Hypotheses involving a form of turbulence known as low-frequency “Alfvénic” turbulence are supported by observations by spacecraft and would explain the transportation of energy outwards from the Sun. “Astrophysicists have several different ideas about how the magnetic-field energy could be converted into heat to explain the heating, but most have difficulty explaining some aspect of observations.” “We know from measurements and theory that the sudden temperature jump is related to magnetic fields which thread out of the Sun’s surface,” the lead author of the study, Jonathan Squire, said in a statement. Temperatures in the corona regularly measure more than 1 million degrees Celsius, and scientists believe that the process that generates this intense heat so far from the Sun’s core may govern how powerfully the solar wind flows from the Sun. The Sun’s surface is relatively temperate compared with the Sun’s upper atmosphere, or corona, the wispy tendrils of plasma seen around the edge of the Moon during a total eclipse and ranging from a few hundred kilometers to five million kilometers above the surface. The corona is therefore the key to understanding the phenomena that control the effects of the Sun on climate change.As the outer edge of a massive ball of gas superheated by thermonuclear reactions fusing hydrogen atoms into helium atoms, the surface of the Sun is extremely hot – a blistering 6,000 degrees Celsius.
Within the heliosphere and immersed in the solar wind, the planetary magnetospheres are continuously perturbed by the Sun's magnetic and eruptive activity. The solar corona has become the subject of particular interest for space agencies worldwide, because it is the ring of conjunction between the Sun and the heliosphere. This is the instrument chosen by the European Space Agency as the scientific payload on the Solar Orbiter, the space probe that will first enter Mercury's orbit and then deviate more than 30 degrees from the solar equatorial plane to observe the still unexplored solar poles. The success of this new coronagraph technology is important because it is the same that will be used by METIS (Multi Element Telescope for Imaging and Spectroscopy). From a technological point of view, the experiment has demonstrated that one telescope can observe emissions from the external corona in wavelengths from visible to the extreme UV, thanks to the use of multilayer-coated optics. This result indicates that there are considerable variations in the composition of the solar atmosphere. The structure of the corona differs considerably depending on whether SCORE observes the helium or hydrogen emissions. Hydrogen is the most abundant element in the Sun and helium is the second and this result constitutes the first measurement of the abundance of helium in the corona information of great importance for understanding solar wind formation. Initial analyses of the data have confirmed the complete scientific success of the experiment and as expected, the first image of the helium emission in the solar corona has been obtained. SCORE was designed to obtain images of the coronal emission in the visible, ultraviolet and extreme ultraviolet wavelengths. The mission, part of the HERSCHEL programme (HElium Resonance Scattering in the Corona and HELiosphere, homonymous with the ESA infrared telescope), is the fruit of collaboration between ASI and NASA and was developed in Italy by research groups from the INAF-Astronomical Observatory and ALTEC in Turin, and the Universities of Florence and Pavia. The credit for this achievement goes to SCORE, (Sounding-rocket Coronagraphic Experiment), the Italian instrument for studying the Sun's external atmosphere, which was successfully launched (after various postponements due to technical and meteorological problems) on board a NASA rocket from the White Sands Missile Range base in New Mexico on 14 September. For the first time, a telescope has trained its eyes on the Sun and managed to photograph the helium emissions that burst from the corona of our star (in the photo on the left).
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