Seeing The Invisible

October 27, 1998

One of the most important frontiers in space has also been the closest - and the hardest to see. Indeed, it didn't even have a name - magnetosphere - until 1959, and scientists are still discovering how it works.

"This is an immense volume," said Dr. Mark Moldwin of the Florida Institute of Technology in Melbourne, Fla. "We're doing single-point missions in a lot of regions and drawing cartoons to connect the dots."

Drawing the right cartoon and linking it to an accurate model that predicts what the magnetosphere does will help us understand not only what happens here at Earth, but in solar flares and even in magnetars. Moldwin was speaking to the New Millennium Magnetosphere Workshop which opened on Monday in Guntersville, Ala. It is sponsored by NASA and the National Science Foundation.

Mankind had always had a hint that outer space was more than "empty space." The aurora borealis, or Northern Lights, had entranced humans since the first people mover northward. In 1958, the Explorer 1 satellite carried instruments that revealed the presence of radiation trapped by Earth's magnetic field into two belts encircling the planet.

Not until 1959 was the term "magnetosphere" coined by Dr. Thomas Gold of Cornell University, noted Dr. James Burch of Southwest Research Institute in San Antonio, Texas. Substorms - storms of particles that brighten the aurora, disrupt communications, and cause other effects - were not formally recognized until "the last page" in a set of three articles in Journal of Geophysical Research in 1968.

Meanwhile, public attention was readily taken by interplanetary missions that returned pictures of Earth and other worlds.

"When people see these images, they have an immediate connection to something they think they know," said Dr. J.D. Craven of the University of Alaska in Fairbanks. "When you start showing them something like this [an image of the aurora seen by Polar from space] they get more interested." And an image of the aurora seen from the Space Shuttle "brought a whole new dimension to it - the aurora has altitude."

The United States and other nations have launched dozens of spacecraft to study the magnetosphere. Yet even with the most ambitious campaign - the International Solar Terrestrial Physics (ISTP) Program - has comprised fewer than a dozen spacecraft. From a scientific standpoint, it's been like setting up that many weather stations and then generalizing about weather and climate across the globe.

Yet, as Moldwin pointed out, scientists can offer a number of striking artist's concepts that depict the anatomy of the magnetosphere.

"When we talk about a global picture, we're really talking about a statistical picture," he said. "We're averaging over many events to get this picture."

This is because the magnetosphere is largely invisible.

"We are data poor," Moldwin said, even though several gigabytes of data have been returned in four decades of studies. "Where we can sample, we have a lot of information that we need to tie together."

The first picture of the magnetosphere was taken by special ultraviolet camera carried to the moon by the Apollo 16 mission (at right). This showed only discrete portion, the geocorona, a ring of electrified helium circling the Earth and glowing in ultraviolet light.

More recently, the Dynamics Explorer 1 (launched in 1981) and Polar spacecraft (1995) have carried cameras that take visible, ultraviolet, and even X-ray images of the auroral regions from space.

"What's missing now is how to map these images out into the magnetosphere," Burch said, because the images of the magnetosphere are still just cartoons drawn from countless data points collected along a narrow set of paths allowed a satellite.

In recent years, though, scientists have started developing some innovative tools - new methods and even new cameras - that would let them take a true picture of the entire magnetosphere.

An exciting approach that Burch and others described is taking pictures by using neutral atoms in space. Most of what is out there is electrified (stripped of one or more electrons) and is captive to the magnetic field. When one of these ions hits a hydrogen atom, it steals an electron back and becomes neutral, free to fly off in a straight line.

Polar carries instruments to that measure the direction and mass of these atoms. With special math tools, scientists can then derive some information about the magnetosphere in the direction the atom as traveling.

The problem is, the atom could have originated 10 meters or 10,000 kilometers away. It's a bit like looking through a fog.

But it's promising. Burch showed an image, taken by the Imaging Proton Spectrometer (IPS) on Polar, looking down the magnetotail (the portion of the magnetosphere that the solar wind drags into deep space). He then showed how the image closely matched activities in the aurora.

The method is limited and will be expanded in the year 2000 with the launch of the IMAGE, the Imaging Magnetosphere Explorer, carrying an array of specialized cameras. Some will borrow technology from the Advanced X-ray Astrophysics Facility (AXAF). Optical cameras will use an array of filters and other tricks to produce images of the magnetosphere in visible, ultraviolet, and X-rays. The "non-imaging" cameras will capture and measure neutral atoms to make more sophisticated depictions than Polar can now provide, and a 500-meter (1,640-ft) long dipole antenna will probe the magnetosphere with radio waves.

Still, scientists will face to conflicting demands.

"We need to look at the big picture," Moldwin said, "and we need to look at the microscale physics." This is akin to watching global weather circulation while keeping an eye on small rainstorms.

To do this, NASA and other agencies are looking at several ambitious missions, including one that would orbit hundreds of microspacecraft to take data simultaneously at that many locations.

The Magnetosphere Constellation and Tomography (MAGCAT) mission would deploy a smaller number spacecraft to probe the magnetosphere with multiple radio beams and build an image much as a medical CT-scan shows a cross section of the body. Better understanding of how the magnetosphere works will have applications beyond better predictions of how magnetospheric substorms may affect communications and power grids on Earth. It will also help in exploring the planets - Jupiter has the strongest magnetosphere, one that even makes its moon, Io, light up in the dark. And it will become a tool for deciphering what is happening in the newest cosmic oddity, magnetars, highly magnetized neutron stars that give off blinding flashes of gamma radiation.

NASA/Marshall Space Flight Center--Space Sciences Laboratory

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