What is exactly?
Did you hear a transit static noise on the radio for a well-prepared station? Guess what, maybe that was a coronal mass ejection that hit the Earth.
A Coronal Mass Ejection (CME) is a huge cloud of high-energy plasma with an intrinsic magnetic field ejected from the Sun, and hurled into space with speeds in the order of thousands of kilometres per second. It is one of the most spectacular phenomena of space weather, which is the field concerned with studying the near-Earth space environment.
The Sun is a mid-sized, relatively young star. It is believed that it was formed about 5 billion years ago since it was just the nebula cloud remnants of interstellar gases from an old exploded star. Under its own gravity, the cloud begun to collapse on itself and the temperature, pressure, and density increased dramatically at the cloud’s center and a nuclear fusion reaction was ignited. That is how our Sun was born.
It’s so big, a million Earth-sized planets can easily fit inside the Sun, and it mainly consists of Hydrogen (about 80%), Helium (about 19%), and traces of other metallic elements (about 1%). It is so dynamic an object that, since it is a giant ball of plasma (i.e. excited gas), each latitude layer rotates with a different speed relative to its neighboring layers. And because of that, the solar magnetic field gets tangled and becomes complex at some regions. These regions are often called “active regions” or “sunspots” and can be seen using a special telescope, as dark spots on the sun’s photosphere. The magnetic field in these regions is almost a thousand time stronger than that of a neighboring quiet region, and it is where the real action happens.
A CME at the right-side as observed by the LASCO coronagraph onboard SOHO satellite. The white circle represents the sun behind the occultation disk of the coronagraph. The bright feature on the top-left side is called “coronal streamer” that is a stream of high-energetic particles ejected from the solar corona at high-speeds.
At the sunspot group, when opposite magnetic field lines reconnect with each other, they release their potential energy as a sudden-bright flash of high intensity X-rays emitted, known as a “solar flare”, and often it is associated with a large high-speed CME. If the intrinsic magnetic field of the CME was opposite to that of our Earth, that is a nightmare! –Probably not.
Illustration of a coronal mass ejection moving beyond the planets toward the heliopause
Our Earth has a natural magnetic shield that protects us from being burned by the cosmic radiation coming from the sun or from the deep space, and it can deflect most of the incoming threats away from us. But in some cases, the main event is strong enough to cause horrible things, like destroying the satellites, frying the transformers and cutting the electricity from the power grid, disrupt the radio communications, cause corrosion in gas pipelines, threaten the astronauts’ life onboard the space stations, and it may alter our climate for the worse.
That is why space weather researchers and scientists worldwide study this kind of phenomena, trying to predict it to protect ourselves and our infrastructure from being harmed, using a set of instruments onboard satellites and at the ground stations.
CMEs are a truly magnificent phenomenon, but equally devastating.
- Source: References: Moldwin, M. (2008). An introduction to space weather. Cambridge University Press, Hundhausen, A. (1999). Coronal mass ejections. In The Many Faces of the Sun (pp. 143-200). Springer New York