A composite image of the Sun showing the hydrogen (left) and helium (center and right) in the low corona. The helium at depletion near the equatorial regions is evident. Credit: NASA Helium is the second most abundant element in the universe after hydrogen. But scientists aren’t sure just how much there actually is in the Sun’s atmosphere, where it is hard to measure. Knowing the amount of helium in the solar atmosphere is important to understanding the origin and acceleration of the solar wind—the constant stream of charged particles from the Sun.
In 2009, NASA launched a sounding rocket investigation to measure helium in the extended solar atmosphere —the first time we’ve gathered a full global map. The results, recently published in Nature Astronomy , are helping us better understand our space environment.
Previously, when measuring ratios of helium to hydrogen in the solar wind as it reaches Earth, observations have found much lower ratios than expected. Scientists suspected the missing helium might have been left behind in the Sun’s outermost atmospheric layer—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 atmospheric helium and hydrogen, […]
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