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Solar Flares and Coronal Mass Ejections
August 12, 2004
SOHO image of an X-class flare Solar Flares are powerful bursts of electromagnetic energy in the Sun's atmosphere. Credit: NASA

The Sun we observe every day appears constant and quiescent, dependably providing the planet with the energy necessary to maintain life. However, the occasional dark blemishes on its face - sunspots - give hints of the dangers to us lurking above the surface in the unseen Sun.

Sunspots are locations on the Sun where extremely strong magnetic fields have cooled the hot plasma (electrically charged gas) to slightly less than that of the surrounding regions. They are actually footprints of active regions where enormous loops of magnetic force trap plasma within them in the corona (atmosphere) of the Sun. The plasma in these magnetic loops is heated to the point that it gives off ultraviolet light. Sometimes these loops become twisted or over-stretched, and they rapidly change back to simpler forms. When this happens, plasma can be violently smashed down into the Sun's surface - a solar flare - or squirted out into interplanetary space - a coronal mass ejection (CME). Energy is radiated away from these explosions in the form of X-rays, gamma rays, and high energy particles of matter.

To better understand the processes that cause solar storms and space weather, NASA, in partnership with other national and international agencies, conducts space missions to study the Sun-Earth Connection. Missions such as SOHO, TRACE, GOES, and RHESSI monitor the Sun's activity. Other satellites, such as WIND and ACE, study how solar storm explosions travel from the Sun to Earth; and FAST, IMAGE, and Polar study the effects such activity has on Earth and its inhabitants.

SOHO image of a coronal mass ejection (CME) A CME is a huge bubble of gas threaded with magnetic field lines that are ejected from the Sun over the course of several hours. Credit: NASA

High-energy-charged particles of matter released during a CME are sometimes directed toward Earth. They travel more slowly than light and therefore arrive a few minutes later than electromagnetic radiation such as X-rays. These particles themselves are mostly deflected by Earth's sphere of magnetic influence - its magnetosphere - and the rest are almost all absorbed by the atmosphere. Thus, we ground dwellers are pretty safe from their menace.

Astronauts in low-Earth orbit are mostly protected by the magnetosphere, but do receive higher doses of radiation than people on the ground, especially near the magnetic poles of Earth. The greatest radiation danger would be to astronauts who participate in exploration of the Moon and Mars. The astronauts would be located far outside the protection of Earth's shields, where the effect from a CME-driven shock wave can bombard them with as much radiation as 300,000 chest X-rays at once! It would take only 45,000 simultaneous chest x-rays to kill you.

These high-energy particles' effect on Earth is less severe. Their energy is absorbed by Earth's magnetosphere, which can then rebound and accelerate charged matter within it toward Earth. This current of electricity flowing into Earth's atmosphere causes the Northern and Southern Lights, also called the Aurora. If the CME was very intense, it can disturb the magnetosphere and induce electrical currents on Earth's surface, which can overload power grids. In the past, there have been wide-spread power outages resulting from geomagnetic storms, which were ultimately caused by the Sun's fury.

In comparison to high-energy particles from CMEs, the doses of X-rays from solar flares are not terribly damaging to living tissues. Plus, those of us on Earth are protected by its atmosphere, which shields us from such harmful rays of electromagnetic radiation. The X-rays from solar flares can also affect our technology on the ground and in space. The X-rays absorbed by Earth's atmosphere deepen its ionosphere, which affects shortwave radio communications on the ground. Electrons stripped from the ionosphere can interact with satellites in low-Earth orbit and cause damage to their electrical systems. The outer atmosphere is also heated by the incoming radiation and bloats up to a larger size. This creates additional frictional drag on satellites in low-Earth orbit, which can degrade their orbits.

In order to safely continue our exploration of space, we must actively study the hazards unleashed by the Sun, so that we can predict Solar dangers and protect humans and our technology.

Current Missions Studying the Sun-Earth Connection from NASA and Its Partners:

Solar Wind:

Classroom Lessons about Solar Flares and CMEs:

Dr. Bryan Mendez (with Dr. Laura Peticolas and Karin Hauck)
UC Berkeley/Center for Science Education

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Page Last Updated: September 18th, 2014
Page Editor: Holly Zell