Nasa says, 'A solar prominence (also known as a filament when viewed against the solar disc) is a large, bright feature extending outward from the Sun's surface.
'Prominences are anchored to the Sun's surface and extend outwards into the Sun's hot outer atmosphere, called the corona.
'Scientists are still researching how and why prominences are formed.
'An erupting prominence occurs when such a structure becomes unstable and bursts outward, releasing the plasma.
Nasa's Solar Dynamics Observatory frequently captures the phenomenon - although often as violent eruptions, rather than the eerie sphere of this week's activity.
It is not uncommon for prominence material to drain back to the surface as well as escape during an eruption, says Holly Gilbert a Goddard solar physicist.
Prominences are large structures, so once the magnetic fields supporting the mass are stretched out so that they are more vertical, it allows an easy path for some of the mass to drain back down.