Earth’s magnetic shield behaves like a sieve

When the Earth’s magnetic field and the interplanetary magnetic field are aligned, for example in a northward orientation as indicated by the white arrow in this figure, Kelvin–Helmholtz waves are generated at low (equatorial) latitudes. (Courtesy: ESA/AOES Medialab)

The Earth’s magnetic field is more permeable than previously thought, according to researchers analysing data from the European Space Agency’s Cluster mission. The findings have implications for modelling the dangers posed by space weather and could also help us better understand the magnetic environments around Jupiter and Saturn.
The Cluster mission, launched in 2000, comprises four identical satellites flying in a tetrahedral formation in close proximity to Earth. With highly elliptical orbits, the satellites are able to sweep in and out of the Earth’s magnetic environment, building up a 3D picture of interactions between the solar wind and our planet. The solar wind is a stream of charged particles from the outer layers of the Sun blowing into the solar system. The Earth’s magnetic field is thought to form a protective barrier against it.
It is well known, however, that if the magnetic field of the incoming solar wind has the opposite orientation to the Earth’s magnetic field, then the field lines can break and join up again in a process known as “magnetic reconnection”. This process allows the plasma from the solar wind to breach the boundary of the Earth’s magnetic field – the magnetopause – where it can then potentially reach our planet…..
Read more: physicsworld.com

A curious cold layer in the atmosphere of Venus

Venus terminator

Venus Express has spied a surprisingly cold region high in the planet’s atmosphere that may be frigid enough for carbon dioxide to freeze out as ice or snow.

The planet Venus is well known for its thick, carbon dioxide atmosphere and oven-hot surface, and as a result is often portrayed as Earth’s inhospitable evil twin.
But in a new analysis based on five years of observations using ESA’s Venus Express, scientists have uncovered a very chilly layer at temperatures of around –175ºC in the atmosphere 125 km above the planet’s surface.

The curious cold layer is far frostier than any part of Earth’s atmosphere, for example, despite Venus being much closer to the Sun.

The discovery was made by watching as light from the Sun filtered through the atmosphere to reveal the concentration of carbon dioxide gas molecules at various altitudes along the terminator – the dividing line between the day and night sides of the planet.

Armed with information about the concentration of carbon dioxide and combined with data on atmospheric pressure at each height, scientists could then calculate the corresponding temperatures.

“Since the temperature at some heights dips below the freezing temperature of carbon dioxide, we suspect that carbon dioxide ice might form there,” says Arnaud Mahieux of the Belgian Institute for Space Aeronomy and lead author of the paper reporting the results in the Journal of Geophysical Research.

Terminator temperature profile

Clouds of small carbon dioxide ice or snow particles should be very reflective, perhaps leading to brighter than normal sunlight layers in the atmosphere.

“However, although Venus Express indeed occasionally observes very bright regions in the Venusian atmosphere that could be explained by ice, they could also be caused by other atmospheric disturbances, so we need to be cautious,” says Dr Mahieux.

The study also found that the cold layer at the terminator is sandwiched between two comparatively warmer layers.

“The temperature profiles on the hot dayside and cool night side at altitudes above 120 km are extremely different, so at the terminator we are in a regime of transition with effects coming from both sides.

“The night side may be playing a greater role at one given altitude and the dayside might be playing a larger role at other altitudes.”

Similar temperature profiles along the terminator have been derived from other Venus Express datasets, including measurements taken during the transit of Venus earlier this year.

Models are able to predict the observed profiles, but further confirmation will be provided by examining the role played by other atmospheric species, such as carbon monoxide, nitrogen and oxygen, which are more dominant than carbon dioxide at high altitudes.

“The finding is very new and we still need to think about and understand what the implications will be,” says Håkan Svedhem, ESA’s Venus Express project scientist.

“But it is special, as we do not see a similar temperature profile along the terminator in the atmospheres of Earth or Mars, which have different chemical compositions and temperature conditions.”
www.esa.int

Journey to the Center of the Earth

Un voyage au centre de la Terre

Les trois satellites Swarm seront déployés à 530 kilomètres d'altitude pour l'un et à 460 kilomètres pour les deux autres

Les trois satellites européens de la constellation Swarm, fabriqués par l’industriel franco-allemand, Astrium, seront lancés cet été depuis la base russe de Plesetsk par une fusée Rockot. Une fois déployés sur leur orbite définitive, à 530 kilomètres d’altitude pour l’un et à 460 kilomètres pour les deux autres, ces trois sondes identiques, en forme de guitare électrique, mesureront le champ magnétique terrestre avec une précision inégalée de 1 milliardième de tesla.

Généré par la rotation du noyau de fer niché au cœur de notre belle planète, ce phénomène physique joue un rôle indispensable de bouclier en détournant le flux de particules (ions, électrons) éjectées par le soleil, responsable des aurores boréales visibles près des pôles. Mais les effets de ce vent solaire sont particulièrement délétères. Sans cette précieuse magnétosphère, toute vie, à commencer par la nôtre, serait impossible sur Terre. D’où l’importance de la mission Swarm, financée par l’Agence spatiale européenne, à hauteur de 220 millions d’euros, lancement compris, dans le cadre de son programme Earth Explorer.

Pendant quatre ans, durée théorique de la mission, les cinq instruments scientifiques présents à bord, en particulier le magnétomètre ASM fourni par le Centre national d’études spatiales (Cnes) et le laboratoire d’électronique (Leti) du CEA, mesureront les variations d’intensité de ce champ magnétique protecteur. Ce qui permettra, le cas échéant, de diffuser des bulletins d’alerte prévenant de l’arrivée de rayons nocifs à la surface de la Terre.

Swarm aidera également à mieux comprendre l’incidence du Soleil sur les cycles météorologiques et le climat, et à mieux prévoir les orages magnétiques susceptibles de perturber les communications terrestres, d’endommager des satellites ou de porter atteinte à la santé des astronautes présents à bord de la Station spatiale internationale (ISS). Les données fournies par Swarm contribueront enfin à améliorer la précision de la navigation pour le trafic aérien et mari­time.

Sur un plan plus fondamental, Swarm permettra d’étudier, depuis l’espace, la structure et les processus internes de notre planète, comme la composition du manteau ou le fonctionnement de la «dynamo terrestre» à l’origine du champ magnétique. «Cent cinquante ans après Jules Verne, nos trois satellites permettront aux scientifiques de réaliser un véritable Voyage au centre de la Terre », s’est félicité, Evert Dudok, le directeur de la division satellites d’Astrium, lors de la présentation de la mission, vendredi, à Munich.

Pour mener à bien toutes ces missions, il a fallu relever un énorme défi technique: «Les scientifiques veulent mesurer le champ magnétique de la Terre, pas celui des satellites», explique M. Dudok. Pour que ces derniers soient magnétiquement neutres, les ingénieurs de l’ESA et d’Astrium ont éliminé tous les matériaux susceptibles de s’aimanter, y compris les céramiques. «La structure est en fibre de carbone, l’antenne est déployable et les circuits électriques sont compensés», explique Yvon Menard, responsable du projet à l’ESA. Du grand art…..

En lire plus: lefigaro.fr

Cosmic particle accelerators get things going


This composition shows a number of diverse astronomical sources where shocks have been detected. Shock waves arise when supersonic flows of plasma are faced with an obstacle, such as a planet or a star with a magnetic field, or when they encounter a slower moving flow. Depicted in the composition are: a bow shock around the very young star, LL Ori, in the Great Orion Nebula (upper row, left image); shock waves around the Red Spider Nebula, a warm planetary nebula (upper row, central image); very thin shocks on the edge of the expanding supernova remnant SN 1006 (central row, left image); artist’s impressions of the bow shock created by the Solar System as it moves through the interstellar medium of the Milky Way (upper row, right image) and of Earth’s bow shock, formed by the solar wind as it encounters our planet’s magnetic field (central row, right image); shock-heated shells of hot gas on the edge of the lobes of the radio galaxy Cygnus A (lower row, left image); a bow shock in the hot gas in the merging galaxy cluster 1E 0657-56, also known as the ‘Bullet Cluster’. The image of a galaxy (NGC 6744) in the centre of the composition serves to give a rough idea of the relative scales, sub- and super-galactic alike, of the shock waves present across the Universe. Credit: NASA/ESA and The Hubble Heritage Team STScI/AURA

ESA’s Cluster satellites have discovered that cosmic particle accelerators are more efficient than previously thought. The discovery has revealed the initial stages of acceleration for the first time, a process that could apply across the Universe.
All particle accelerators need some way to begin the acceleration process. For example, the Large Hadron Collider at CERN employs a series of small accelerators to get its particles up to speed before injecting them into the main 27 km-circumference ring for further acceleration.
In space, large magnetic fields guide particles known as cosmic rays across the Universe at almost the speed of light, but are notoriously bad at getting them moving in the first place.
Now ESA’s Cluster mission has shown that something similar to the ‘staging’ process used at CERN is happening above our heads in the natural particle accelerators of space.
On 9 January 2005, Cluster’s four satellites passed through a magnetic shock high above Earth. The spinning craft were aligned almost perfectly with the magnetic field, allowing them to sample what was happening to electrons on very short timescales of 250 milliseconds or less.
The measurements showed that the electrons rose sharply in temperature, which established conditions favourable to larger scale acceleration.

Artist's impression of the four Cluster spacecraft flying through the thin layer of Earth's bow shock. The crossing, which took place on 9 January 2005, showed that the shock's width was only about 17 kilometres across. Credits: ESA/AOES Medialab

It had long been suspected that shocks could do this, but the size of the shock layers and the details of the process had proved difficult to pin down. Not any more.
Steven J. Schwartz, Imperial College London, and colleagues used the Cluster data to estimate the thickness of the shock layer. This is important because the thinner a shock is, the more easily it can accelerate particles.
“With these observations, we found that the shock layer is about as thin as it can possibly be,” says Dr Schwartz.
Thin in this case corresponds to about 17 km. Previous estimates had only been able to tie down the width of the shock layers above Earth at no more than 100 km.
This is the first time anyone has seen such details of the initial acceleration region.
The knowledge is important because shocks are everywhere in the Universe. They are created wherever a fast-flowing medium hits an obstacle or another flow.
For example, a supersonic aeroplane collides continuously with the atmosphere before the air has a chance to get out of the way, piling it up into a shock in front of the aircraft that we hear as a sonic boom.
In the Solar System, the Sun gives out a fast-moving, electrically charged wind. As it encounters the magnetic field of Earth, a permanent shock wave is created in front of our planet.
Cluster has been instrumental in studying this phenomenon and the new results in this local environment may be applicable on large scales. Shocks are also found around exploding stars, young stars, black holes and whole galaxies. Space scientists suspect that these may be the origin of the high-energy cosmic rays that fill the Universe.
Cluster has shown that very narrow shocks may be vital to kick-starting the acceleration process in those locations. It may not be the only way of starting things off, but it is definitely one way of doing it.
“This new result reveals the size of the proverbial ‘black box’, constraining the possible mechanisms within it involved in accelerating particles,” says Matt Taylor, ESA Cluster project scientist.
“Yet again, Cluster has provided us with a clear insight into a physical process that occurs throughout the Universe.”
Provided by European Space Agency
www.physorg.com

Universe May Not Be a Hologram After All

Some time ago, a group of researchers proposed that we may be living in a three-dimensional projection of a bi-dimensional space. The hologram Universe theory rallied a number of adepts, but a new research is proving that some of its most basic tenants are flawed.
Astrophysicist Craig Hogan first proposed that the Universe is in fact a hologram in October 2010, when he published the result of a scientific study he conducted using data collected by the GEO600 gravitational wave experiment.
This research was meant to collect data on the quantum fuzziness of the Universe. The expert used two atomic clocks to conduct measurements that would reveal the existence of hypothesized Planck units…… Continue reading Universe May Not Be a Hologram After All

ATV Johannes Kepler preparing for fiery destruction


ATV Johannes Kepler has been an important part of the International Space Station since February. Next week, it will complete its mission by undocking and burning up harmlessly in the atmosphere high over an uninhabited area of the Pacific Ocean.
Serving the International Space Station is a valuable job but it will come to a spectacular end: ESA’s second Automated Transfer Vehicle, packed with Station rubbish, will deliberately plummet to its destruction on Tuesday in Earth’s atmosphere.
Just like the tonnes of natural space debris that collide with our planet every day, the 10-tonne ferry will burn up on reentry.
Only a few hardy pieces might survive and splash into the uninhabited South Pacific. The area’s air and sea traffic has been warned and a no-fly zone will prevent any accidents.
The racks inside ATV have been filled with some 1200 kg of waste bags and unwanted hardware by the crew.
Mission so far
ATV Johannes Kepler delivered about seven tonnes of much-needed supplies to the Space Station, including 1170 kg of dry cargo, 100 kg of oxygen, 851 kg of propellants to replenish the Station tanks and 4535 kg of fuel for the ferry itself to boost the outpost’s altitude and make other adjustments.
ATV-2 manoeuvred the complex on 2 April to avoid a collision with space debris.
During the hectic mission of Johannes Kepler, two Space Shuttles and Japan’s HTV cargo carrier visited the Station, along with two Progress and Soyuz spacecraft. These required several changes of Station attitude, mostly controlled by ATV’s thrusters.
Big boosts and preparations for dive
ATV’s last important task was to give the Station’s orbit a big boost. One important sequence was performed 12 June, another on 15 June and the last one this afternoon, 17 June.
The combined effect of these manoeuvres was to raise the Station’s orbit to around 380 km.
The crew will close the hatches between the Station and ATV-2 on Sunday afternoon at 15:30 GMT (17:30 CEST). Undocking follows on Monday, at 14:51 GMT (16:51 CEST), with ATV’s thrusters gently increasing the distance from the outpost.
On 21 June, Johannes Kepler will fire its engines twice to descend from orbit.
The first burn, at 17:07 GMT (19:07 CEST) will drop it towards Earth. The second burn, at 20:05 GMT (22:05 CEST), will direct it precisely towards its Pacific target.
Hitting the upper atmosphere, ATV will tumble, disintegrate and burn, and any remains will strike the ocean at around 20:50 GMT (22:50 CEST).
Useful up to last moments

ATV-1 fireball over Pacific, 2008

Some aspects of a controlled destructive entry are still not well known, so ATV’s last moments will be recorded by a prototype ‘black box’.
The Reentry Breakup Recorder will gather measurements on the location, temperature, pressure and attitude of the vehicle’s breakup before ejecting.
Once it reaches an altitude of about 18 km, it will transmit the information via the Iridium satphone system.
With this last phone call home, Johannes Kepler will be productive right to the very end of a fruitful mission.
Read more: http://www.esa.int