A
piano-sized NASA satellite is poised to launch spaceward Wednesday afternoon on
a mission that, astronomers hope, will reveal the unsolved mysteries of Earth's
highest clouds.
The Orbital
Sciences-built Aeronomy
of Ice in the Mesosphere (AIM) spacecraft is poised to rocket spaceward on
a two-year mission to scan noctilucent,
or 'night-shining,' clouds that can only observed after sunset. An
air-launched Pegasus XL booster is due to loft the AIM probe at 4:23 p.m. EDT
(2023 GMT) in a space shot to begin at California's Vandenberg Air Force Base.
"We are exploring
clouds that literally are at the very edge of space," James Russell, AIM's
principal investigator at Hampton University in Hampton, Virginia, said in a
prelaunch mission briefing.
Also known
as Polar Mesospheric Clouds (PMCs), noctilucent clouds are made up of ice
crystals and hover some 50 miles (80 kilometers) above the surface of the
Earth. The cloudy phenomena tend to be seen above the Earth's polar regions and
have been observed from the ground and space, though not at the levels of
detail expected from AIM, researchers said.
"This
mission is the first mission dedicated to the study of noctilucent clouds,"
Russell said. "We have observed them with satellites [in the past], and all
it's done is left us wanting."
Ice
Cloud Oddities
Researchers
first observed noctilucent clouds in 1885 following the eruption of the
Krakatoa volcano, though the exact nature of their genesis remains a mystery.
Added to the pot is the clouds' odd increase in frequency in recent years,
sometimes in regions previously void of such displays, prompting some
researchers to link their formation to worldwide climate changes such as global
warming.
"It's a
natural question to ask 'Why are we seeing them now when we haven't before,'"
Russell said.
Noctilucent
clouds tend to occur between about May 15 to Aug. 20, with a peak in
activity about 20 days after the summer solstice on June 21, AIM researchers
said. During their two-year mission, AIM's instruments are expected to scan
four noctilucent cloud seasons -- two in the Northern Hemisphere and the other
in the Southern Hemisphere -- and will hopefully shed some let on the clouds'
variety.
"They're
brighter in the north than in the south, for example," Russell said.
Similar
clouds have been observed high above the surface of Mars, leading researchers
to believe that a better understanding of the phenomena will aid future
missions to the red planet by yielding fundamental knowledge on the interaction
of the Sun's energy and planetary atmospheres.
"These
clouds are indicators of conditions in the upper reaches of the Earth's
atmosphere, and are an important link in the chain of processes that result in
the deposition of solar energy into Earth's atmosphere," Mary Mellott, AIM
program scientist, NASA's Washington D.C. headquarters, said in a statement. "AIM
will provide an understanding of how and why these clouds form, an important
contribution toward the NASA goals of understanding the fundamental physical
processes of our space environment and how the habitability of planets is
affected by the interaction of planetary magnetic fields and atmospheres with
solar variability."
Scanning
the Mesosphere
The
430-pound (195-kilogram) AIM spacecraft carries three primary tools to scan the
highest clouds on the planet:
- The Cloud
Imaging and Particle Size (CIPS) is laden with four cameras, each
positioned at a different angle, to return two-dimensional images at
noctilucent clouds that are expected to yield sizes for the ice particles
in each formation and generate a daily panorama of the polar ice cap.
- The Solar
Occultation for Ice Experiment (SOFIE) is designed to measure the
particles, temperatures atmospheric gases that make up each cloud to reveal
their chemical composition and formation environment.
- The
Cosmic Dust Experiment is designed to record the amount of interstellar
dust that enters the Earth's atmosphere so researchers can study its role
in noctilucent cloud formation.
Together, the
instruments are designed to tackle six primary target areas that include
long-term changes in the Earth's upper atmosphere, temperature variations,
hydrogen chemistry, and the influence of gravity waves on cloud formation. They
will scan clouds in the Earth's mesosphere, a region of the atmosphere that
sits above the stratosphere.
The
spacecraft relies
on six solar panels, wrapped around the probe at launch, to generate the
216 watts of power required to support its science instruments.
"The whole
deployment sequence takes about 20 minutes," said Chris Savinell, NASA's AIM
mission manager at the agency's Goddard Space Flight Center in Greenbelt, Maryland, in a preflight briefing.
AIM is one
of NASA's Small Explorer missions designed to develop relatively low-cost space
science and exploration expeditions.
"This
Small Explorer mission is a good example of the huge science returns we can get
for a relatively small cost investment," said Vicki Elsbernd, NASA's AIM
program executive, in a statement.
NASA will broadcast the AIM mission launch live via NASA TV
beginning at 3:00 p.m. EDT (1900 GMT).
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