SWAP to Determine Where the Sun and Ice Worlds Meet

http://www.swri.org/9what/releases/2004/SWAP.htm

SWAP to determine where the sun and ice worlds meet
Southwest Research Institute
June 8, 2004

San Antonio -- The Solar Wind Around Pluto (SWAP)
instrument aboard the New Horizons spacecraft is designed to measure the
interactions of Pluto and Charon with the solar wind, the high-speed
stream of charged particles flowing out from the sun. Understanding these
interactions will expand researchers' knowledge of the astrophysical
processes affecting these bodies and that part of the solar system.

The space science community understands the extremes (called the bounding
states) of solar wind interactions with planets, comets and other bodies,
but no one knows what kind of interaction is present at Pluto. Comet
Borrelly represents a strong interaction with the solar wind, while Venus
represents a weak one.

"We expect solar wind interactions at Pluto to lie somewhere between the
strong and weak extremes," says SWAP Principal Investigator Dr. David J.
McComas, a senior executive director at Southwest Research Institute®
(SwRI®).

After taking measurements at Pluto, researchers plan to use the SWAP data
to define basic parameters about the system. For example, once researchers
know how such material comes off Pluto, they can then estimate the amount
of Pluto's atmosphere that escapes into space. This will reveal insights
into the structure and destiny of the atmosphere itself.

SWAP would go on to take similar measurements at Charon and at least one
Kuiper belt object; however, the team expects those interactions to be
much weaker simply because the atmospheres of these objects are expected
to be less extensive and not likely to emit much material.

Another of the many Pluto mysteries is where the interactions of the solar
wind will occur around the planet, so science plans call for SWAP to take
continuous measurements as it nears and passes Pluto.

"We know when and where to use some of the instruments to take an image or
a measurement at Pluto," says McComas. "Solar wind interactions, however,
present quite a challenge because we're trying to measure this invisible
thing surrounding Pluto at an uncertain distance from it."

"The science we expect SWAP to perform is impossible to accomplish without
actually going to Pluto-Charon and directly sampling its environment. That
capability is something that NASA pioneered and which, to this day, only
the United States can do," says Dr. Alan Stern, principal investigator of
New Horizons and an executive director at SwRI.

The incredible distances of Pluto from the sun required that the SWAP team
build the largest aperture instrument ever used to measure the solar wind.
It allows SWAP to make measurements even when the solar wind is very
tenuous. The instrument also combines a retarding potential analyzer (RPA)
with an electrostatic analyzer (ESA) to enable extremely fine, accurate
energy measurements of the solar wind.

"Should the interaction between Pluto and the solar wind turn out to be
very small, the RPA and ESA combination will allow us to measure minute
changes in solar wind speed," says Scott Weidner, the SWAP instrument
manager and an SwRI principal scientist.

The various instruments aboard New Horizons were designed and are being
built independently, yet they are expected to work together to reveal
significant new insights about Pluto, Charon and their Kuiper belt
neighbors. SWAP measures low energy interactions, such as those caused by
the solar wind. Its complement, the Pluto Energetic Particle Spectrometer
Science Investigation, or PEPSSI, will look at higher energy particles,
such as pickup ions. The top of SWAP's energy range can measure some
pickup ions, and PEPSSI picks up where SWAP leaves off to see the highest
energy interactions.

The sun and its solar wind affect the entire solar system and should
create interesting science opportunities for SWAP throughout its planned
nine-year voyage to Pluto. SWAP will operate for more than a month each
year and will sample heliospheric pickup ions-ions that originate in
interstellar space and get ionized when they come near the sun. Other
pickup ions come from material inside the solar system. Researchers have
shown that even collisions between Kuiper belt objects result in tiny
grains that drift toward the sun, evaporate and become ionized. The
Cassini spacecraft, when it reaches Saturn this July, will allow
researchers to observe
these so-called "outer source" pickup ions to 10 astronomical units (AU,
the distance from the Earth to the sun), the region where pickup ions from
the outer source are believed to begin.

"We'll be out to 30 AU before New Horizons even reaches Pluto. While we're
targeting a Kuiper belt object, we could be anywhere from 30 to 50 AU,
where the influence of heliospheric pickup ions becomes greater and
greater in the solar wind," says McComas. "On the journey out to Pluto,
we'll be able to validate or disprove the outer source theory, which is an
exciting warm up to reaching Pluto itself."

Editors: The SWAP instrument is currently under construction at Southwest
Research Institute and is scheduled for delivery this summer to the Johns
Hopkins University Applied Physics Laboratory (Laurel, Maryland) for
integration with the spacecraft electronics and structure. For more
information about SWAP and the other instruments flying aboard the first
mission to the last planet, visit the New Horizons website at
http://pluto.jhuapl.edu/.

For more information, contact Maria Martinez, Communications, (210)
522-3305, Southwest Research Institute, PO Drawer 28510, San Antonio, TX
78228-0510.

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On a sunny day (9 Jun 2004 17:36:45 -0700) it happened
(Ron) wrote in :


"We expect solar wind interactions at Pluto to lie somewhere between the
strong and weak extremes,
Well, where else could it be?


"says SWAP Principal Investigator Dr. David J.
McComas, a senior executive director at Southwest Research Institute®
(SwRI®).
Executive director, was he running Coca Cola before this?
JP
X --- press X to extinguish flame.


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