Similar to the green and mushy algal moss seen on a wet rock structure near water bodies, Sun, too, has similar moss-like patchy structures made of plasma in the solar atmosphere. Under strong magnetic conditions, this moss grows and blossoms around the centre of a sunspot group.
NASA in its latest study led by an Indian astronomer has claimed to have identified what makes the solar corona, the outermost peripheral part of the Sun’s atmosphere, extremely hot.
Any variations in the solar corona can affect the space weather and subsequently, the activities on Earth. Hence solar physicists have been engaged in deciphering the composition and behaviours of corona for many decades now. Among the commonest features displayed by the solar corona are loops, streams, plumes and ejections.
Similar to the green and mushy algal moss seen growing on a wet rock structure near water bodies, Sun, too, has similar moss-like patchy structures made of plasma in the solar atmosphere. Under strong magnetic conditions, this moss grows and blossoms around the centre of a sunspot group. The moss-like structure is mainly due to chromospheric jets or ‘spicules’ interspersed with extreme ultraviolet emission elements.
The moss region is connected to the Sun’s lower atmosphere and the temperatures here can go as high as 5.5 lakh degree Celsius, which is over a 100 times hotter than the immediate layer below. This long-standing mystery of over 25 years has been partly addressed in the latest NASA study.
NASA scientists used solar observations obtained from two of its missions — the High Resolution Coronal Imager (Hi-C) sounding rocket and Interface Region Imaging Spectrograph (IRIS) in order to decode the superheating mechanism.
Launched in 2013, IRIS is a small satellite-based explorer mission which has routinely captured high resolution images and spectra of the solar chromosphere and the transition region. Being a sounding rocket, Hi-C is an imager designed to perform short observations of the lower coronal of the Sun in the Extreme Ultraviolet wavelength.
Magnetic field is present everywhere on the Sun. It is this magnetic field which primarily controls the dynamics of the solar atmosphere, the recent paper published in the journal Nature Astronomy said.
The Hi-C and IRIS observations were combined with complex 3D simulations and revealed that electrical currents may be contributing to heating the moss. The moss region is dominated by a mess of intertwined magnetic field lines, and their interactions were creating electrical currents, which, in turn, was healing heat the material upto 1 million degrees Fahrenheit.
Souvik Bose, research scientist at Lockheed Martin Solar & Astrophysics Lab and NASA Ames Research Centre, told The Indian Express, “The superheating of the moss region was caused by the interactions between strong magnetic fields generating electric currents.The electrical currents are certainly dependent (that is, proportional) on the magnetic field strength.”
Sunspots host the strongest magnetic fields on the Sun’s surface and the strength of the magnetic field can differ from region to region.
“The ‘moss’ can have a much stronger field than the average quiet-Sun, but they are slightly weaker than the sunspots. It is the tangling of the magnetic fields close to the footpoints in a moss region which leads to the heating of the outer solar atmospheres, including the chromosphere and the lower corona. This occurs through the dissipation of the electrical currents in the form of Joule heating,” explained Bose, paper’s lead author and former MTech graduate from the Indian Institute of Astrophysics.
In the third week of April, NASA flew Hi-C and the scientists plan to deepen their studies in the area.
Source:indianexpress.com