The Silent War

DATA BANK: SOLAR FLARE

The minor star that humans call the Sun is a seething, restless million-kilometer-wide thermonuclear reactor. Deep in its core, where the temperature exceeds thirty million degrees, intact atoms cannot exist. They are totally ionized, their electrons stripped from their nuclei. Under those immense temperatures and pressures hydrogen nuclei—bare protons—are forced together to create nuclei of helium. This process of fusion releases particles of electromagnetic energy called photons, which make their tortuous way through half a million kilometers of incredibly dense ionized gas, called plasma, toward the Sun’s shining surface.

Furiously boiling, gigantic bubbles of plasma rise and sink again, cooling and reheating, in an endless cycle of convection. Immense magnetic fields play through the plasma, warping it, shredding it into slender glowing filaments longer than the distance between the Earth and its Moon. Vast arches of million-degree plasma form above the solar surface, expanding, hurling themselves into space or pouring back down into the Sun in titanic cascades.

Over cycles of roughly eleven years the Sun’s violence waxes and wanes. During periods of maximum solar activity the Sun’s shining face is blotched with sunspots, slightly cooler regions that look dark compared to the surrounding chromosphere. Solar flares erupt, sudden bursts of energy that can release in a few seconds the equivalent of a hundred million billion tons of exploding TNT: more energy than the entire human race consumes in fifty thousand years.

The electromagnetic radiation from such a flare—visible light, radio waves, ultraviolet and X-rays —reaches the Earth’s vicinity in about eight minutes. This is the warning of danger to come. Close behind, a few minutes or a few hours, comes the first wave of extremely energetic protons and electrons, traveling at velocities close to the speed of light.

The energy in these particles is measured in electron volts. One electron volt is a minuscule bit of energy: It would take five million electron volts to light a fifty-watt lamp. But protons with energies of forty to fifty million electron volts can easily penetrate a quarter-inch of lead, and particles from solar flares with energies of more than fifteen thousand billion electron volts have reached the Earth.

Yet the most violent effects of the solar flare are still to come.

The flare has ejected a gigantic puff of very energetic plasma into interplanetary space. The cloud expands as it moves outward from the Sun, soon growing to dimensions larger than the Earth. When such a cloud hits the Earth’s magnetosphere it rattles the entire geomagnetic field, causing a magnetic storm.

The auroras at Earth’s north and south poles flare dramatically, and the “northern lights” (and southern) are seen far south (and north) of their usual haunts. The ionosphere—the belt of ionized particles some eighty kilometers above Earth’s surface—runs amok, making a shambles of long-range radio transmissions that are normally reflected off its ionized layers.

On the Moon and even out in the Asteroid Belt all surface activity is halted when a solar flare bathes the region in lethal radiation. All spacecraft that operate beyond the Moon carry protective electromagnetic shielding to divert the energetic particles of the flare’s cloud. Otherwise the people in those spacecraft would swiftly die, killed by the invisible bullets of ionizing radiation.

Within a few days the deadly cloud wafts away, dissipates in interplanetary space. Earth’s ionosphere settles down. The auroras stop flaring. Space-suited workers can return to the surface of the Moon and the asteroids. The solar system returns to normal. Until the next solar flare.