Here's a breakdown of what forms it:

* Extremely hot, low-density plasma: The corona is composed of superheated, ionized gas (plasma) that has a temperature of millions of degrees Celsius. This plasma is incredibly thin, making the corona very faint.

* Magnetic fields: The Sun's magnetic field plays a crucial role in shaping the corona. These fields create loops and arches that trap the plasma, and they are responsible for many of the corona's dynamic features, like solar flares and coronal mass ejections.

* Solar wind: The corona is also the source of the solar wind, a continuous stream of charged particles that flow outward from the Sun.

* Energy from the Sun's interior: While the exact mechanism is still debated, it is believed that energy from the Sun's interior is transferred to the corona through various processes, including waves and magnetic reconnection, leading to its extreme temperature.

The corona is a fascinating and dynamic region of the Sun, and studying it helps us understand the processes that power our star and its effects on the solar system.