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The Sun is a star which, according to Merriam-Webster, is a gaseous spheroidal celestial body, with self-luminosity and energy coming from its many nuclear fusion reactions.
Our Sun is a G-type, main-sequence star. These are also referred to as G stars or yellow dwarfs.
Main Sequence Stars with the Sun displayed as a G star. Image Credit: Universe Today
4.6 billion years ago, within a large molecular cloud, the matter experienced gravitational collapse. A lot of the mass was focused on the center. The outer part flattened into a disc orbiting the larger center.
The dust and particles within the disc collided, becoming larger bodies of mass such as asteroids or planets. The more rockier planets being found closest to the Sun. It is believed that this is due to the solar wind blowing gasses further away, and the Suns gravity attracting the heavier elements.
Let there be light
The Sun has a large abundance of Hydrogen and Helium. These elements are used during nuclear fusion reactions. These nuclear fusion reactions happen when two lighter elements collide to form heavier elements. It is estimated that in the core of the Sun about 600 million tons of helium and hydrogen fuse together every second. During these reactions there are often leftover 'waste' material, as the resultant heavier element does not constitute the entire mass of the previous elements. The leftover mass is therefore released as energy. About 4 million tons of matter is converted into energy per second. This energy can be released in many different ways. Eventually leading to events such as coronal mass ejections, and flares.
Electrically-charged particles of plasma rise through to the surface, known as the photosphere, of the Sun . Solar wind is the outward expansion of plasma, forming the Sun's corona. The heat from the solar wind overpowers the gravity and allows for the plasma to escape along the Sun's magnetic field lines.
Map of the Suns layers. Image Credit: NASA
In summary, the Sun can be seen as a big ball of fire and gas (FYI it's actually made of plasma)!
A rocky start
We lie within the 'Goldilocks' (habitable) zone. Where is it not too hot and not too cold. The conditions are just right for rocky materials to form, as well as allow for hydrogen and oxygen to exist together in liquid form, eventually leading to life.
The solar systems Goldilocks zone. Image Credit: Petigura/UC Berkeley, Howard/UH-Manoa, Marcy/UC Berkeley
Within the Earths atmosphere, the abundance of elements differ from the Sun and are as follows:
78% Nitrogen
21% Oxygen
0.93% Argon
0.04% Carbon dioxide
Other trace elements such as neon, helium, methane, krypton, ozone, hydrogen, and water vapor
However, Earth is not just a ball of gas. It has layers that can exist in other phases.
Much like the way that the gaseous planets venture far from the centre of the solar system, due to being less attracted to the Suns gravity, the lighter elements are more concentrated in the Earths atmosphere and the heavier elements are found closer to the core. Element abundances, therefore, vary throughout the Earths different layers. The geological history shows that the Earth has been through multiple different conditions with chemistry changing throughout time. Whereby there were times of tumultuous asteroid hits, such as the one suspected to have happened during the formation of our moon, and volcanic eruptions of super volcanoes. In terms of intelligent life, we have occupied this blue planet for just a brief time whilst Earths conditions have been perfect, or might we say suitable, for our existence.
Nevertheless, how can life be sustained with the Sun constantly throwing harmful particles towards us?
Planetary defense: The solar systems magnetic fields
Magnetic fields are fairly common within the solar system. The Earth, the Sun, our terrestrial cousin Mercury, and the gaseous giants Jupiter, Saturn, Uranus and Neptune all exhibit one.
The solar magnetic field is made through complex self-sustaining dynamo systems. Where the Suns plasma supports magnetic fields through it's electrical conductivity. These magnetic fields then have forces that affect the plasma, with the fluids motion maintaining continuous systems.
The Suns magnetic field has two poles, which flip every 11 years when the Sun is at it's peak of activity.
Suns magnetic field flips. Image Credit: NASA
The solar wind, blows the magnetic field away from the Sun, where it then travels through the solar system.
The first place for solar wind to go to is Mercury. The closest planet to the Sun. Solar wind, solar radiation, and micrometeorites hit the surface of Mercury leading to a thin exosphere forming. The atoms in the exosphere often escape into space. The planet also has a weak magnetic field, that is generated by a dynamo process from its convective liquid iron core. It has 1% the strength of Earths magnetic field. Although it is weaker than Earth's magnetic field, it is strong enough to deflect some solar wind, and allow for a small magnetosphere, which keeps the exosphere from blowing away.
The next planet for solar wind to arrive at is Venus, this planet does not have a magnetic field generated by an internal dynamo effect. It has a thick atmosphere with plenty of carbon dioxide and sulfuric acid. This planet has a runaway greenhouse effect, it the hottest in the solar system and is highly toxic. The solar wind interacts with the planets ionosphere, causing an external magnetic field which makes the solar winds plasma go away from the planet and also protects its atmosphere.
The Earths magnetic field works much like that of Mercury's, being generated from an internal dynamo process from a liquid iron core. Nonetheless, it is larger. The solar wind, hitting Earth at around 72 million kilometres per hour, is mostly deflected by the Earths magnetic field. Nevertheless, some plasma can leak through where the magnetic field is not as strong, such as at the poles. When solar wind particles interact with the Earths atmosphere, it can trigger aurora.
Image of the Northern Lights. Image Credit: Shutterstock
Solar wind interacts with other bodies in our solar system. With it blowing the atmosphere away from Mars whilst mingling with the atmosphere of Comets, called coma.
Space Weather
The Earths magnetic field sustains our current atmosphere from being blown away. This is not the first atmosphere that the Earth has housed, and it could potentially not be its last. The magnetic field, the ozone layer and the rest of the atmosphere allow for the major condition of life: to breathe. The atmosphere also deflects dangerous UV rays, insulates heat for warmth (especially at night preventing drastic changes in temperature), and drives wind circulation through changes in pressures and temperatures in the atmospheric layers.
Studies have shown that there is a chance for serious health conditions to occur where the ozone layer is depleted. Depletion of the ozone layer can occur with manufactured chemicals such as solvents and propellants causing gradual thinning of this protective layer. Furthermore, in recent years the hole has been record breaking.
We must remind ourselves that space weather is Earth weather.
The heliosphere and instellar medium, separated by a hydrogen wall. Image credit: Francisco R. Villatoro
Space weather from the Sun can be separated into four types: solar flares, coronal mass ejections, high-speed solar wind, and solar energetic particles. Understanding the nature of the different groups is important, and in the future of human spaceflight, it might be a necessity to understand the effect of solar wind on our bodies.
There are plenty of missions to further characterise the Sun. For example, the Solar Orbiter Mission, which was launched in 2020, will take the closest images of the Sun. This missions aim is to further comprehend how the Sun creates and controls the heliosphere, which includes the magnetosphere, astrosphere and outermost atmospheric layer around the sun (engulfing the solar system).
To conclude: it is paramount for us to monitor space weather - as the activity at the Sun increases, our natural defenses continue to deplete, and we become more dependent on technology which will be effected by a solar event.