— The Solar-B spacecraft will probe the triggers of potentially hazardous ejections of gas from the Sun (Illustration: NASA)
A spacecraft capable of obtaining unprecedented views of the Sun's magnetic field is set to launch on Friday. Called Solar-B, it should help scientists understand how changes in the Sun's magnetic field cause solar eruptions that can wreak havoc here on Earth.
These eruptions of charged particles, called coronal mass ejections (CMEs), can damage electronics on Earth-orbiting satellites, knock out power grids, and pose a radiation hazard to astronauts. Watch a coronal mass ejection (mpeg format) recorded by the SOHO spacecraft.
Scientists still do not know what triggers these ejections, but many suspect that sudden changes in the Sun's magnetic field are responsible. Proving that hypothesis has been difficult, however, because of a lack of sufficiently detailed measurements of the Sun's ever-changing magnetic field.
That problem should soon be solved with the launch of the Solar-B spacecraft at 2200 GMT on 22 September from Japan's Uchinoura Space Center.
The mission is led by the Japan Aerospace Exploration Agency (JAXA) with participation from NASA, the UK's Particle Physics and Astronomy Research Council (PPARC), and the European Space Agency. It is the successor to the Solar-A spacecraft, also called Yohkoh, which studied the Sun in X-rays and was launched in 1991.
Solar-B will be able to measure the strength of the Sun's magnetic field in three dimensions. All other spacecraft, like NASA's Solar and Heliospheric Observatory (SOHO), have been able to measure the strength of the magnetic field in only one direction, along the line of sight to Earth.
By measuring the alignment of the electric fields, or polarisation, of light emitted from the Sun, Solar-B will be able to work out the 3D strength of the Sun's magnetic field, revealing the direction in which the magnetic field lines are pointing.
This information is important because it tells scientists where the field lines have been stretched and bent, a phenomenon that always accompanies coronal mass ejections. Stretched field lines can suddenly snap into different configurations in events called magnetic reconnections, which are thought to trigger the ejections.
"We hope to learn eventually how to use these types of measurements to predict when these space weather events will happen," says Ted Tarbell of Lockheed Martin's Solar and Astrophysical Laboratory in Palo Alto, California, US, which helped build the instruments for Solar-B's visible light telescope.
The spacecraft is also equipped with an ultraviolet telescope, which should be able to measure the way gas flows in the vicinity of magnetic reconnection events. A third telescope aboard Solar-B will image the Sun in X-rays, the wavelength where the coronal mass ejections can be seen.
"With this complement of instruments, hopefully we'll be able to tie the physics down so that we understand how magnetic fields and high-temperature plasmas interact," says John Davis of NASA's Marshall Space Flight Center in Huntsville, Alabama, US.
Mission scientists hope that Solar-B will also help crack the mystery of how the outermost part of the Sun's atmosphere, or corona, gets heated to millions of degrees Celsius. That is far hotter than the Sun's visible surface, or photosphere, which makes up the lowest layer of its atmosphere and reaches only a few thousand degrees.
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