar data from Martinique and Air Force Reserve Hurricane Hunter aircraft reports indicated that Maria made landfall on Dominica around 9:15 p.m. AST/EDT (0115 UTC) with estimated winds of 160 mph (260 kph). Dominica is an island in the Caribbean Sea that has mountainous terrain, natural hot springs and tropical rainforests.

NASA Puts Maria's Past Track in Motion

An animation of NOAA's GOES East satellite imagery from Sept. 15 at 7:45 a.m. EDT (1145 UTC) to Sept. 19 ending at 4:45 a.m. EDT (0845 UTC) showed Hurricane Jose moving north along the U.S. East coast and Hurricane Maria move through the Leeward Islands and strengthen to a Category 5 hurricane. The animation shows Maria's landfall in Domenica. The imagery revealed a clear, cloudless eye.

video
GOES-East Video of Jose and Maria

Video above: This animation of NOAA's GOES East satellite imagery from Sept. 15 at 7:45 a.m. EDT (1145 UTC) to Sept. 19 ending at 4:45 a.m. EDT (0845 UTC) shows Hurricane Jose moving north along the U.S. East coast and Hurricane Maria moving through the Leeward Islands and strengthening to a Category 5 hurricane. Video Credits: NASA/NOAA GOES Project.

NOAA manages the GOES Series of satellites. The animation was created by the NASA/NOAA GOES Project at NASA's Goddard Space Flight Center in Greenbelt, Maryland.

NASA's 3-D Look at Maria


Image above: On Sept. 18, the Global Precipitation Measurement (GPM) satellite saw an impressively tall cell of precipitation in Hurricane Maria that stretched into the lower stratosphere at 16.75 km altitude. Image Credits: NASA / JAXA, Owen Kelley.

Also at NASA Goddard, a 3-D image of Hurricane Maria was made to understand what was happening within the storm. The dual-frequency radar on the Global Precipitation Measurement (GPM) satellite saw an impressively tall thunderstorms cell of precipitation in the compact eyewall of Hurricane Maria on Monday, Sept.18, 2017. "Enough water vapor was condensing into rain inside of this cell that rapid updrafts developed, rapid enough to lift the precipitation until it froze and then even higher until it penetrated into the lower stratosphere at 16.75 km altitude," said Owen Kelley of NASA Goddard's Precipitation Processing System..

"This tall cell (also known as a "hot tower") was part of a sequence of such cells that were seen by infrared satellite instruments, such as the one on the recently launched GOES-16 satellite. Meanwhile, Maria put on an unexpectedly fast intensification from category 1 to category 3 on the Saffir-Simpson scale on Monday (Sept. 18)."

Research conducted at NASA, at the University of Maryland, Baltimore County, and elsewhere suggests that a sequence of hot towers, also known as a "convective burst," is one a way to detect that a hurricane's heat engine going into high gear.  The end result is intensified winds circling the eye at the ocean's surface.

Maria continued to intensify after GPM passed overhead and reached Category 5 status that night.

A Stunning Infrared View of Maria

On Sept. 19 at 2:15 a.m. EDT (0615 UTC) the Moderate Resolution Imaging Spectroradiometer or MODIS instrument aboard NASA's Aqua satellite analyzed Maria's cloud top temperatures in infrared light.


Image above: This infrared image of Hurricane Maria's frigid cloud top temperatures was captured by the MODIS instrument aboard NASA's Aqua satellite on Sept. 19 at 2:15 a.m. EDT (0615 UTC) as it moved through the Leeward Islands. Image Credits: NASA/NRL.

MODIS found cloud top temperatures of strong thunderstorms in Maria's eyewall as cold as or colder than minus 80 degrees Fahrenheit (minus 62.2 Celsius). Cloud top temperatures that cold indicate strong storms that have the capability to create heavy rain.

Warnings and Watches in Effect

The National Hurricane Center warned "potentially catastrophic Hurricane Maria continues west-northwestward toward the Virgin Islands and Puerto Rico."

A Hurricane Warning is in effect for Guadeloupe, Dominica, St. Kitts, Nevis, and Montserrat, the U.S. Virgin Islands, the British Virgin Islands, Puerto Rico, Culebra, and Vieques. A Tropical Storm Warning is in effect for Antigua and Barbuda, Saba and St. Eustatius, St. Maarten, Anguilla and Martinique.

A Hurricane Watch is in effect for Saba and St. Eustatius, St. Maarten, St. Martin and St. Barthelemy, Anguilla, Isla Saona to Puerto Plata.

Maria's Location and Status on Sept. 19

At 11 a.m. AST/EDT (1500 UTC), the eye of Hurricane Maria was located near 16.3 degrees north latitude and 63.1 degrees west longitude. That's about 115 miles (180 k) west of Guadeloupe and about 150 miles (240 km) southeast of St. Croix.

Maria was moving toward the west-northwest near 10 mph (17 kph), and this general motion is expected to continue through Wednesday night, Sept. 20. Maximum sustained winds are near 160 mph (260 kph) with higher gusts.  Maria is a potentially catastrophic category 5 hurricane on the Saffir-Simpson Hurricane Wind Scale.  Some fluctuations in intensity are likely during the next day or two, but Maria is forecast to remain an extremely dangerous category 4 or 5 hurricane until it moves near or over the Virgin Islands and Puerto Rico.

The minimum central pressure based on data from an Air Force Reserve Hurricane Hunter aircraft is 927 millibars.

On the forecast track, the eye of Maria will move over the northeastern Caribbean Sea today, Sept. 19 and then pass near or over the Virgin Islands and Puerto Rico on Wednesday, Sept. 20.

For updates and effects on wind, storm surge and rainfall, visit: http://www.nhc.noaa.gov/

Aqua Satellite: https://www.nasa.gov/mission_pages/aqua/index.html

GOES (Geostationary Environmental Operational Satellites): http://www.nasa.gov/goes/

GPM (Global Precipitation Measurement): http://www.nasa.gov/mission_pages/GPM/main/index.html

Hurricanes: http://www.nasa.gov/mission_pages/hurricanes/main/index.html

Images (mentioned), Video (mentioned), Text, Credits: NASA's Goddard Space Flight Center, by Rob Gutro.

Greetings, Orbiter.ch

Solar antics

NASA & ESA - SOHO Mission patch.

19 September 2017

The Sun’s recent activity has caught the interest of scientists and space weather forecasters worldwide, highlighting the need to keep a watchful eye on our star and its awesome power.

On 6 and 10 September, our Sun produced a pair of solar flares, the strongest observed in over 10 years. They were accompanied by huge eruptions of billions of tonnes of matter into space.

video
Mass ejection seen by SOHO

While many such eruptions fall back onto the hot surface, these two did not and became ‘coronal mass ejections’ (CMEs) – clouds of electrically charged atomic particles escaping the Sun and expanding into interplanetary space.

This cloud containing protons, electrons and heavy ions can be detected by sensors on satellites around our planet and on probes in interplanetary space.

The flares and accompanying CMEs burst out of an ‘active region’ on the Sun’s photosphere, which is the surface we see from Earth.

“Appearance of this active region producing strong flares and several CMEs was very interesting after months of very low solar activity,” says Juha-Pekka Luntama, responsible for space weather within ESA’s Space Situational Awareness office.

“Although these eruptions are very difficult to predict, and the active region that produced these events has now rotated around to the far side of the Sun, we are keeping watch on the situation, particularly when the active region rotates back into view.”

First big event

The first eruption occurred on 6 September, and produced a severe geomagnetic storm when it reached Earth on the evening of 7 September. Its arrival was detected by a number of ESA and NASA spacecraft watching our Sun or orbiting Earth.

ESA/NASA Sun-watching SOHO spacecraft

The arrival also gave rise to increased auroras on 7 and 8 September, visible as far south as northern Germany in Europe and the northern USA in North America.

The flare and CME were accompanied by a flood of energetic atomic particles from the Sun. These could be detected by satellites in orbit, but not at ground level owing to the shielding effect of our atmosphere.

Second big event

The second eruption occurred on 10 September (see video above). This was associated with a large solar flare that also emitted a strong pulse of X-rays and a flood of extremely high-speed protons, some travelling near to the speed of light.

This CME was faster than the first one, but it, too, travelled off the direct Sun–Earth path and only a tail end of it washed across our planet on 12 September.

This event caused a strong increase in energetic particles, with increased levels of radiation detected at Earth’s surface by monitoring networks, and a moderate geomagnetic storm was observed on 12 and 13 September.

Effects on satellites and communications

The radiation that arrived in advance of the second CME was sufficient to cause the navigation cameras on some satellites to be temporarily blinded, and was expected to disrupt radio communications temporarily at high latitudes.

In one case, ESA’s Integral satellite, an orbiting gamma-ray observatory whose instrument electronics are especially sensitive to radiation, had to rely on its onboard autonomy to configure its instruments into a ‘safe mode’, to wait until radiation levels fell.

Integral

“Our instruments were off during one 64-hour revolution, which unfortunately meant that we lost some high-priority observing time,” says Integral operations manager Richard Southworth. “They instruments were reactivated with no sign of damage.”

ESA’s Gaia star mapper also experienced some comparatively minor effects.

Gaia mapping the stars of the Milky Way

“Gaia’s telescope temporarily experienced a very high number of ‘false’ star detections, which resulted in correspondingly data generation and some small variations in the spacecraft’s attitude,” says operations manager David Milligan.

“The false detections can be removed from the data catalogue and Gaia continues working very well.”

Keep an eye on the Sun

The second event was also notable because it emanated from an active region on the Sun that had already rotated across the disc as seen from Earth, and disappeared out of view very soon afterwards.

“We have no spacecraft on that side of the Sun to keep an eye on current activity,” says Juha-Pekka.

“What we really need are more ways to view the side of the Sun that is rotating to face Earth, which would enable us to improve our forecasting and predictions.”

ESA is already defining a future mission to the Sun that would improve our space weather monitoring and forecasting capability.

Related articles:

Two Significant Solar Flares Imaged by NASA's SDO
https://orbiterchspacenews.blogspot.ch/2017/09/two-significant-solar-flares-imaged-by.html

Sun Erupts With Significant Flare
https://orbiterchspacenews.blogspot.ch/2017/09/sun-erupts-with-significant-flare.html

Related links:

ESA Space Weather Service Network: http://swe.ssa.esa.int/

ESA's SOHO home page: http://sohowww.estec.esa.nl/

ESA Space Environments and Effects: http://space-env.esa.int/

International GNSS Service (IGS): http://igscb.jpl.nasa.gov/

International Space Environment Service: http://www.ises-spaceweather.org/

European Space Weather Portal: http://www.spaceweather.eu/

The Sun now: http://www.esa.int/Our_Activities/Space_Science/The_Sun_now

Images (mentioned), Video (mentioned), Text, Credits: ESA/D. Ducros /ATG medialab; Sun: SOHO (ESA & NASA)/ESO/S. Brunier.

Greetings, Orbiter.ch

How Herschel unlocked the secrets of star formation












ESA - Hershel Mission patch.

19 September 2017

Surveying the sky for almost four years to observe the glow of cold cosmic dust embedded in interstellar clouds of gas, the Herschel Space Observatory has provided astronomers with an unprecedented glimpse into the stellar cradles of our Galaxy. As a result, giant strides have been taken in our understanding of the physical processes that lead to the birth of stars and their planetary systems.

video
Herschel: star formation

Video above: Herschel: star formation. Video Credits: ESA/Herschel/NASA/JPL-Caltech; acknowledgement: T. Pyle & R. Hurt (JPL-Caltech).

"We are made of star stuff," the astronomer Carl Sagan famously said, as the atoms that make us – our bodies, our homes, our planet – come largely from previous generations of stars.

Indeed, stars and planets are continually born in the densest and coldest pockets of molecular clouds, where they take shape from a mixture that consists largely of gas but also contains small amounts of dust mixed in.

As part of a cosmic recycling process, stars also return their re-processed material after their demise, enriching this interstellar medium that pervades all galaxies, including our Milky Way, with heavy elements produced in their nuclear furnaces and during the violent explosions that end the lives of the most massive stars.


Image above: Herschel's view of the W3/W4/W5 complex. Image Credits: ESA/Herschel/NASA/JPL-Caltech, CC BY-SA 3.0 IGO; Acknowledgement: R. Hurt (JPL-Caltech).

Astronomers have long been aware that stars take shape as interstellar material comes together and condenses, then breaks up into fragments – the seeds of future stars – but many details of this complex process remained unclear until not so long ago.

What turned the tables in the understanding of how stars are born was ESA's Herschel Space Observatory, a trailblazing mission that was launched in 2009 and operated until 2013.

A unique observatory

Making sense of the Universe we live in is a fascinating endeavour forged over thousands of years by the incessant work of countless dedicated early thinkers, philosophers, and more recently, by scientists. This continuous process is punctuated by major discoveries, often made possible by the onset of new instrumentation that opens another window on the world, amplifying or expanding our senses.

Enabling astronomers to observe farther and in greater detail for the past four centuries, the telescope has been key to establishing our physical understanding of the cosmos. Similarly, the progress in astronomical detectors – from the human eye to photographic plates, a couple of hundred years ago, and to a wide variety of electronic devices over the past century – has been just as revolutionary for the development of these investigations.

The discovery of light at wavelengths other than the visible band, in the nineteenth century, and its application to astronomy in the twentieth, have furthered this process, revealing entirely new classes of cosmic sources and phenomena, as well as unexpected aspects of known ones.

Herschel Spacecraft. Image Credit: ESA

The cooler an object is, the longer the wavelengths of light it emits, so observing the sky in the far-infrared and sub-millimetre domains provides access to some of the coldest sources in the Universe, including cool gas and dust with temperatures of 50 K and even less.

Boasting a telescope with a 3.5-metre primary mirror – the largest ever to observe at far-infrared wavelengths – and detectors cooled to just above absolute zero, Herschel could perform observations with unprecedented sensitivity and spatial resolution at the wavelengths that are crucial to delve into the tangle of star-forming clouds.

This made Herschel much more capable of mapping the direct emission from cold dust than its predecessors, which include the US-Dutch-British Infrared Astronomical Satellite (IRAS), ESA's Infrared Space Observatory (ISO), NASA's Spitzer Space Telescope, and JAXA's Akari satellite.

Dust is a minor but crucial component of the interstellar medium that obscures observations at optical and near-infrared wavelengths. As such, it had long stood in the way of astronomers getting to the bottom of star formation, in our Milky Way as well as in other, more distant galaxies.


Image above: Herschel's view of Orion B. Image Credits: ESA/Herschel/NASA/JPL-Caltech, CC BY-SA 3.0 IGO; Acknowledgement: R. Hurt (JPL-Caltech).

Herschel turned the situation around completely. Rather than being a problem, the dust became a crucial asset for astronomers: shining brightly at the long wavelengths probed by the observatory, dust could be used as a tracer of interstellar gas across the Galaxy and, most importantly, of its densest regions – the molecular clouds – where star formation unfolds.

In addition, Herschel provided the unique possibility to observe, with unprecedented spectral coverage and resolution, a vast number of lines in the spectra of gas clouds produced by atoms and molecules that are present, albeit in small amounts, in the gas. Together with the observation of dust, these atomic and molecular lines were instrumental in tracking down the properties of gas in a vast number of star-forming clouds.


Image above: Herschel's view of Rho Ophiuchi. Image Credits: ESA/Herschel/NASA/JPL-Caltech, CC BY-SA 3.0 IGO; Acknowledgement: R. Hurt (JPL-Caltech).

Several of Herschel's Key Programmes were dedicated to studying the birth of stars in molecular clouds, near and far, in our Galaxy.

Prominently among them, the Herschel Gould Belt Survey concentrated on areas close to home, gathering exceptionally detailed observations of the nearest star-forming regions, which are located in clouds collectively forming a giant ring out to 1500 light-years from the Sun. Another project, the Herschel imaging survey of OB Young Stellar objects, looked specifically at how massive stars are born. And finally, the Herschel infrared Galactic Plane Survey performed a complete census of stellar nurseries across the Milky Way by collecting a 360-degree view of the Galactic Plane.

These three observing programmes alone spent over 1500 hours of observations to investigate star formation.

Filaments galore

The most striking discovery that emerged from these extensive surveys was a vast and intricate network of filamentary structures weaving their way through the Galaxy.

Finding filaments per se was not a novelty – similar structures had already been detected in previous decades – but their ubiquitous presence was definitely remarkable.


Image above: The filamentary structure of the Galactic Plane. Image Credits: ESA/PACS & SPIRE Consortium, S. Molinari, Hi-GAL Project.

Herschel was the first observatory to reveal filaments nearly everywhere in the interstellar medium, from small ones, only a few light-years long, to giant threads extending over hundreds of light-years.

Such structures were spotted in all types of clouds, also in those with no ongoing star formation. Astronomers wondered: why do some filaments produce stars, while others do not?

The bounty of new data revealed not only that filaments are omnipresent, but also that they seem to have very similar properties, at least in our local neighbourhood. Regardless of their length, all filaments observed in nearby clouds have a universal width – about one third of a light-year.


Image above: Herschel's view of the Taurus molecular cloud. Image Credits: ESA/Herschel/NASA/JPL-Caltech, CC BY-SA 3.0 IGO; Acknowledgement: R. Hurt (JPL-Caltech).

The origin of these interstellar filaments and of their universal width is likely linked to the turbulent dynamics of gas in interstellar clouds. In fact, the width corresponds to the typical scale where gas undergoes the transition from supersonic to subsonic state, suggesting that filaments arise as a result of supersonic turbulence in the clouds.

Low-mass star formation

After 2010, when the first studies of Herschel observations were published, it became clear that interstellar filaments are crucial elements in the process of star formation.

Evidence from Herschel observations continued to pile up over the following years.

Filaments appear to precede the formation of stars in our Galaxy and, in some cases, they facilitate it. But only filaments that exceed a minimum density threshold seem to be active in the production of stars.

Taking account of the accumulating evidence, astronomers developed a new model to explain how stars of low mass, like our Sun, are born. In this two-step scenario, first a web of filaments arises from turbulent, supersonic motions of gas in the interstellar material. Later, but only in the densest filaments, gravity takes over: filaments then become unstable and fragment into clumps which, in turn, start to contract and eventually create pre-stellar cores – the seeds of future stars.


Image above: Herschel image of the Polaris Flare. Image Credits: ESA/Herschel/SPIRE/Ph. André (CEA Saclay) for the 'Gould Belt survey' Key Programme Consortium and A. Abergel (IAS Orsay) for the 'Evolution of Interstellar Dust' Key Programme Consortium.

Even if ubiquitous, filaments represent a small fraction of the total mass that makes up the Galaxy's interstellar medium, and only the densest of them partake in the highly inefficient process of star formation.


Image above: Herschel image of IC 5146. Image Credits: ESA/Herschel/SPIRE/PACS/D. Arzoumanian (CEA Saclay) for the 'Gould Belt survey' Key Programme Consortium.

While dense filamentary structures are beyond doubt the preferred sites for stellar birth, Herschel also observed some stars that appear to be forming in regions where filaments have not been identified.

High-mass star formation

Massive stars, exceeding several times the mass of the Sun, are rare but extremely bright and powerful objects that have a significant impact on their environment. Their formation has been a conundrum that has eluded explanation for many decades because of the difficulty in reconciling the enormous radiation pressure that arises as they take shape with the fact that this is sufficient to disperse the material and stop the accretion process entirely.


Image above: Massive stars forming in Cygnus X. Image Credits: ESA/PACS/SPIRE/Martin Hennemann & Frédérique Motte, Laboratoire AIM Paris-Saclay, CEA/Irfu - CNRS/INSU - Univ. Paris Diderot, France.

Because of the larger masses and energy outputs involved, these stars must come to life in conditions that are quite different from those found in the birthplaces of their lower-mass counterparts. As revealed by Herschel's observations, massive stars appear to form in the vicinity of gigantic structures such as ridges (massive, high-density filaments) and hubs (spherical clumps of matter) that may arise at the intersection of ordinary filaments.


Image above: Intense star formation in the Westerhout 43 region. Image Credits: ESA/Herschel/PACS, SPIRE/Hi-GAL Project. Acknowledgement: UNIMAP / L. Piazzo, La Sapienza – Università di Roma; E. Schisano / G. Li Causi, IAPS/INAF, Italy.

With their enormous reservoirs of gas and dust, ridges and hubs can provide the sustained flow of material needed to support the growth of huge stellar embryos. In these extreme environments, also called 'mini-starbursts', star formation can reach very intense levels, eventually giving rise to stellar clusters hosting primarily massive stars.

While highlighting the different phenomena that lead to the formation of high- and low-mass stars, Herschel has also brought them together within a common framework. As part of a continuous process taking place on all scales, the interstellar material is stirred up, compressed and confined in a variety of filamentary structures, whose later collapse under gravity and subsequent fragmentation gives rise to a multiplicity of different stars.

From new answers to new questions

Within less than a decade, astronomers using Herschel's extraordinary data have shown how the seemingly complex phenomenon of star formation can be understood in terms of simple and universal processes. Observations of nearby galaxies indicate that similar processes might be at play also beyond the confines of our Milky Way.

During its surveys of star-forming regions, Herschel has also observed many protoplanetary disks around very young stars, providing a glimpse into the raw material that will eventually build up these stars' planetary systems.

However, as new observations offer an answer to old questions, many new questions arise, some of which remain unanswered. Astronomers are still investigating a number of crucial aspects of star formation, such as the origin of filaments in molecular clouds, the dynamics of matter accretion, and the role of magnetic fields in the process.

To address some of these questions, in particular the formation of filaments, Herschel observations of various molecular clouds have been compared with measurements of the magnetic field in these clouds, obtained using ESA's Planck satellite and ground-based observatories, as well as with predictions of numerical simulations. The comparisons show that the magnetic fields tend to be perpendicular to the densest, star-forming filaments and parallel to lower-density filaments, known as striations, that flow into the denser ones, contributing to their growth.

Future studies and even more detailed observations will be needed to confirm and elucidate how magnetic fields do, as suggested, play a strong role in the process of star formation, contributing to deepening our understanding of this fascinating phenomenon.

More information:

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

Herschel was launched on 14 May 2009 and completed science observations on 29 April 2013.

All Herschel data can be accessed from the Herschel Science Archive at http://archives.esac.esa.int/hsa/whsa/

Related Links:

Herschel astronomers' website: https://www.cosmos.esa.int/web/herschel/home

Herschel Science Archive: http://archives.esac.esa.int/hsa/whsa/

NASA Herschel Science Centre: https://www.herschel.caltech.edu/

ESA Hershel website: http://sci.esa.int/herschel/

Images (mentioned), Video (mentioned), Text, Credits: ESA/Pedro García-Lario/Göran Pilbratt.

Best regards, Orbiter.ch

lundi 18 septembre 2017

Farewell to Iapetus












NASA - Cassini Mission to Saturn patch.

Sept. 18, 2017


Cassini bids farewell to Saturn’s yin-and-yang moon, Iapetus. This image is from the last set of observations Cassini made of this world of striking contrasts. The spacecraft helped scientists better understand Iapetus, solving a centuries-old mystery of why it should be bright on one side and dark on the other.

Cassini observations of Iapetus (914 mile or 1471 kilometers across) support the prevailing theory that led to the understanding that the dichotomy of the surface is due to a combination of infalling dust from outside of the moon followed by a migration of water ice from the darker (therefore warmer) areas to the cold, brighter surfaces. See PIA11690 for more details.

This false-color view is a composite of individual frames obtained using filters sensitive to ultraviolet (centered at 338 nanometers), green (centered at 568 nanometers) and infrared light (centered at 930 nanometers). The view has been enhanced to accentuate subtle color differences and fine-scale surface features.

This view looks toward the Saturn-facing hemisphere of Iapetus. North on Iapetus is up and rotated 12 degrees to the left.

The view was acquired on May 30, 2017, at a distance of approximately 1.5 million miles (2.5 million kilometers) from Iapetus. Image scale is 9 miles (15 kilometers) per pixel.

The Cassini mission is a cooperative project of NASA, ESA (the European Space Agency) and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colorado.

Related link:

PIA11690: https://photojournal.jpl.nasa.gov/catalog/PIA11690

For more information about the Cassini-Huygens mission visit https://saturn.jpl.nasa.gov and https://www.nasa.gov/cassini. The Cassini imaging team homepage is at http://ciclops.org and ESA's website: http://www.esa.int/Our_Activities/Space_Science/Cassini-Huygens

Image, Text, Credits: NASA/Tony Greicius/JPL-Caltech/Space Science Institute.

Greetings, Orbiter.ch

Three Spacewalks Scheduled, Crew Researches Life Science












ISS - Expedition 53 Mission patch.

September 18, 2017

International Space Station (ISS). Image Credit: NASA

Expedition 53 is gearing up for three maintenance spacewalks set to take place in October over a period of two weeks. Meanwhile, the six-member crew continued researching today how their long-term missions in space affect their bodies.

Commander Randy Bresnik began unpacking spacewalking gear today ahead of the first of three spacewalks set to begin Oct. 5. He will lead all three spacewalks with NASA astronauts Mark Vande Hei and Joe Acaba. Vande Hei will join him on the first two and Acaba will participate in the final spacewalk. The trio will replace one of the two end effectors on the Canadarm2 robotic arm, lubricate the new component and replace cameras at two locations on the station’s truss.


Image above: This night time view of southern Europe prominently features the “boot” of Italy, the home of current Expedition 53 crew member Paolo Nespoli of the European Space Agency. Image Credit: NASA.

Flight Engineers Paolo Nespoli and Sergey Ryazanskiy are exploring how living in space impacts their bone marrow. The study takes a look at blood and breath samples with the blood being processed in a centrifuge. Bresnik is also collecting his blood and urine samples that scientists will later analyze for any physiological changes caused by microgravity.

Related links:

Bone marrow: https://www.nasa.gov/mission_pages/station/research/experiments/1931.html

Physiological changes: https://www.nasa.gov/mission_pages/station/research/experiments/981.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

Images (mentioned), Text, Credits: NASA/Mark Garcia.

Best regards, Orbiter.ch

A Day in the Life of NASA's Voyagers










NASA - Voyager 1 & 2 Mission patch.

Sept. 18, 2017


Image above: An illustration of Voyager 1’s entry to interstellar space. Image Credit: NASA.

At more than 10 billion miles away from Earth, there is no day and night. Time and space are fathomless and our Sun is a distant point of starlight — a faint reminder of the home NASA’s twin Voyagers, humanity’s farthest and longest-lived spacecraft, left behind 40 years ago. Voyager 1, which launched on Sept. 5, 1977, and Voyager 2, launched on Aug. 20, 1977, continue to return data that shape our view and understanding of our place in the universe.

We often think of space as empty, but even the vacuum of space is filled with the remnants of stellar explosions from millions of years ago and dominated by invisible magnetic forces. Such magnetic forces carve out unique space environments throughout the galaxy, each one like a neighborhood with its own distinct feel. Voyager has helped scientists define the boundaries of our own stellar neighborhood — which scientists call the heliosphere — by returning observations about the conditions where the Sun’s influence wanes and interstellar space begins.

“Voyager is seeking out our place in the galaxy: How does the solar system interact with the rest of the galaxy and how does that affect us?” said Eric Christian, a space scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “If anything embodies the spirit of discovery, it’s Voyager.” Christian served as Voyager program scientist for NASA Headquarters between 2002 and 2008, and continues to do scientific work with the mission. These questions are key to understanding our own star and enabling human space exploration, but they could also shed light on the workings and potential habitability of other star systems.

The heliosphere is generated by the Sun’s constant outward flow of magnetic solar material, called the solar wind. This high-speed wind fills the solar system and forms a vast bubble, more than 20 billion miles across, where the space inside is different from space outside. Within the heliosphere, space is influenced by the dynamic properties of the Sun carried in the solar wind — including magnetic fields, energetic particles and ionized gases called plasma. The Sun and entire heliosphere move through interstellar space, and this relative motion shapes the heliosphere.

video
Where is the Edge of the Solar System?

Video above: The Voyagers have explored the far reaches of our solar system, and Voyager 1 entered interstellar space in August 2012. Exactly where the solar system ends depends on the criteria used to define it. Video Credits: NASA’s Goddard Space Flight Center/Genna Duberstein.

Exploring Our Interstellar Backyard

Traveling at speeds of more than 35,000 mph, the Voyagers travel about 900,000 miles farther from Earth each day, a distance equal to roughly 36 times Earth’s circumference. Five years ago, in August 2012, Voyager 1 crossed the edge of the heliosphere, called the heliopause, venturing for the first time into the space between stars, where no spacecraft had gone before.

The mission has informed researchers that inside the heliosphere, Earth and the rest of the solar system are shielded from cosmic radiation and wisps of hot hydrogen and helium gases composing what’s known as the Local Fluff — a series of massive clouds, each one several light-years wide, of interstellar medium through which the heliosphere is currently traveling. No longer cocooned by the heliosphere, Voyager 1 is currently exploring our interstellar backyard, measuring one of these clouds and searching the Fluff for clues to our origins, and those of nascent solar systems.

video
Voyager 1 Trajectory through the Solar System

Video above: This visualization tracks the trajectory of the Voyager 1 spacecraft through the solar system. Launched on Sept. 5, 1977, it was one of two spacecraft sent to visit the giant planets of the outer solar system. Voyager 1 flew by Jupiter and Saturn before being directed out of the solar system. Video Credits: NASA’s Scientific Visualization Studio/Tom Bridgman.

“We’re not in a typical part of the galaxy, if there is a typical part of the galaxy,” Christian said. “We’re in a bubble where multiple supernovas blew up, and it’s amazing to be traveling through that. It would almost make you feel insignificant, if there wasn’t also plenty of things to learn here.”

Studying the Nature of Space Itself

The probes’ planetary instruments were turned off after they passed the outer planets, but a suite of instruments carries out their interstellar mission. Voyager 1 currently has four working instruments that measure the magnetic fields, charged energetic particles (two instruments are responsible for this) and low-frequency radio waves of its surroundings. Voyager 2 also has these four, and additionally a working plasma sensor, which directly measures the solar wind.

Day in and day out, both Voyagers constantly beam data back to Earth. This feed of data is only received, however, when NASA’s Deep Space Network locks onto the spacecraft. The project goal is to acquire at least 16 hours of real-time data per spacecraft each day, but the actual amount of time varies depending on the network’s resources.

Voyager 1, now almost 13 billion miles from Earth, travels through interstellar space north out of the plane of the planets, while Voyager 2, almost 11 billion miles away, travels south and is expected to enter interstellar space in the next few years. The different locations of the two Voyagers allow scientists to compare two regions of space where the heliosphere interacts with the surrounding interstellar medium. Once Voyager 2 crosses into the interstellar medium, they will also be able to sample this space from two different locations simultaneously.

video
Voyager 2 Trajectory through the Solar System

Video above: This visualization tracks the trajectory of the Voyager 2 spacecraft through the solar system. Launched on Aug. 20, 1977, it was one of two spacecraft sent to visit the giant planets of the outer solar system. Like Voyager 1, Voyager 2 flew by Jupiter and Saturn, but the Voyager 2 mission was extended to fly by Uranus and Neptune before being directed out of the solar system. Video Credits: NASA’s Scientific Visualization Studio/Tom Bridgman.

The Final Frontier

Throughout their 40 years in space, the pioneering Voyagers have redefined what scientists consider the final frontier. “Decades ago, the joke among scientists was that the estimation of the edge of the heliosphere was moving out at the same rate that Voyager was,” Christian said.

Their scientific legacy is unparalleled, and the mission still enables fascinating discoveries. More recently, Voyager 1 hinted that the magnetic field of the local interstellar medium is wrapped around the heliosphere. Data from the probes also suggested an entirely new picture of the heliosphere — one that is much more compact and rounded than previously thought. 

Communications with the spacecraft will be maintained until the Voyagers' nuclear power sources can no longer supply enough electricity to operate the satellites. Engineers expect each spacecraft to continue operating at least one science instrument until around 2025.

However, even after the spacecraft go silent, thanks to remarkable engineering, they’ll otherwise be in good condition. Barring catastrophic collisions, the Voyagers are expected to continue to prosper on their lonely, boundless journeys, cruising at their present speed and completing an orbit around the center of the Milky Way every 225 million years.

The Voyager spacecraft were built by NASA’s Jet Propulsion Laboratory in Pasadena, California, which continues to operate both. The Voyager Interstellar Mission is currently part of the NASA Heliophysics System Observatory, sponsored by the Heliophysics Division of the Science Mission Directorate.

For more information about the Voyager spacecraft, visit:

http://www.nasa.gov/voyager
http://voyager.jpl.nasa.gov

Related article:

NASA’s Voyager Spacecraft Still Reaching for the Stars After 40 Years
http://orbiterchspacenews.blogspot.ch/2017/08/nasas-voyager-spacecraft-still-reaching.html

Related links:

NASA’s Deep Space Network: https://deepspace.jpl.nasa.gov/about/

NASA’s twin Voyagers: https://voyager.jpl.nasa.gov/

Image (mentioned), Videos (mentioned), Text, Credits: NASA/Rob Garner/Goddard Space Flight Center, by Lina Tran.

Best regards, Orbiter.ch

NASA Sees Maria Intensify into a Major Hurricane














NASA - EOS Aqua Mission logo / NOAA & NASA - GOES Mission logo / NASA & JAXA - GPM Mission patch.

Sept. 18, 2017

Maria (Atlantic Ocean)

NASA and NOAA satellites have provided data on Maria as it strengthened into a major Hurricane headed toward the Leeward Islands. NASA's Aqua satellite provided an infrared look at Maria that showed cooling cloud top temperatures and NOAA's GOES satellite provided an animation of imagery that showed the storm developing and strengthening. The GPM satellite found "Hot" towering clouds that indicated strengthening was occurring before Maria became a major hurricane.

video
ATLANTICalleyeastrso

Video above: This animation of NOAA's GOES East satellite imagery from Sept. 14 at 1:45 p.m. EDT (1745 UTC) to Sept. 18 ending at 7:45 a.m. EDT (1145 UTC). The animation shows Hurricane Jose moving north along the U.S. East coast, the development strengthening of Hurricane Maria and its approach to the Leeward Islands, and Tropical Depression Lee in the Eastern Atlantic. TRT: 00:08. Video Credits: NASA-NOAA GOES Project.

Warnings and Watches on Sept. 18

The National Hurricane Center (NHC) issued a Hurricane Warning for Guadeloupe, Dominica, St. Kitts, Nevis, and Montserrat, Martinique, St. Lucia, U.S. Virgin Islands and the British Virgin Islands. A Tropical Storm Warning is in effect for Antigua and Barbuda, Saba and St. Eustatius, St. Maarten and Anguilla.

A Hurricane Watch is in effect for Puerto Rico, Vieques, and Culebra, Saba and St. Eustatius, St. Maarten, St. Martin and St. Barthelemy, and Anguilla. A Tropical Storm Watch is in effect for Barbados, St. Vincent and the Grenadines.

Maria's Development

On Saturday, Sept. 16 the National Hurricane Center was watching Potential Tropical Cyclone Fifteen. The depression formed at 2 p.m. EDT that day. Three hours later it strengthened into a tropical storm and was named "Maria." At 5 p.m. EDT on Sunday, Sept. 17, Maria strengthened into a hurricane and continued to strengthen.

GPM Finds "Hot Towers" in Maria Before Strengthening


Image above: On Sept. 17, 2017 at 1001 p.m. EDT the GPM core satellite showed that Maria found rain falling at a rate of over 6.44 inches (163.7 mm) per hour in powerful storms northeast of Maria's eye. Intense thunderstorms were found towering to above 9.7 miles (15.7 km). Image Credits: NASA/JAXA, Hal Pierce.

The Global Precipitation Measurement mission (GPM) core observatory satellite had an excellent view of hurricane Maria when it passed almost directly above the hurricane on Sept. 17, 2017 at 1001 p.m. AST/EDT (Sept. 18 0201 UTC).  GPM's Microwave Imager (GMI) and Dual-Frequency Precipitation Radar (DPR) showed that Maria had well defined bands of precipitation rotating around the eye of the tropical cyclone. GPM's radar (DPR Ku band) found rain falling at a rate of over 6.44 inches (163.7 mm) per hour in one of these extremely powerful storms northeast of Maria's eye.

NASA obtained a look at Maria's precipitation structure using data from GPM's Radar (DPR Ku band). Intense thunderstorms were found towering to above 9.7 miles (15.7 km). This kind of chimney cloud, also called a "hot tower" (as it releases a huge quantity of latent heat by condensation). These tall thunderstorms in the eye wall are often a sign that a tropical cyclone is becoming more powerful.

About Hot Towers

A "hot tower" is a tall cumulonimbus cloud near the center of a tropical cyclone, often seen prior to intensification. The cloud tops reach at least to the top of the troposphere, the lowest layer of the atmosphere which is approximately 9 miles/14.5 km high in the tropics. These towers are called "hot" because they rise to such altitude due to the large amount of latent heat. Water vapor releases this latent heat as it condenses into liquid. Those towering thunderstorms have the potential for heavy rain. Energy released by rainfall into the center of a tropical cyclone provides the energy upon which tropical cyclones thrive.

Cloud Top Temperatures Show Strengthening

The Atmospheric Infrared Sounder or AIRS instrument aboard NASA's Aqua satellite analyzed Hurricane Maria in infrared light. Infrared light provides scientists with temperature data and that's important when trying to understand how strong storms can be. The higher the cloud tops, the colder and the stronger they are. So infrared light as that gathered by the AIRS instrument can identify the strongest sides of a tropical cyclone.


Image above: On Sept. 18 at 1:35 a.m. EDT (0535 UTC) the AIRS instrument aboard NASA's Aqua satellite captured this false-colored infrared image of Hurricane Maria. Some cloud top temperatures in strong storms were as cold as minus 63 degrees Fahrenheit (minus 53 degrees Celsius). Image Credits: NASA JPL, Ed Olsen.

When NASA's Aqua satellite flew over Maria on Sept. 18 at 1:35 a.m. EDT (0535 UTC) AIRS detected that cloud top temperatures had cooled indicating they were higher into the atmosphere. Cloud top temperatures were as cold as minus 81.6 degrees Fahrenheit (minus 63.1 degrees Celsius). Storms with cloud top temperatures that cold have the capability to produce heavy rainfall.

Satellite View of Maria Strengthening Over Time


Image above: This visible image of Hurricane Maria was taken from NOAA's GOES East satellite on Sept. 18 at 10:45 a.m. EDT (1445 UTC) as it strengthened to a Category 3 hurricane just east of the Leeward Islands. Image Credits: NASA/NOAA GOES Project.

At NASA's Goddard Space Flight Center in Greenbelt, Md. the NASA/NOAA GOES Project created an animation of NOAA's GOES East satellite imagery from Sept. 14 at 1:45 p.m. EDT (1745 UTC) to Sept. 18 ending at 7:45 a.m. EDT (1145 UTC). The animation shows Hurricane Jose moving north along the U.S. East coast, the development strengthening of Hurricane Maria and its approach to the Leeward Islands, and Tropical Depression Lee in the Eastern Atlantic.

NHC noted the estimated central pressure inside the 10 nautical mile-wide eye has fallen to 959 millibars. The small eye is also apparent in radar data from Martinique.

Maria's Status on Sept. 18

The NHC said at 11 a.m. AST/EDT (1500 UTC), the center of Hurricane Maria was located near 14.7 degrees north latitude and 60.1 degrees west longitude.                      

Maria was moving toward the west-northwest near 10 mph (17 kph), and this motion with some decrease in forward speed is expected through Tuesday night, Sept. 19.  On the forecast track, the center of Maria will move across the Leeward Islands late today and tonight, over the extreme northeastern Caribbean Sea Tuesday and Tuesday night, and approach Puerto Rico and the Virgin Islands on Wednesday, Sept. 20.

Reports from an Air Force Reserve Hurricane Hunter aircraft indicate that maximum sustained winds have increased to near 120 mph (195 kph) with higher gusts.  Maria is a category 3 hurricane on the Saffir-Simpson Hurricane Wind Scale. Additional rapid strengthening is forecast during the next 48 hours, and Maria is expected to be a dangerous major hurricane as it moves through the Leeward Islands and the northeastern Caribbean Sea.

Hurricane-force winds extend outward up to 15 miles (30 km) from the center and tropical-storm-force winds extend outward up to 125 miles (205 km). The minimum central pressure estimated from the Hurricane Hunter aircraft data is 959 millibars.

NHC expects Maria's eye to move through the Leeward Islands during the afternoon or evening today, Sept. 18.

For updates on Maria, visit: http://www.nhc.noaa.gov/

Aqua Satellite: https://www.nasa.gov/mission_pages/aqua/index.html

GOES (Geostationary Environmental Operational Satellites): http://www.nasa.gov/goes/

GPM (Global Precipitation Measurement): http://www.nasa.gov/mission_pages/GPM/main/index.html

Hurricanes: http://www.nasa.gov/mission_pages/hurricanes/main/index.html

Images (mentioned), Video (mentioned), Text, Credits: NASA/Lynn Jenner/Goddard Space Flight Center, By Rob Gutro/Hal Pierce.

Greetings, Orbiter.ch