New international satellite to study our explosive Sun
Posted: April 9, 2001

Life on Earth would be impossible without the light and heat generated by our nearest star, the Sun. However, this giant ball of hydrogen and helium gas can affect our world in many different ways.

The Sun produces the most energetic explosions in the Solar System, sometimes leading to the ejection of up to one thousand million kilograms of material. Some of these are directed towards Earth producing auroras and 'space weather effects'. For example, violent explosions on the Sun can destroy satellites, disrupt communications, threaten astronauts with radiation and cause power blackouts on Earth.

Not surprisingly, scientists want to learn as much as possible about our powerful, erratic neighbour, so spacecraft that can observe the Sun continuously from above the atmosphere are essential tools.

An artist's concept of the Solar-B satellite. Photo: NASA/MSFC
Dr. Louise Harra of the Solar Physics Group, Mullard Space Science Laboratory (MSSL), discussed SOLAR-B, a new purpose-built orbital observatory, at the UK National Astronomy Meeting in Cambridge last week. Dr. Harra is a member of the team of UK, Japanese and US scientists who are working together to build a suite of advanced instruments for the mission.

"Solar-B will allow us to study in unprecedented detail the forces that create these explosions," said Dr. Harra. "The instruments will reveal how the Sun's magnetic field interacts with the solar atmosphere to produce these large explosions."

Solar-B will be launched into orbit around the Earth in the autumn of 2005.

"The spacecraft's polar orbit will allow its instruments to stay in continuous contact with the Sun for nine months each year," explained Professor Len Culhane of MSSL, the UK Principal Investigator on Solar-B.

The Solar-B mission consists of a matched set of instruments that are sensitive in the optical, extreme ultraviolet and X-ray regions of the electromagnetic spectrum. They will observe the magnetic fields on the Sun's surface (the photosphere) and the Sun's outer atmosphere.

There will be three instruments on board Solar-B. Japanese and US groups are providing the optical and X-ray telescopes.

The optical telescope has a 0.5 metre aperture and will measure the strength and direction of the magnetic field with a spatial resolution of 150 km, and follow the evolution of magnetic features with time.

The X-ray telescope will provide images of the million-degree gas in the Sun's corona and will have a higher resolution and wider temperature coverage than any such telescope flown previously.

The final instrument is an extreme-ultraviolet imaging spectrometer which is being led by UK groups, with involvement by the US and Japan. This will image the explosions in the Sun's atmosphere and measure the velocities, temperatures and densities of the gas, which is continually in turmoil.

"This will be the first time we will be able to measure accurately the velocities of the explosions with excellent time resolution," said Dr Harra.

The Mullard Space Science Laboratory (University College London) is leading the construction of this instrument with involvement from the Rutherford Appleton Laboratory and the University of Birmingham. The design phases are now complete and the building of the instruments has begun in earnest.