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Voyager:
The Great Adventure Continues
The twin
Voyager spacecraft are now exploring the outer reaches of the solar system
and beyond. A supersonic wind from the Sun creates a bubble in interstellar
space called the heliosphere. Solar matter is dominant inside the heliosphere,
while matter from other stars dominates outside. |
Click
images for larger version.
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For the
next two decades, the Voyager spacecraft will race to reach interstellar
space while they still have enough electrical power to transmit data to
Earth. In the next several years, Voyager 1 may pass the termination shock,
the first feature on its journey to interstellar space. |
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Voyager
1
Voyager
1 is the most distant human-made object in the universe, twice as far from
the Sun as Pluto. It was deflected northward above the plane of the planets'
orbits when it swung by Saturn in 1980 and is now speeding outward from
the Sun at nearly one million miles per day, a rate that would take it from
Los Angeles to New York in less than four minutes. Long-lived nuclear batteries
are expected to provide electrical power until at least 2020 when Voyager
1 will be more than 13 billion miles from Earth and may have reached interstellar
space. |
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Voyager
2
Voyager
2 has visited more planets than any other spacecraft, swinging by Jupiter,
Saturn, Uranus and Neptune. Voyager 2 was deflected downward by Neptune
and is heading southward below the plane of the planets. With a somewhat
lower speed than Voyager 1, it is about eighty percent as far from the
Sun. |
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Sun
Our
Sun is a star that holds about 99.9 percent of all the matter in the solar
system. Its hot atmosphere expands supersonically outward, creating a flow
of electrically charged ions called the solar wind that sweeps outward past
all the planets at nearly one million miles per hour. |
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Please refer to the graphic
below for the following definitions.
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Heliosphere
The supersonic solar wind of
charged ions creates a bubble around the Sun called the heliosphere that extends
far past the orbits of the planets. An external view of this bubble is represented
by the yellow and green regions. A long wind-sock-like tail forms as the heliosphere
moves with the Sun through interstellar space. The red arrows representing solar
wind are seen being deflected at the front of the heliosphere, turning back
and moving down the tail of the heliosphere.
Termination Shock
As the million-mile-per-hour
solar wind approaches the boundary of the heliosphere, a termination shock,
shown by the red circle, forms where the wind abruptly slows down to about 250,000
miles per hour. As the wind, indicated by the red arrows, continues beyond the
termination shock, it turns and heads down the tail of the heliosphere.
Heliopause
As the solar wind expands outward
from the sun, deep within the yellow sphere in this graphic, its pressure declines.
The solar wind expands until its declining pressure balances the inward pressure
of the surrounding interstellar matter. When this happens, the outward flow
of the solar wind turns around the side of the heliospheric bubble. The heliopause
is the resulting outer boundary of the heliosphere that separates the flows
of the internal solar wind and the external interstellar wind.
Interstellar Wind
The moving white arrows illustrate
a faint wind in nearby interstellar space that flows around the heliosphere,
deforming it into a wind-sock-like shape.
Bow shock
As the heliosphere plows through
the ionized interstellar gas, a bow shock forms, much as forms in front of a
boulder in a stream.
Solar Apex
The solar apex
is the direction toward which the Sun and the solar system are moving. The interstellar
wind flows from a nearby direction. The heliosphere, with our solar system inside,
is highlighted in this animation.
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