For thousands of years, the aurora borealis or "northern lights" have lit the skies and human imagination with ghostly incandescence. Most often seen in Arctic regions but occasionally visible as far south as theMediterranean, they have inspired awe, fright and a fair measure of misunderstanding.
Tiberius Caesar mistook their red glows for a fire in progress and dispatched an army to Ostia in 34 A.D. to inspect damage. But until the 19th century, no one seriously thought that they could hurt anybody --unless, as an Old Norse legend warned, you happened to whistle at one!
Now we know better. Technological advances have made it possible for auroras and other "storms" in space to make themselves felt in the form of power blackouts, satellite failures and even pipeline explosions.
Space weather generally varies with the 11-year sunspot cycle: the more sunspots, the more storms and the more voluminous the "solar wind," as scientists call the stream of charged particles that incessantly blows off the face of the sun. Already, we are well on the way to the next solar maximum, expected to peak next year.
The maximum usually coincides with an increase in two other kinds of extremely bad "space weather." In one, powerful solar flares hurl protons and electrons almost to the speed of light. That acceleration produces blasts of X-rays that radiate into space. Both the particles and radiation can disrupt short-wave communication on Earth.
Were that not enough, the sun also can spawn billion-ton clouds of plasma and their associated magnetic fields. Traveling at more than 1 million mph,some of these "coronal mass ejections" (CMEs) may arrive at the Earth in only a few days.
In many ways, they actually are more noxious than the more familiar solar flares. CMEs pummel Earth's magnetic field like a sledgehammer 1 million miles wide and upset the delicate balances of trapped particles in the VanAllen radiation belts and elsewhere within the boundaries of Earth's magnetic field. [See illustration below].
The first indication that space weather has worsened usually is a spectacular auroral display in Arctic regions. When the solar wind hits theEarth's magnetic field, electrons and protons inside the field are accelerated into currents that flow along the gossamer-thin magnetic field lines and converge on the polar regions.
As they enter the thickening atmosphere about 500 miles above our heads,the particles collide with atoms and molecules of oxygen and nitrogen,which shed their added energy as light, producing ethereal shapes and colors.
But that's not all. The motion of other populations of charged particles within Earth's magnetic field causes great currents of charged particles to circulate in space like a 10,000-mile-wide river. These invisible stratospheric rivers can alter the geomagnetic field temporarily and produce "magnetic storms."
Humanity began feeling the effects of the solar maximum as soon as technology became sophisticated enough to respond. During the late 1800s,vast networks of wires were strung to carry telegraph and telephone traffic, setting the stage for a giant-scale reenactment of one of history's most famous physics experiments.
English physicist Michael Faraday discovered in his lab that, if you take a magnet and move it near a loop of wire, electrical current flows in the wire. The moving field induced a corresponding motion of charge in the wire. Faraday's "magnetic induction" soon was put to use in the first electric generator.
Exactly the same thing happened when solar storms triggered changes inEarth's magnetism, affecting thousands of miles of telegraph wires.Electrical currents induced by the changing fields often were so powerful that telegraphers didn't need battery power to send their information. Some operators were even treated to near-electrocution!
Placing wires under the ocean made no difference. In the Atlantic cable between Scotland and Newfoundland, 2,600-volt surges were recorded during a magnetic storm in March 1940. Short-wave broadcasts often were blocked for hours, and "technical difficulties" were expected and even jokingly
tolerated.
Some effects of solar storms were far beyond the nuisance level, especially at higher latitudes. In August 1972, a 230,000-volt transformer at theBritish Columbia Hydroelectric Authority blew up when shifting magnetic fields induced a current spike. On March 13, 1989, a storm plunged Quebec into a complete power blackout, affecting millions.
Over the years, such failures -- which follow the sunspot cycle -- have caused hundreds of millions of dollars in damage.
Earlier in this decade, the North American Electric Reliability Council,which oversees the entire U.S. electrical grid, estimated that a storm only slightly stronger than the one that hit Quebec could cascade into theUnited States. Such a disruption then would have cost the U.S. economy between $3 billion and $6 billion, about the damage inflicted by HurricaneHugo in September 1989.
THE PIPELINE PROBLEM
Long uninterrupted pipelines also can bring solar storms "down to Earth."Magnetic storm currents acting on pipelines are known to enhance the rate of corrosion over time, with potentially catastrophic cumulative effects.
On June 4, 1989, a gas pipeline explosion demolished part of theTrans-Siberian Railway, engulfing two passenger trains in flames and killing 500 people.
Unlike the Siberian pipeline, the Alaskan oil pipeline built during the mid-1970s is a newer technology specifically designed to minimize corrosive currents now well known to modern pipeline engineers.
Since the last solar maximum in 1990, hundreds of millions of people have come to depend on flawless, reliable work by an armada of satellites worth tens of billions of dollars. They are increasingly vulnerable.
In orbit above the protective layers of the atmosphere, they are prey to potentially hazardous dosages of radiation. The most destructive element seems to be high-energy electrons that penetrate deep into a spacecraft and affect delicate electronics.
Data bits in critical control programs can change suddenly from "1" to "0"or vice versa. The resulting false commands can put satellites into unplanned, and even fatal, operating modes.
In addition, many satellites have attitude control systems that sense the direction of Earth's magnetic field to determine up from down. During magnetic storms, polarities can change abruptly, causing satellites to upend themselves.
The list of major satellites incapacitated by adverse space weather is long and costly. Recent examples include an AT&B Telstar 401 satellite that experienced a massive power failure in 1997 only days after a solar storm arrived at Earth.
Last May, PanAmSat's Galaxy IV satellite, insured for $165 million,mysteriously lost attitude control and halted service for 45 million pager sin North America. Several new Motorola Iridium satellites suffered attitude control failures about the same time. In 1998, satellite insurance companies paid $1.8 billion in claims, of which half was for satellite failures in orbit.
PERILS IN ORBIT
Space storms don't even have to take a direct swipe to harm a satellite.Many satellites are placed in low Earth orbit (LEO) only a few hundred miles above the surface. During heightened solar activity, the added energy puffs the atmosphere up like a balloon, increasing atmospheric friction onLEO objects.
One result has been the premature demise of such satellites as the SolarMaximum Mission in 1990 and Skylab in 1979.
The planned International Space Station, also designed for LEO, will have to be periodically reboosted in orbit to avoid the same fate. Its assembly will involve 1,200 hours of spacewalks, mostly between 2000 and 2002 during the peak of the sunspot cycle.
Atmospheric friction causes other headaches. During the Quebec blackout inMarch 1989, the U.S. Space Command had to recompute orbits for more than 1,300 objects affected by momentarily increased air resistance.Nonetheless, LEO is considered prime orbital real estate for the latest generations of communication satellite networks.
According to one estimate, as many as 1,000 new satellites will be launched between 1997 and 2007, virtually all in LEO. During the next six years, the demand for voice and data transmission services will increase substantially, and the fraction carried by satellite services will reach$80 billion a year.
With the next solar maximum nearly underway, many institutions are responding. To safeguard the power grid, electric companies have begun to hire space weather forecasters and use advanced warning of inclement geospace conditions.
Many new commercial satellites, however, may be more susceptible to solar storm damage than their less sophisticated predecessors only a decade older because they lack adequate shielding and radiation-hardened circuitry.
The type of shielding needed depends on where you are going and how long you want to keep working. In geosynchronous orbit about 22,500 miles aboveEarth where most communication satellites operate, the interior of a satellite equipped with as little as one-fourth of an inch of aluminum would receive about 1,000 rads (a unit of radiation dosage) a year.
As a rule, damage to sensitive electrical components becomes a problem at about 30,000 rads, considerably more than a satellite would accumulate in atypical 10- to 15-year lifetime.
For most satellites, the degree of shielding is a matter of cost. Shielding is dead weight, but launching it into space costs just as much as launching million-dollar technology -- an average of between $5,000 and $10,000 a pound. Thus, engineers design many satellites with the least amount of shielding and the most sophisticated and vulnerable technology possible.
PATCHWORK MODELS
How much shielding is enough? Engineers use mathematical models to estimate the total radiation dosage during a satellite's planned operating lifetime given the thickness of the spacecraft's skin, the kinds of particles involved and their energies. In the mid-1960s, NASA became a leader in developing and refining such models.
These older models do not factor in effects of solar flare events, which can produce a year's worth of radiation damage in a few days or less.Still, these models are used widely today.
Since the mid-1980s, NASA has invested millions of dollars in research satellites, and soon a new generation of more accurate models will be ready. In the interim, designers rely on a patchwork of older models to calculate shielding needs.
How the new armada of LEO satellites will survive the coming solar maximum is unknown.
If you hear about power outages or satellite failures over the next 18 months, don't blame El Nino. Instead, consider blaming ol' Mr. Sun. After all, he's been up to the same shenanigans for about 4 billion years.
Sten Odenwald is education and public outreach manager for NASA's IMAGEsatellite program.
. . . Here comes the solar maximum
Earth has a magnetic field that presumably is generated by the flow of currents or conductive metals within its core and extends tens of thousands of miles into space.
When electrically charged particles from the sun hit that field, they are deflected sideways. The same principle is used in your television set to bend beams from the "electron gun" at the back of the picture tube so they strike different parts of the screen.
But when an event such as a solar flare bombards Earth with an abnormal amount of particles, previously trapped particles in distant parts of the geomagnetic field are accelerated. Those particles stream down the field lines into the polar regions.
But sometimes the particles form streams that generate their own magnetic fields. In that case, excellent conductors such as metals are subject tote induction effect, the principle that makes electric generators work.
The "alternator" in your car actually is a generator that charges the battery and supplies most of the electrical power. It consists of a rotating magnet (the rotor) surrounded by a dense coil of wire (the stator). The coil of wire on the rotor is energized by an electrical current from the voltage regulator so the rotor acts like a small electromagnet.
When the rotor spins at several thousand revolutions per minute, its changing magnetic field induces electrical energy to flow in the coils of wire in the stator.
In the same way, solar storms produce changing magnetic fields that can induce current flow in power lines and other conductors.
Human flesh is a partial electrical conductor. Otherwise, nerves and muscles wouldn't work. But the threat to people comes from what high-energy radiation and particles can do to DNA.
High-energy particles such as protons and neutrons can collide with the atoms that make up the DNA molecule, breaking chemical bonds and potentially causing errors to appear in genetic information. Because people are constantly surrounded by radiation from the ground, air and food, some of this damage cannot be avoided.
Outside the bulk of Earth's atmosphere, however, the risk rises dramatically. Astronaut Shannon Lucid reported that, on the Russian Mir space station, the typical radiation dosage was the equivalent of about eight daily chest X-rays. During a solar storm at the end of 1990, Mir cosmonauts received a full year's dosage in a few days.
The maximum career dosage for radiation is about 400 rem. A rem is a unit of radiation that measures the amount of energy delivered to organic material. A single chest X-ray produces about .06 rem of radiation dosage,and our natural background environment supplies about .35 rem each year.
Major solar flares can deliver from 100 to several thousand rems in a few hours or days for an astronaut inside a space suit. That would lead to radiation sickness, and in extreme cases, death. Space station construction workers caught off-guard during even minor flares would be grounded for several years after such an encounter.
Incidentally, you don't have to be in low Earth orbit to be affected.
Although the atmosphere protects most airline flights well from space radiation, transcontinental flights taking the polar route pass through regions of Earth's magnetic field where particles become concentrated.
Airline flight crews who travel these routes frequently can accumulate as many as .9 rem a year. This is more than the allowed annual dosages for nuclear plant operators and comparable to what shuttle astronauts receive during a typical one-week mission.
Blowing Up a Storm
When currents flow -- or, more generally, whenever electrically charged objects move -- they create magnetic fields.
You can observe the effect by hooking one end of a copper wire to a battery, making a couple of loops and then holding the free end near the other battery terminal. Set a compass next to the loops. When you touch the wire to the terminal, allowing current to flow, the compass needle will twitch, registering the magnetic field you have created.
Currents also flow in the sun. Although an ordinary atom is electrically neutral, the temperature inside the sun is hot enough to strip electrons off atoms, producing a stew of negatively charged electrons and positively charged atomic nuclei called a plasma.
These plasmas boil like oatmeal in a pot, heated by the 15 million-degree nuclear hot plate deep in the core. As they rise toward the surface, they cool and begin to sink in a process called convection. Convection current stake up nearly one-third of the outer portion of the sun.
By means still unknown, rivers of charged particles sometimes generate powerful magnetic fields that loop like gigantic ropes and sometimes push to the surface. When they emerge, they create sunspots.
We see these as dark spots because intense magnetic fields stifle local convective flow of energy from the interior, making gases in the spots about 4,000 degrees Fahrenheit cooler than the surrounding solar surface,which is about 10,400 degrees. As a result, the spots -- typically the diameter of Earth or larger -- appear relatively dark, although they actually are brighter than the full moon.
Sunspot fields become more or less numerous on a cycle that averages 11 years from a minimum of a few to a maximum of nearly 200. No one knows why it's that particular span of time. But it seems to be associated with the predictable reversal of the sun's magnetic field: Every 10 to 12 years,north becomes south, and south becomes north.
Observers do know very well that periods of high sunspot activity produce much greater volume of "solar wind," the spray of atomic nuclei, electrons and other particles that are blown off the sun's surface at about 1 million mph and eventually arrive at Earth.
Ordinarily, the wind isn't very strong, averaging about 80 particles per cubic inch. Every few weeks or so during peak years of solar activity, the sun hurls clouds of particles into space. These can double or triple the density of the solar wind near Earth for hours or days.
These "coronal mass ejections" and their more fleeting companions, "solar flares," appear to be more common during sunspot maximum periods.