Physicist Rob Decker is obsessed with a region of space that has an ominous name: the termination shock.
It's out there, at the very edge of the solar system, 90 times as far away as Earth is from the sun. It is the region where solar wind comes to a halt.
There you will find huge, constant collisions as solar wind - the waves of hydrogen and helium plasma that shoot out from the sun at 1 million mph - crashes into a dense haze of charged particles flowing through interstellar space.
Decker and his team at the Johns Hopkins Applied Physics Lab in Laurel used an instrument aboard the venerable Voyager 2 spacecraft this month to give astronomers the first detailed look at that smashup - in a region long shrouded in scientific mystery.
Decker's group published findings in the July 3 issue of the journal Nature based on measurements taken with the spacecraft's Low Energy Charged Particle Instrument. It gave astronomers a better picture of how the sun - and stars like it - interact with the space that surrounds them.
"Every star is doing this, but the sun is the only one we can see doing it," said Eugene Parker, a physicist at the University of Chicago who was not involved in the research.
The report, with others published this month on Voyager's trip into the termination shock, could compel astronomers to revise their theories about what goes on at the edge of the solar system, an area known as the heliosheath.
"Hundreds of papers have been published about this topic over the past 20 years. Now we have to start all over again," said APL's Stamatios "Tom" Krimigis, a co-author of the article.
Parker described the work as a major step toward understanding solar wind and how it behaves. "Things are always more complicated than your first groping theories would indicate," he said.
The existence of solar wind was not confirmed until the early 1960s - a few years after Parker, now 81, published a paper predicting its existence. The discovery was greeted skeptically, but researchers say it opened the door to a new field in astrophysics.
"The question since then has been, 'Where does the solar wind stop? Where is this termination shock?' " said Krimigis, who has worked with Voyager 2 since its launch 31 years ago. "What we've learned is, it certainly goes a lot farther out than anyone thought and it behaves differently than almost anyone believed."
Another question has been why solar wind cools as it reaches the termination shock.
