vendredi 27 janvier 2012

Astronaut Jerry Ross, First Seven-Time Flier, Retires

NASA logo.

Jan. 27, 2012

Jerry Ross, the first person to launch into space seven times, has retired from NASA. In a career that spanned more than three decades, Ross spent almost 1,400 hours in space and conducted nine spacewalks to rank third on the list of most extravehicular activity time in space.

"Jerry has been instrumental in the success of many of NASA's human spaceflight missions and numerous spacewalks," said Peggy Whitson, chief of the Astronaut Office. "Not only were his skills and operational excellence key in major spaceflight activities but his expertise and vigilance also helped all those who followed in his footsteps. We are the better for his years of dedication to the corps and NASA."

Ross joined NASA in 1979 as a payload officer and flight controller. In 1980, he was selected as an astronaut. He and Franklin Chang-Diaz are the only two astronauts to have flown into space seven times. In addition to Ross' spaceflight mission accomplishments, he went on to serve NASA in the critical role of managing the Vehicle Integration Test Office.

Astronaut Jerry Ross

"Jerry was equally invaluable leading this critical team, especially through space station assembly, the transition to the space shuttle retirement, and during the initial phases of our future programs," said Janet Kavandi, director of Flight Crew Operations. "He was considered a mentor to many he worked with there. We wish him the best in his well-deserved retirement."

Of his seven flights into orbit, Ross flew on space shuttles Endeavour and Columbia once each and a record-setting five times on shuttle Atlantis, including his first and last missions. His first flight was on the STS-61B mission in 1985. His final flight into space was on the STS-110 mission in 2002.

During his seven missions, he assisted in deploying a number of satellites and other payloads. He performed experiments in life, material and Earth sciences, and physics, robotics and astronomy. Ross was a member of the STS-74 mission's crew, the second mission to dock to the Russian space station Mir. He also traveled to the then-fledgling International Space Station, where he helped connect the U.S.-built Unity node to the Russian Zarya module. On the STS-110 mission, Ross' final trip to space, he was instrumental in delivering and installing the S0 (S-Zero) truss. Ross accumulated more than 1,393 hours in space, including 58 hours and 18 minutes on nine spacewalks.

For Ross' complete biography, visit:

Image, Text, Credit: NASA.

Best regards,

jeudi 26 janvier 2012

Vesta Likely Cold and Dark Enough for Ice

NASA - Dawn Mission patch.

Jan. 26, 2012

This image obtained by the framing camera on NASA's Dawn spacecraft shows the south pole of the giant asteroid Vesta. Image credit: NASA / JPL-Caltech / UCLA / MPS / DLR / IDA.

Though generally thought to be quite dry, roughly half of the giant asteroid Vesta is expected to be so cold and to receive so little sunlight that water ice could have survived there for billions of years, according to the first published models of Vesta's average global temperatures and illumination by the sun.

"Near the north and south poles, the conditions appear to be favorable for water ice to exist beneath the surface," says Timothy Stubbs of NASA's Goddard Space Flight Center in Greenbelt, Md., and the University of Maryland, Baltimore County. Stubbs and Yongli Wang of the Goddard Planetary Heliophysics Institute at the University of Maryland published the models in the January 2012 issue of the journal Icarus. The models are based on information from telescopes including NASA's Hubble Space Telescope.

Vesta, the second-most massive object in the asteroid belt between Mars and Jupiter, probably does not have any significant permanently shadowed craters where water ice could stay frozen on the surface all the time, not even in the roughly 300-mile-diameter (480-kilometer-diameter) crater near the south pole, the authors note. The asteroid isn't a good candidate for permanent shadowing because it is tilted on its axis at about 27 degrees, which is even greater than Earth's tilt of roughly 23 degrees. In contrast, the moon, which does have permanently shadowed craters, is tilted at only about 1.5 degrees. As a result of its large tilt, Vesta has seasons, and every part of the surface is expected to see the sun at some point during Vesta's year.

As this global map of average surface temperature shows, the warmer equatorial zone of the giant asteroid Vesta is likely too warm to sustain water ice below the surface. Image credit: NASA / GSFC / UMBC.

The presence or absence of water ice on Vesta tells scientists something about the tiny world's formation and evolution, its history of bombardment by comets and other objects, and its interaction with the space environment. Because similar processes are common to many other planetary bodies, including the moon, Mercury and other asteroids, learning more about these processes has fundamental implications for our understanding of the solar system as a whole. This kind of water ice is also potentially valuable as a resource for further exploration of the solar system.

Though temperatures on Vesta fluctuate during the year, the model predicts that the average annual temperature near Vesta's north and south poles is less than roughly minus 200 degrees Fahrenheit (145 kelvins). That is the critical average temperature below which water ice is thought to be able to survive in the top 10 feet or so (few meters) of the soil, which is called regolith.

Near Vesta's equator, however, the average yearly temperature is roughly minus 190 degrees Fahrenheit (150 kelvins), according to the new results. Based on previous modeling, that is expected to be high enough to prevent water from remaining within a few meters of the surface. This band of relatively warm temperatures extends from the equator to about 27 degrees north and south in latitude.

"On average, it's colder at Vesta's poles than near its equator, so in that sense, they are good places to sustain water ice," says Stubbs. "But they also see sunlight for long periods of time during the summer seasons, which isn't so good for sustaining ice. So if water ice exists in those regions, it may be buried beneath a relatively deep layer of dry regolith."

New modeling shows that, under present conditions, Vesta's polar regions are cold enough (less than about 145 kelvins) to sustain water ice for billions of years, as this map of average surface temperature around the asteroid's south pole indicates. Image credit: NASA / GSFC / UMBC.

The modeling also indicates that relatively small surface features, such as craters measuring around 6 miles (10 kilometers) in diameter, could significantly affect the survival of water ice. "The bottoms of some craters could be cold enough on average -- about 100 kelvins -- for water to be able to survive on the surface for much of the Vestan year [about 3.6 years on Earth]," Stubbs explains. "Although, at some point during the summer, enough sunlight would shine in to make the water leave the surface and either be lost or perhaps redeposit somewhere else."

So far, Earth-based observations suggest that the surface of Vesta is quite dry. However, the Dawn spacecraft is getting a much closer view. Dawn is investigating the role of water in the evolution of planets by studying Vesta and Ceres, two bodies in the asteroid belt that are considered remnant protoplanets – baby planets whose growth was interrupted when Jupiter formed.

Dawn is looking for water using the gamma ray and neutron detector (GRaND) spectrometer, which can identify hydrogen-rich deposits that could be associated with water ice. The spacecraft recently entered a low orbit that is well suited to collecting gamma ray and neutron data.

"Our perceptions of Vesta have been transformed in a few months as the Dawn spacecraft has entered orbit and spiraled closer to its surface," says Lucy McFadden, a planetary scientist at NASA Goddard and a Dawn mission co-investigator. "More importantly, our new views of Vesta tell us about the early processes of solar system formation. If we can detect evidence for water beneath the surface, the next question will be is it very old or very young, and that would be exciting to ponder."

The modeling done by Stubbs and Wang, for example, relies on information about Vesta's shape. Before Dawn, the best source of that information was a set of images taken by NASA's Hubble Space Telescope in 1994 and 1996. But now, Dawn and its camera are getting a much closer view of Vesta.

"The Dawn mission gives researchers a rare opportunity to observe Vesta for an extended period of time, the equivalent of about one season on Vesta," says Stubbs. "Hopefully, we'll know in the next few months whether the GRaND spectrometer sees evidence for water ice in Vesta's regolith. This is an important and exciting time in planetary exploration."

Dawn's mission to Vesta and Ceres is managed by NASA's Jet Propulsion Laboratory, Pasadena, Calif., for NASA's Science Mission Directorate in Washington. JPL is a division of the California Institute of Technology in Pasadena. Dawn is a project of the directorate's Discovery Program, managed by NASA's Marshall Space Flight Center in Huntsville, Ala. UCLA is responsible for overall Dawn mission science. Orbital Sciences Corp. in Dulles, Va., designed and built the spacecraft. The German Aerospace Center, the Max Planck Institute for Solar System Research, the Italian Space Agency and the Italian National Astrophysical Institute are international partners on the mission team. The asteroid modeling by Stubbs and Wang is an extension of analysis originally applied to the moon and partially funded by the NASA Lunar Science Institute.

For more information about Dawn Mission, visit: and

Images (mentioned), Text, Credit: NASA / Goddard Space Flight Center / Elizabeth Zubritsky / JPL / Jia-Rui Cook.


NASA's Kepler Announces 11 Planetary Systems Hosting 26 Planets

NASA - Kepler Mission patch.

Jan. 26, 2012

NASA's Kepler mission has discovered 11 new planetary systems hosting 26 confirmed planets. These discoveries nearly double the number of verified planets and triple the number of stars known to have more than one planet that transits, or passes in front of, the star. Such systems will help astronomers better understand how planets form.

(Click on the image for enlarge)

Kepler's Planetary Systems: The artist's rendering depicts the multiple planet systems discovered by NASA's Kepler mission. Image credit: NASA Ames / Jason Steffen, Fermilab Center for Particle Astrophysics.

The planets orbit close to their host stars and range in size from 1.5 times the radius of Earth to larger than Jupiter. Fifteen are between Earth and Neptune in size. Further observations will be required to determine which are rocky like Earth and which have thick gaseous atmospheres like Neptune. The planets orbit their host star once every six to 143 days. All are closer to their host star than Venus is to our sun.

"Prior to the Kepler mission, we knew of perhaps 500 exoplanets across the whole sky," said Doug Hudgins, Kepler program scientist at NASA Headquarters in Washington. "Now, in just two years staring at a patch of sky not much bigger than your fist, Kepler has discovered more than 60 planets and more than 2,300 planet candidates. This tells us that our galaxy is positively loaded with planets of all sizes and orbits."

Kepler identifies planet candidates by repeatedly measuring the change in brightness of more than 150,000 stars to detect when a planet passes in front of the star. That passage casts a small shadow toward Earth and the Kepler spacecraft.

Each of the new confirmed planetary systems contains two to five closely spaced transiting planets. In tightly packed planetary systems, the gravitational pull of the planets on each other causes some planets to accelerate and some to decelerate along their orbits. The acceleration causes the orbital period of each planet to change. Kepler detects this effect by measuring the changes, or so-called Transit Timing Variations (TTVs).

Kepler's Planetary Systems' Orbits: The image shows an overhead view of orbital positions of the planets in systems with multiple transiting planets discovered by NASA's Kepler mission.Image credit: NASA Ames / Dan Fabrycky, University of California, Santa Cruz.

Planetary systems with TTVs can be verified without requiring extensive ground-based observations, accelerating confirmation of planet candidates. The TTV detection technique also increases Kepler's ability to confirm planetary systems around fainter and more distant stars.

Five of the systems (Kepler-25, Kepler-27, Kepler-30, Kepler-31 and Kepler-33) contain a pair of planets where the inner planet orbits the star twice during each orbit of the outer planet. Four of the systems (Kepler-23, Kepler-24, Kepler-28 and Kepler-32) contain a pairing where the outer planet circles the star twice for every three times the inner planet orbits its star.

"These configurations help to amplify the gravitational interactions between the planets, similar to how my sons kick their legs on a swing at the right time to go higher," said Jason Steffen, the Brinson postdoctoral fellow at Fermilab Center for Particle Astrophysics in Batavia, Ill., and lead author of a paper confirming four of the systems.


Kepler's Planetary Systems in Motion: The animation shows an overhead view of the orbital position of the planets in systems with multiple transiting planets discovered by NASA's Kepler mission. All the colored planets have been verified. More vivid colors indicate planets that have been confirmed by their gravitational interactions with each other or the star. Several of these systems contain additional planet candidates (shown in grey) that have not yet been verified. Video credit: NASA Ames / Dan Fabrycky, University of California, Santa Cruz.

Kepler-33, a star that is older and more massive than our sun, had the most planets. The system hosts five planets, ranging in size from 1.5 to 5 times that of Earth. All of the planets are located closer to their star than any planet is to our sun.

The properties of a star provide clues for planet detection. The decrease in the star's brightness and duration of a planet transit, combined with the properties of its host star, present a recognizable signature. When astronomers detect planet candidates that exhibit similar signatures around the same star, the likelihood of any of these planet candidates being a false positive is very low.

"The approach used to verify the Kepler-33 planets shows the overall reliability is quite high," said Jack Lissauer, planetary scientist at NASA Ames Research Center at Moffett Field, Calif., and lead author of the paper on Kepler-33. "This is a validation by multiplicity."


Transit Timing Variations: The animation shows the difference between planet transit timing of single and multiple planet system. In tightly packed planetary systems, the gravitational pull of the planets among themselves causes one planet to accelerate and another planet to decelerate along its orbit. The acceleration causes the orbital period of each planet to change. Kepler detects this effect by measuring the change known as Transit Timing Variations (TTVs). Video credit: NASA Ames / Kepler mission.

These discoveries are published in four different papers in the Astrophysical Journal and the Monthly Notices of the Royal Astronomical Society.

Ames manages Kepler's ground system development, mission operations and science data analysis. NASA's Jet Propulsion Laboratory, Pasadena, Calif., managed the Kepler mission's development.

For more information about the Kepler mission and to view the digital press kit, visit:

Images (mentioned), Videos (mentioned), Text, Credit: NASA Ames Research Center / Michele Johnson.


mercredi 25 janvier 2012

INTEGRAL reveals new facets of the Vela pulsar wind nebula

ESA - INTEGRAL Mission patch.

25 Jan 2012

Astronomers studying the Vela pulsar wind nebula with ESA's INTEGRAL observatory have successfully resolved its morphology in the hard X-ray band, for the first time. This pulsar-powered nebula is the most extended individual source yet observed at these energies. The study exploited a special imaging technique to reveal a new component of the source that likely consists of highly energetic electrons that have escaped from the core of the nebula in the last few thousand years.

All-sky image obtained with INTEGRAL at hard X-ray energies. The Vela pulsar wind nebula is shown in the insert. Credit: All-sky image: ESA/INTEGRAL/IBIS/F. Lebrun / CEA, Saclay; Insert: ESA / INTEGRAL / IBIS-ISGRI / F. Mattana et al.

One of the milestones in modern astrophysics was the discovery, in the late 1960s, of the Vela and Crab pulsars. These pulsating sources were the first of their kind to be detected within the remnants of supernova explosions. By providing the first evidence for a causal link between the then recently discovered class of sources and the demise of massive stars, these observations clarified the nature of pulsars: rapidly spinning and strongly magnetised neutron stars.

Like all pulsars powered by their own rotation, the Vela pulsar gradually releases its rotational kinetic energy by driving a steady wind of highly energetic electrons and positrons. Pulsar winds create clouds of charged particles, known as pulsar wind nebulae (PWN), that radiate energy across the electromagnetic spectrum and are thus observable in several bands. During its early phases, the highly pressurised PWN expands at high speed in its denser environment, which consists of ejected material from the supernova explosion that created the pulsar and swept up material from the surrounding interstellar medium. This structure, known as a supernova remnant (SNR), in turn expands into the diffuse interstellar medium. Interactions between the expanding components produce a number of interesting effects affecting the dynamical evolution and, subsequently, the morphology of PWN.

Image of the Vela pulsar wind nebula obtained with INTEGRAL at hard X-ray energies, between 18 and 40 keV. The angular size of the full Moon is shown for comparison.Credit: ESA / INTEGRAL / IBIS-ISGRI / F. Mattana et al.

At a distance of about 900 light-years, the Vela PWN is one of the nearest of its kind and thus offers an opportunity for detailed investigations. It has been studied extensively at X- and gamma-ray energies, as well as in radio waves. A recent study led by Fabio Mattana from the Laboratoire APC – AstroParticule et Cosmologie, Paris, France, has used data from ESA's INTEGRAL mission to image the Vela PWN at hard X-ray energies, between 18 and 40 keV. By resolving a PWN at these energies for the first time, the study opens up a new and revealing spectral window on these intriguing objects.

Multiwavelength observations of a PWN help to sample populations of particles with different energies that exist in the cloud. In particular, X-rays are released by electrons as they move along the pulsar's magnetic field (synchrotron emission); in contrast, gamma-ray emission arises from a different physical mechanism: the energy boost that synchrotron photons experience when they scatter off electrons (Inverse Compton emission). This means that, somewhat counterintuitively, the most energetic particles in a PWN are revealed by observations in the hard X-ray, rather than the gamma-ray, spectral band.

"Since the most energetic particles in a PWN are the ones with the shortest lifetime, our observations of the Vela PWN in hard X-rays provide a fresh look at this source's recent history," comments Mattana. The study used data from the IBIS imager on board INTEGRAL and applied a special data analysis technique that was developed in 2006 to further exploit the capabilities of the instrument. Originally optimised to study point sources, with this method IBIS is also suitable for the observation of extended sources and the characterisation of their morphology.

The Vela pulsar wind nebula in the X- and gamma-ray bands. Credit: ESA / INTEGRAL / IBIS-ISGRI / F. Mattana et al./ROSAT/ H.E.S.S. / Spacelab 2.

"Besides confirming the results of previous observations of the Vela PWN, which showed a cocoon-shaped cloud to the south-west of the pulsar at soft X-ray and gamma-ray wavelengths, the new INTEGRAL image reveals a previously unknown component at a rather unexpected location, north-east of the pulsar," Mattana adds.

The well-known asymmetric structure of the Vela PWN, with the 'cocoon' on one side of the pulsar, is typical of an evolved PWN. This object is in fact a prototype of PWN undergoing this phase of their evolution. As the expanding SNR sweeps up material from the surrounding interstellar medium, it produces two shock waves, moving outwards and inwards, respectively. When the latter, known as the 'reverse' shock, eventually hits the boundary of the PWN, a few thousand years after the supernova explosion, it compresses and distorts the cloud, giving it a chaotic and filamentary structure. In the process, as a consequence of the SNR expansion into an inhomogeneous interstellar medium asymmetries in the cloud shape and displacements of the PWN with respect to the pulsar often arise.

The newly detected component, seen only in hard X-rays so far, can also be explained as an effect of the reverse shock. "We believe that the newly-revealed region is a 'recently' born cloud, consisting of particles that have been injected by the pulsar after the supernova reverse shock has 'wiped away' the pre-existing nebula from the pulsar surroundings," explains Mattana. "In this case, the displaced lobe would only be populated by freshly injected particles, released by the Vela pulsar in the last couple of thousand years; these shine brightly at hard X-ray energies," he adds. This scenario is also consistent with the spectral analysis of data from INTEGRAL and from the Japanese-US Suzaku mission, also performed during the same study. Mattana and his colleagues hope that more clues about the nature of the newly-detected lobe will emerge with future observations of the source at lower X-ray energies, to be performed with ESA's XMM-Newton X-ray observatory and other facilities.

This study presents the first INTEGRAL image of extended emission around the Vela pulsar in this energy range. With an angular size of about 50 arc minutes on each side, the Vela PWN is the most extended individual source observed at hard X-ray energies thus far. It is also the first time that the application of this imaging technique has allowed a detailed investigation of the source's morphology.

"The result is a significant achievement for INTEGRAL and showcases the versatility of the instruments on board the observatory as well as the creativity of its user community," comments Chris Winkler, INTEGRAL Project Scientist at ESA. "With this technique, we have a new way to investigate the hard X-ray sky, and we look forward to its application to other sources, such as nearby supernova remnants."

Notes for editors:

The study presented here is based on observations performed with IBIS, the coded-mask imager on board INTEGRAL, with its low-energy detector ISGRI, which is sensitive to the energy range between 15 keV and 1 MeV.

As with all coded-mask imagers, IBIS does not produce images directly but via a reconstruction algorithm. The design of IBIS is optimised for the study of point sources in the hard X-ray sky and the standard reconstruction technique used to obtain images from IBIS data strongly concentrates on the portions of the sky where the radiation flux peaks. This has the disadvantage of centralising possibly extended sources at the expense of their flux, reducing them to apparent point sources with a tenfold dimmer flux.

In order to employ IBIS to study extended sources, a novel approach has been developed to overcome this drawback. This method takes account of the telescope point spread function over the entire field of view in order to properly rescale the flux in the images. A correct image of the source over its entire angular extent is then achieved. The method has been developed by Matthieu Renaud (currently at Laboratoire Univers et Particules de Montpellier, France) and collaborators in 2006 and is described in M. Renaud, et al. (2006).

INTEGRAL is an ESA project with instruments and science data centre funded by ESA Member States (especially the Principal Investigator countries: Denmark, France, Germany, Italy, Spain, Switzerland) and Poland, and with the participation of Russia and the USA.

Related publications:

F. Mattana, et al., "Extended Hard X-Ray Emission from the Vela Pulsar Wind Nebula", 2011, The Astrophysical Journal Letters, 743, 18
DOI: 10.1088/2041-8205/743/1/L18

M. Renaud, et al., "Imaging extended sources with coded mask telescopes: application to the INTEGRAL IBIS/ISGRI instrument", 2006, Astronomy and Astrophysics, 456, 389
DOI: 10.1051/0004-6361:20065156

For more information about INTEGRAL, visit:

Images (mentioned), Text, Credits: Laboratoire APC – AstroParticule et Cosmologie Université Paris Diderot Paris, France / INTEGRAL Project Scientist Research and Scientific Support Department Directorate of Science and Robotic Exploration ESA, The Netherlands.


Microsatellite "Chibis-M" was launched into orbit

ROSCOSMOS - Microsatellite Chibis-M patch.


January 25 in Moscow 03.18.30 small spacecraft "Chibis-M" separated from the cargo vehicle (THC), "Progress M-13M" and began its autonomous flight.

Dropping of microsatellite "Chibis-M" in orbit

According to the ballistic Service Mission Control Center microsatellite was launched with the following parameters:

    • The minimum height above the surface of the Earth - 497.535 km;

    • The maximum height above the surface of the Earth - 513.607 km;

    • period - 94.55 minutes;

    • inclination - 51.62 degrees.

A few minutes after separation, "Shibis-M" was produced the first telemetry data, which confirmed that the office of the device are included.

Small Spacecraft "Chibis-M" was delivered to the International Space Station (ISS), THC, "Progress M-13M" November 2, 2011. After flights to the ISS January 24, 2012 a cargo ship with a set of microsatellite It undocked from the station and transferred to a higher orbit. For the first time that a tug was used THC such as "Progress".

This maneuver was performed in order to launch into the working orbit "Chibisa-M", intended to implement a new geophysical experiment designed to study complex physical processes in atmospheric lightning discharges.


Microsatellite "Chibis-M" was created at the Institute of Space Research Institute in conjunction with other scientific organizations.

Approximately one-third the mass of the satellite is a complex of scientific equipment (KPA), "The Storm". For the first time on a single satellite has a set of devices, "overlapping" range from gamma to radio waves, which are intended research will "see" the largest possible number of processes that occur when a lightning discharge.

In the KPA "The Storm" includes x-ray detectors, gamma, ultraviolet and radio waves (30-50 MHz), generated by lightning discharge at an altitude of 13-20 km. In the KPA also includes instruments for studying the plasma oscillations. To understand whether these are accompanied by flashes of lightning radiation, the KPA equipped with a digital camera.

X-ray detector and gamma-radiation and UV detector set at the Research Institute of Nuclear Physics. DV Skobeltsyn University. Radio frequency analyzer is designed to IKI. In the KPA is also a digital camera digital camera (IKI), which will take pictures of Earth in the optical and detector analyzers electromagnetic radiation (0,1-40000 Hz) - magnetic plasma ERM complex, created by Ukrainian and Hungarian scientists.

"Chibis-M" is in line with several devices, which are also involved in the study of phenomena and lightning discharges in the upper atmosphere.

Weight about 40 kg microsatellite.

Dimensions in the open state (antenna and solar panels) 1250x966 mm.

Original text in Russian:

Image, Video, Text, Credit: Press-service of Federal Space Agency (Roscosmos PAO), and PCOs / Translation:


The Wild Early Lives of Today's Most Massive Galaxies

ESO - European Southern Observatory logo.

25 January 2012

Dramatic star formation cut short by black holes

 Distant star-forming galaxies in the early Universe

Using the APEX telescope, a team of astronomers has found the strongest link so far between the most powerful bursts of star formation in the early Universe, and the most massive galaxies found today. The galaxies, flowering with dramatic starbursts in the early Universe, saw the birth of new stars abruptly cut short, leaving them as massive — but passive — galaxies of aging stars in the present day. The astronomers also have a likely culprit for the sudden end to the starbursts: the emergence of supermassive black holes.

Astronomers have combined observations from the LABOCA camera on the ESO-operated 12-metre Atacama Pathfinder Experiment (APEX) telescope [1] with measurements made with ESO’s Very Large Telescope, NASA’s Spitzer Space Telescope, and others, to look at the way that bright, distant galaxies are gathered together in groups or clusters.

The position of the Extended Chandra Deep Field South in the constellation of Fornax

The more closely the galaxies are clustered, the more massive are their halos of dark matter — the invisible material that makes up the vast majority of a galaxy’s mass. The new results are the most accurate clustering measurements ever made for this type of galaxy.

The galaxies are so distant that their light has taken around ten billion years to reach us, so we see them as they were about ten billion years ago [2]. In these snapshots from the early Universe, the galaxies are undergoing the most intense type of star formation activity known, called a starburst.

Distant star-forming galaxies in the early Universe (zoom)

By measuring the masses of the dark matter halos around the galaxies, and using computer simulations to study how these halos grow over time, the astronomers found that these distant starburst galaxies from the early cosmos eventually become giant elliptical galaxies — the most massive galaxies in today’s Universe.

“This is the first time that we've been able to show this clear link between the most energetic starbursting galaxies in the early Universe, and the most massive galaxies in the present day," explains Ryan Hickox (Dartmouth College, USA and Durham University, UK), the lead scientist of the team.

Furthermore, the new observations indicate that the bright starbursts in these distant galaxies last for a mere 100 million years — a very short time in cosmological terms — yet in this brief time they are able to double the quantity of stars in the galaxies. The sudden end to this rapid growth is another episode in the history of galaxies that astronomers do not yet fully understand.

Distant star-forming galaxies in the early Universe (pan)

“We know that massive elliptical galaxies stopped producing stars rather suddenly a long time ago, and are now passive. And scientists are wondering what could possibly be powerful enough to shut down an entire galaxy’s starburst,” says Julie Wardlow (University of California at Irvine, USA and Durham University, UK), a member of the team.

The team’s results provide a possible explanation: at that stage in the history of the cosmos, the starburst galaxies are clustered in a very similar way to quasars, indicating that they are found in the same dark matter halos. Quasars are among the most energetic objects in the Universe — galactic beacons that emit intense radiation, powered by a supermassive black hole at their centre.

There is mounting evidence to suggest the intense starburst also powers the quasar by feeding enormous quantities of material into the black hole. The quasar in turn emits powerful bursts of energy that are believed to blow away the galaxy’s remaining gas — the raw material for new stars — and this effectively shuts down the star formation phase.

“In short, the galaxies’ glory days of intense star formation also doom them by feeding the giant black hole at their centre, which then rapidly blows away or destroys the star-forming clouds,” explains David Alexander (Durham University, UK), a member of the team.


[1] The 12-metre-diameter APEX telescope is located on the Chajnantor plateau in the foothills of the Chilean Andes. APEX is a pathfinder for ALMA, the Atacama Large Millimeter/submillimeter Array, a revolutionary new telescope that ESO, together with its international partners, is building and operating, also on the Chajnantor plateau. APEX is itself based on a single prototype antenna constructed for the ALMA project. The two telescopes are complementary: for example, APEX can find many targets across wide areas of sky, which ALMA will be able to study in great detail. APEX is a collaboration between the Max Planck Institute for Radio Astronomy (MPIfR), the Onsala Space Observatory (OSO) and ESO.

[2] These distant galaxies are known as submillimetre galaxies. They are very bright galaxies in the distant Universe in which intense star formation occurs. Because of this extreme distance, their infrared light from dust grains heated by starlight is redshifted into longer wavelengths, and the dusty galaxies are therefore best observed in submillimetre wavelengths of light.

More information:

This research is presented in a paper to appear in the journal Monthly Notices of the Royal Astronomical Society on 26 January 2012.

The team is composed of Ryan C. Hickox (Dartmouth College, Hanover, USA; Department of Physics, Durham University (DU); STFC Postdoctoral Fellow, UK), J. L. Wardlow (Department of Physics & Astronomy, University of California at Irvine, USA; Department of Physics, DU, UK), Ian Smail (Institute for Computational Cosmology, DU, UK), A. D. Myers (Department of Physics and Astronomy, University of Wyoming, USA), D. M. Alexander (Department of Physics, DU, UK), A. M. Swinbank (Institute for Computational Cosmology, DU, UK), A. L. R. Danielson (Institute for Computational Cosmology, DU, UK), J. P. Stott (Department of Physics, DU, UK), S. C. Chapman (Institute of Astronomy, Cambridge, UK), K. E. K. Coppin (Department of Physics, McGill University, Canada), J. S. Dunlop (Institute for Astronomy, University of Edinburgh, UK), E. Gawiser (Department of Physics and Astronomy, The State University of New Jersey, USA), D. Lutz (Max-Planck-Institut für extraterrestrische Physik, Germany), P. van der Werf (Leiden Observatory, Leiden University, The Netherlands), A. Weiß (Max-Planck-Institut für Radioastronomie, Germany).

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”.

ALMA, an international astronomy facility, is a partnership of Europe, North America and East Asia in cooperation with the Republic of Chile. ALMA construction and operations are led on behalf of Europe by ESO, on behalf of North America by the National Radio Astronomy Observatory (NRAO), and on behalf of East Asia by the National Astronomical Observatory of Japan (NAOJ). The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.


    Research paper:

    Information about APEX:

    Images related to APEX:

Images, Text, Credit: ESO, APEX (MPIfR / ESO / OSO), A. Weiss et al., NASA Spitzer Science Center/IAU and Sky & Telescope / Videos: ESO, APEX (MPIfR / ESO / OSO), A. Weiss et al., NASA Spitzer Science Center, Digitized Sky Survey 2, and A. Fujii. Music: John Dyson (from the album Moonwind).

Best regards,

mardi 24 janvier 2012

Durable NASA Rover Beginning Ninth Year of Mars Work

NASA - Mars Exploration Rover "Opportunity" (MER-B) patch.

Jan. 24, 2012

 NASA's Opportunity rover hits 8-year mark on Mars
Eight years after landing on Mars for what was planned as a three-month mission, NASA's enduring Mars Exploration Rover Opportunity is working on what essentially became a new mission five months ago.

Opportunity reached a multi-year driving destination, Endeavour Crater, in August 2011. At Endeavour's rim, it has gained access to geological deposits from an earlier period of Martian history than anything it examined during its first seven years. It also has begun an investigation of the planet's deep interior that takes advantage of staying in one place for the Martian winter.

Opportunity landed in Eagle Crater on Mars on Jan. 25, 2004, Universal Time and EST (Jan. 24, PST), three weeks after its rover twin, Spirit, landed halfway around the planet. In backyard-size Eagle Crater, Opportunity found evidence of an ancient wet environment. The mission met all its goals within the originally planned span of three months. During most of the next four years, it explored successively larger and deeper craters, adding evidence about wet and dry periods from the same era as the Eagle Crater deposits.

This mosaic of images taken in mid-January 2012 shows the windswept vista northward (left) to northeastward (right) from the location where NASA's Mars Exploration Rover Opportunity is spending its fifth Martian winter, an outcrop informally named "Greeley Haven." Image credit: NASA / JPL-Caltech / Cornell / Arizona State Univ.

In mid-2008, researchers drove Opportunity out of Victoria Crater, half a mile (800 meters) in diameter, and set course for Endeavour Crater, 14 miles (22 kilometers) in diameter.

"Endeavour is a window further into Mars' past," said Mars Exploration Rover Program Manager John Callas, of NASA's Jet Propulsion Laboratory, Pasadena, Calif.

The trek took three years. In a push to finish it, Opportunity drove farther during its eighth year on Mars -- 4.8 miles (7.7 kilometers) -- than in any prior year, bringing its total driving distance to 21.4 miles (34.4 kilometers).

The "Cape York" segment of Endeavour's rim, where Opportunity has been working since August 2011, has already validated the choice of Endeavour as a long-term goal. "It's like starting a new mission, and we hit pay dirt right out of the gate," Callas said.

The first outcrop that Opportunity examined on Cape York differs from any the rover had seen previously. Its high zinc content suggests effects of water. Weeks later, at the edge of Cape York, a bright mineral vein identified as hydrated calcium sulfate provided what the mission's principal investigator, Steve Squyres of Cornell University, Ithaca, N.Y., calls "the clearest evidence for liquid water on Mars that we have found in our eight years on the planet."

Mars years last nearly twice as long as Earth years. Entering its ninth Earth year on Mars, Opportunity is also heading into its fifth Martian winter. Its solar panels have accumulated so much dust since Martian winds last cleaned them -- more than in previous winters -- the rover needs to stay on a sun-facing slope to have enough energy to keep active through the winter.

The rover team has not had to use this strategy with Opportunity in past winters, though it did so with Spirit, farther from the equator, for the three Martian winters that Spirit survived. By the beginning of the rovers' fourth Martian winter, drive motors in two of Spirit's six wheels had ceased working, long past their design lifespan. The impaired mobility kept the rover from maneuvering to an energy-favorable slope. Spirit stopped communicating in March 2010.

All six of Opportunity's wheels are still useful for driving, but the rover will stay on an outcrop called "Greeley Haven" until mid-2012 to take advantage of the outcrop's favorable slope and targets of scientific interest during the Martian winter. After the winter, or earlier if wind cleans dust off the solar panels, researchers plan to drive Opportunity in search of clay minerals that a Mars orbiter's observations indicate lie on Endeavour's rim.

"The top priority at Greeley Haven is the radio-science campaign to provide information about Mars' interior," said JPL's Diana Blaney, deputy project scientist for the mission. This study uses weeks of tracking radio signals from the stationary rover to measure wobble in the planet's rotation. The amount of wobble is an indicator of whether the core of the planet is molten, similar to the way spinning an egg can be used to determine whether it is raw or hard-boiled.

Opportunity's Panoramic Camera (Pancam) took the component images as part of full-circle view being assembled from Greeley Haven. Image credit: NASA / JPL-Caltech / Cornell / Arizona State Univ.

Other research at Greeley Haven includes long-term data gathering to investigate mineral ingredients of the outcrop with spectrometers on Opportunity's arm, and repeated observations to monitor wind-caused changes at various scales.

The Moessbauer spectrometer, which identifies iron-containing minerals, uses radiation from cobalt-57 in the instrument to elicit a response from molecules in the rock. The half-life of cobalt-57 is only about nine months, so this source has diminished greatly. A measurement that could have been made in less than an hour during the rover's first year now requires weeks of holding the spectrometer on the target.

Observations for the campaign to monitor wind-caused changes range in scale from dunes in the distance to individual grains seen with the rover's microscopic imager. "Wind is the most active process on Mars today," Blaney said. "It is harder to watch for changes when the rover is driving every day. We are taking advantage of staying at one place for a while."

NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Mars Exploration Rover Project for the NASA Science Mission Directorate, Washington. More information about Opportunity is online at: and . You can follow the project on Twitter at and on Facebook at .

Images (mentioned), Video, Text, Credit: NASA / JPL / JPL-Caltech / Guy Webster.


LHC physics: More than just the Higgs search

CERN - European Organization for Nuclear Research logo.

Jan. 24, 2012

Events containing a muon pair and a photon detected by the ATLAS calorimeter. The three peaks are events consistent with different quarkonium decay states. The scale on the horizontal axis is mass. (Credit: ATLAS)

The LHC has been in the limelight recently with the first tantalizing hints concerning the Higgs boson. But there's more to physics at the LHC. Two of the LHC experiments have recently made discoveries in other areas of particle physics.

In November the LHCb experiment reported a new effect in the decays of particles containing a charm quark (or antiquark). The result could be the first evidence for CP violation  - a tiny difference in the behaviour of matter and antimatter - in charmed particles. The effect is very small, but more data should reveal whether it points to physics beyond the Standard Model.

 The ATLAS detector

Dimensions: 46 feet long, 25 meters wide, 25 feet high, ATLAS is the largest detector ever built.
  -   Weight: 7000 tons
  -   Configuration: Barrel and caps
  -   Location: Meyrin, Switzerland.

In December the ATLAS experiment announced the discovery of a new "quarkonium state", containing a beauty quark bound with its antiquark. Predicted by theory, it is known as the χb(3P). The new state will help in understanding the force that binds quarks (and antiquarks) together.

Watch out for more discoveries in 2012!


The European Organization for Nuclear Research (French: Organisation européenne pour la recherche nucléaire), known as CERN, is an international organization whose purpose is to operate the world's largest particle physics laboratory, which is situated in the northwest suburbs of Geneva on the Franco–Swiss border. Established in 1954, the organization has twenty European member states.

The term CERN is also used to refer to the laboratory itself, which employs just under 2400 full-time employees/workers, as well as some 7931 scientists and engineers representing 608 universities and research facilities and 113 nationalities.

find out more:

    LHCb website:

    Quantum diaries: Charm and beauty - LHCb has it all!:

    ATLAS discovers its first new particle:

    Quantum diaries: New compostie particle discovered by ATLAS:

Images, Text, Credit: CERN.


A solar flare strikes Earth

NASA / ESA - SOHO Mission patch / NASA - Solar Dynamics Observatory (SDO) patch.

Jan. 24, 2012

The largest solar flare since 2005 has begin to hit the Earth, bombarding the planet magnetic particles that could disrupt satellite communications, announced Monday the U.S. authorities.

The eruption was triggered Sunday near the center of the sun. It should project particles of protons toward Earth until Wednesday. This geomagnetic storm is the strongest since 2005. Ranked 3 on a scale of 5, it is "strong" but not "severe." It may be that the people of Europe and Asia see the Northern Lights.

 Aurora Borealis over Eastern Europe from the International Space Station

Long Duration M3.2 Class Solar Flare and CME


Video above: The Solar Dynamics Observatory (SDO) captured this video of the M3.2 solar flare on January 19, 2012. The graph at the top indicates corresponding X-ray measurements taken by the GOES-15 satellite. Credit: NASA / SDO / GOES-15.

A long duration M-class flare began erupting on the sun at 8:42 AM ET on Thursday, January 19. The flare is shown in the above movie from the Solar Dynamics Observatory in a combination of light wavelengths. An earth-directed coronal mass ejection was associated with the solar flare. 

SOHO Sees Jan 19, 2012 CME


Video above: A coronal mass ejection beginning at about 10 AM ET on January 19, 2012, as captured by the Solar Heliospheric Observatory's LASCO C2 camera. Please Note: This video loops 3 times. Credit: NASA / SOHO.

01.22.12: SOHO's View of Earth-directed CME


Video above: The Solar Heliospheric Observatory captured the coronal mass ejection (CME) in this video (which shows the sun's activity from January 19 to January 23). The CME is associate with an M8.7 class solar flare from AR1402. The end of the movie shows the interference caused by the onslaught of fast, energetic solar particles emitted from the sun. Credit: SOHO/ESA & NASA

 An earth-directed coronal mass ejection was associated with the solar flare. NASA's Space Weather Services estimates that it is traveling at over 630 miles per second and will reach Earth some time on Saturday, January 24, when strong geomagnetic storms are possible and viewers can be on the look out for increased aurora.

01.22.12: SDO's View of M8.7 Solar Flare


Video above: Solar Dynamics Observatory captured the flare, shown here in teal as that is the color typically used to show light in the 131 Angstrom wavelength, a wavelength in which it is easy to view solar flares. The flare began at 10:38 PM ET on Jan. 22, peaked at 10:59 PM and ended at 11:34 PM.

Radiation Belt's Reaction to Geomagnetic Storms


From October to December 2003, the radiation belts swelled and shrank in response to geomagnetic storms as particles entered and escaped the belts. At one point, 3 radiation belts are detected.

Under the wave of energetic particles from the Halloween 2003 solar storm events, the Earth's radiation belts underwent significant changes in structure. This visualization is constructed using daily-averaged particle flux data from the SAMPEX satellite installed in a simple dipole model for the Earth's magnetic field.

What is a solar flare? What is a coronal mass ejection?

For answers to these and other space weather questions, please visit the Spaceweather Frequently Asked Questions page:

Videos (mentioned), Image, Text, Credit: ESA / NASA Goddard Space Flight Center / Karen C. Fox / Translation:


lundi 23 janvier 2012

Cassini Flyby of Saturn's Largest Moon Dione

NASA / ESA - Cassini "insider's" logo.

Jan. 23, 2012

 Past Night

Saturn's moon Mimas peeks out from behind the night side of the larger moon Dione in this Cassini image captured during the spacecraft's Dec. 12, 2011, flyby of Dione.

Dione is 698 miles, or 1,123 kilometers, across and its day side dominates the view on the right of the image. Smaller Mimas is on the left and measures 246 miles, or 396 kilometers, across.

Lit terrain seen here is on the Saturn-facing side of Mimas and in the area between the trailing hemisphere and anti-Saturn side of Dione. North on the moons is up and rotated 20 degrees to the right.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera. The view was obtained at a distance of approximately 58,000 miles (94,000 kilometers) from Dione and at a Sun-Dione-spacecraft, or phase, angle of 42 degrees. Image scale is 1,833 feet (559 meters) per pixel on Dione. The view was obtained at a distance of approximately 380,000 miles (611,000 kilometers) from Mimas and at a Sun-Mimas-spacecraft, or phase, angle of 41 degrees. Image scale is 2 miles (3 kilometers) per pixel on Mimas.

The Cassini-Huygens mission is a cooperative project of NASA, 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, D.C. 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, Colo.

For more information about the Cassini-Huygens mission visit and . The Cassini imaging team homepage is at

Dione's image gallery:

Image, Text, Credit: NASA / JPL-Caltech / Space Science Institute.

Best regards,

The two faces of Titan's dunes

NASA / ESA - Cassini Mission to Saturn patch.

23 January 2012

A new analysis of radar data from the international Cassini spacecraft has revealed regional variations amongst Titan's sand dunes. The result yields new clues to the giant moon's climatic and geological history.

Dune fields are common on Titan, the largest moon of Saturn, second only to the seemingly uniform plains that cover most of the surface.

They cover about 13% of Titan, stretching over 10 million sq km, roughly equivalent to the area of Canada. Thus they offer a large-scale insight into the moon's environment.

Though similar in shape to the linear sand dunes found in the deserts of Namibia or southern Arabia, Titan's dunes are gigantic by Earthly standards. They are on average 1–2 km wide, hundreds of kilometres long and around 100 m high.

Dunes on Titan and Earth

However, their size and spacing vary across the surface, betraying the environment in which they have formed and evolved.

Another difference is that sand on Titan is not made of silicates as on Earth, but of solid hydrocarbons that precipitate out of the atmosphere. These then aggregate into millimetre-sized grains by a still unknown process.

Using radar data from the NASA–ESA–ASI Cassini spacecraft, Alice Le Gall, of LATMOS-UVSQ, Paris and NASA–JPL, California, and collaborators have discovered that the size of Titan's dunes is controlled by at least two factors: altitude and latitude.

The main dune fields on Titan are found in lowland areas. Dunes at higher elevations tend to be narrower and more widely separated, and the gaps between them appear brighter to Cassini's radar, indicating a thinner covering of sand.

This suggests that there is relatively little sand available at higher elevations to build dunes, while more is present in the lowlands.

In terms of latitude, the dunes on Titan are confined to its equatorial region, in a band between 30°S and 30°N.

However, they tend to become narrower and more widely spaced at northern latitudes. Dr Le Gall and colleagues think that this may be due to Saturn's elliptical orbit.

Titan orbits Saturn and so the moon's seasons are controlled by Saturn's path around the Sun. Because Saturn takes about 30 years to complete an orbit, each season on Titan lasts for just over seven years. The slightly elliptical nature of Saturn's orbit means that the southern hemisphere of the moon has shorter but more intense summers.

Cassini orbiting Titan

As a result, in southern regions, surface wetness due to ethane and methane vapour in the soil is reduced. The drier the sand grains, the more easily they can be transported by the winds to make dunes.

"As one goes to the north, the soil moisture probably increases, making the sand particles less mobile and, as a consequence, the development of dunes more difficult," says Dr Le Gall.

Backing up this hypothesis is the fact that Titan's lakes and seas of liquid ethane and methane are predominantly found in the northern hemisphere, suggesting again that the soil may be moister towards the north, again making it harder to transport sand grains by the wind.

"Understanding how the dunes form as well as explaining their shape, size and distribution on Titan's surface is of great importance to understanding Titan's climate and geology," says Nicolas Altobelli, ESA's Cassini–Huygens project scientist.

"As their material is made out of frozen atmospheric hydrocarbons, the dunes might provide us with important clues on the still puzzling methane/ethane cycle on Titan, comparable in many aspects with the water cycle on Earth." 

For more Information about Cassini Mission, visit:

Images, Text, Credits: NASA / JPL–Caltech / ASI / ESA and USGS.


Satellites detect abundance of fresh water in the Arctic

ESA logo.

23 January 2012

 Rising seas in Arctic Ocean (CPOM/UCL/ESA/Planetary Visions)

ESA satellites show that a large dome of fresh water has been building up in the Arctic Ocean over the last 15 years. A change in wind direction could cause the water to spill into the north Atlantic, cooling Europe.

The results are remarkable: since 2002, the sea surface in the studied area has risen by about 15 cm, and the volume of fresh water has increased by some 8000 cubic km – around 10% of all the fresh water in the Arctic Ocean.

Researchers from the Centre for Polar Observation and Modelling (CPOM) at University College London and the UK’s National Oceanography Centre used data from ESA’s ERS-2 and Envisat satellites to measure sea-surface height over the western Arctic from 1995 to 2010.

The results were published yesterday in the online version of the scientific journal, Nature Geoscience. 

The scientists conclude that the dome could be a result of strong Arctic winds accelerating a large ocean circulation known as the Beaufort Gyre, causing the sea surface to bulge.

A change in the direction of the wind would cause the fresh water to spill into the rest of the Arctic Ocean and even reach the north Atlantic.

This could slow a key ocean current, stemming from the Gulf Stream, and subsequently cool Europe.

Mean sea surface

This current keeps the continent relatively mild compared to other areas at similar latitudes.

“When we looked at our data on a year-to-year basis, we noticed that the changes in the sea surface height did not always follow what the wind was doing, so we thought about reasons why this might happen,” said Katharine Giles, CPOM research fellow and lead author of the study.

“One idea is that sea ice forms a barrier between the atmosphere and the ocean. So as the sea ice cover changes, the effect of the wind on the ocean might also change.

“Our next step is to look into how changes in the sea ice cover might affect the coupling between the atmosphere and the ocean in more detail to see if we can confirm this idea.”

Sea ice can be measured by different types of satellite data. Radar altimeters on satellites such as the two used in the study, Envisat and ERS-2, can be particularly useful when observing inaccessible areas like the Arctic.

Envisat image of Arctic

Envisat, the largest Earth observation satellite ever built, will mark 10 years in orbit in March.

ERS-2 was retired in July 2011, but 20 years of data from it and predecessor ERS-1 on oceans, land, ice and atmosphere will continue to be used by scientists for years to come.

“We were able to produce the Beaufort Gyre results thanks to the overlap of the ERS-2 and Envisat missions and long-term satellite data availability,” said Seymour Laxon, director of CPOM and co-author of the paper.

ESA will continue to monitor the Arctic with the upcoming Sentinel series of Earth-observing satellites for Europe’s Global Monitoring for Environment and Security (GMES) programme.

Later this year, the first results of seasonal changes in sea-ice thickness from data acquired by ESA’s CryoSat-2 satellite will be presented.

Related links:
Nature Geoscience:

Centre for Polar Observation and Modelling:

National Oceanography Centre:


Related missions:

Envisat overview:

ERS-2 overview:

Sentinels overview:


Images, Animation, Text, Credits: ESA / CPOM / UCL / Planetary Visions/ DMI / NIC.