Recalculating the Distance to Interstellar Space

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Jia-Rui Cook 818-354-0850
Jet Propulsion Laboratory, Pasadena, Calif.
jccook@jpl.nasa.gov

Feature: 2011-182 June 15, 2011

Recalculating the Distance to Interstellar Space

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2011-182&cid=release_2011-182

Scientists analyzing recent data from NASA's Voyager and Cassini spacecraft have
calculated that Voyager 1 could cross over into the frontier of interstellar space at any time
and much earlier than previously thought. The findings are detailed in this week's issue of
the journal Nature.

Data from Voyager's low-energy charged particle instrument, first reported in December
2010, have indicated that the outward speed of the charged particles streaming from the
sun has slowed to zero. The stagnation of this solar wind has continued through at least
February 2011, marking a thick, previously unpredicted "transition zone" at the edge of our
solar system.

"There is one time we are going to cross that frontier, and this is the first sign it is upon us,"
said Tom Krimigis, prinicipal investigator for Voyager's low-energy charged particle
instrument and Cassini's magnetospheric imaging instrument, based at the Johns Hopkins
University Applied Physics Laboratory in Laurel, Md.

Krimigis and colleagues combined the new Voyager data with previously unpublished
measurements from the ion and neutral camera on Cassini's magnetospheric imaging
instrument. The Cassini instrument collects data on neutral atoms streaming into our solar
system from the outside.

The analysis indicates that the boundary between interstellar space and the bubble of
charged particles the sun blows around itself is likely between 10 and 14 billion miles (16 to
23 kilometers) from the sun, with a best estimate of approximately 11 billion miles (18 billion
kilometers). Since Voyager 1 is already nearly 11 billion miles (18 billion kilometers) out, it
could cross into interstellar space at any time.

"These calculations show we're getting close, but how close? That's what we don't know,
but Voyager 1 speeds outward a billion miles every three years, so we may not have long to
wait," said Ed Stone, Voyager project scientist, based at the California Institute of
Technology in Pasadena.

Scientists intend to keep analyzing the Voyager 1 data, looking for confirmation. They will
also be studying the Voyager 2 data, but Voyager 2 is not as close to the edge of the solar
system as Voyager 1. Voyager 2 is about 9 billion miles (14 billion kilometers) away from the
sun.

Launched in 1977, the Voyager twin spacecraft have been on a 33-year journey. They are
humanity's farthest working deep space sentinels enroute to reach the edge of interstellar
space. The Voyagers were built by NASA's Jet Propulsion Laboratory in Pasadena, Calif.,
which continues to operate both spacecraft. The Voyager missions are a part of the NASA
Heliophysics System Observatory, sponsored by the Heliophysics Division of NASA's
Science Mission Directorate in Washington. JPL is managed for NASA by Caltech.

More information about Voyager is available at: http://www.nasa.gov/voyager and
http://voyager.jpl.nasa.gov .

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