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Earth's cosmic battle zone exposed - European spacecraft sheds new light on near-earth space

Press Release From: Particle Physics and Astronomy Research Council
Posted: Friday, February 16, 2001

Peter Barratt
PPARC Press Office
01793 442025
peter.barratt@pparc.ac.uk

Our home - Planet Earth - is surrounded by a raging battle zone that begins only a few hundred kilometres above our heads, and yet most of us are totally oblivious to the fact. Now scientists are poised to understand this turbulent war zone following the first scientific results announced today [16 February 2001] from the four Cluster spacecraft orbiting this no-mans land of space between the Earth and the Sun. Once fully understood we should be able to protect our satellites and Earth based power and communication systems more effectively from this raging firefight of cosmic particles.

Our natural defence from this onslaught is the Earth's magnetosphere - an invisible bubble - surrounding our entire planet. Acting like a cosmic punchbag the magnetosphere is subjected to legions of solar particles [known as the Solar Wind] charging outwards from the Sun at supersonic speeds and constantly bombarding this protective bubble. But some break through, resulting in the spectacular Aurora Borealis and, perhaps more dramatically, magnetic storms, which can knock out power and communication systems on Earth, as well as on satellites.

A critical area for observation has been the bow shock wave, the point at which the Solar Wind slams into the Earth's magnetic bubble, where it abruptly slows down and forms a shock wave in front of it, just like that ahead of a supersonic aircraft. This bow shock wave becomes the Earth's first line of defence.

Commenting on these first results Prof. Ian Halliday, Chief Executive of the Particle Physics and Astronomy Research Council, the UK's strategic space science investment agency said, " This is the first time we have seen the bow shock in such remarkable detail. Although we expected it to be a complex, dynamic, three-dimensional structure which is subjected to rapid changes by the Solar Wind, this is the first time we can confirm it with scientific data". Halliday added, " Understanding this hazardous region of near-Earth space is critical. This is where the world's communication, navigation and weather monitoring satellites fly. The more we know about the conditions in this environment, the better equipped these spacecraft can be to withstand the onslaught of magnetic and solar storms, which can, and indeed do, destroy them".

Dozens of instruments on board the four Cluster spacecraft have now begun to probe the complex processes that take place in near-Earth space. This is the first time in the history of space exploration that four identical spacecraft have explored the Earth's magnetosphere, delving into the different regions of this defensive and invisible magnetic "bubble" that surrounds planet Earth.

As the quartet fly in [tetrahedral] formation around our planet, their suite of scientific sensors is carrying out the most comprehensive, three-dimensional investigation of the cosmic battle zone that links the Earth and our nearest star - the Sun.

In the last few months, and culminating in today's announcement, scientists have been able to sample the first intriguing morsels from the feast of fascinating information that will accumulate over the two-year-long duration of the mission. Preliminary analysis of this early data is already providing new insights into the interaction between the electrically charged particles of the solar wind and our planet's magnetic field.

The UK has played a major part in all four Cluster spacecraft. " Research groups in the UK have provided three of the eleven instruments on each of the four Cluster spacecraft and British scientists, in collaboration with our European partners, will be analysing the data. A clear indication of the UK's expertise in this important field of space research", added Halliday.

Notes for Editors
For further information, please contact:

Peter Barratt
Head of Communications, Particle Physics and Astronomy Research Council

Tel: 01793 442025 Mobile: 07879 602899
Email: peter.barratt@pparc.ac.uk

Images:

1. low resolution available on request from Mark Wells Tel: 01793 442100 Email: mark.wells@pparc.ac.uk,
2. high resolution - see PPARC website:www.pparc.ac.uk


UK scientists available for comment on Friday 16 February, contact:

Dr Hugo Alleyne
University of Sheffield
Tel: 0114 282 5235
Email: h.alleyne@sheffield.ac.uk

Prof. Sandra Chapman
University of Warwick
Tel: 02476 523390
Mobile: 07740 291984
Email: sandrac@astro.warwick.ac.uk

Prof. Mike Lockwood
Rutherford Appleton Laboratory
Tel: 01235 446496
Email: m.lockwood@rl.ac.uk

Background notes

* The four, European Space Agency [ESA], Cluster spacecraft were launched in batches of two from the Baikonur Cosmodrome in Kazakhstan in June and August last year [2000].

* The four spacecraft are identical and each carry eleven scientific research instruments to study one of the most important phenomena that effects life on Earth - the interaction between the Sun and the protective bubble of the Earth's magnetic field - the magnetosphere.

* Cluster is the first space science mission in which four identical spacecraft have been launched to fly in formation in closely matched orbits. By flying in this configuration the Cluster spacecraft will be able to study the Earth-Sun space environment in three dimensions and provide the most detailed study of the Earth's magnetosphere ever.

* The two year mission, which will cover a period when the Sun is most active, will lead to a better understanding of the physics of plasmas in space such as those produced in supernova explosions, apart from revealing a detailed picture of the magnetosphere and its behaviour.

* Several of the onboard instruments have been built by UK research teams supported by the Particle Physics and Astronomy Research Council [PPARC]. These include:
1. The Fluxgate Magnetometer [FMG] constructed by researchers at Imperial College London to measure the tiny variations in magnetic fields.
2. The Digital Wave Processor [DWP] built by Sheffield University to measure electric and magnetic wave components.
3. The Plasma Electron and Current Experiment [PEACE] built by the Mullard Space Science Laboratory and the Rutherford Appleton Laboratory to measure electron velocities in the space plasma.

Other UK universities have also contributed to these and other projects and the Rutherford Appleton Laboratory is also involved in spacecraft operations and data handling.

First Results: Magnetopause Waves, Bow Shock and Cusp in 3-D

Cluster's first glimpses of the continuously fluctuating battleground came on 9 November 2000, when the quartet made their first crossings of the Magnetopause. This detection of the boundary between interplanetary space (where the solar wind reigns supreme) and the Earth's region of magnetic domination was a surprise for the Cluster science team, since it occurred about one week earlier than predicted.

Data from PEACE, FGM and the five WEC (wave consortium) experiments on Cluster clearly showed that gusts in the solar wind were causing the magnetosphere to balloon in and out. These rapid fluctuations in size meant that the Cluster spacecraft were alternately inside and outside Earth's magnetic field.

At the peak of the Sun-storm, the spacecraft were exposed to the solar wind for more than 2 hours until the compression of the magnetosphere decreased and the spacecraft moved back inside the Earth's domain.

"PEACE detected a high flux (count) of electrons that we believe marked the Magnetopause," said ESA Cluster Project Scientist, Philippe Escoubet. "Magnetometer and wave consortium experiment data also observed many changes in the magnetic field, indicating that we crossed the Magnetopause many times."

Since then, the Cluster spacecraft have made regular measurements of the Magnetopause as they fly into interplanetary space and back into the magnetosphere. One of the most interesting discoveries has been the confirmation of the existence of wavelike features that mark the ever-shifting boundary of the magnetosphere.

"Until now, these plasma waves have only existed in simulations. Previous spacecraft measurements didn't contradict it, but didn't prove it either," explained Dr. Nicole Cornilleau-Wehrlin of CETP in Vlizy, Principal Investigator on the STAFF experiment. "Cluster has made the first three-dimensional study of the magnetopause and proved that it really is characterised by such wave structures. Further studies will enable us to discover more about what happens there and why."

By late December, the elliptical Cluster orbits carried the quartet close to another important boundary in near-Earth space - the bow shock - some 100,000-km from the planet. Cluster's battery of instruments recorded in great detail what happens at this turbulent barrier, where the particles in the solar wind slow to subsonic speeds after slamming into Earth's magnetic shield at more than 1 million km/h.

Once again, gusts in the stream of solar particles caused compressions in the magnetosphere. This caused the bow shock region to migrate through space, crossing and re-crossing the Cluster spacecraft at irregular intervals.

Sometimes the satellites were flying through the supersonic solar wind, sometimes they were immersed in the magnetosheath - a transition region between the bow shock and the Magnetopause.

"Some of the crossings were relatively simple," said Professor Andr Balogh of Imperial College London, the Principal Investigator for the FGM experiment on Cluster. "For example, at one time the bow shock was hovering very close to spacecraft 2 (Salsa), then it moved Sun-ward of all the spacecraft, and then, for a time, it hovered between spacecraft 2 and the other three spacecraft."

"Later still, the magnetic field in the solar wind changed, causing the bow shock to become unstable, so that it oscillated between the solar wind and the magnetosheath," he said. "This is the first time we have ever seen the bow shock in such remarkable detail."

Such comparisons will also be essential for in-depth studies of other parts of the magnetosphere, such as the cusps and the tail. The first Cluster observations of the northern cusp were made on 14 January 2001.

Although the spacecraft were expected to merely skim the edge of the cusp, shifts in the solar wind caused the spacecraft to pass right through this narrow "window" in the magnetic envelope at an altitude of about 64,000 km. The EISCAT ground-based radar located in Svalbard, which lay beneath the Cluster spacecraft at that time, confirmed the abrupt change in the position of the polar cusp region.

Preliminary analysis of data from the CIS experiment indicates that the upper regions of the cusp were moving through space at around 30 km/s. Further studies of the different data sets are expected to provide valuable new insights into the physical processes taking place in these key regions above the Earth's magnetic poles.

"This is a very dynamic region, but it has only been studied previously by single spacecraft," said Dr. Escoubet. "This is why the Cluster measurements are so important, because with four spacecraft we can obtain a three-dimensional view of its motion and interpret the physical processes that affect the charged particles as they enter the cusp."


Additional Background

Cluster and the Solar and Heliospheric Observatory spacecraft (SOHO) make up the Solar-Terrestrial Science Programme - one of the Cornerstones of ESA's Horizons 2000 long term science plan. Both missions play key roles in international efforts to investigate the physical connection between the Sun and Earth.

Cluster involves four identical spacecraft flying in tetrahedral formation in an orbit, which passes over both of the Earth's poles. After their dual launches last summer, the quartet were manoeuvred into highly elongated orbits which take them between 19,000 and 119,000 km from the planet - almost one third of the way to the Moon. Sometimes, they are inside the Earth's magnetic shield and sometimes they are outside, fully exposed to the supersonic solar wind.

By flying in tetrahedral formation along these 'stretched' orbits, the spacecraft are able to study the Earth's magnetosphere in unprecedented detail. The 42 instruments on Cluster are now providing the first three-dimensional view of the battleground between the Earth and our nearest star.

The flood of data to be returned by Cluster over the next two years will dramatically improve our understanding of the physical processes taking place in near-Earth space. Hundreds of scientists across Europe and the world are eagerly awaiting the unique data that Cluster will provide.

Apart from their pure scientific value, Cluster data will have more down-to-earth significance. When solar storms interact with the Earth, they may create enormous electrical currents around Earth, cause widespread power cuts, damage communication satellites (affecting TV signals and phone calls) and even increase corrosion in oil pipelines.


European Space Agency [ESA], contact details:

ESA - Communication Department
Media Relations Office

Tel: +33 (0) 1.53.69.71.55
Fax: +33 (0) 1.53.69.76.90

Prof. Andre Balogh
Principal Investigator for Cluster's FGM experiment
Imperial College, London
Tel: 0207 594 7768
Email: a.balogh@ic.ac.uk

Dr. Philippe Escoubet, ESA Cluster Project Scientist
ESA - Estec (Noordwijk, Nl)
Tel: +31 71 565 3454
Email: cpescoub@estec.esa.nl

Dr. Nicole Cornilleau-Wehrlin, Principal Investigator for Cluster's STAFF experiment
CETP (Velizy, France)
Tel: 33139254898
Email: nicole.cornilleau@cetp.ipsl.fr


Further information on Cluster and the ESA Science Programme can be found on the World-wide Web at: http://sci.esa.int/cluster

The Particle Physics and Astronomy Research Council (PPARC) is the UK's strategic science investment agency. It funds research, education and public understanding in four broad areas of science - particle physics, astronomy, cosmology and space science.

PPARC is government funded and provides research grants and studentships to scientists in British universities, gives researchers access to world-class facilities and funds the UK membership of international bodies such as the European Laboratory for Particle Physics, CERN, and the European Space Agency. It also contributes money for the UK telescopes overseas on La Palma, Hawaii, Australia and in Chile, the UK Astronomy Technology Centre at the Royal Observatory, Edinburgh and the MERLIN/VLBI National Facility.

PPARC's Public Understanding of Science and Technology Awards Scheme provides funding to both small local projects and national initiatives aimed at improving public understanding of its areas of science.

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