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Scientists are studying the aurora using orbiting spacecraft and
ground-based observatories because many aspects of the Earth's glimmering
auroral lights are a mystery. But we do know the basics. First, the
steady stream of charged particles from the Sun, which is known as the
solar wind, interacts with Earth's magnetic field. This dynamic
interaction accelerates the charged particles of the solar wind, and also
those from our upper atmosphere, to higher speeds and subsequently
funnels them into the upper atmosphere. These charged particles then
impact the atoms and molecules of the upper atmosphere, primarily oxygen,
nitrogen and hydrogen, and produce the colorful displays of the aurora,
with each type of molecule generating a characteristic color.
There are at least two reasons. First of all, since the aurora is one of the magnificent natural wonders of our planet, scientists would love to understand what causes it. Already they know that it's caused by--and is associated with--the flow of charged particles from the Sun into Earth's magnetic field. But what they don't completely understand at the moment are the processes the charged particles undergo in order to be accelerated into Earth's atmosphere. This question has puzzled scientists for the past 40 years. The other reason scientists study the aurora is that the phenomenon provides them with a window into what 99 percent of the known universe is made of--plasma. Both the interiors and atmospheres of the Sun and other stars--and a good deal more--are predominantly plasma, too. So the displays of Earth's aurora provide scientists with an easily accessible, natural laboratory for studying the charged particles that make up the stuff of the universe.
NASA's Polar spacecraft was launched on Feb. 24, 1996. The spacecraft is
part of the International Solar-Terrestrial Physics program and is named
Polar because it orbits the Earth's poles. It's primary mission is the
study of the Earth's aurora.
Polar carries a host of scientific instruments, including the
Visible Imaging System
(VIS), which consists of three low-light level cameras.
Two of these cameras share primary and some secondary optics and are
designed to provide images of the nighttime auroral oval at altitudes of
about 1 to 8 Earth radius as viewed from the eccentric, polar orbit of
the spacecraft. A third camera is used to monitor the directions of the
fields-of-view of the auroral cameras with respect to the sunlit Earth.
The VIS captures pictures of Earth's auroras, dayglow, ozone layer and
nightglow in visible and ultraviolet light at the rate of about 5,000
images per day. The current VIS image is available
live.
The auroral images are obtained with filters with narrow passbands at
visible wavelengths. The emissions of interest include those from
N2+ at 391.4 nm, OI at 557.7 and 630.0 nm, HI at 656.3 nm and
OII at 732.0 nm.
Why is Polar in the right place at the right time?
Solar maximum is approaching. Every 11 years, the Sun's activity appears to peak. It's a time when the Sun produces more sun spots, more solar flares, and other magnetic phenomenon. This means that the Polar spacecraft is ready to observe whatever effects this increase in solar activity will have on Earth. If nature cooperates, for example, Polar should get a global view of what happens in space when large solar storms occur, the ones that allow the aurora to be seen as far south as the Rio Grande or Rome. It's a puzzle why some big solar disturbances penetrate so far to the south, while others don't penetrate much at all. It may have to do with the timing of the arrival of the bursts of plasma from the Sun, or something that combines with their arrival to drive the aurora much further toward the equator than normal. This knowledge has great practical value as it would help scientists predict just when such large solar storms are about to play havoc with our power systems and communications satellites.
Louis A. Frank
is the Carver/James A.Van Allen Professor of Physics at The University of
Iowa, where he has been a member of the faculty since 1964. He received
his doctorate from the University of Iowa in 1964. He has been an
experimenter, co-investigator, or principal investigator on 42 spacecraft
for which he has designed instruments to examine such phenomena as
energetic charged particles, space plasmas (or thin gases), and--with the
use of specially designed cameras--Earth's auroras.
Dr. Frank is the principal investigator for the auroral imaging instruments for the Dynamics Explorer Mission, the plasma instrumentation for the Galileo Mission to Jupiter, the U.S. plasma instrumentation for the Japanese Geotail spacecraft, and the camera for visible wavelength light for the Polar spacecraft of the International Solar Terrestrial Physics (ISTP) Program.
His publications in professional journals include such topics as the first direct measurements of the terrestrial ring current and of the polar cusp, the current systems in Earth's magnetotail, the plasma tori (or donut-shaped rings) at Jupiter and at Saturn, and the global imaging of Earth's auroral zones and atmosphere. He is also the discoverer of small comets.
He has served on various NASA and National Academy of Sciences/National Research Council committees and is a Fellow of the American Physical Society, a member of the American Astronomical Society, American Association for the Advancement of Science and the International Academy of Astronautics. He is a Fellow of the American Geophysical Union and a recipient of the National Space Act Award.
John B. Sigwarth
is a senior research scientist at The University of Iowa, where he
currently serves as project scientist for the Visible Imaging System
(VIS), one of 11 instruments on board the Polar spacecraft. He designed
the VIS low resolution and medium resolution optics, and the optical
relays for the three sensors vital to the imager. Also, he is responsible
for the analysis, manufacture and testing of the VIS optical systems. He
designed the VIS optical calibration setup, wrote instrument test
procedures, developed image analysis software, completed calibration
tests and performed analysis of the calibration data.
As VIS project scientist, he has day-to-day oversight responsibility for all aspects of the project, including direction of development team tasks, personnel management, and interaction with NASA officials. He also participates in post-launch operations and has a lead role in scientific analysis of VIS images.
Dr. Sigwarth received his doctorate from the University of Iowa in 1989. His research interests include the study of small comets and their effects on the solar system. Dr. Sigwarth is a member of the American Geophysical Union.
William R. Paterson
is a senior research scientist at the University of Iowa engaged in
studies of planetary magnetospheres including those of Earth and Jupiter.
Magnetospheric plasmas, fed by energy from the sun, are known to be
responsible for the dynamic auroral emissions seen and recorded by the
VIS cameras on the Polar spacecraft, and generally similar processes are
known to occur at Jupiter.
Dr. Paterson's research is based on the analysis of measurements from plasma analyzers on the Galileo spacecraft, now in orbit at Jupiter, and the Geotail spacecraft, a joint U.S.-Japan effort to explore Earth's magnetosphere. Both sets of instrumentation were designed and built at the University of Iowa with funding provided by NASA. Dr. Paterson received his doctorate from the University of Iowa in 1990, and since that time has conducted research there as part of the scientific staff of the Department of Physics and Astronomy.