Like the prow of a ship carving its way through an icy sea, fields of force generated by our sun reach out before us and split open the interstellar dust and gases that our solar system is sailing through.

Charged particles from the sun continually slam into these clouds of galactic dirt and radiation, and have been doing so for 4.6 billion years. For more than three decades, researchers have suspected there must be a shock wave amid all this violent galactic weather. And since the early 1990s, they have sought out the swath of glowing particles they expect will reveal its location.

After all, the shock wave -- called the "bow shock," like the ripple of water raised by a boat's bow as it moves through the water -- is the solar system's protective womb, and we'd like to know more about it.

While space is often imagined as a vacuum, the visible portion of the interstellar medium is thought to make up roughly 15 percent of the mass of our Milky Way galaxy. About 1 percent of the visible part is composed of dust, and the rest of it is gas.

Charged particles from the sun spiral into this not-so-empty space, following magnetic field lines and filling a region of space called the heliosphere. The solar particles at the edge of the heliosphere form the bow shock, which acts as a barrier to deflect incoming cosmic rays that are up to a million times more energetic than the solar wind. At the front line, charged particles are lit up by all this interaction.

For some 200,000 years or so, the solar system has been meandering through an interstellar cloud of relatively low density. That will someday change, having as-yet unknown consequences for Earth.

If the solar system encounters a denser cloud, the bow shock could be pushed closer to the sun, Schwadron explained in a telephone interview.

A related inner shell of force, known as the termination shock, might be pushed as far inward as the orbit of Jupiter. The termination shock is a region where the solar wind first feels the interstellar medium, dropping its speed from several hundred kilometers per second to less than half that.

The termination shock and the bow shock combine to provide two lines of defense against cosmic rays.

"If you suddenly shrink that whole interaction, you bring in the source of cosmic rays much closer to Earth," Schwadron said. "It's not completely clear what would happen. It would undoubtedly change the radiation environment."

The study by Ben Jaffel and his colleagues builds on models constructed by other researchers, including the University of Chicago's Priscilla Frisch and Gary Zank of the University of Delaware.

"Ben Jaffel and his colleagues have taken the modeling to the next very important step, looking at the structure of the interaction of the interstellar medium with [the] heliosphere," Zank told SPACE.com.

Sometime in the next 10,000 to 100,000 years, Zank says, we will likely encounter a denser interstellar cloud. It could be small and go undetected. Though Zank stressed that the effects can't be predicted, it's possible that Earth's own protective magnetosphere might be altered, ultimately affecting our atmosphere and climate.

By studying a region of the sky free of bright stars, Ben Jaffel and his colleagues used Hubble to provide a spectral signature of the ultraviolet glow from the bow shock. The Voyager craft, not yet even at the termination shock, was close enough to map the distribution of the glow.

The study also showed that the heliosphere is tilted with respect to the path along which the sun travels by about 12 degrees, which allows the researchers to determine the direction of the interstellar magnetic field that causes the tilt.

"We know how our solar system is reacting with the surrounding interstellar medium," Ben Jaffel told SPACE.com. "We can now describe the influence on the inner heliosphere and the planets with more confidence."

Other research relies on the Ulysses and SOHO spacecraft to study interstellar particles as they reach the inner heliosphere. Ben Jaffel and his colleagues hope that a proposed even longer-distance mission, the Interstellar Probe, will get the nod from NASA.

The Interstellar Probe would pass through the boundaries of the heliosphere and explore nearby interstellar space.

In the meantime, Ben Jaffel said an as-yet unplanned space telescope could be deployed to study the Fermi glow and build a 3-D model of the bow shock. One goal would be to watch for oncoming interstellar clouds of higher density.

"Depending on the detection time, we could have up to few centuries to decide to stay or leave," he said.