vendredi 10 février 2012

Transforming Galaxies

NASA - Hubble Space Telescope patch.


Many of the Universe's galaxies are like our own, displaying beautiful spiral arms wrapping around a bright nucleus. Examples in this stunning image, taken with the Wide Field Camera 3 on the NASA/ESA Hubble Space Telescope, include the tilted galaxy at the bottom of the frame, shining behind a Milky Way star, and the small spiral at the top center.

Other galaxies are even odder in shape. Markarian 779, the galaxy at the top of this image, has a distorted appearance because it is likely the product of a recent galactic merger between two spirals. This collision destroyed the spiral arms of the galaxies and scattered much of their gas and dust, transforming them into a single peculiar galaxy with a unique shape.

This galaxy is part of the Markarian catalogue, a database of over 1500 galaxies named after B. E. Markarian, the Armenian astronomer who studied them in the 1960s. He surveyed the sky for bright objects with unusually strong emission in the ultraviolet.

Hubble Space Telescope in orbit

Ultraviolet radiation can come from a range of sources, so the Markarian catalog is quite diverse. An excess of ultraviolet emissions can be the result of the nucleus of an "active" galaxy, powered by a supermassive black hole at its center. It can also be due to events of intense star formation, called starbursts, possibly triggered by galactic collisions. Markarian galaxies are, therefore, often the subject of studies aimed at understanding active galaxies, starburst activity, and galaxy interactions and mergers.

Hubble is a project of international cooperation between NASA and the European Space Agency. NASA's Goddard Space Flight Center in Greenbelt, Md., manages the telescope. The Space Telescope Science Institute (STScI) conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy in Washington. For images and more information about the findings, visit: and

ESA Hubble site:

Image, Text, Credit: ESA / Hubble & NASA.


SMOS water mission turns hurricane hunter

ESA - SMOS Mission logo.

10 February 2012

ESA’s Earth Explorers have again shown how they are surpassing expectations. Designed to map soil moisture and ocean salinity, the versatile SMOS satellite has demonstrated that it can also offer unique information to improve hurricane forecasts.

The Soil Moisture and Ocean Salinity (SMOS) satellite carries a novel microwave radiometer to capture images of ‘brightness temperature’. These images correspond to radiation emitted from the surface of Earth and can be used to work out how much water is held in soil and how much salt is in the surface waters of the oceans.

Hurricane Igor surface winds

This information is leading to a better understanding of the water cycle and the processes that link Earth’s surface and atmosphere.

The SMOS sensor works in the ‘L-band’, at frequencies around 1.4 GHz, which also allows surface wind speeds over oceans to be derived, even in cloudy and rainy conditions. 

When winds reach gale force over oceans, breaking waves and whitecaps affect the microwave radiation being emitted from the surface. This means that when a storm builds, changes in the emitted radiation can be linked directly to the strength of the wind over the sea.

In addition, the radiation detected by SMOS is far less disturbed by rain and atmospheric effects than higher microwave frequencies.


Since clouds and rain are typical of tropical cyclones, measurements from SMOS uniquely complement observations made in extreme conditions, when measurements from other satellites become less accurate.

This means that SMOS has the potential to improve accuracy for forecasting the strength of tropical cyclones.

SMOS’s new-found capability was demonstrated by analysing SMOS data over Hurricane Igor, which reached category 5 in the North Atlantic in 2010.

The large swath and frequent revisits allowed the satellite to pass over the hurricane nine times during 11–19 September.

Surface wind speeds were estimated from SMOS brightness temperature images using a technique developed by scientists from the French Research Institute for Exploration of the Sea, Ifremer, and Collect Localisation Satellites, CLS, through ESA’s Earth Observation Support to Science Element programme.

Hurricane Igor

The animation at the top shows the result of their work. The estimates of surface-wind speed agree with hurricane model forecasts and data taken over the hurricane by NOAA aircraft.

This information can be particularly useful in the early stages of developing hurricanes in the east of the tropical Atlantic basin and over cyclones in the middle of the Pacific. Since these areas are far from land, they are difficult to reach by plane.

The contributions that SMOS can make are of great interest for operational forecasting of hurricane strength.

SMOS has also achieved another success: it has shown that salinity in the surface waters change in the wake of a hurricane. This is the first time that such changes have been detected from space.

Hurricane Igor changes salinity

As the animation to the left shows, Hurricane Igor caused the freshwater plume from the Amazon to mix with deeper saltier waters, increasing the salinity at the surface.

The combination of salinity data from SMOS with sea-surface temperature and sea-surface height information will improve the monitoring of fresh and warm water in relation to hurricane intensity.

Although ESA’s Earth Explorers are developed to address specific scientific issues, they continue to demonstrate their versatility and complementary role, not only in advancing our understanding of Earth , but also their potential for everyday applications.

Related links:

Ifremer–Cersat Salinity Center:



Access SMOS data:


Images, Animation, Text, Credits: ESA / AOES Medialab / Ifremer / N. Reul / NASA.


Could Venus be shifting gear?

ESA - Venus Express Mission patch.

10 February 2012

ESA’s Venus Express spacecraft has discovered that our cloud-covered neighbour spins a little slower than previously measured. Peering through the dense atmosphere in the infrared, the orbiter found surface features were not quite where they should be.

Using the VIRTIS instrument at infrared wavelengths to penetrate the thick cloud cover, scientists studied surface features and discovered that some were displaced by up to 20 km from where they should be given the accepted rotation rate as measured by NASA’s Magellan orbiter in the early 1990s.

Animation of Venus

These detailed measurements from orbit are helping scientists determine whether Venus has a solid or liquid core, which will help our understanding of the planet’s creation and how it evolved.

If Venus has a solid core, its mass must be more concentrated towards the centre. In this case, the planet’s rotation would react less to external forces.

The most important of those forces is due to the dense atmosphere – more than 90 times the pressure of Earth’s and high-speed weather systems, which are believed to change the planet’s rotation rate through friction with the surface.

Venus Express

Earth experiences a similar effect, where it is largely caused by wind and tides. The length of an Earth day can change by roughly a millisecond and depends seasonally with wind patterns and temperatures over the course of a year.

In the 1980s and 1990s, the Venera and Magellan orbiters made radar maps of the surface of Venus, long shrouded in mystery as well as a dense, crushing and poisonous atmosphere. These maps gave us our first detailed global view of this unique and hostile world.

Over its four-year mission, Magellan was able to watch features rotate under the spacecraft, allowing scientists to determine the length of the day on Venus as being equal to 243.0185 Earth days. .

However, surface features seen by Venus Express some 16 years later could only be lined up with those observed by Magellan if the length of the Venus day is on average 6.5 minutes longer than Magellan measured.

This also agrees with the most recent long-duration radar measurements from Earth.

Shift in Venus features

“When the two maps did not align, I first thought there was a mistake in my calculations as Magellan measured the value very accurately, but we have checked every possible error we could think of,” said Nils Müller, a planetary scientist at the DLR German Aerospace Centre, lead author of a research paper investigating the rotation.

Scientists, including Özgur Karatekin of the Royal Observatory of Belgium, looked at the possibility of short-term random variations in the length of a Venus day, but concluded these should average themselves out over longer timescales.

On the other hand, other recent atmospheric models have shown that the planet could have weather cycles stretching over decades, which could lead to equally long-term changes in the rotation period. Other effects could also be at work, including exchanges of angular momentum between Venus and the Earth when the two planets are relatively close to each other.

“An accurate value for Venus’ rotation rate will help in planning future missions, because precise information will be needed to select potential landing sites,” noted Håkan Svedhem, ESA’s Venus Express project scientist.

While further study is needed, it’s clear that Venus Express is penetrating far deeper into the mysteries of this enigmatic planet then anyone dreamed.

Notes for Editors

“Atmospheric angular momentum variations of Earth, Mars and Venus at seasonal time scales,” O. Karatekin, et al., Planetary and Space Science 59 (2011) 923–933.

“Rotation period of Venus estimated from Venus Express VIRTIS images and Magellan altimetry,” N.T. Mueller, et al., Icarus 217(2), 474–483. 

Last update: 10 February 2012.

Related links:

Submitting your pictures of Venus is now easier:

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Starsem - the Soyuz:

Where is Venus Express now?:

Postcards from Venus:

Images, Video, Text, Credits: ESA / C. Carreau / NASA / JPL / Magellan / P. Ford / ESA / Venus Express / P. Drossart / G. Piccioni.


jeudi 9 février 2012

New Views Show Old NASA Mars Landers

NASA - Mars Reconnaissance Orbiter (MRO) patch.

February 09, 2012

The High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter recorded a scene on Jan. 29, 2012, that includes the first color image from orbit showing the three-petal lander of NASA's Mars Exploration Rover Spirit mission. Spirit drove off that lander platform in January 2004 and spent most of its six-year working life in a range of hills about two miles to the east.

Another recent image from HiRISE, taken on Jan. 26, 2012, shows NASA's Phoenix Mars Lander and its surroundings on far-northern Mars after that spacecraft's second Martian arctic winter.  Phoenix exceeded its planned mission life in 2008, ending its work as solar energy waned during approach of its first Mars winter.

Near the lower left corner of this view is the three-petal lander platform that NASA's Mars Exploration Rover Spirit drove off in January 2004. Image credit: NASA/JPL-Caltech/Univ. of Arizona.

The image showing Spirit's lander platform as a small, bright feature southwest of Bonneville Crater is at The new image of Phoenix is at .

Spirit's lander platform. Image credit: NASA / JPL-Caltech

Previous color images from HiRISE have shown the Spirit rover itself, but all previous HiRISE views of the lander that delivered Spirit were in black and white.

Although neither Phoenix nor Spirit still send data to Earth, scientific findings from both missions continue as researchers analyze the wealth of data from the two. A recent report based on inspection of Martian soil particles with microscopes on Phoenix concluded that the soil has experienced very little interaction with liquid water over the past 600 million years or more (see ).

This image, taken Jan. 26, 2012, shows NASA's no-longer-active Phoenix Mars Lander spacecraft after its second Martian arctic winter. Image credit: NASA/JPL-Caltech/Univ.

The Mars Reconnaissance Orbiter has been examining Mars with six science instruments since 2006. Now in an extended mission, the orbiter continues to provide insights into the planet's ancient environments and how processes such as wind, meteorite impacts and seasonal frosts are continuing to affect the Martian surface today. This mission has returned more data about Mars than all other orbital and surface missions combined.

NASA's Phoenix Mars Lander. Image credit: NASA / JPL-Caltech

More than 21,000 images taken by HiRISE are available for viewing on the instrument team's website: . Each observation by this telescopic camera covers several square miles, or square kilometers, and can reveal features as small as a desk.

HiRISE is operated by the University of Arizona, Tucson. The instrument was built by Ball Aerospace & Technologies Corp., Boulder, Colo.  The Mars Reconnaissance Orbiter Project and the Mars Exploration Rover Project are managed by the Jet Propulsion Laboratory, Pasadena, Calif., for NASA's Science Mission Directorate, Washington. JPL is a division of the California Institute of Technology, also in Pasadena. Lockheed Martin Space Systems, Denver, built the orbiter.  For more information about the Mars Reconnaissance Orbiter, see .

The University of Arizona led the Phoenix mission with project management at JPL and development partnership at Lockheed Martin. International contributions came from the Canadian Space Agency; the University of Neuchatel, Switzerland; the universities of Copenhagen and Aarhus in Denmark; the Max Planck Institute in Germany; the Finnish Meteorological Institute; and Imperial College of London.

Images (mentioned), Text, Credit: NASA / JPl / Guy Webster.


NASA's Mars Science Laboratory - Spacecraft Computer Issue Resolved

NASA - Mars Science Laboratory (MSL) patch.


Mars Science Laboratory Mission Status Report

Engineers have found the root cause of a computer reset that occurred two months ago on NASA's Mars Science Laboratory and have determined how to correct it.

The fix involves changing how certain unused data-holding locations, called registers, are configured in the memory management of the type of computer chip used on the spacecraft. Billions of runs on a test computer with the modified register configuration yielded no repeat of the reset behavior. The mission team made this software change on the spacecraft's computer last week and confirmed this week that the update is successful.

The reset occurred Nov. 29, 2011, three days after launch, during use of the craft's star scanner. The cause has been identified as a previously unknown design idiosyncrasy in the memory management unit of the Mars Science Laboratory computer processor. In rare sets of circumstances unique to how this mission uses the processor, cache access errors could occur, resulting in instructions not being executed properly. This is what happened on the spacecraft on Nov. 29.

"Good detective work on understanding why the reset occurred has yielded a way to prevent it from occurring again," said Mars Science Laboratory Deputy Project Manager Richard Cook of NASA's Jet Propulsion Laboratory, Pasadena, Calif. "The successful resolution of this problem was the outcome of productive teamwork by engineers at the computer manufacturer and JPL."

This artist concept features NASA's Mars Science Laboratory Curiosity rover, a mobile robot for investigating Mars' past or present ability to sustain microbial life. Image credit: NASA / JPL-Caltech.

The Mars-bound spacecraft performed a brief alignment activity using its star scanner and sun sensor on Jan. 26. During the alignment observations, the star scanner detected Mars.

"Our target is in view," said JPL's Steve Collins, attitude control subsystem engineer for Mars Science Laboratory's cruise from Earth to Mars.

The spacecraft began normal use of its star tracker and true celestial navigation this week after its software update.

The Mars Science Laboratory mission will use its car-size rover, Curiosity, to investigate whether the selected region on Mars inside Gale Crater has offered environmental conditions favorable for supporting microbial life and favorable for preserving clues about whether life existed. Curiosity will land on Mars on Aug. 6, 2012, Universal Time and Eastern Daylight Time (evening of Aug. 5, Pacific Daylight Time).

The spacecraft's cruise-stage solar array is producing 704 watts. The telecommunications rates are 1 kilobit per second for uplink and 800 bits per second for downlink. The spacecraft is spinning at 1.97 rotations per minute.

Mars Science Laboratory Curiosity Rover Animation

As of 9 a.m. PST (noon EST, or 1700 Universal Time) on Friday, Feb. 10, the spacecraft will have traveled 127 million miles (205 million kilometers) of its 352-million-mile (567-million-kilometer) flight to Mars. It will be moving at about 17,800 miles per hour (28,600 kilometers per hour) relative to Earth and at about 63,700 mph (102,500 kilometers per hour) relative to the sun.

JPL, a division of the California Institute of Technology in Pasadena, manages the Mars Science Laboratory mission for the NASA Science Mission Directorate, Washington. More information about Curiosity is online at: and . You can follow the mission on Facebook at: and on Twitter at: .

Image (mentioned), Video, Text, Credit: NASA / JPL / Guy Webster.

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mercredi 8 février 2012

Cracks in the wing: all the Airbus A380 will be examined

Aerospace Engineering logo.

Feb. 9, 2012

The European Aviation Safety Agency had previously conducted a review of some devices, but now they are all inspected.

All Airbus A380 will be examined because of cracks discovered in the wing of some of them. (Photo by Airbus).

Cracks in the wing: all the Airbus A380 will be examined

The European Aviation Safety Agency had previously conducted a review of some devices, but now they are all  scrutinized.

Video above: Wing Cracks Found On Airbus A380 Aircraft - Qantas, Singapore Airlines and Emirates Jets Affected.

The European Aviation Safety Agency (EASA) will recommend Wednesday the inspection of all 67 Airbus A380s currently in service, due to cracks appeared in the wings of some of them, said a spokesman.

January 20, EASA had advocated the examination of aircraft which have accumulated the highest number of flight hours, or twenty aircraft from Airbus.

"Given the outcome of this review, it was decided to extend it to the entire fleet in circulation," added the spokesman.

"The idea is to ensure that there is no security problem with this device," he said.

Upper wing panels or cracks were detected on the Qantas A380

Among the twenty aircraft initially to be inspected, eight having performed over 1,800 flights, had to be within four days and twelve in six weeks.

The most urgent inspections involved six aircraft and two of Singapore Airlines, Emirates, Dubai-based company.

Airbus has repeatedly said that safety of its aircraft was not affected and the companies felt that there was no risk to the safety of their passengers.

(Click on the image for enlarge) Airbus A380 cutaway description

On his side, Wednesday, the Australian airline Qantas has grounded one of its Airbus 380 because of these micro-cracks in the wing of the superjumbo, according to her safely to flight safety.

The A380 is the largest airliner in the world capable of carrying over 500 passengers and more than 800 passengers when configured in economy class only. It was commissioned

Images, Text, Credits / AFP / Airbus / Video: AviationExplorer / Translation:


Young Stars at Home in Ancient Cluster

NASA - Hubble Space Telescope èatch.


Looking like a hoard of gems fit for an emperor's collection, this deep sky object called NGC 6752 is in fact far more worthy of admiration. It is a globular cluster, and at over 10 billion years old is one the most ancient collections of stars known. It has been blazing for well over twice as long as our solar system has existed.

NGC 6752 contains a high number of "blue straggler'' stars, some of which are visible in this image. These stars display characteristics of stars younger than their neighbors, despite models suggesting that most of the stars within globular clusters should have formed at approximately the same time. Their origin is therefore something of a mystery.

Studies of NGC 6752 may shed light on this situation. It appears that a very high number -- up to 38 percent -- of the stars within its core region are binary systems. Collisions between stars in this turbulent area could produce the blue stragglers that are so prevalent.

Lying 13,000 light-years distant, NGC 6752 is far beyond our reach, yet the clarity of Hubble's images brings it tantalizingly close.

For more information about Hubble Space Telescope, visit:

NASA Hubble site:

ESA Hubble  site:

Image, Text, Credit: ESA / Hubble & NASA.


NASA's Chandra Finds Milky Way's Black Hole Grazing on Asteroids

NASA - Chandra X-ray Observatory patch.


The giant black hole at the center of the Milky Way may be vaporizing and devouring asteroids, which could explain the frequent flares observed, according to astronomers using data from NASA's Chandra X-ray Observatory.

Image above: Supermassive black hole Sagittarius A* at the center of the Milky Way. (X-ray: NASA / CXC / MIT / F. Baganoff et al.; Illustrations: NASA / CXC / M.Weiss).

For several years Chandra has detected X-ray flares about once a day from the supermassive black hole known as Sagittarius A*, or "Sgr A*" for short. The flares last a few hours with brightness ranging from a few times to nearly one hundred times that of the black hole's regular output. The flares also have been seen in infrared data from ESO's Very Large Telescope in Chile.

"People have had doubts about whether asteroids could form at all in the harsh environment near a supermassive black hole," said Kastytis Zubovas of the University of Leicester in the United Kingdom, and lead author of the report appearing in the Monthly Notices of the Royal Astronomical Society. "It's exciting because our study suggests that a huge number of them are needed to produce these flares."

Zubovas and his colleagues suggest there is a cloud around Sgr A* containing trillions of asteroids and comets, stripped from their parent stars. Asteroids passing within about 100 million miles of the black hole, roughly the distance between the Earth and the sun, would be torn into pieces by the tidal forces from the black hole.

These fragments then would be vaporized by friction as they pass through the hot, thin gas flowing onto Sgr A*, similar to a meteor heating up and glowing as it falls through Earth's atmosphere. A flare is produced and the remains of the asteroid are swallowed eventually by the black hole.

"An asteroid's orbit can change if it ventures too close to a star or planet near Sgr A*," said co-author Sergei Nayakshin, also of the University of Leicester. "If it's thrown toward the black hole, it's doomed."

The authors estimate that it would take asteroids larger than about six miles in radius to generate the flares observed by Chandra. Meanwhile, Sgr A* also may be consuming smaller asteroids, but these would be difficult to spot because the flares they generate would be fainter.

These results reasonably agree with models estimating of how many asteroids are likely to be in this region, assuming that the number around stars near Earth is similar to the number surrounding stars near the center of the Milky Way.

"As a reality check, we worked out that a few trillion asteroids should have been removed by the black hole over the 10-billion-year lifetime of the galaxy," said co-author Sera Markoff of the University of Amsterdam in the Netherlands. "Only a small fraction of the total would have been consumed, so the supply of asteroids would hardly be depleted."

Planets thrown into orbits too close to Sgr A* also should be disrupted by tidal forces, although this would happen much less frequently than the disruption of asteroids, because planets are not as common. Such a scenario may have been responsible for a previous X-ray brightening of Sgr A* by about a factor of a million about a century ago. While this event happened many decades before X-ray telescopes existed, Chandra and other X-ray missions have seen evidence of an X-ray "light echo" reflecting off nearby clouds, providing a measure of the brightness and timing of the flare.

"This would be a sudden end to the planet's life, a much more dramatic fate than the planets in our solar system ever will experience," Zubovas said.

Very long observations of Sgr A* will be made with Chandra later in 2012 that will give valuable new information about the frequency and brightness of flares and should help to test the model proposed here to explain them. This work could improve understanding about the formation of asteroids and planets in the harsh environment of Sgr A*.

NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory controls Chandra's science and flight operations from Cambridge, Mass.

For Chandra images, multimedia and related materials, visit:

For an additional interactive image, podcast, and video on the finding, visit:

Image, Text, Credits: NASA / Trent J. Perrotto / Chandra X-ray Center/Megan Watzke / Marshall Space Flight Center / Janet Anderson.


NASA Small Explorer Mission Celebrates Ten Years and Forty Thousand X-Ray Flares

NASA - HESSI Mission logo.



A combined movie from RHESSI and the Transition Region and Coronal Explorer, or TRACE mission. TRACE shows the solar surface, while RHESSI data dances over it: red contour lines show soft X-ray sources, and blue lines show hard X-ray sources. Together such information has helped show how and where particles move around during solar eruptions. Credit: NASA/GSFC/Scientific Visualization Studio.

On February 5, 2002, NASA launched what was then called the High Energy Solar Spectroscopic Imager (HESSI) into orbit. Renamed within months as the Ramaty High Energy Solar Spectroscopic Imager (RHESSI) after Reuven Ramaty, a deceased NASA scientist who had long championed the mission, the spacecraft's job was to observe giant explosions on the sun called solar flares.

During a solar flare, the gas soars to over 20 million degrees Fahrenheit, and emits X-rays that scientists can use as fingerprints to study these events on the sun. X-rays cannot penetrate Earth's atmosphere, however, so RHESSI observes them from space. Its goal is simple: to understand how the sun so efficiently shoots out such huge amounts of energy and particles.

Ten years since its launch, RHESSI has observed more than 40,000 X-ray flares, helped craft and refine a model of how solar eruptions form, and fueled additional serendipitous science papers on such things as the shape of the sun and thunder-storm-produced gamma ray flashes.

RHESSI is in a class of NASA spacecraft called Small Explorers – missions that cost under $120 million with highly focused research goals. Launching just after the sun reached its period of maximum activity, known as solar maximum, in 2001, RHESSI was poised to see many explosive bursts of energy from the sun, including both solar flares and another eruption of solar material called coronal mass ejections.

An artist's representation of RHESSI. Flying up above Earth's radiation-blocking atmosphere, the spacecraft can observe X-rays and gamma rays from the sun to study solar flares. Credit: NASA/Goddard/Conceptual Image Lab.

"Except, thanks in part to RHESSI, we don't even separate the biggest explosions into categories like that anymore," says Brian Dennis, the mission scientist for RHESSI at NASA's Goddard Space Flight Center in Greenbelt, Md. "RHESSI has taught us that 'Thou shalt instead say Solar Eruptive Events.' Now we know that one burst of energy in the sun's atmosphere creates both kinds of eruptions. Part of the energy shoots into the sky and becomes a CME (coronal mass ejection). Part of the material is driven down to the sun's surface and appears as the flare. RHESSI's 10 years of observations have helped fill in the holes in this picture."

To accomplish this, RHESSI made use of its one, and only one, instrument, which records both X-rays and even shorter wavelengths of light, gamma rays. The instrument combines high-resolution solar images with "spectroscopic" images that delineate the spectrum of energy coming from any particular point in the image. Together, this helps physically map out energy levels during an explosive event on the sun, as well as track the energy's movement.

For example, to understand how a solar flare forms, one has to understand where the energy to power it comes from. Early RHESSI observations of a flare on April 15, 2002, showed two X-ray sources – one higher in the sun's atmosphere and one lower. RHESSI's unique spectroscopic imaging capability allowed scientists to interpret this to mean that a huge energy release had originally happened between the two spots: that crucial initiation in the current picture of solar eruptions where a single energy burst in the sun's atmosphere, creates both a CME and a flare.

Since RHESSI observes gamma rays as well as X-rays, it has been able to compare how events emit these two forms of radiation. X-rays generally represent electron activity and gamma rays represent activity from protons and other heavier charged particles called ions, so comparing both helps show how different particle populations move around. Scientists have spotted several flares, including their first one using RHESSI in October 2003, where the gamma rays and X-ray sources do not line up. Such a spatial difference was entirely unexpected and suggests that different circumstances guide the movements of different particle populations.

"This opens up new questions for our model," says Dennis. "The electrons and ions have different masses, but we'd still expect them to appear at the same locations in the flare. Perhaps the ions are accelerated in a different way and end up traveling on different magnetic field lines from the electrons."

In addition to observations of giant solar flares, RHESSI has observed more than 25,000 of a smaller version, known as microflares. These much smaller energy releases are also believed to play a role in how the sun transports energy from its surface up into its atmosphere. RHESSI has found that such flares all occur in active regions over the same range of latitudes on the sun as for the bigger events, so perhaps they are just smaller versions of the same phenomenon.

This diagram shows the sun’s oblateness (in blue) magnified 1000 times, so the difference from a true sphere (in red) is visible. The blue curve traces the sun's shape averaged over a three month period. The black asterisked curve traces a shorter 10-day average. The wiggles in the 10-day curve are real, caused by strong magnetic ridges in the vicinity of sunspots. Credit: NASA.

Another interesting result from RHESSI has nothing to do with flares at all, but with the very shape of the sun. Due to its spin, one expects the sun to be slightly flattened and not a perfect sphere, much the same as the slight flattening of the Earth. Pre-RHESSI measurements of the sun, however, showed it to be much flatter than physics would dictate, raising questions of whether scientists had overlooked some fundamental piece of information about the sun's rotation.

RHESSI helped by providing information simply gathered as part of its constant assessment of where its instrument points. To keep perfectly oriented, RHESSI precisely records the position of the sun's horizon, or "limb," some 16 times per second. With such an extensive collection of data, scientists could determine the best ever measurement of the sun's shape. This data suggests the true shape more closely matches what physics predicts.

RHESSI's monitoring of gamma rays throughout the sky also made it a prime tool to measure what are called terrestrial gamma-ray flashes (TGFs), bursts of gamma rays emitted from high in the Earth's atmosphere over lightning storms. The first of these had been spotted before, but RHESSI showed that they are more common and more luminous than previously thought. With RHESSI's help, scientists soon realized they occurred upwards of 50 times per day. Indeed, current numbers suggest there may be as many as 400 TGFs daily from thunderstorms at different locations around the world.

"RHESSI made great strides by taking the first high-resolution movies of flares using their high energy radiation," says Dennis. "The original mission was only for two years and we quickly achieved our initial science goals – but RHESSI didn't stop there. The mission has been extended several times, and this small mission just keeps going and going, collecting great data."

In 2009, NASA extended the mission yet again. Now scientists are working to integrate RHESSI flare observations with data from other solar telescopes such as the Solar TErrestrial RElations Observatory (STEREO), Solar Dynamics Observatory (SDO), SOlar and Heliophysics Observatory (SOHO), and Hinode as they watch the sun's activity rise toward yet another solar maximum, currently predicted for 2013.

The Explorers Program Office at Goddard provides management and technical oversight for the RHESSI mission under the direction of NASA's Science Mission Directorate in Washington, D.C.

For more information about the mission, go to:

Images, Video, Text, Credits: NASA's Goddard Space Flight Center / Karen C. Fox.


Saturn's Rings and Enceladus

ESA - Cassini Mission to Saturn logo.

8 February 2012

 Saturn's rings and Enceladus

A crescent Enceladus appears with Saturn’s rings in this Cassini spacecraft view of the moon.

The famed jets of water ice emanating from the south polar region of the 504 km-diameter moon are faintly visible.

They appear as a small white blur below the dark pole, down and to the right of the illuminated part of the moon’s surface. The image’s contrast was enhanced to increase their visibility.

The sunlit terrain seen here is on the trailing hemisphere of Enceladus; north is up. This view looks toward the northern, sunlit side of the rings from just above the ringplane. The image was taken with Cassini’s narrow-angle camera on 4 January at a distance of 291 000 km from Enceladus. Image scale is about 2 km per pixel. 

Notes to editors:

The Cassini–Huygens mission is a cooperative project of NASA, ESA and the Italian space agency, ASI. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Science Mission Directorate in Washington. The Cassini orbiter and its two cameras were designed, developed and assembled at JPL. The imaging team is based at the Space Science Institute, Boulder, Colorado, USA.

For more informations about Cassini Mission, visit: and

Image, Text, Credits: NASA / ESA / JPL–Caltech / Space Science Institute.


VLT Takes Most Detailed Infrared Image of the Carina Nebula

ESO - European Southern Observatory logo.

8 February 2012

 ESO’s VLT reveals the Carina Nebula's hidden secrets

ESO’s Very Large Telescope has delivered the most detailed infrared image of the Carina Nebula stellar nursery taken so far. Many previously hidden features, scattered across a spectacular celestial landscape of gas, dust and young stars, have emerged. This is one of the most dramatic images ever created by the VLT.

Excerpts from VLT image of the Carina Nebula in infrared light

Deep in the heart of the southern Milky Way lies a stellar nursery called the Carina Nebula. It is about 7500 light-years from Earth in the constellation of Carina (The Keel) [1]. This cloud of glowing gas and dust is one of the closest incubators of very massive stars to the Earth and includes several of the brightest and heaviest stars known. One of them, the mysterious and highly unstable star Eta Carinae, was the second brightest star in the entire night sky for several years in the 1840s and is likely to explode as a supernova in the near future, by astronomical standards. The Carina Nebula is a perfect laboratory for astronomers studying the violent births and early lives of stars.

Infrared/visible-light comparison of the Carina Nebula

Although this nebula is spectacular in normal visible-light pictures (eso0905), many of its secrets are hidden behind thick clouds of dust. To penetrate this veil a European team of astronomers, led by Thomas Preibisch (University Observatory, Munich, Germany) has used the power of ESO’s Very Large Telescope along with an infrared-sensitive camera called HAWK-I [2].

The Carina Nebula in the constellation of Carina

Hundreds of individual images have been combined to create this picture, which is the most detailed infrared mosaic of the nebula ever taken and one of the most dramatic images ever created by the VLT. It shows not just the brilliant massive stars, but hundreds of thousands of much fainter stars [3] that were previously invisible.

Digitized Sky Survey Image of Eta Carinae Nebula 

The dazzling star Eta Carinae itself appears at the lower left of the new picture. It is surrounded by clouds of gas that are glowing under the onslaught of fierce ultraviolet radiation. Across the image there are also many compact blobs of dark material that remain opaque even in the infrared. These are the dusty cocoons in which new stars are forming.

Infrared/visible-light comparison view of the Carina Nebula

Over the last few million years this region of the sky has formed large numbers of stars both individually and in clusters. The bright star cluster close to the centre of the picture is called Trumpler 14. Although this object is seen well in visible light, many more fainter stars can be seen in this infrared view. And towards the left side of the image a small concentration of stars that appear yellow can be seen. This grouping was seen for the first time in this new data from the VLT: these stars cannot be seen in visible light at all. This is just one of many new objects revealed for the first time in this spectacular panorama.

Zooming in on a new infrared view of the Carina Nebula


[1] Carina is the keel of the mythological ship Argo, of Jason and the Argonauts fame.

[2] Dusty regions of space absorb and scatter short wavelength blue light more than the longer wavelength red. This effect also explains why sunsets on Earth are often red, particularly when the atmosphere is dusty. In some dusty parts of the sky, particularly in star formation regions such as the Carina Nebula, this effect is so strong that no visible light gets through at all. Astronomers overcome this problem by observing in infrared light using special cameras such as HAWK-I on ESO’s VLT or the VISTA infrared survey telescope.

[3] One of the main goals of the astronomers was to search for stars in this region that were much fainter and less massive than the Sun. The image is also deep enough to allow the detection of young brown dwarfs.

More information:

The year 2012 marks the 50th anniversary of the founding of the European Southern Observatory (ESO). ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive astronomical observatory. It is supported by 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. 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 the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 40-metre-class European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.


    Research paper describing the infrared observations of the Carina Nebula:

    Thomas Preibisch’s Carina web page:

    Observations of the Carina Nebula with APEX/LABOCA:

    X-ray observations of the same region from the Chandra Carina Project:

    Photos of the VLT:

Images, Text, Credits: ESO / T. Preibisch / IAU and Sky & Telescope/Digitized Sky Survey 2. Acknowledgment: Davide De Martin / Videos: ESO / Nick Risinger ( / Digitized Sky Survey 2 Music: John Dyson (from the album Moonwind) / T. Preibisch.

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lundi 6 février 2012

ESA's Mars Express radar gives strong evidence for former Mars ocean

ESA - Mars Express Mission patch.

6 February 2012

ESA's Mars Express has returned strong evidence for an ocean once covering part of Mars. Using radar, it has detected sediments reminiscent of an ocean floor within the boundaries of previously identified, ancient shorelines on Mars.

The MARSIS radar was deployed in 2005 and has been collecting data ever since. Jérémie Mouginot, Institut de Planétologie et d'Astrophysique de Grenoble (IPAG) and the University of California, Irvine, and colleagues have analysed more than two years of data and found that the northern plains are covered in low-density material.

"We interpret these as sedimentary deposits, maybe ice-rich," says Dr Mouginot. "It is a strong new indication that there was once an ocean here."

Ancient northern ocean on Mars

The existence of oceans on ancient Mars has been suspected before and features reminiscent of shorelines have been tentatively identified in images from various spacecraft. But it remains a controversial issue.

Two oceans have been proposed: 4 billion years ago, when warmer conditions prevailed, and also 3 billion years ago when subsurface ice melted following a large impact, creating outflow channels that drained the water into areas of low elevation. 

"MARSIS penetrates deep into the ground, revealing the first 60–80 metres of the planet's subsurface," says Wlodek Kofman, leader of the radar team at IPAG.

"Throughout all of this depth, we see the evidence for sedimentary material and ice."

Mars Express radar investigation

The sediments revealed by MARSIS are areas of low radar reflectivity. Such sediments are typically low-density granular materials that have been eroded away by water and carried to their final destination.

This later ocean would however have been temporary. Within a million years or less, Dr Mouginot estimates, the water would have either frozen back in place and been preserved underground again, or turned into vapour and lifted gradually into the atmosphere.

"I don't think it could have stayed as an ocean long enough for life to form."

In order to find evidence of life, astrobiologists will have to look even further back in Mars' history when liquid water existed for much longer periods.

Nevertheless, this work provides some of the best evidence yet that there were once large bodies of liquid water on Mars and is further proof of the role of liquid water in the martian geological history.

"Previous Mars Express results about water on Mars came from the study of images and mineralogical data, as well as atmospheric measurements. Now we have the view from the subsurface radar," says Olivier Witasse, ESA's Mars Express Project Scientist.

"This adds new pieces of information to the puzzle but the question remains: where did all the water go?"

Mars Express continues its investigation.

Related links:

High Resolution Stereo Camera:

Behind the lens:

Frequently asked questions:

For specialists:

ESA Planetary Science archive (PSA):

NASA Planetary Data System:

HRSC data viewer:

Images, Text, Credits: ESA / C. Carreau.

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Remnant of a Supernova

NASA - Chandra X-ray Observatory patch.

Feb. 6, 2012

Vital clues about the devastating ends to the lives of massive stars can be found by studying the aftermath of their explosions. In its more than twelve years of science operations, NASA's Chandra X-ray Observatory has studied many of these supernova remnants sprinkled across the galaxy.

The latest example of this important investigation is Chandra's new image of the supernova remnant known as G350.1-0.3. This stellar debris field is located some 14,700 light years from the Earth toward the center of the Milky Way.

Evidence from Chandra and from ESA's XMM-Newton telescope suggest that a compact object within G350.1+0.3 may be the dense core of the star that exploded. The position of this likely neutron star, seen by the arrow pointing to "neutron star" in the inset image, is well away from the center of the X-ray emission. If the supernova explosion occurred near the center of the X-ray emission then the neutron star must have received a powerful kick in the supernova explosion.

Data suggest this supernova remnant, as it appears in the image, is 600 and 1,200 years old. If the estimated location of the explosion is correct, this means the neutron star has been moving at a speed of at least 3 million miles per hour since the explosion.

Another intriguing aspect of G350.1-0.3 is its unusual shape. Many supernova remnants are nearly circular, but G350.1-0.3 is strikingly asymmetrical as seen in the Chandra data in this image (gold). Infrared data from NASA's Spitzer Space Telescope (light blue) also trace the morphology found by Chandra. Astronomers think that this bizarre shape is due to stellar debris field expanding into a nearby cloud of cold molecular gas.

The age of 600-1,200 years puts the explosion that created G350.1-0.3 in the same time frame as other famous supernovas that formed the Crab and SN 1006 supernova remnants. However, it is unlikely that anyone on Earth would have seen the explosion because of the obscuring gas and dust that lies along our line of sight to the remnant.

These results appeared in the April 10, 2011 issue of The Astrophysical Journal.

For more informations about Chandra X-ray Observatory, visit:

Image, Text, Credits: X-ray: NASA / CXC / SAO / I. Lovchinsky et al; IR: NASA / JPL-Caltech.


CryoSat breaks the ice with ocean currents

ESA - CRYOSAT Mission logo.

6 February 2012

Ocean measurements from ESA’s CryoSat mission are being exploited by the French space agency CNES to provide global ocean observation products in near-real time. Understanding sea-surface currents is important for marine industries and protecting ocean environments.

As it orbits from pole to pole, CryoSat’s main objective is to measure the thickness of polar sea ice and monitor changes in the ice sheets that blanket Greenland and Antarctica. But the satellite also features an innovative radar altimeter that not only detects tiny variations in the height of the ice, but can also measure sea level and the height of the waves.

Ocean surface currents

Starting today , CryoSat ocean measurements are being processed by CNES and distributed to the oceanography community. These products will be assimilated using models from the MyOcean project in near-real time to enhance sea surface products and to improve the quality of the model forecasts. 

“This achievement is the result of the long-standing collaboration and partnership between ESA and CNES,” says Tommaso Parrinello, CryoSat Mission Manager.

Radioactive pollution

“Through a fusion of processors derived from operational altimeters and experimental software developed specifically for CryoSat’s innovative instrument, CNES experts will be able to transform raw ocean data flows from CryoSat into a quasi-operational end-user ocean product of high quality.

“Ocean topography is an important key environmental parameter to understand how ocean circulation responds to climate change.”

Oil spill movement prediction

Coastal models and applications will also benefit from the additional coverage provided by CryoSat. Users can obtain these products through the AVISO website or MyOcean data portal.

Within the Global Monitoring for Environment and Security (GMES) programme, the MyOcean project is responsible for the development of marine monitoring services.

During major crises such as the Deepwater Horizon and Fukushima disasters, MyOcean models exploited remote sensing data – in particular, altimetry data – to help monitor these crises.

Altimetry data is of highest importance to predict the evolution of local marine currents in near-real time.

Sea-surface topography

A wide range of operational marine applications and services with social and economic benefits needs sea-surface currents: oil spill or marine debris tracking and prediction, fishery and offshore industry support, including cost and risk reduction, optimised ship routing, iceberg detection and alert for worldwide ship racing.

Since the launch of the first European Remote Sensing satellite in 1991, radar altimetry has been used to observe ocean surface topography and geostrophic currents continuously. It has become an invaluable asset for the accurate forecast modelling of ocean currents.

Related links:




Cryosat 2, Earth Explorers:

Images, Video, Text, Credits: ESA / MyOcean / Mercator-Ocean / Univ. Colorado / CNES / AVISO / GOES SST / Radarsat-2.

Best regards,