Helium is the second most abundant element in the universe after hydrogen. But scientists aren’t really sure how much is actually in the Sun’s atmosphere, which is difficult to measure. Knowing the amount of helium in the solar atmosphere is important to understanding the origin and acceleration of the solar wind – a constant stream of charged particles from the Sun.
In 2009, NASA has conducted an acoustic missile investigation to measure helium in the expanding Sun’s atmosphere – we have obtained a full global map for the first time. The results, recently published in Natural Astronomy, is helping us to better understand our spatial environment.
In the past, when measuring the ratio of helium to hydrogen in the solar wind when it reached Earth, observations had found a much lower than expected ratio. Scientists suspect the missing helium may have been left behind in the Sun’s outer atmosphere – the corona – or perhaps in a deeper layer. Discovering how this happens is key to understanding how the solar wind is accelerated.
To measure the amount of helium and hydrogen in the atmosphere, NASA’s Helium Resonance Scattering technology in the Corona and the Heliosphere, or HERSCHEL, the rocket’s locator has imaged the corona. Led by the Naval Research Laboratory in Washington, DC, HERSCHEL is in international collaboration with Turin astrophysical observatory in Italy and Institute of Space Astronomy Physics At France.
Observations of HERSCHEL show that helium is not evenly distributed around the corona. The equatorial region has almost no helium while the mid latitude regions have the most. Comparison with images from ESA / NASA’s Sun Observatory and Heliospheric (SOHO), scientists were able to show diversity in the mean latitudes that overlap with where the Sun’s magnetic field lines unfold in the Solar system.
This shows that the ratio of helium to hydrogen is closely related to the magnetic field and the speed of the solar wind in the corona. The equatorial regions, where measurements of low helium are found, match those from the solar wind near Earth. This suggests that the sun’s atmosphere is more dynamic than scientists think.
The investigation of the HERSCHEL sonic missile adds to a working group looking to understand the origin of the slow component of solar wind. HERSCHEL remotely investigates the elemental composition of the area where the solar wind is accelerated, which can be analyzed in parallel with the local measurements of the inner solar system, such as that of the Parker Solar Probe. . While the Sun’s heat is enough to power the lightest element – ionized hydrogen protons – to escape the Sun in the form of hypersonic winds, other physics must help fuel the family. the speed of heavier elements such as helium. Understanding the element’s abundance in the Sun’s atmosphere, therefore, provides more information as we try to understand the full story of how the solar wind is accelerated.
In the future, scientists plan to make more observations to explain differences in abundance. Two new devices – Metis and EUI aboard the ESA / NASA solar orbit ship – can perform similar global abundance measurements and will help provide new information on the helium ratio in the corona.
References: “Measurements of the global helium in corona” by John D. Moses, Ester Antonucci, Jeffrey Newmark, Frédéric Auchère, Silvano Fineschi, Marco Romoli, Daniele Telloni, Giuseppe Massone, Luca Zangrilli, Mauro Focardi, Federico Landini, Maurizio Pancrazzi, Guglielmo Rossi, Andrea M. Malvezzi, Dennis Wang, Jean-Christophe Leclec’h, Jean-Pierre Moalic, Frédéric Rouesnel, Lucia Abbo, Aurélien Canou, Nicolas Barbey, Chloé Guennou, John M. Laming, James Lemen , Jean-Pierre Wuelser, John L. Kohl and Lawrence D. Gardner, July 27, 2020, Natural Astronomy.
DOI: 10.1038 / s41550-020-1156-6