Small Plasma Bombs Make Red-Hot Corona
Magnetic collisions that cause small explosions of intense heat might explain why the corona is millions of degrees warmer than the Sun’s surface.
Since the 1940s, astronomers have known that the Sun’s outer atmosphere, the corona, behaves in a way that is beyond all reason. Although the corona is further away from the star’s centre, where the merciless heat originates, it is millions of degrees hotter than the surface, which is closer to the centre.
Astronomers have discovered that the mysterious phenomenon could be due to small solar eruptions known as nanoflares – and an underlying principle known as magnetic recombination. Nanoflares are small solar eruptions that are about one billion times weaker than the normal ones. Nevertheless, they all involve energy corresponding to a hydrogen bomb with an explosive force of 10 megatonnes of TNT. The small eruptions carry red-hot plasma from the Sun’s interior to the corona. According to leading scientists, millions of nanoflares occur on the surface every second. New observations from NASA’s IRIS mission, the Japanese Hinode satellite, etc., support the theory. The satellites recorded warming of the corona without the presence of normal solar eruptions.
The Parker Solar probe's detailed corona studies will contribute to determining if nanoflares heat the corona.
outer atmosphere, the corona, varies between one and three million degrees.
So, the corona is 200-500 times warmer than the surface (it can be compared to the air immediately above a hotplate, which is hundreds of times warmer than the plate itself). That is not only contrary to reason, it is also inconsistent with the second law of thermodynamics, according to which thermal energy always flows from a warm object to a colder one.
Astronomers have different theories as to why this is so. One of them is that mil-lions of small solar eruptions known as nanoflares are taking place across the Sun’s surface, the photosphere, every second. In combination, they release enough energy to cause partial heating of the corona, according to the theories. Nanoflares are a billion times weaker than ordinary solar eruptions. Another explanation is based on Alfvén waves (named after Swedish Nobel Prize laureate Hannes Alfvén). The waves are small ripples on coronal loops, which are magnetic field lines penetrating the Sun’s surface to reach into the atmosphere. The Alfvén waves are believed to speed up and down the field lines, carrying plasma into the corona, which is hence heated.
MARS TO BE SAVED BY HUGE MAGNET
The probe will also come very close to the source of the phenomenon that Eugene Parker discovered in 1957 and which has a direct influence on Earth. The solar wind, which primarily consists of protons and electrons that are ejected from the corona at very high speeds, causes the phenomenon known as space weather.
Space weather causes auroras. During powerful solar eruptions, large quantities of plasma are sent into the solar wind as a result of a phenomenon known as coronal mass ejection. If Earth is in the line of fire of this massive discharge of charged particles, a geomagnetic storm arises on Earth. Such a storm does not only destroy electronics and computers aboard satellites, it can also have major consequences on Earth’s surface, where the extra charges can overheat transformer stations and cause massive global power failure. By taking a close look at how the solar wind arises and develops, astronomers can become better at predicting when and how satellites are to be protected against the potentially harmful particle discharges.
The new knowledge about the Sun will also influence mankind's further exploration of outer space. On Mars, the solar wind is a much more serious problem than on Earth, where the magnetic field bends off the particles, protecting us against magnetic storms. The Red Planet’s magnetic field, on the other hand, is almost nonexistent, and consequently, Mars is highly exposed to the solar’ wind’s merciless particle bombardment. The MAVEN space probe, which is currently orbiting the planet, has revealed that the particles from the solar wind will gradually break down the Martian atmosphere, which is now about 100 times thinner than Earth’s.
As a result, NASA astronomers dream of launching a spacecraft equipped with a powerful electromagnet, which can create a magnetic field around the planet from an orbit between Mars and the Sun. The magnetic field is to protect Mars, so the planet can develop a denser atmosphere over time via slow heating and increased greenhouse effect. By protecting our neighbouring planet against the solar wind, it is theore-tically possible, in a distant future, to convert Mars from a barren and desolate planet into a wet, fertile place, which mankind can one day colonize.