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| Cluster and Double Star pinpoint the source of bright aurorae |
| Colourful aurorae and perturbations of GPS signals are just some of the effects of a magnetospheric phenomenon known as a magnetic substorm. Up to now, the onset of this phenomenon has been explained by two competing models: current disruption and near-Earth reconnection. A new study published 20 January 2007 in Geophysical Research Letters challenges this binary vision of substorm onset. Thanks to simultaneous measurements performed by the four satellites of the ESA/NASA Cluster mission and the CNSA/ESA Double star mission, a third type of substorm onset is now suggested. |
| Date: 11 Sep 2007 |
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| Cluster helps reveal how the Sun shakes the Earth's magnetic field |
| Space is a hostile region for both astronauts and satellites. One constituent of this hazardous environment around the Earth are very energetic electrons, which are able to perturb or permanently damage satellites. Ultra Low Frequency (ULF) waves, which travel along the Earth's magnetic field lines, are a prime candidate for generating these killer electrons, but the source of these waves remains unclear. A recent study reveals how a rare conjunction of ground based instrumentation and a dozen satellites at a range of altitudes provide a means to trace the energy source of these waves from the solar wind into the Earth's magnetosphere down to the ground. Part of this satellite constellation, the four spacecraft of the ESA Cluster mission, was located at the border of the magnetosphere and played a major role in discriminating between the various theoretical ULF wave generation scenarios. |
| Date: 26 Jul 2007 |
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| Cluster unveils a new 3D vision of magnetic reconnection |
| This week in Nature Physics, an international research team, led by Chinese scientists, reports the first observation of two linked magnetic reconnection sites using data collected by the four spacecraft of the ESA Cluster mission. This pioneering discovery will help constrain theoretical models of magnetic reconnection, a universal phenomenon in space related to star formation, solar explosions and the entry of solar wind energy into the near-Earth environment. |
| Date: 29 Jun 2007 |
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| Formation Flying at Closest-Ever Separation |
| After weeks of manoeuvres in space, Samba and Tango, two of the four Cluster satellites, are now flying in formation with a separation distance as small as 17 kilometres. This is the closest distance two ESA satellites have ever been in routine operations and will enable new scientific discoveries by Cluster, the first space mission to observe the Sun-Earth connection in 3D with four identical spacecraft. |
| Date: 21 Jun 2007 |
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| Cluster reveals the reformation of the Earth's bow shock |
| Plasma shock waves are some of the most spectacular, visually striking and energetic events in the Universe (Image 1). Generated by the explosion of stars (supernovae) or induced by stellar winds (Image 2), they can have a number of important effects. |
| Date: 11 May 2007 |
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| Cluster finds new clues on what triggers space tsunamis |
| In high-latitude regions like Scandinavia or Canada, auroras appear in many different shapes. The aurora in the early evening often forms a motionless green arc that stretches across the sky in the east-west direction (Image 1). But several times a year, such a static display suddenly changes to many colourful auroral forms dancing in the sky (Image 1). These sudden changes in aurora are the visual manifestation of space disturbances known as substorms. These perturbations can affect our daily lives, in particular by affecting GPS reception. |
| Date: 12 Apr 2007 |
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| First direct evidence in space of magnetic reconnection in turbulent plasma |
| Magnetic reconnection is a universal process in space, playing a key role in various astrophysical phenomena such as star formation, solar explosions or the entry of solar material within the Earth's environment. Reconnection has been observed at large-scale boundaries between different plasma environments such as the boundary between Earth and the interplanetary space. Irregular behaviour of particle flows and magnetic fields, known as plasma turbulence, also occur throughout the Universe. In a turbulent plasma many small-scale boundaries can form, where models predict reconnection to occur. However, magnetic reconnection in turbulent plasma has never been directly observed before. Using measurements of the four ESA Cluster satellites, a study published this week in Nature Physics shows, for the first time, experimental evidence of magnetic reconnection in turbulent plasma. This discovery opens new perspectives to better understand the behaviour of turbulent plasmas in the Universe. |
| Date: 26 Mar 2007 |
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| A leap forward in probing magnetic reconnection in space |
| Magnetic reconnection is a fundamental physical process in the Universe, playing a major role in various phenomena such as star formation or solar explosions, but also preventing plasma confinement in fusion reactors on Earth. However, a lack of precise measurements at the heart of this physical process prevents a full understanding of this phenomenon. High-resolution data from the 4 satellites of the ESA/NASA Cluster mission have enabled, for the first time, the derivation of a new physical quantity, which improves our understanding of the role of the electric field in this process. |
| Date: 12 Mar 2007 |
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| New insights in the auroral electrical circuit revealed by Cluster |
| Giant electrical circuits power the magical open-air light show of the aurora, forming arcs in high-latitude regions like Scandinavia. It is known that two different types of electrical circuits, each associated with its own type of electric potential structure, close at low altitude along these arcs, but little was known about the source of this difference. For the first time, two consecutive crossings by two satellites of the ESA/NASA Cluster mission captured the reconfiguration from one type to the other. Published 13 January 2007 in the Journal of Geophysical Research, this result is in agreement with predictions by [Marklund et al., 2004], also based on Cluster data. |
| Date: 09 Feb 2007 |
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| 1000th Orbit for the Cluster Mission |
| Today, 29 December 2006, marks the 1000th orbit around the Earth of the four ESA satellites composing the Cluster mission. Launched in the summer 2000, these spacecraft are delivering a unique harvest of in-situ scientific data of the Earth environment, from 25 000 to 125 000 kilometres altitude. |
| Date: 29 Dec 2006 |
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| Cluster finds magnetic reconnection within giant swirls of plasma |
| On 20 October 2006, a team of European and American scientists revealed the presence of magnetic reconnection within giant swirls of plasma of ~40 000 km size on the flank of the magnetosphere. These giant swirls were identified to be the result of the Kelvin-Helmholtz or 'wind over water' instability and were shown to facilitate the transport of solar wind material into the magnetosphere. This result improves our knowledge on how, where and under which conditions the solar wind manages to penetrate the Earth's magnetic shield, thanks to data collected by the four satellites composing the ESA/NASA Cluster mission. |
| Date: 06 Dec 2006 |
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| Cluster takes a new look at the plasmasphere |
| Using dedicated multipoint analysis tools developed for the ESA/NASA Cluster mission, scientists have unraveled properties of density structures in three dimensions on large, medium and small scales in the outer regions of the plasmasphere. Together with remote sensing data collected by the NASA IMAGE mission, these results show that this is a surprisingly dynamic place! This article emphasizes recent scientific highlights on this region obtained during a PhD thesis performed in Belgium and defended in France (June 2006), awarded with high honours. Since the launches of the Cluster spacecraft, more than 25 PhDs based on Cluster data have been defended successfully so far. |
| Date: 13 Nov 2006 |
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| Double Star and Cluster witness pulsated reconnection for several hours |
| Using coordinated observations of the CNSA/ESA Double Star and ESA/NASA Cluster missions, a team of European and US scientists reveals new features of magnetic reconnection at the Earth's magnetopause. These results improve our knowledge on how, where and under which conditions the solar wind manages to penetrate the Earth's magnetic shield on the flank of the magnetosphere. |
| Date: 03 Oct 2006 |
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| Double Star and Cluster witness pulsated reconnection for several hours |
| Using coordinated observations of the CNSA/ESA Double Star and ESA/NASA Cluster missions, a team of European and US scientists reveals new features of magnetic reconnection at the Earth's magnetopause. These results improve our knowledge on how, where and under which conditions the solar wind manages to penetrate the Earth's magnetic shield on the flank of the magnetosphere. |
| Date: 03 Oct 2006 |
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| Cluster links magnetic substorms and Earthward directed high-speed flows |
| High-speed flows of plasma, known as bursty bulk flows (BBF), are propagating in the inner central plasma sheet of the Earth's magnetotail at velocities higher than 300 kms-1. They are the carriers of decisive amounts of mass, energy and magnetic flux towards the Earth but their link to magnetic substorms was never absolutely established.
Based on data recorded during July-October 2001 and 2002 by three spacecraft of the Cluster mission, a statistical study reveals, for the first time, that more than 95% of magnetic substorms observed in this time period are accompanied by BBF. It also shows that BBF last longer than previously estimated and may account for up to 20% of the energy transport of a substorm. Published 7 April 2006 in the Journal of Geophysical Research, these results enhance previous studies based on single spacecraft measurements. |
| Date: 24 Aug 2006 |
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| Magnetic heart of a 3D reconnection event revealed by Cluster |
| Magnetic reconnection is a phenomenon of fundamental importance in space and laboratory plasmas. So far, the three dimensional magnetic structure of a magnetic null - the core region of this physical process - was never observed in situ, as it requires at least 4 simultaneous points of measurements to characterize it. For the first time, four spacecraft flying in formation, the Cluster mission, have directly observed it in the Earth's magnetotail. Published in the July edition of Nature Physics, an international team led by Chinese scientists not only report this observational first, they also reveal fundamental topological and physical properties of such a null, including its spatial extent. This scientific breakthrough is a truly experimental "tour de force". |
| Date: 18 Jul 2006 |
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| Cluster and Double Star discover density holes in the solar wind |
| Based on recent observations by the Cluster and the Double Star TC-1 satellites, a team of American, European and Chinese scientists have discovered the presence of ion density holes in the solar wind, upstream of the Earth's bow shock, of thousands kilometers in size. More than 140 of such density holes were found, always observed with upstream particles (propagating against the solar wind flow), suggesting that backstreaming energetic particles interacting with the solar wind are important. |
| Date: 20 Jun 2006 |
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| Cluster and Double Star discover density holes in the solar wind |
| Based on recent observations by the Cluster and the Double Star TC-1 satellites, a team of American, European and Chinese scientists have discovered the presence of ion density holes in the solar wind, upstream of the Earth's bow shock, of thousands kilometers in size. More than 140 of such density holes were found, always observed with upstream particles (propagating against the solar wind flow), suggesting that backstreaming energetic particles interacting with the solar wind are important. |
| Date: 20 Jun 2006 |
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| New Microscopic Properties of Magnetic Reconnection Derived by Cluster |
| Magnetic reconnection is considered to be the most efficient mechanism for solar material to penetrate the Earth's magnetic shield and to convert magnetic energy to particle energy (generating plasma jets and plasma heating). However, our understanding of this fundamental physical process is far from being complete. High resolution data by the Cluster mission reveal new microscopic properties at the heart of the reconnection process, in a region called the electron diffusion region. Published 17 December 2005, in Geophysical Research Letters, these multipoint measurements enable, in particular, a direct estimation of the spatial thickness of this central region. |
| Date: 19 May 2006 |
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| Cluster and Double Star reveal the extent of neutral sheet oscillations |
| For the first time, neutral sheet oscillations observed simultaneously at tens of thousands kilometres distance are reported, thanks to observations by 5 satellites of the Cluster and the Double Star Program missions. Published 8 November 2005 in Annales Geophysicae, this new observational first provides further constraint to model this large-scale phenomenon in the magnetotail. |
| Date: 30 Mar 2006 |
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