Skip to navigation | Skip to content

Plasma plume defends Earth

The violent Sun close up

Scientists have observed a plasma plume from the Earth reaching out and linking up with a coronal mass ejection shooting out from the Sun (Source: NASA/SDO/GSFC)

Plasma Storm Scientists have observed a plume of dense plasma reaching out from the Earth's atmosphere to help shield the planet from a coronal mass ejection blasting out of the Sun.

The research, reported in the journal Science, will help improve our ability to predict the severity of geomagnetic storms, which can overload power supplies, effect communications networks, damage spacecraft, and endanger astronauts.

Geomagnetic storms, also known as space weather, are generated by powerful streams of highly charged particles thrown out by solar flares and coronal mass ejections on the Sun.

"Typically, Earth's magnetic field, or magnetosphere, protects us from a lot of the effects of coronal mass ejections," says the study's lead author Dr Brian Walsh of NASA's Goddard Space Flight Centre.

"But when there are large storms, a lot of energy can be transmitted through this boundary and really shake up our magnetic field."

When these streams of charged particles collide with Earth's magnetosphere in a process called magnetic reconnection, they create powerful electrical currents flowing along Earth's magnetic field lines.

Space observations

For this latest study the researchers combined ground- and space-based observations to monitor the flow of a plasma plume streaming during a solar storm in January 2013.

Walsh checked the date against the trajectories of three NASA THEMIS spacecraft orbiting Earth to study auroras, the spectacular southern and northern lights, also produced by space weather events.

The three probes crossed the same point in the magnetosphere where plasma plumes had been detected from the ground.

"We identified a plasmaspheric plume, an outward extension of the Earth's atmosphere, which met an incoming coronal mass ejection at the edge of Earth's magnetic bubble," Walsh says.

The cold, dense plasma plumes originate from a region of the atmosphere called the plasmasphere, which is located just above the ionosphere, and extends out about 29,000 kilometres (4.5 Earth radii).

"The plasmasphere is so far out it's primarily ionised hydrogen where the electrons and protons have been stripped apart by ultraviolet radiation from the Sun," says Walsh.

"Normally these particles are sticking around the Earth, just drifting around, but when these large storms are going on, the outer region of this plasmasphere gets ripped off, and travels towards the Sun, reaching distances of 10 Earth radii (about 64,444 kilometres)."

The data from the THEMIS spacecraft confirmed the same cold, dense plasma plume stretched all the way to where the solar storm made contact with Earth's magnetic field.

This plasma slows down the magnetic reconnection process, according to the study's co-author Dr John Foster of the Massachusetts Institute of Technology.

"This weakens the strength of the geomagnetic storm, so the impact of the Sun on the Earth is less violent," says Foster.

"Instead the material gets swept back into the Earth's magnetic tail on the night side of the planet."

According to Walsh, the mechanism powering the plasmasphere plume are electric fields generated by the charged particles in the incoming coronal mass ejection.

However, the system isn't fail safe. It firstly depends on there being a reservoir of charged particles in the plasmasphere.

"The second piece is the magnitude of the coronal mass ejection, if it's a small one it's not going to be enough to cause the plasma to reach out to the edge of the magnetic bubble," says Walsh.

The findings, according to Walsh, imply coronal mass ejections that are either very powerful or very weak are likely to get through, with only moderately sized coronal mass ejections being shielded by the plasma plume.

Tags: stars