One of the biggest mysteries of the Sun is the reason why its upper atmosphere, also called crown, is more than 200 times hotter than its surface. For an unknown reason, this region that spans millions of kilometers in space is overheated – while the surface temperature hovers around 5,500 degrees Celsius, the corona can reach 2 million degrees Celsius.
In a study published in Nature Astronomy, NASA scientists are getting ready to understand this strange phenomenon.
When analyzing the data collected by one of the space agency's solar observation satellites, the researchers discovered jets emerging from sunspots and projecting up to 3,000 miles into the inner ring. The jets had a voluminous head and a thin tail, so they looked like tadpoles swimming through the layers of the sun.
Sunspots are areas that appear temporarily on the surface of the sun. They are much colder than the surrounding areas and are very magnetized.
Previously, there were two main assumptions about what was heating the solar corona. The first concerns nanoflars, where explosions caused by the reconnection of magnetic lines release energy into the atmosphere and heat it. The second involves electromagnetic waves, charged particles being pushed into the atmosphere of the Sun. The discovery of the tadpole adds a third possibility to the mixture.
Scientists have discovered that tadpoles were entirely made of plasma – the fourth state of matter, consisting of an electrically conductive material consisting of charged particles. Tadpoles (also known as "pseudo-shocks") can help heat the solar corona at specific times in its eleven-year cycle – especially during the solar maximum, when activity on the Sun's surface is increased.
It is thought that pseudo-shocks occur when magnetic field lines entangle and produce explosions. This often occurs around sunspots, but can occur in other areas of magnetized space.
Computer simulations have shown that tadpoles can carry enough energy to heat the inner corona.
"We were looking for waves and plasma ejectas, but instead we have noticed these dynamic pseudo-shocks, like disconnected plasma jets, that do not look like real shocks but are very energetic to offset Sun's radiative losses." , wrote the principal author Abhishek Srivastava, of the Indian Institute. of technology, said in a statement.
The sun is coming to the end of its last cycle – called Solar Cycle 24 – and will enter the next one at some point this year. As the new cycle begins, sunspot activity will begin to increase before reaching a peak, called solar maximum, which should be around 2024.
Previously, scientists have suggested that the sunspot cycle may be lower than the current cycle, which could eventually result in an overall cooling period. However, this has largely been ruled out, as a team of scientists in India recently predicted that the next solar cycle could be even more powerful than the current one.
In their article published in Nature Astronomy, the authors stated: "We conclude that near-Earth and interplanetary space-based environmental conditions and solar radiative forcing of the climate on the sunspot cycle 25 (that is, the next decade) will likely be similar or slightly more extreme compared to what has been observed over the last decade during the current solar cycle ".