Space Weather Signal Buried in X-ray Noise

Sometimes even noise can produce a gold mine of information. Back in 1964, scientists at Bell Laboratories, listening for faint radio signals they had bounced off of an early communications satellite, detected static that seemed to be emanating in space from all directions. That static turned out to be cosmic background radiation left over from the big bang. In the decades since, studies of that radiation have underpinned much of what we know about the universe.

Now another incident of noise promises to yield a breakthrough in our understanding of space weather. The case involves images taken by the XMM-Newton spacecraft and other telescopes of x-ray emissions from distant stars. Some of the images contained the equivalent of overexposure or graininess, which astronomers traced to the existence of comets approaching the sun. It turns out that the solar wind generates low-energy x-rays when its charged particles hit neutral atoms in the tails of comets approaching the sun, which muddles images if x-ray telescopes happen to be pointed in the direction of the tails.

When the astronomers consulted with a team led by space physicist Michael Collier of NASA's Goddard Space Flight Center in Greenbelt, Maryland, about the phenomenon, the scientists discovered something else: Solar wind particles produce the same x-rays whenever they strike neutral atoms just above Earth's magnetosphere, the bubble produced by Earth's magnetic field that surrounds the planet and protects it from harmful solar radiation. In the current issue of the journal Eos, Collier's team argues that the emissions, which are easy to detect with x-ray telescopes, could produce a display of the entire magnetosheath, the part of the magnetosphere that is bombarded by incoming solar particles. And that display could enable scientists to generate, in real-time, global, space-weather images, just as high-flying meteorological satellites provide real-time images of weather on Earth.

Such ability would constitute a major advance. At present, monitoring space weather is a hit-or-miss proposition. Instead of a global network of satellites and sensors on the ground, like the ones serving meteorologists, space scientists have had to rely on a few satellites, whose data recordings cover only a small part the magnetosphere and produce no images. When sudden bursts of intense radiation from the sun pierce the magnetosphere's protective bubble, they set off events that can fry the delicate electronic equipment aboard orbiting satellites, interfere with or kill telecommunications signals, and even overload electric power grids on the ground. Operators of those systems currently have no way of knowing whether solar activity is the culprit, except after the fact. Space physicist and co-author David Sibeck, also of NASA Goddard, says the magnetosheath images would allow engineers immediately to rule out mechanical or other failure and deal with the radiation problem.

Further down the road, Sibeck says, x-ray telescopes installed aboard interplanetary spacecraft could probe how the solar wind affects every other body in the solar system with an atmosphere, such as Venus, Mars, the gas-giant planets, and Saturn's big moon, Titan.

The potential for using the new data to track space weather is "wide open," says space physicist Stephen Fuselier of the Lockheed Martin Advanced Technology Center in Palo Alto, California. To best image the x-rays, he suggests mounting one or two small x-ray telescopes on spacecraft orbiting above Earth's poles around half the distance to the moon. Such a high vantage point could take in the whole sun-facing side of the magnetosphere at once, he says.

This article corrects a previous version, which stated that David Sibeck was the research team leader instead of Michael Collier.

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