[Vision2020] 6-27-13 NY Times: "Going, Going, Still Going? Voyager 1 at Solar System’s Edge"

[Ted Moffett]

Amazing that Voyager 1 is still sending data to Earth that can be received,
still making discoveries...

http://www.nytimes.com/2013/06/28/science/space/going-going-still-going-voyager-1-at-solar-systems-edge.html?src=un&feedurl=http%3A%2F%2Fjson8.nytimes.com%2Fpages%2Fscience%2Findex.jsonp

By KENNETH CHANG<http://topics.nytimes.com/top/reference/timestopics/people/c/kenneth_chang/index.html>
Published:
June 27, 2013At the edge of the solar system, there are no signs that
proclaim, “You are now entering interstellar space.

NASA’s Voyager 1 spacecraft, launched more than 35 years ago and now 11.5
billion miles from where it started,
<http://voyager.jpl.nasa.gov/where/>is closing in on this boundary. In
recent years scientists have been
waiting eagerly for it to become the first artificial object to leave the
solar system and enter the wider reaches of the Milky Way, which they fully
expect it to do. But there has been at least one false alarm.

On Thursday, scientists reported that, no, Voyager 1 still had not reached
interstellar space, but it had entered a region that no one expected and no
one can yet explain, a curious zone that is almost certainly the last layer
of our Sun’s empire — technically speaking, the heliosphere. Three papers
published in the journal Science describe in detail the sudden and
unpredicted changes encountered in the surroundings of Voyager 1, which
left Earth about three months after the original “Star Wars” movie was
released and is heading for the cosmos at 38,000 miles per hour.

Scientists had expected that Voyager 1 would detect two telltale signs as
it passed through the heliosheath, the outermost neighborhood of the solar
system, which is thought to abut the heliopause, as the actual boundary is
known. Happily, the key instruments on Voyager 1, as well as those on its
twin, Voyager 2, are still working after all these years, and its nuclear
power source will last until at least 2020.

Last summer, one of the two events occurred, but not the other, leaving
scientists perplexed. Scientists had predicted that at the boundary between
solar system and interstellar space, the solar wind — a stream of charged
particles blown out by the Sun — would fade away, and that Voyager 1 would
no longer detect it. That happened.

They also expected that the direction of the magnetic field would change as
Voyager 1 emerged from the Sun’s magnetic bubble. That did not.

“Nature is far more imaginative than we are,” said Stamatios M. Krimigis, a
scientist at the Johns Hopkins Applied Physics Laboratory who is the
principal investigator of an instrument that records charged particles
hitting Voyager 1. Dr. Krimigis is an author of one of the papers in
Science<http://www.sciencemag.org/content/early/2013/06/26/science.1235721>.


Last July, the spacecraft — which is roughly 1,600 pounds and would fit
inside a cube about 13 feet on each side, according to
NASA<http://voyager.jpl.nasa.gov/faq.html>— observed a momentary dip
in the intensity of the solar wind. “It was
exciting,” said Edward C. Stone, the project scientist for the two
Voyagers. “We had never seen such a drop before. It happened in less than a
day. Then five days later, it was back up.”

In mid-August, there was a deeper momentary dip.

Then, on Aug. 25, the solar wind dropped by a factor of more than a
thousand, vanishing to imperceptible levels, and it has remained at
essentially zero since. At the same time, the number of cosmic rays from
outside the solar system jumped by 9.3
percent<http://www.sciencemag.org/content/early/2013/06/26/science.1236408>.


“It looked like we were outside,” Dr. Stone said.

But the magnetic field has steadily, stubbornly pointed in the same
direction, indicating that Voyager 1 is still ensconced within the Sun’s
magnetic field. Scientists guess that in this region the magnetic fields of
the solar system partly connect to those of the surrounding interstellar
space, allowing the solar particles to escape. (Charged particles travel
along magnetic field lines.) They have named the zone through which Voyager
1 is hurtling the heliosheath depletion
region<http://www.sciencemag.org/content/early/2013/06/26/science.1235451>.


“I think it’s clear we do not have a model which explains all of this,” Dr.
Stone said.

Voyager 2, which is moving slightly more slowly and is not as far from the
Sun, has not yet encountered this region.

Dr. Stone noted that when the two Voyagers launched in 1977 on a grand tour
of Jupiter, Saturn, Uranus and Neptune, the space age was just 20 years
old, and there was no way to know that NASA had built something that would
last 35 years, long after it passed the planets. But the designers of the
mission were prescient to be prepared if they lasted that long.

“It turns out that in fact we designed the cosmic ray instrument
specifically for this phase of this mission,” Dr. Stone said. “We were
planning, and it really paid off. We’ve begun to see what’s outside even
though the magnetic field says you’re not outside.”

As for actually reaching the outside of the solar system, Dr. Stone said,
“it could be a few months, or it could be several more years.”
   A version of this article appeared in print on June 28, 2013, on
page A19of the New
York edition with the headline: Voyager 1 Reaches Edge of Sun’s Realm.
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Vision2020 Post: Ted Moffett
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