vendredi 11 novembre 2011

Lutetia: a Rare Survivor from the Birth of the Earth

ESO - European Southern Observatory logo / ESA - Rosetta Mission patch.

11 November 2011

 An image of the strange asteroid Lutetia from the ESA Rosetta probe

New observations indicate that the asteroid Lutetia is a leftover fragment of the same original material that formed the Earth, Venus and Mercury. Astronomers have combined data from ESA’s Rosetta spacecraft, ESO’s New Technology Telescope, and NASA telescopes. They found that the properties of the asteroid closely match those of a rare kind of meteorites found on Earth and thought to have formed in the inner parts of the Solar System. Lutetia must, at some point, have moved out to its current location in the main asteroid belt between Mars and Jupiter.

A team of astronomers from French and North American universities have studied the unusual asteroid Lutetia in detail at a very wide range of wavelengths [1] to deduce its composition. Data from the OSIRIS camera on ESA’s Rosetta spacecraft [2], ESO’s New Technology Telescope (NTT) at the La Silla Observatory in Chile, and NASA’s Infrared Telescope Facility in Hawaii and Spitzer Space Telescope were combined to create the most complete spectrum of an asteroid ever assembled [3].

Artist's impression of the asteroid Lutetia making a close approach to a planet in the early Solar System

This spectrum of Lutetia was then compared with that of meteorites found on Earth that have been extensively studied in the laboratory. Only one type of meteorite — enstatite chondrites— was found to have properties that matched Lutetia over the full range of colours.

Enstatite chondrites are known to be material that dates from the early Solar System. They are thought to have formed close to the young Sun and to have been a major building block in the formation of the rocky planets [4], in particular the Earth, Venus and Mercury [5]. Lutetia seems to have originated not in the main belt of asteroids, where it is now, but much closer to the Sun.

“But how did Lutetia escape from the inner Solar System and reach the main asteroid belt?” asks Pierre Vernazza (ESO), the lead author of the paper.

Artist's impression of the development of the Solar System

Astronomers have estimated that less than 2% of the bodies located in the region where Earth formed, ended up in the main asteroid belt. Most of the bodies of the inner Solar System disappeared after a few million years as they were incorporated into the young planets that were forming. However, some of the largest, with diameters of about 100 kilometres or more, were ejected to safer orbits further from the Sun.

Lutetia, which is about 100 kilometres across, may have been tossed out from the inner parts of the young Solar System if it passed close to one of the rocky planets and thus had its orbit dramatically altered [6]. An encounter with the young Jupiter during its migration to its current orbit could also account for the huge change in Lutetia’s orbit [7].

“We think that such an ejection must have happened to Lutetia. It ended up as an interloper in the main asteroid belt and it has been preserved there for four billion years,” continues Pierre Vernazza.

The unusual history of the asteroid Lutetia

Earlier studies of its colour and surface properties showed that Lutetia is a very unusual and rather mysterious member of the asteroid main belt. Previous surveys have shown that similar asteroids are very rare and represent less than 1% of the asteroid population of the main belt. The new findings explain why Lutetia is different — it is a very rare survivor of the original material that formed the rocky planets.

“Lutetia seems to be the largest, and one of the very few, remnants of such material in the main asteroid belt. For this reason, asteroids like Lutetia represent ideal targets for future sample return missions. We could then study in detail the origin of the rocky planets, including our Earth,” concludes Pierre Vernazza.


[1] The electromagnetic spectrum represents the complete range of wavelengths covered by the different types of electromagnetic radiation. Visible light is the most familiar form, but many others exist. Many of these types of radiation are used in everyday life, such as radio waves, microwaves, infrared and ultraviolet light and X-rays.

[2] The Rosetta spacecraft, on its way to comet 67P/Churyumov-Gerasimenko, flew past Lutetia on 10 July 2010.

[3] Rosetta’s OSIRIS camera provided data in the ultraviolet, ESO’s NTT provided data in visible light, while NASA’s Infrared Telescope Facility in Hawaii and Spitzer Space Telescope provided data in the near-infrared and mid-infrared respectively.

[4] The enstatite chondrites (E chondrites) are a unique class of meteorites that account for only about 2% of the recovered meteorite falls. The unusual mineralogy and chemistry of E chondrites is consistent with formation relatively close to the Sun. This is further supported by isotope measurements (verified for oxygen, nitrogen, ruthenium, chromium and titanium): E chondrites are the only groups of chondrites that have the same isotopic composition as the Earth and Moon system. This strongly suggests that the Earth formed from enstatite chondrite-type materials and also that E chondrites formed at about the same distance from the Sun as the Earth.

In addition it has been recently shown that formation from enstatite chondrite bodies can explain Mercury's unusual and previously inexplicable composition. This suggests that Mercury — like the Earth — largely accreted from enstatite chondrite-like materials.

[5] Although they all formed from similar material, it remains a mystery why the inner three planets are so different.

[6] This process is very much like the gravitational assist methods used to change the direction and speed of space probes by arranging for them to fly close to a planet.

[7] Some astronomers think that the gaseous giant may have been closer to the Sun in the early days of the Solar System, before moving outwards to its current position. This would have caused havoc in the orbits of other objects of the inner Solar System due to the huge gravitational pull of Jupiter.

More information:

This research was presented in a paper, “Asteroid (21) Lutetia as a remnant of Earth’s precursor planetesimals”, to appear in the journal Icarus.

The team is composed of P. Vernazza (Laboratoire d’Astrophysique de Marseille (LAM), France; European Southern Observatory, Germany), P. Lamy (LAM, France), O. Groussin (LAM, France), T. Hiroi (Department of Geological Sciences, Brown University, USA), L. Jorda(LAM, France), P.L. King (Institute for Meteoritics, University of New Mexico, USA), M.R.M. Izawa (Department of Earth Sciences, University of Western Ontario, Canada), F. Marchis (Carl Sagan Center at the SETI Institute, USA; IMCCE, Observatoire de Paris (OBSPM), France), M. Birlan (IMCCE, OBSPM, France), R. Brunetto (Institut d'Astrophysique Spatiale, CNRS, France).

ESO, the European Southern Observatory, 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: “Asteroid (21) Lutetia as a remnant of Earth’s precursor planetesimals”:

    Photos of La Silla:

    More information about Rosetta:

Images, Text, Credit: ESA / MPS for OSIRIS Team MPS /UPD / LAM / IAA / RSSD / INTA / UPM / DASP / IDA ESO / L. Calçada / M. Kornmesser and N. Risinger ( / Video: ESO / M. Kornmesser, Nick Risinger (


30 Doradus: The Growing Tarantula Within

NASA - Chandra X-ray Observatory patch.

Nov. 11, 2011

The star-forming region, 30 Doradus, is one of the largest located close to the Milky Way and is found in the neighboring galaxy Large Magellanic Cloud. About 2,400 massive stars in the center of 30 Doradus, also known as the Tarantula Nebula, are producing intense radiation and powerful winds as they blow off material.

Multimillion-degree gas detected in X-rays (blue) by the Chandra X-ray Observatory comes from shock fronts -- similar to sonic booms --formed by these stellar winds and by supernova explosions. This hot gas carves out gigantic bubbles in the surrounding cooler gas and dust shown here in infrared emission from the Spitzer Space Telescope (orange).

30 Doradus is also known as an HII (pronounced "H-two") region, created when the radiation from hot, young stars strips away the electrons from neutral hydrogen atoms (HI) to form clouds of ionized hydrogen (HII). It is the most massive and largest HII region in the Local Group of galaxies, which contains the Milky Way, Andromeda and about 30 other smaller galaxies including the two Magellanic Clouds. Because of its proximity and size, 30 Doradus is an excellent target for studying the effects of massive stars on the evolution of an HII region.

The Tarantula Nebula is expanding, and researchers have recently published two studies that attempt to determine what drives this growth. The most recent study concluded that the evolution and the large-scale structure of 30 Doradus is determined by the bubbles of hot, X-ray bright gas confined by surrounding gas, and that pressure from radiation generated by massive stars does not currently play an important role in shaping the overall structure. A study published earlier in 2011 came to the opposite conclusion and argued that radiation pressure is more important than pressure from hot gas in driving the evolution of 30 Doradus, especially in the central regions near the massive stars. More detailed analysis and deeper Chandra observations of 30 Doradus may help decide between these different ideas.

Read more/access all images:

Image, Text, Credits: X-ray: NASA/CXC/PSU/L. Townsley et al.; Infrared: NASA/JPL/PSU/L. Townsley et al / Janet Anderson / Megan Watzke.


jeudi 10 novembre 2011

Hubble Uncovers Tiny Galaxies Bursting with Starbirth in Early Universe

ESA - Hubble Space Telescope logo.

10 November 2011

 Tiny galaxies brimming with star birth

Using its infrared vision to peer nine billion years back in time, the NASA/ESA Hubble Space Telescope has uncovered an extraordinary population of tiny, young galaxies that are brimming with star formation.

The galaxies are churning out stars at such a rate that the number of stars in them would double in just ten million years. For comparison, the Milky Way has taken a thousand times longer to double its stellar population.

These newly discovered dwarf galaxies are around a hundred times smaller than the Milky Way. Their star formation rates are extremely high, even for the young Universe, when most galaxies were forming stars at higher rates than they are today. They have turned up in the Hubble images because the radiation from young, hot stars has caused the oxygen in the gas surrounding them to light up like a fluorescent sign.

Hubble Spies Tiny Galaxies Aglow with Star Birth

Astronomers believe this rapid starbirth represents an important phase in the formation of dwarf galaxies, the most common galaxy type in the cosmos.

“The galaxies have been there all along, but up until recently astronomers have been able only to survey tiny patches of sky at the sensitivities necessary to detect them,” says Arjen van der Wel of the Max Planck Institute for Astronomy in Heidelberg, Germany, lead author of a paper that will appear in a forthcoming issue of the Astrophysical Journal. “We weren’t looking specifically for these galaxies, but they stood out because of their unusual colours.”

The observations were part of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS), an ambitious three-year survey to analyse the most distant galaxies in the Universe. CANDELS is the first census of dwarf galaxies at such an early epoch on the Universe’s history.

Dwarf galaxies in the UDS field

“In addition to the images, Hubble has captured spectra from a handful of these galaxies that show us the detailed physics of what’s happening within them and confirm their extreme star-forming nature,” says co-author Amber Straughn at NASA’s Goddard Space Flight Center in Greenbelt, USA.

The observations of ancient galaxies are somewhat at odds with recent detailed studies of the dwarf galaxies that are currently orbiting the Milky Way.

“Those studies suggest that star formation was a relatively slow process, stretching out over billions of years,” explains Harry Ferguson of the Space Telescope Science Institute (STScI) in Baltimore, USA, co-leader of the CANDELS survey. “The CANDELS finding that there were galaxies of roughly the same size forming stars at very rapid rates at early times is forcing us to re-examine what we thought we knew about dwarf galaxy evolution.”

Team member Anton Koekemoer, also of STScI, who is producing the Hubble imaging for the survey adds: “As our observations continue, we should find many more of these young galaxies and gather more details on their star-forming histories.”

Zoom on dwarf galaxies in the GOODS field

The CANDELS team uncovered the 69 young dwarf galaxies in near-infrared images taken with Hubble’s Wide Field Camera 3 and Advanced Camera for Surveys. The observations concentrated on two regions of the sky called the Great Observatories Origins Deep Survey-South and the UKIDSS Ultra Deep Survey (part of the UKIRT Infrared Deep Sky Survey).

The observations suggest that the newly discovered galaxies were very common nine billion years ago. But it is a mystery why the newly found dwarf galaxies were making batches of stars at such a high rate. Computer simulations show that star formation in small galaxies may be episodic. Gas cools and collapses to form stars. The stars then reheat the gas through, for example, supernova explosions, which blow the gas away. After some time, the gas cools and collapses again, producing a new burst of star formation, continuing the cycle.

“While these theoretical predictions may provide hints to explain the star formation in these newly discovered galaxies, the observed ‘bursts’ are much more intense than those reproduced by the simulations,” says van der Wel.

Hubble in orbit

The NASA/ESA/CSA James Webb Space Telescope, an infrared observatory scheduled to be launched later this decade, will be able to probe these faint galaxies at an even earlier era to see the glow of the first generation of stars, providing detailed information of the galaxies’ chemical composition.

“With Webb, we’ll probably see even more of these galaxies, perhaps even pristine galaxies that are experiencing their first episode of star formation,” Ferguson says. “Being able to probe down to dwarf galaxies in the early Universe will help us understand the formation of the first stars and galaxies.”


The Hubble Space Telescope is a project of international cooperation between ESA and NASA.

The international team of astronomers in this study consists of A. van der Wel (Max Planck Institute for Astronomy, Germany), A. N. Straughn (NASA Goddard Space Flight Center, USA) , H.-W. Rix (Max-Planck Institute for Astronomy, Germany), S. L. Finkelstein (Texas A&M University, USA), A. M. Koekemoer (Space Telescope Science Institute, USA), B. J. Weiner (University of Arizona, USA), S. Wuyts (Max-Planck Institute for Extraterrestrial Physics, Germany), E. F. Bell (University of Michigan, USA), S. M. Faber (UCO/Lick Observatory, USA), J. R. Trump (UCO/Lick Observatory, USA), D. Koo (UCO/Lick Observatory, USA), H. C. Ferguson (Space Telescope Science Institute, USA), C. Scarlata (University of Minnesota, USA), N. P. Hathi (Observatories of the Carnegie Institution of Washington, USA), J. S. Dunlop (University of Edinburgh, UK), J. A. Newman (University of Pittsburgh, USA), M. Dickinson (National Optical Astronomy Observatory, USA), B. W. Salmon (Texas A&M University, USA), D. F. de Mello (Catholic University of America and Goddard Space Flight Center, USA), D. D. Kocevski (UCO/Lick Observatory, USA), K. Lai (UCO/Lick Observatory, USA), N. A .Grogin (Space Telescope Science Institute, USA), S. A. Rodney (Johns Hopkins University, USA), Yicheng Guo (University of Massachusetts, USA), E. G. McGrath (UCO/Lick Observatory, USA), K.-S. Lee (Yale Center for Astronomy and Astrophysics, USA), G. B. Calvo (UCO/Lick Observatory, USA), and K.-H. Huang (Johns Hopkins University, USA)

Image credit: NASA, ESA, A. van der Wel (Max Planck Institute for Astronomy), H. Ferguson and A. Koekemoer (Space Telescope Science Institute), and the CANDELS team.


    Images of Hubble:

    Research paper:

    NASA release:

Images, Text, Credits: NASA / ESA / A. van der Wel (Max Planck Institute for Astronomy) / H. Ferguson and A. Koekemoer (Space Telescope Science Institute) and the CANDELS team / Videos: NASA / ESA and G. Bacon.


mercredi 9 novembre 2011

Roscosmos - Russian probe fails to set course to Mars

ROSCOSMOS - Phobos-Grunt Mission poster.

Nov. 9, 2011

A robotic spacecraft to the Mars moon Phobos launched early on Wednesday has failed to reach a flying orbit after separation from the launch vehicle, the head of Russia’s Federal Space Agency said.

The Zenit-2 launch vehicle carrying the Phobos-Grunt probe lifted off from the Baikonur space center at 00.16 a.m. Moscow time (20:16 GMT on Tuesday). The spacecraft was supposed to use its own booster to reach the designated flying trajectory, but failed to do so.

Phobos-Grunt (on Celestia)

“It has been a tough night for us because we could not detect the spacecraft [after the separation],” Vladimir Popovkin said. “Now we know its coordinates and we found out that the [probe's] engine failed to start.”

“It is a complex trajectory, and the on-board computers could have simply failed to send a “switch on” command to the engine,” Popovkin said, adding that it is an emergency situation, which has been anticipated and could be corrected.

“We will attempt to reboot the program. The spacecraft is currently on a support orbit, the fuel tanks have not been jettisoned, and the fuel has not been spent,” he said.

According to Popovkin, the technicians have three days to start the on-board engine and put the probe on the designated trajectory before the batteries run out.

The ambitious Phobos-Grunt mission is aimed at bringing back soil samples from Phobos in 2014 to pave the way for the exploration of the Red Planet.

The $163-million spacecraft carries an array of 20 instruments designed to gather and transmit data from the vicinity of Mars and from the surface of Phobos.

The potential loss of the Phobos-Grunt probe could deliver another serious blow to the country’s space exploration program as Russia has previously failed several attempts to send unmanned spacecraft to Mars.

Russia has two weeks to put Mars probe back on track

Phobos-Grunt description

Engineers have up to two weeks to correct the path of a Russian probe bound for Mars, a top space official said on Wednesday.

The Phobos-Grunt probe launched from the Baikonur Space Center in Kazakhstan on Wednesday, but its engines failed to put it on course for the Red Planet.

The mission is Russia’s first foray into deep space since losing a Mars-bound lander in 1996.

The craft, designed to bring back rock and soil samples from the Martian moon Phobos, is currently stuck in a “support orbit.”

Vladimir Popovkin, the head of Russia’s space agency Roscosmos, said engineers had two weeks to re-start the probe's booster before its batteries ran out.

“A more thorough analysis of the orbit’s parameter and the supply of fuel onboard has shown that such commands must be delivered within two weeks,” Popovkin said, adding that the craft can stay in the orbit for up to four weeks.

The Phobos-Grunt is also carrying China’s first Mars satellite, Yinghuo-1.

For more informations about the Phobos-Grunt Mission, visit:

Images, Text, Credits: Roscomos PAO / RIA Novosti.


mardi 8 novembre 2011

Launch of the ILV Zenit-2SB Rocket with AIS Phobos-Grunt

ROSCOSMOS - Phobos-Grunt Mission poster.


Launch of the ILV Zenit-2SB Rocket with AIS Phobos-Grunt

Launch Complex 45 area Baikonur starting calculations enterprise space industry in Russia and Ukraine made launching space rocket "Zenit-2SB," designed for launching into orbit of Russia's automatic interplanetary station (AIS) "Phobos-Grunt".

After 688 seconds of flight AMC cleanly separated from the second stage booster.

Lift-off occurred successfully at 00.16 GMT on 9 November 2011 from Baikonur Cosmodrome. The spacecraft is expected to reach Mars' orbit in September 2012, with landing on Phobos scheduled for February 2013.

Russia's automatic interplanetary station (AIS) "Phobos-Grunt" (Artist's view)

Phobos-Grunt (Russian: Фобос-Грунт, lit.«Phobos-Ground») is a sample return mission to Phobos, one of the moons of Mars. Funded by the Russian space agency Roscosmos and developed by NPO Lavochkin and the Russian Space Research Institute, Phobos-Grunt is to become the first Russian interplanetary mission since the failed Mars 96. It is also set to become the first spacecraft to return a macroscopic extraterrestrial sample from a planetary body since Luna 24 in 1976.

Phobos-Grunt Mission schematic description

The return vehicle, carrying up to 200 g of soil from Phobos, is expected to be back on Earth in August 2014.

For more informations about the Phobos-Grunt Mission, visit:

Images, Video, Text, Credits: Press Service of the Russian Space Agency (Roscosmos PAO) / Roscosmos TV / Aerospace / Translation:


Battered Tharsis Tholus volcano on Mars

ESA - Mars Express Mission patch.

8 November 2011

The latest image released from Mars Express reveals a large extinct volcano that has been battered and deformed over the aeons.

By Earthly standards, Tharsis Tholus is a giant, towering 8 km above the surrounding terrain, with a base stretching over 155 x 125 km. Yet on Mars, it is just an average-sized volcano. What marks it out as unusual is its battered condition.

Battered volcano Tharsis Tholus

Shown here in images taken by the HRSC high-resolution stereo camera on ESA's Mars Express spacecraft, the volcanic edifice has been marked by dramatic events.

At least two large sections have collapsed around its eastern and western flanks during its four-billion-year history and these catastrophes are now visible as scarps up to several kilometres high.

The main feature of Tharsis Tholus is, however, the caldera in its centre.

It has an almost circular outline, about 32 x 34 km, and is ringed by faults that have allowed the caldera floor to subside by as much as 2.7 km.

It is thought that the volcano emptied its magma chamber during eruptions and, as the lava ran out onto the surface, the chamber roof was no longer able to support its own weight.

So, the volcano collapsed, forming the large caldera.

Tharsis Tholus in context

November is a busy month for Mars exploration: Russia and NASA both plan launches this month.

Russia's Phobos–Soil (formerly known as Phobos–Grunt) is designed to land on Phobos, the larger of Mars' two moons, to collect samples, and return them to Earth in 2014. It also carries the first Chinese spacecraft to Mars, Yinghuo-1.

Mars Express HRSC digital elevation models of Phobos were used by Russian scientists to assess the mission's potential landing sites and ESA is also providing telecommunications support for both Phobos–Soil and Yinghuo-1.

 Tharsis Tholus in perspective

In return, the European scientific community will have access to data obtained by both spacecraft.

NASA's mission is the Mars Science Laboratory, a large rover known as Curiosity, with experiments designed to detect organic molecules – past or present – on the Red Planet.

Also worth noting is the simulated Mars mission, Mars500, which ended on Friday when the hatch was opened for the first time since June 2010. For 520 days, the international crew had been working in a simulated spacecraft in Moscow.

Tharsis Tholus in perspective

 Tharsis Tholus in perspective

 Tharsis Tholus in perspective

 Tharsis Tholus in perspective

 Tharsis Tholis in high resolution

 Tharsis Tholus in 3D

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 / DLR / FU Berlin (G. Neukum) / NASA / MGS /  MOLA Science Team.


NASA Captures New Images of Large Asteroid Passing Earth

NASA - Asteroid Watch logo.

Nov. 7, 2011

NASA's Deep Space Network antenna in Goldstone, Calif. has captured new radar images of Asteroid 2005 YU55 passing close to Earth.

The asteroid safely will fly past our planet slightly closer than the moon's orbit on Nov. 8. The last time a space rock this large came as close to Earth was in 1976, although astronomers did not know about the flyby at the time. The next known approach of an asteroid this size will be in 2028.

Image above: Asteroid 2005 YU55 Approaches Close Earth Flyby. This radar image of asteroid 2005 YU55 was obtained on Nov. 7, 2011, at 11:45 a.m. PST (2:45 p.m. EST/1945 UTC), when the space rock was at 3.6 lunar distances, which is about 860,000 miles, or 1.38 million kilometers, from Earth. Image credit: NASA / JPL-Caltech.

The image was taken on Nov. 7 at 11:45 a.m. PST, when the asteroid was approximately 860,000 miles (1.38 million kilometers) away from Earth. Tracking of the aircraft carrier-sized asteroid began at Goldstone at 9:30 a.m. PDT on Nov. 4 with the 230-foot-wide (70-meter) antenna and lasted about two hours, with an additional four hours of tracking planned each day from Nov. 6 - 10.

Radar observations from the Arecibo Planetary Radar Facility in Puerto Rico will begin Nov. 8, the same day the asteroid will make its closest approach to Earth at 3:28 p.m. PST.

Image above: This radar image of asteroid 2005 YU55 was obtained on Nov. 6, 2011, at 1:45 p.m. PST (4:45 p.m. EST/2145 UTC). Image credit: NASA / JPL-Caltech.

The trajectory of asteroid 2005 YU55 is well understood. At the point of closest approach, it will be no closer than 201,700 miles (324,600 kilometers) as measured from the center of Earth, or about 0.85 times the distance from the moon to Earth. The gravitational influence of the asteroid will have no detectable effect on Earth, including tides and tectonic plates. Although the asteroid is in an orbit that regularly brings it to the vicinity of Earth, Venus and Mars, the 2011 encounter with Earth is the closest it has come for at least the last 200 years.

Animation of the trajectory for asteroid 2005 YU55 - November 8-9, 2011. Image credit: NASA / JPL-Caltech

NASA detects, tracks and characterizes asteroids and comets passing close to Earth using both ground- and space-based telescopes. The Near-Earth Object Observations Program at the Jet Propulsion Laboratory (JPL) in Pasadena, Calif., commonly called "Spaceguard," discovers these objects, characterizes some of them, and plots their orbits to determine if any could be potentially hazardous to our planet. JPL manages the Near-Earth Object Program Office for NASA's Science Mission Directorate in Washington.

The new radar images are online at:

For more information about asteroids and near-Earth objects, visit:

More information about asteroid radar research is available online at:

For more information about NASA's Deep Space Network, visit:

Images, Animation, Text, Credit: NASA / JPL-Caltech.

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lundi 7 novembre 2011

Proba-1 charting Earth’s radiation belts for a decade

ESA logo.

7 November 2011

ESA’s Proba-1 recently celebrated its tenth birthday in orbit. Kept busy as an Earth-observing mission, the microsatellite has also been building a detailed picture of changes in our planet’s radiation belts.

Smaller than a cubic metre, the technology-testing Proba-1 was launched on 22 October 2001. Among the payloads was ESA’s SREM standard radiation environment monitor, which was turned on a week later.

The size of a shoebox, the monitor records high-energy charged particles, whether radiating from the Sun, the cosmos or trapped inside radiation belts entwined in Earth’s magnetic field. 


The monitor’s main purpose is to identify radiation hazards to its host mission but it is also building a detailed picture of the space radiation environment.

“Proba-1’s data demonstrate how Earth’s radiation belts change with time and location,” explained Eamonn Daly of ESA’s Space Environments and Effects section.

“In particular, they show the effects of magnetospheric storms and solar particle events that inject more radiation into the near-Earth environment.

Proba-1's radiation measurements of upper and lower radiation belts

“The satellite is in a low-altitude polar orbit – with an altitude ranging between 560 km and 680 km – and passes continuously in and out of Earth’s radiation belts.

“At high polar latitudes it crosses geomagnetic field lines that are linked to higher altitudes, allowing it to monitor the state of the ‘outer’ radiation belt.”

This is a dynamic environment where radiation levels rise and fall as a consequence of geomagnetic disturbances seen in the upper panel. In addition, solar particle events appear as vertical streaks in the data.

“Proba-1 also encounters Earth’s ‘inner’ radiation belt in a region where it dips near Earth, called the ‘South Atlantic Anomaly,” added Eamonn.

“This is much more stable, and the regular short-term variations are due to orbital effects.”

Proba-1's SREM

The long-term upward trend observed in the lower radiation belt data is due to the gradual effect of the 11-year solar cycle on Earth’s atmosphere. Radiation belt particles are usually lost in collisions with neutral particles, but solar activity is now at a low point.

This reduced solar energy has the effect of shrinking the atmosphere, allowing radiation levels to rise over time.

There are several SREMs flying on ESA missions, giving insights into the radiation environment ranging across space:

    in medium orbit aboard the GIOVE-B navigation test satellite
    in eccentric high orbit on the Integral gamma-ray observatory, up to 153 000 km from Earth
    around the distant second Lagrangian point aboard the Herschel and Planck observatories, a point in space 1.5 million km behind Earth where combined solar and terrestrial gravity cancel out
    on the Rosetta comet mission, venturing out beyond the orbit of Mars.

Protection against space radiation is an important factor in satellite design. A contract was recently signed with RUAG in Switzerland to develop a replacement for the highly successful SREM series.

The NGRM next-generation radiation monitor should fly on many future European spacecraft and also be available commercially.

Related links:

SREM instrument:


ESA Space Environments & Effects: