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 pounds. 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

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

. In 1859 a giant solar storm erupted hurtling hot plasma in the form of a Coronal Mass Ejection (CME) toward the Earth. As this was before the space age, the main effect was disruption to telegraph lines and sightings of aurora in unusual locations. If such a storm were to be repeated today, the effects would be more dramatic as satellites ringing the Earth would take the brunt of the impact! Forecasts suggest that such a major outburst from the Sun would have a similar economic impact to a category 5 hurricane! The 1859 storm is also significant because it was the first occasion when scientists directly linked a solar flare to the aurora seen on Earth 12 hours later. This was observed by UK scientist Richard Carrington for which he was honoured by the Royal Astronomical Society.

. August 1972 saw a solar storm that is legendary at NASA. It occurred between two Apollo missions, with one crew just returned from the Moon and another preparing for launch. If an astronaut had been on the Moon at the time, they might have received a 400 rem (Roentgen Equivalent man) radiation dose. Not only would this have caused radiation sickness, but without rapid medical treatment such a sudden dose could be fatal. Astronauts on the ISS are safer – spaceships provide considerable shielding from solar storms and the ISS is within the protective magnetic field of the Earth. Humans exploring the Moon or Mars need carefully designed shelters that can protect them without the benefit of a magnetic field.

. CMEs can also affect power grids. On March 13th 1989, a CME hitting the Earth caused magnetic disruptions that induced currents in the power grid. This caused a series of transformers to trip, leaving 6 million people in Quebec without power, as well as knocking out the power in other countries.

. A particularly violent CME occurred on October 31st 2003. This blinded Mars Express for a day and significantly degraded the solar panels on a number of spacecraft including Mars Express, SOHO and Cluster.

. CMEs also interfere with radio systems that use the ionosphere to reflect signals over long distances

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:

. SECCHI (Sun-Earth Connection Coronal and Heliospheric Investigation) which is formed of an extreme ultraviolet imager, two white-light coronographs and the heliospheric imager (HI – the UK component). These will study the 3D evolution of CMEs from birth near the Sun’s surface, through the corona, into the interplanetary medium to their eventual impact on Earth. If the STEREO mission is extended beyond its current 2-year term, the HI cameras will eventually (due to the geometry of the orbit) look back together towards the Earth and beyond, providing a unique stereo view of the solar system. Twin wide-field cameras in space also provide unexpected science opportunities. Possible investigations now being considered involve looking for extra-solar planets and studies of comets and the interplanetary medium.

. SWAVES (STEREO/ WAVES) is a radio burst tracker that will trace the generation and evolution of travelling radio disturbances from the Sun to the Earth.

. IMPACT (In-situ Measurements of Particles and CME Transients) will sample the 3D distribution and characteristics of solar energetic particles

. PLASTIC (PLAsma and SupraThermal Ion Composition) will measure the properties of protons, alpha particles and heavy ions, to study how the plasma of CME differs from the ambient plasma of the corona.

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 ejections (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 radiation and can affect spacecraft, communications and power systems, and present a hazard to astronauts.

Facts and Figures

STEREO

. The observatories are each about the size of a commercial refrigerator and the solar arrays extend to the length of a soccer net.

. Mass: 1,364 pounds (620 kilograms)

. Dimensions: 3.75 feet (1.14 meters) tall, 4.00 feet (1.22 meters) wide (launch configuration) 21.24 feet (6.47 meters) wide (solar arrays deployed) 6.67 feet (2.03 meters) deep

. Power consumption 475 watts

. Data downlink 720 kilobits per second

. Memory 1 gigabyte

. Launch Site: Cape Canaveral Air Force Station

. Expendable Launch Vehicle: Delta II 7925-10L rocket

The Sun

. The Sun has an 11-year cycle of activity determined by the reversal of its magnetic poles (north pole becomes south pole).

. The Sun is 4.6 billion years old.

. 1 million Earths would fit inside the Sun. 20 planet Earths could fit in one very large sunspot.

. Light takes 8 minutes to travel the 93 million miles from the photosphere to Earth.

. Filaments are formed in magnetic loops that hold relatively cool, dense gas suspended above the surface of the Sun.

. When we see a filament in profile against the dark sky it looks like a stretched out, glowing loop. These are called prominences.

. Sun’s composition: 70% hydrogen; 28% helium; 2% heavier elements by mass.

. The Sun has no solid surface, just layers of atmosphere which extend beyond Earth, thinning as it goes.

. Different layers and latitudes of the Sun’s atmosphere rotate at different speeds. Sun’s equator takes 26 days to rotate, while the Sun’s poles rotate every 36 days.

. Sun’s inner 70% rotates like a solid body, once every 27 days, just 1 day slower than outer layers at the equator.

. Differential rotations twist and create Sun’s magnetic field from north to south. The twisted fields can rise and poke through surface as the loops seen above sunspots or as solar prominences.

CMEs

. During the active phase of the Sun, there are an average of 2 CMEs per day, of which 4 per week will come towards the Earth. During the less active phase, one per fortnight will head Earthwards.

. CMEs erupt when loops of solar material snap, hurling a high (hundreds of thousands of degrees) temperature plasma into space. The plasma is formed of electrons and ions of Hydrogen and Helium.

. Each CME has an energy equivalent to 100 the global nuclear arsenal.

. Each CME contains mass equivalent to 1/100 the mass of Mount Everest

. The power of a CME is about 1015 Watts or 300,000 power stations

. When a CME hits the Earth, most of the power is deflected by the magnetosphere but 1-2% (2000 Power stations) is dropped into the atmosphere, causing the aurora.

. During the minimum of the solar cycle, there are fewer CMEs, but they tend to be more energetic events.

More information

STEREO website http://www.nasa.gov/stereo

CCLRC Project webpage http://www.sstd.rl.ac.uk/stereo/mission.htm

STEREO Science writer’s guide (very helpful for definitions) http://www.nasa.gov/pdf/139023main_STEREO_science_guide.pdf

Contacts

Julia Maddock
PPARC Press Office
Email: Julia.maddock@pparc.ac.uk
Tel +44 1793 442094
Mobile: +44 7901 514 975

Peter Barratt
PPARC Press Office
Email: peter.barratt@pparc.ac.uk
Tel +44 1793 442025

Professor Richard Harrison
CCLRC Rutherford Appleton Laboratory
Email: R.A.Harrison@rl.ac.uk
Tel: (44) 1235 44 6884

Dr Chris Davis
CCLRC Rutherford Appleton Laboratory
Email: C.J.Davis@rl.ac.uk
Tel: +44 1235 446710

Dr Chris Eyles
University of Birmingham
Email: cje@star.sr.bham.ac.uk
Tel: +44 121 4146461

Rachel Weintraub
NASA Public Affairs
Tel +1 301 286 0918
Email Rachel.weintraub@nasa.gov

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.