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From Eurek Alert, August 17, 2006


Our Sun's fiery outbursts - seen in 3D

UK solar scientists are eagerly awaiting the launch of NASA's STEREO mission which will provide the first ever 3D views of the Sun. STEREO (Solar TErrestrial RElations Observatory) comprises two nearly identical observatories that will orbit the Sun to monitor its violent outbursts – Coronal Mass Ejections (CMEs) – and the 'space weather' it creates that can impact the Earth, satellites and astronauts. STEREO is due for launch on August 1st 2006.

Professor Richard Harrison of the CCLRC Rutherford Appleton Laboratory (RAL), part of the UK team working on STEREO said "Whilst our Sun may seem a calm familiar object in the sky, in reality it is rather more manic! It generates constantly changing knots of magnetic fields that twist and churn and, occasionally, snap like an over-stretched rubber band producing CME outbursts. At the moment, we cannot recognise the tell-tale signals that precede an outburst, but we expect STEREO will change that."

In order to understand and, most importantly, predict and protect against the effects of the Sun's outbursts, such as CMEs, we need to monitor our parent star very closely. CMEs are powerful eruptions that can blow up to 10 billion tonnes of material from the Sun's atmosphere into space. Typically, CMEs send about 1 billion tonnes of material into space, travelling at one million miles per hour. They can create major disturbances in the interplanetary medium (the dust, plasma and gas in the space between the planets) and if they reach Earth, trigger severe magnetic storms that affect satellites, communications, power grids and aircraft. CME-driven shocks also play a significant role in accelerating solar energetic particles that can damage spacecraft and harm astronauts. Despite their significance, scientists don't fully understand the origin and evolution of CMEs yet.

Dr Chris Davis, also of RAL, said "Understanding CMEs is key to the future of human activities in space, including the many activities in daily life that rely on communication and navigation satellites. As satellite technology becomes more miniaturised, the smaller microchips are actually more vulnerable to "killer electrons" – the very energetic particles that a CME shock can produce."

STEREO will provide key data on CMEs and will be the first mission to watch CMEs directly as they head towards the Earth (which can happen as frequently as 4 times a week during the active phase of the Sun's cycle). STEREO comprises two nearly identical observatories that will be placed in orbits almost the same as that of the Earth around the Sun (their orbits will be 346 and 388 days).

Dr Chris Eyles of the University of Birmingam said "One spacecraft will slowly move ahead of the Earth, the other lag behind - the resulting offset will allow the two spacecraft to have 'depth perception' and give them stereo vision such as humans have."

UK scientists and engineers have contributed to STEREO by building the HI (Heliospheric Imager) cameras for the SECCHI (see Notes below) package on each observatory. HI is a wide angled imaging system (meaning it has a broad field of view) and will be studying how CMEs propagate, particularly those that are likely to affect the Earth. HI was funded by the Particle Physics and Astronomy Research Council investment of £1.88million. CCLRC Rutherford Appleton Laboratory is responsible for the scientific exploitation of the heliospheric imagers as well as providing the detectors used in all of STEREO's camera systems. Both heliospheric imagers were built in the UK at the University of Birmingham.

Commenting on the mission objectives, PPARC's CEO Professor Keith Mason said "Predicting the timing and strength of solar eruptions is clearly important if we want to mitigate the threat of CMEs and STEREO's twin observatories will be our sentinels, providing a unique insight into the evolution of these huge outbursts."

Professor Mason added "The UK has a strong history in solar physics and STEREO builds on the legacy of extremely successful satellites such as YOHKOH and SOHO, which have changed our understanding of the Earth's parent star. The STEREO mission is a prime example of how we can make the most of British expertise by joining with international agencies such as NASA."

Notes for Editors

Launch Details
Launch is currently scheduled for August 1st 2006 at 19.42-19.44 or 20.50-21.05 BST. Launches may slip due to bad weather or other factors, please see http://www.nasa.gov/stereo for the latest details. CCLRC RAL will be holding an event to follow the launch live, taking the NASA TV feed and speaking to UK scientists at the launch. For more information about attending the launch event, please contact Natalie Bealing (press@cclrc.ac.uk) or email LaunchEvent@rl.ac.uk. The event will be shown live on the UK stereo website www.stereo.rl.ac.uk for those unable to attend.

Images are available from http://www.pparc.ac.uk/Nw/stereo_images.asp or from the NASA website. Video A broadcast quality VNR is available with animations of the STEREO mission, images of the Sun and sound-bites from the NASA project team. Contact Julia Maddock for a copy

CME/Solar Storm Incidents

Nearly Identical?
The twin STEREO observatories orbit the Sun such that one spacecraft is ahead of the Earth and the other is behind it. Because the high-gain dish antennas need to be pointed at Earth for command and telemetry, one spacecraft must fly "upside down" relative to the other. This requires the identical instruments on each craft to be placed in slightly different locations. Also one observatory's main structure is a little thicker so that it can support the weight of the second observatory during launch. The slightly larger observatory will retain a portion of the separation fitting or ring used to connect the two during their ride into space.

STEREO Instruments
Each STEREO observatory contains four instrument packages:

Launch and Manoeuvres
STEREO mission designers found that the most efficient way to get the twin observatories into space was to launch them aboard a single rocket and use lunar swingbys to place them into their respective orbits. This is the first time that lunar swingbys have been used to manipulate the orbits of more than one spacecraft. Solar Cycle There is an approximately 11-year pattern in the number of sunspots, coronal mass ejec¬tions (CMEs), solar flares, and other solar activity. About every 11 years the Sun's magnetic field changes from north to south. Eleven years later it will flip back. People may have heard of this as the 22-year cycle because after two 11 year cycles the Sun's magnetic field will be back the way it was at the start of the 22 years.

What exactly is Space Weather?
At the centre of the solar system is the Sun, a magnetic variable star that drives the Earth and all the planets of the solar system. The modulation of the Sun on space conditions is the result of the interplay of three forces, pressure, gravity, and magnetic forces. As these forces vary, they produce effects collectively known as space weather, such as changes in the solar wind, solar flares and CMEs. Solar flares and CMEs originate at the Sun and can cause disturbances near Earth and throughout the solar system. There are several examples of space weather effects: this solar activity, as well as its interaction with Earth's magnetic fields, can produce dangerous radiation in the forms of high-speed particles or electromagnetic radia¬tion and can affect spacecraft, communications and power systems, and present a hazard to astro¬nauts.

Facts and Figures

The SunCME's

More information
STEREO Website CCLRC Project webpage STEREO writer's guide

STEREO is sponsored by NASA's Science Mission Directorate. NASA Goddard Space Flight Centre's Solar Terrestrial Probes Programme Office manages the mission, instruments and science centre. The Johns Hopkins University Applied Physics Laboratory is designing, building and will operate the twin observatories for NASA during the 2 year mission.

The School of Physics and Astronomy (and previously the Department of Space Research) at the University of Birmingham has over four decades of heritage of successfully building instruments for flight on spacecraft and sounding rockets.

CCLRC, the Council for the Central Laboratory of the Research Councils, is one of eight UK research councils and is one of Europe's largest multidisciplinary research organisations, supporting scientists and engineers across the world. It operates world-class large scale research facilities, provides strategic advice to the government on their development and manages international research projects in support of a broad cross-section of the UK research community.

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 Particle Physics Laboratory, CERN, the European Space Agency and ESO, the European Southern Observatory. 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.

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