Voyager 1 at the edge of the Solar System?

well, someone had to be first to post to this particular forum!!!

cheerio, Voyager 1 . . .

John F.
SDAS



Voyager 1 has phoned in from the edge of the solar system to let us know what it's like out there. Now scientists are arguing over whether the 26-year-old spacecraft has really reached a telltale and important boundary.

Controversy is brewing over whether Voyager 1 has crossed the termination shock, a poorly understood envelope some 8.4 billion miles (13.5 billion kilometers) away, where supersonic particles from the Sun -- riding out on the so-called solar wind -- should slam into interstellar plasma and drop to subsonic speeds.

New Voyager data show something is up, but it's not clear what.

Astronomers expect the boundary to be somewhere between 85 and 120 astronomical units from the Sun (1 AU is the distance from Earth to the Sun). Launched in 1977, Voyager 1 is 90 AU from the Sun as of today -- farther from Earth than anything else that's ever left this world and well beyond the solar system's nine planets.

Voyager 1, the most distant spacecraft, is at or near the termination shock, where the solar wind first meets interstellar plasma. The paths of the two Voyagers (but not their current locations) are shown.

Two interpretations
Voyager recorded a large increase of a certain type of energetic particles, hinting that the craft has detected the expected drop in solar wind speed and has encountered interstellar plasma, according to research led by Stamatios Krimigis of the Applied Physics Lab at John Hopkins University.

Krimigis and his colleagues argue the spacecraft exited the supersonic solar wind, possibly beyond the termination shock, on about Aug. 1, 2002 at a distance of 85 AU from the Sun and re-entered it about 200 days later at 87 AU.

Another team, however, has a different take on the data. A study led by Frank McDonald at the University of Maryland concludes Voyager has yet to reach the termination shock.

"Either way, Voyager 1 has entered a region of our solar system that has never yet been explored," says University of Michigan professor Len Fisk, who was not involved in either study.

The two interpretations were discussed at a NASA press conference today and will be published in the Nov. 6 issue of the journal Nature.

Outbound
Voyager 1 will eventually pass the termination shock and, barring catastrophe, other expected boundaries. That will put the craft in interstellar space. Scientists are eager to learn as much as possible during this first trip through the edge of the solar system before the machine runs out of fuel in about the year 2020, rendering it unable to communicate.

Voyager 2, launched in the same year, is about 70 AU away. Both robotic explorers are headed toward two other boundaries beyond the termination shock. The heliopause marks the region where the solar wind no longer exists and interstellar plasma rules. Then there is the bow shock, created by the entire heliosphere plowing through space. The bow shock is akin to the ripple of water raised by a boat's bow.

Previously, Voyager data was paired with observations from the Hubble Space Telescope to find evidence that the outer shell, the bow, shock, in fact exists as theory predicts.

Communications will be lost with both Voyagers before either can reach the bow shock.

In figuring out Voyager 1's environment, researchers are hampered by a non-working onboard plasma detector. It would have directly measured the solar wind speed definitively.

Krimigis' team instead measured one sort of particle, deciding that their quantity and type show the solar wind must have slowed down. McDonald's team analyzed a different sort of energetic particles and determined they were accelerated somewhere else, out beyond Voyager's location, and suggest Voyager has yet to reach the termination shock.

Fisk, who analyzed the two papers for Nature, says the termination shock is probably not a fixed boundary anyway. Its location will vary depending on solar activity and may in fact be moving outward now and for the next few years.

Advantage Krimigis
"I tend to agree with Krimigis [and colleagues] that their data can most readily be explained if the termination shock has been crossed," Fisk writes. He says it's possible the shock front then moved outward, putting Voyager back inside it. Fisk said McDonald's analysis suggests either Krimigis is wrong or the termination shock could have a more complex shape than scientists expected.

Only more data from Voyager 1 -- if it encounters the boundary either again or for the first time -- will settle the issue, Fisk said.

The twin Voyager missions explored all the gas giant planets before trekking out beyond Pluto. Voyager 1 is the most distant manmade object. Each spacecraft carries a gold record that serves as a "greeting to the universe," with sounds and images selected to portray the diversity of life and culture on Earth.

Oops!

it looks like Voyage hasn't quite bade farewell just yet!!!

John F.
SDAS


DISCOVERY CHANNEL NEWS:-

Nov. 20, 2003 — Even at eight billion miles from home, Voyager 1 is not quite free of Old Sol yet, said researchers who think recent announcements of the durable spacecraft dipping into interstellar space are a bit premature.

"The question is whether or not we've crossed the shock," said Len Burlaga of NASA's Goddard Space Flight Center in Maryland. The "termination shock" Burlaga referred to is a changeable zone where the outward flowing supersonic solar wind drops from 700,000 miles-per-hour to 100,000 miles-per-hour because of the inward rush of the interstellar or galactic wind. "We're close to it, but we're probably not past it," he said.

Burlaga and several of his colleagues published their interpretation of Voyager 1's proximity to interstellar space in the current issue of Geophysical Research Letters.