Rain on the sun astounds researchers

Coronal plasma gene detected at unexpected site of the sun's surface

In this plasma loop, hot plasma falls back onto the sun's surface like a waterfall. Now researchers have discovered this coronary plasma gene in surprisingly small bows. © NASA / SDO
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Surprising find: On the sun, it can not only rain plasma - it does so in an unexpected place. For so far, scientists suspected the condensation of plasma only in the world's most outstanding magnetic field loops. But now researchers have discovered the plasma gene in other, much smaller solar structures. The find could help solve the old riddle of coronary heating.

The sun and the complex happenings in its seething plasma masses are still a mystery. This includes the interaction of solar plasma and magnetic field lines, but also the extreme heat of the corona: The solar atmosphere is million degrees hotter than its surface, but their "heating" has not been identified yet. The coronary rain is also puzzling: hot plasma falls back on the sun's surface in some places like a waterfall.

Plasma fall in plasma loops

"In coronary rain, hot plasma high in the solar corona experiences a rapid cooling of around one million Kelvin to 10, 000 Kelvin, condenses and falls back to the surface, " explain Emily Mason of NASA's Goddard Space Flight Center and her colleagues. These waterfalls of plasma can reach a fall speed of 200, 000 kilometers per hour. But how exactly the rain is created and in which structures it occurs is so far unclear.

To clarify the puzzle, Mason and her team have specifically searched in the largest magnetic loops of the sun's surface for the sun's rain, the so-called helmet streams. These arcuate outbreaks of plasma protrude more than a million kilometers into space and are also visible from the earth in the corona during solar eclipses. According to models, the plasma gene should be particularly pronounced there. The researchers therefore evaluated images and data from NASA's Solar Dynamics Observatory (SDO) for five months.

Plasma rain in an unexpected location

The surprising result: Mason and her team found nothing. In none of the large helmets the researchers were able to find even a drop of the solar plasma gene. But according to all models, the plasma in these structures ought to rain out. "Maybe the rain is so small there that we do not see it? We just do not know, "says Mason. display

However, the researchers discovered a whole series of much smaller, just under 50, 000 kilometers high plasma slopes and in these it rained abundantly. "The frequency of the rain and the ease with which it can be observed there indicate that this phenomenon occurs generally in topologies of this order of magnitude, " the researchers say. But that means: The solar plasma gene occurs in more places on the sun than previously thought.

Is this the "oven" of coronary heating?

The exciting thing about it: The new observations could also throw a new light on the search for the heating of the solar corona. According to current models, it can only rain plasma if the base of the magnetic field loops is very hot and the plasma cools off strongly when traveling along the towering field lines. "If a loop has coronary rain, it shows that coronary heating is taking place in the lower ten percent of this loop, " explains Mason.

This could mean that the corona heating is also at the base of these plasma loops. "This narrows down the area where coronary heating could take place, " says Mason. "We still do not know exactly what is heating up the corona, but it has to take place in this layer." The researchers hope the Parker Solar Probe's data will give them more information about the solar plasma gene and the riddle of the Corona heating can supply. The NASA probe is currently traveling in the solar corona. (Astrophysical Journal Letters, 2019; doi: 10.3847 / 2041-8213 / ab0c5d)

Source: NASA / Goddard Space Flight Center

- Nadja Podbregar