Beyond its gravitational influence the Sun affects the atmospheres and magnetic fields of all the planetary bodies in its empire as the solar wind blasts past the planets at mind-blowing speeds toward interstellar space.
Here on Earth, the constant visual luminescence of our life-giving Sun hides a darker side of violent activity that is capable of damaging our technological infrastructure.
To understand the impact of the Sun on Earth it’s important to describe the different types of solar activity.
Solar wind
We have known since the early days of the space age that the atmosphere of the Sun is much hotter than its surface, meaning that the hot gases are constantly expanding out into space forming a solar wind.
The flow of gas takes with it magnetic fields that fill the solar atmosphere. The wind only stops blowing when it encounters the interstellar medium and forms a vast bubble in space in which the Solar System resides.
The Earth is constantly being buffeted by this gusty solar wind that blows with speeds of several hundred kilometres per second.
The vast bubble of solar wind is known as the heliosphere and NASA’s Voyager spacecraft are now exploring its far-reaches almost 40 years after they were launched.
Coronal Mass Ejections (CMEs)
More recently we discovered that the solar wind isn't the only kind of outflow from the Sun that the Solar System gets subjected to. In 1971, ejections of immense bubbles of magnetic field containing charged particles were discovered blasting away from the Sun.
These eruptions travel with speeds of up to 2000 kilometres per second, quickly expand to become many times larger than the Sun itself and are referred to as coronal mass ejections (CMEs).
CMEs are bulk eruptions of bubbles of magnetic field and gas from the solar atmosphere. The gas and the magnetic field are tied together.
These eruptions take anywhere between 1 and 4 days to reach the Earth. We see them leave and have some time to prepare.
When they reach us the magnetic field of the CMEs interacts with that of the Earth, and the particles of the solar gas spiral onto the Earth's magnetic field lines, driving space weather effects such as problems with satellites, power lines, changes to the ionosphere and more.
If the particles that spiral along the Earth's field lines make it all the way down to the atmosphere, they can energise the atmosphere gases and make them glow producing the aurora.
CMEs can head in any direction, including toward the Earth. We have been hit by coronal mass ejections many times in the past and will continue to be hit in the future.
Solar prominence
A solar prominence is the name given to clouds of relatively cool gas that are held aloft in the Sun's hot atmosphere.
We think today that the gas is held up by dips in the magnetic field - everything comes back to magnetic fields!
Prominences are the name given to these features when they are observed at the edge of the Sun. Sometimes the magnetic field of the prominence becomes unstable and it erupts upward away from the Sun carrying the gas with it - a coronal mass ejection is born!
So, prominence eruptions are a subset of all coronal mass ejections. If these reach the Earth the resulting space weather can be strong because they carry so many particles from the Sun's atmosphere.
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