Energy | Pages 144-145 | See Linked Version
Twisted arcs of magnetic force carry spectacular eruptions of solar matter into space. Without Earth's own protective magnetic shield, we would be exposed to lethal doses of high-energy radiation and solar particles.

Twisted arcs of magnetic force carry spectacular eruptions of solar matter into space. Without Earth's own protective magnetic shield, we would be exposed to lethal doses of high-energy radiation and solar particles.

magnetic fields. Earth therefore generates a magnetic field like a giant bar magnet. The magnetic poles happen to lie near the geographic north and south poles of our planet, making compasses useful in navigation. That hasn't always been the case. Earth's magnetic field has weakened, wandered, and flipped many times throughout its history.

Earth's field at the surface is strong enough to drive a compass needle, but it is weak overall. Magnets on your refrigerator are hundreds of times stronger. Even so, Earth puffs a magnetic bubble into space--a "magnetosphere"--that is sturdy enough to shield us from a constant onslaught of charged particles from the Sun and deep space. The magnetosphere deflects some particles around Earth and traps others within belts of radiation that girdle the planet. Without this protective force field, the Sun's blasts would long ago have wiped out life on the planet's surface. The other planets also generate magnetospheres. It comes as no surprise that Jupiter, with its massive core of metallic hydrogen, generates the grandest one in the solar system. If we could see it glow in the night sky, it would appear several times larger than the full Moon.

Planetary magnetic fields are puny compared to those on the Sun. The gaseous outer layers of the Sun spin once every 25 days at the equator and every 31 days near the poles. But the center of the Sun spins like a solid ball. Between the outer and inner layers, astronomers have detected a narrow zone where the Sun's electrically charged gas shears, almost like clouds caught between slow and fast streams of air in Earth's atmosphere. This shearing action generates intense magnetic fields. The fields try to line up but quickly get distorted and fold over on themselves because of the Sun's differential rotation. The physical equations that govern the resulting stresses are related to those that describe tension in a twisted batch of rubber bands. Severely stretched field lines can abruptly snap through the Sun's surface, creating turbulent regions and sunspots. The magnetic turmoil ejects flares of charged particles and blobs of the Sun's atmosphere far into space, much as a naughty schoolchild uses rubber bands to propel wads of paper across the room. When these particles reach Earth, they can harm satellites and disrupt electronic communications. The Sun's particles also collide with air molecules in Earth's upper atmosphere. The molecules temporarily absorb energy and reemit it in the form of visible light. We see the results as auroras--colorful ribbons of light in the sky near the north and south poles.