Tom Armstrong’s office is in south Lawrence, but his livelihood is now leaving the solar system.

For 26 years, Armstrong, a retired Kansas University professor and owner of Fundamental Technologies, has tracked and interpreted radiation data for the Voyager I spacecraft.

In two articles published this week in the journal Nature, scientists presented evidence — gathered in part by Armstrong — that indicates the Voyager, now more than 8.4 billion miles from the sun, has become the first man-made object to leave our solar system and head to interstellar exploration.

“This is of significance to the human race,” Armstrong said. “It says we’ve reached beyond our own solar system. It’s part of our heritage at this point. What is happening with Voyager only happens once in history.”

Armstrong was a professor of physics and astronomy in 1975 when he and a team of researchers from such institutions as Johns Hopkins University, Bell Laboratories and an agency in Germany responded to a request for proposals for a radiation sensor to place aboard Voyager, which would be launched two years later.

‘Wildest dreams’

They came up with an instrument about the size of a bread box, made primarily of aluminum, that moves back and forth on the spacecraft to measure radiation levels looking in different directions in space. They won the contract, but Armstrong never expected to be working on the project 26 years later.

“Not in my wildest dreams,” he said. “Actually, I should say in my wild dreams I just hoped everything went well.”

Voyager kept plodding along at a mere 50,000 mph to gather data and photos of Jupiter, Saturn, Neptune, Uranus and Pluto. Armstrong received radiation data once every three months to interpret.

Tom Armstrong, a retired KU professor, has investigated data from Voyager I for more than a quarter of a century. He believes the spacecraft, pictured at left in a painting, has reached the outer limits of our solar system.

The sun sends out a stream of highly charged particles, called solar wind, that carves out a vast bubble around the solar system. The edge of the solar system — and the beginning of interstellar space — is generally considered to be the area where the solar winds are no longer detected.

Armstrong and his colleagues noticed a severe drop-off in solar wind beginning in July 2002.

“After 26 years of flight, what is clear is Voyager I is now experiencing something new and different than anything it’s ever seen,” he said. “It took a few weeks of this odd behavior and analysis of really skilled and careful scientists. When we made the evaluation, it persuaded me (it had hit the solar system’s edge).”

But some researchers say the evidence isn’t certain.

Not conclusive

Scientists have long theorized that a shock wave exists where the hot solar wind bumps up against the thin gas of the interstellar medium. A similar shock wave precedes aircraft flying faster than the speed of sound, causing a sonic boom.

¢NASA – Voyager¢ KU Audio: Tom Armstrong audio interview (3-19-03)

In space, the violent encounter slows the solar wind from supersonic velocity to subsonic speed, and causes a pileup of particles. As they accumulate, the particles increase in temperature. Also, they skip back and forth across the shock boundary, as they are accelerated and energized.

Scientists have examined data from Voyager I for evidence of any of those activities, which would suggest the one-ton spacecraft has reached the termination shock, but haven’t found that secondary evidence. One instrument that would have measured solar wind velocity and would give somewhat of a definitive answer quit working years ago.

One team of scientists has theorized that the data suggests Voyager I is simply approaching the termination shock.

“We say what we are seeing is exactly what we would expect to see as we approach the shock,” said Frank McDonald, of the University of Maryland, and co-author of one of the studies. “We are not there yet.”

Interstellar

If Voyager I is entering interstellar space, Armstrong said there would still be plenty of information to gather about the radiation makeup of space outside our solar system.

Armstrong retired from KU in May after 35 years. He and his company also have analyzed radiation data from NASA spacecrafts such as Voyager II, Galileo and Cassini.

“My goal is to make sure there’s an honest, complete and useful record of all of this stuff, as carefully explained and as fully documented as it’s feasible to do,” he said. “It’s going to be ages — a long, long time — before there’s a similar set of observations.”

He compared the event’s significance to discovering radiation fields around planets, though not as important as humans landing on the moon.

“It’s a tribute to teamwork, and it’s a proud accomplishment for the human race,” he said. “NASA needs good news. It should be proud of what it’s been able to accomplish in science. It has enough reasons to wonder if it’s doing the right thing, when things fail and sometimes fail fatally.”