Indeed, there are a lot of strange things about the sun, but a leading space probe has just given us the clue we might need to solve one of them.
New observations from the European Space Agency’s (ESA) Solar Orbiter reveal that the constant reconnection of small magnetic field lines may be at least part of the reason why some parts of the sun are warmer than others.
The problem is that the sun’s surface is about 5,500 degrees Celsius (9,932 Fahrenheit) – a normal temperature for a sun-like star. But the material in its atmosphere only gets hotter with distance from the surface, peaking at 2 million degrees Celsius in the highest regions known as the corona.
We’ve known about this coronal temperature inversion since the 1940s, and it’s thought to be a common feature of stars. But what scientists have not been able to pinpoint is the cause. One candidate solution is continuous magnetic reconnection on a small scale.
At least on a large scale, magnetic reconnection is a well-documented solar behavior. Most stars are turbulent balls of incredibly hot plasma. A liquid composed of charged particles interacts strongly with electromagnetic forces. This means that objects like our sun are positively pulsing with highly complex and chaotic magnetic fields. And outside the innermost layer of the sun’s atmosphere, known as its photosphere, these magnetic field lines can intertwine, stretch, capture and reconnect.
This produces a massive burst of energy – the engine that powers solar flares and coronal mass ejections that send particles blasting through the solar system.
On smaller scales, scientists believed that these reconnection events would inject energy into the corona, thus providing it with a heating source. But the sun is so bright and hot that it is difficult to observe it; We simply didn’t have enough resolution to see the small scales on which this process would occur.
And this is where Solar Orbiter comes into the picture. Launched in February 2020, the European Space Agency’s (ESA) solar probe has been closing in on our star, zooming to perilous close-ups in a series of repeated encounters to study its activity in stunning detail.
When the spacecraft made its first approach, it noticed something startling. On March 3, 2022, ultra-high-resolution images at intense ultraviolet wavelengths revealed magnetic reconnection occurring on very fine scales — just 390 kilometers (242 miles) wide.
This is actually unbelievable. Scientists have been able to solve and study a phenomenon slightly smaller than the length of the “Grand Canyon” on the surface of the sun.
Over the course of an hour, the spacecraft recorded a point known as the empty point, where the magnetic field strength drops to zero. This is the point of magnetic reconnection. During this time frame, the zero point temperature was maintained at around 10 million degrees Celsius. The point blank also produced a continuous jet that streamed away at speeds of about 80 kilometers per second, visible as “blobs” of plasma.
This is known as “gentle” reconnection, but the point blank also showed a phase of more violent reconnection. This reconnection process lasted only four minutes, but it showed that the two types of reconnection occurred simultaneously, and on smaller scales than we had previously been able to resolve.
These two types of reconnection would transfer mass and energy to the corona above them, providing a source of heat that could explain at least some of the poorly understood temperature inversion.
The results also indicate that reconnection may occur on scales too small for Solar Orbiter to resolve, at least in this close approach. The next several images, in addition to the one that just happened on April 10, will be zoomed in, which may lead to more high-resolution observations.
Meanwhile, we have the first observational evidence that stable, small-scale magnetic reconnection occurs on the Sun’s surface, validating a long-standing hypothesis about how the corona is heated, and taking us a step closer to knowing how the corona is heated.
The research has been published in the journal Nature Communications.
