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Space
Science News homeAstronomy goes into orbit with John Glenn
Discovery is carrying a battery of telescopes to study the sun, planets, and supernovae
29 October, 1998:
Ultraviolet rays from the sun and the cosmos
are almost completely blocked by Earth's atmosphere.
For those of us
who disdain sunburns the protection afforded by the ozone layer
is a good thing.
For some astronomers it's a nuisance. The sun and planets,
supernovae, and
interstellar clouds of gas are all copious sources of
ultraviolet radiation
that simply can't be seen from Earth's surface.
To study the
cosmos at UV wavelengths it is necessary to go
into orbit above the atmosphere, and
that's what will happen when Discovery takes off later today.
The payload bay of Discovery is packed with no
fewer than six telescopes. Most are mounted on a platform
called the International Extreme Ultraviolet Hitchhiker.
A primary mission of the Ultraviolet Hitchhiker is to
study UV rays from the sun and how
they affect planets throughout the solar
system.
Different telescopes will have different jobs to do during
the mission.
The Solar Extreme Ultraviolet Hitchhiker (SEH), developed
at the University of
Southern California, will
keep an eye on the sun.
SEH is able to
photograph the sun at ultraviolet
wavelengths between 250 and 1,700 angstroms.
UV images like the one below trace hot gas and magnetic
structures in the sun's
atmosphere. Solar activity is on the rise as the sun heads for
a
sunspot maximum in the year 2000. By
operating ultraviolet telescopes during the Sun's increasingly
active phase, scientists hope to explore
the connections between complex solar magnetic
fields and potentially hazardous
solar eruptions.
A Peek InsideShuttle Discovery
On Launch Complex 39B,
the open payload bay doors on the orbiter
Discovery reveal (bottom) International
Extreme Ultraviolet Hitchhiker (IEH-3) and
(above it) Hubble Space Telescope Orbital Systems
Test Platform (HOST), two of the payloads for mission STS-95.
The other payloads include the Spartan solar-observing
deployable spacecraft and SPACEHAB, a single module
containing experiments on space flight and the aging process.
This ultraviolet image of a sunspot group was taken by a telescope
aboard NASA's Transition Region and Coronal Explorer (TRACE) spacecraft.
The bright areas are million degree hot plasma loops trapped in
magnetic bottles above sunspots.
SEH will also measure changes in the Earth's atmosphere
caused by solar EUV and daytime temperatures. Its
observations will be coordinated with
identical instruments on two other spacecraft--a payload to be launched on a
sounding rocket and the ESA/NASA Solar and
Heliospheric Observatory (SOHO)
--to provide tight cross-calibration of the three
instruments.
This ultraviolet image of the sun in the light
of ionized Helium atoms was recorded by SOHO on 13 Oct 1998.
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While SEH watches the sun, another instrument called
UVSTAR will focus on the planets.
UVSTAR actually consists of two telescopes
that cover overlapping regions of of the UV spectrum, from 500 to 900
angstroms and from 850 to 1,250 angstroms. For comparison, visible
light is between 4,000 and 7,000 angstroms. An angstrom is one ten-billionth
of a meter.
One of UVSTAR's telescopes will target Jupiter and the Io plasma
torus. Io, one of Jupiter's four Galilean moons, is the most volcanically
active body in the solar system. It spews sulfur and oxygen ions
into space where they are trapped by Jupiter's magnetic field
to form a giant donut-shaped torus encircling Jupiter. Jupiter and
Io are electrically connected along magnetic field lines that
arc from the torus to Jupiter's north and south poles. Electrical currents
that flow in this system are enormous, carrying more than 10
12 Watts
of power (10
12 is a "1" followed by twelve "0's"). That's
greater than the output of all power plants on Earth combined.
These tremendous currents give rise to magnificent
aurora on both Jupiter and Io, and
extremely powerful radio emissions that can be heard on the loudspeakers of simple
ham radios here on Earth.
Observations of Jupiter and the Io torus by UVSTAR will help
scientists understand the complex Jupiter-Io interaction and how
that system responds to events on the Sun.
A Hubble Space Telescope
image of Jupiter's aurora, seen in ultraviolet light, overlaid on an optical
picture of Jupiter.
Aurora
on Earth occur when electrons from the
solar wind strike the upper atmosphere, but Jupiter's auroras are
caused by particles
spewed out by volcanoes on Io.
Another telescope on UVSTAR, the Extreme Ultraviolet Imager,
will keep an eye on Earth. The EUI will map the intensity of
spectral lines emitted
by helium and oxygen ions in the
atmosphere, allowing
scientists to monitor conditions in the
ionosphere and plasmosphere in concert with the solar observations.
Pictured above is a Hubble image of
the Cygnus Loop, an expanding cloud of gas from a supernova
explosion 15,000 years ago.
While UVSTAR and SEH watch the sun and planets,
a unique all-metal
telescope called STAR-LITE (Spectrograph/Telescope for Astronomical Research)
will look to the stars.
Scientists will use STAR-LITE to study supernova
remnants like the Cygnus Loop, pictured left,
to learn more about what happens after a star explodes.
Other science targets include
nearby star-forming regions and galaxies.
STAR-LITE was made by
University of Arizona scientists from rugged aluminum-silicon carbide.
The strong metal composite material assures that STAR-LITE's
16-inch primary mirror can withstand the forces of launch
better than a primary made of glass. The
composite material also is lightweight, making it an ideal
space payload.
Unlike UVSTAR, which depends on shuttle orientation to see its science target, STAR-LITE can point
anywhere in the shuttle bay, cradled on its rotating platform.
Future stories in this series will cover more science on STS-95, including
human protein experiments, attempts to measure the solar constant, and
microgravity fluid research.
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Author:
Dr. Tony Phillips
Curator:
Bryan Walls
NASA Official:
John M. Horack
