If you see the northern
lights overhead, chances are you are in a chilly, polar climate. But the
cold-weather delights, also known as aurora borealis, high above you are
actually an important source of heat. A new NASA mission hopes to fly through
an active aurora to study this energy exchange process up close. The launch
window for Ion-Neutral Coupling during Active Aurora, or INCAA mission, opens
at the Poker Flat Research Range in Poker Flat, Alaska, on March 23.
As residents of the troposphere, Earth’s lowest
atmospheric layer, we’re used to air made of neutral particles. The oxygen and
nitrogen we breathe are magnetically balanced atoms and molecules with all
their electrons accounted for. But hundreds of miles above us, our air begins
to fundamentally change character. Energized by the Sun’s unfiltered rays,
electrons are pried from their atoms, which then take on a positive charge. A
once-neutral gas transforms into an electrically reactive state of matter known
as plasma.
There is no hard cutoff where neutral gas
ends and plasma begins. Instead, there is an extended boundary layer where the
two populations intermix. Daily winds and magnetic perturbations send the two
populations of particles in different directions, occasionally colliding – and
creating some interesting physics as a result.
“Friction is a great analogy,” said
Stephen Kaeppler, assistant professor of physics and astronomy at Clemson
University in South Carolina, and principal investigator for the INCAA mission.
“We all know that we rub our hands together, you're going to get heat. It’s the
same basic idea, except we're dealing with gases now instead.”
This boundary layer, where neutral
atmosphere and plasma meet, experiences constant friction. But active auroras
turn everything up a notch.
Auroras form when electrons from
near-Earth space suddenly pour into our atmosphere. They eventually collide
with neutral particles, setting them alight.
“It’s like storming the football field
after a college game,” Kaeppler said. “People at the top of the stadium run
towards the field, and as you get closer to the field, the crowd gets thicker
and thicker. This is how it is for electrons facing the increasing neutral
density of the upper atmosphere.”
A conceptual animation
showing electrons traveling down Earth's magnetic field lines, colliding into
particles in in Earth's atmosphere to trigger the aurora. Credits: NASA's
Goddard Space Flight Center/CILab/Bailee DesRocher
Plunging through the crowded atmosphere, these electrons collide with
neutral atoms, generating friction and heat within the aurora. But they also
stir up the broader boundary layer, enhancing the mixing and friction at larger
scales. Figuring out how aurora influence the boundary layer is key to
understanding how much energy they ultimately release into our upper
atmosphere.
To this end Kaeppler and his team are launching INCAA, hoping to fly
through an aurora and measure how it changes this boundary layer where plasma
meets neutral gas.
INCAA is composed of two payloads, each one mounted on a separate sounding
rocket. Sounding rockets are small launch vehicles designed to ascend into
space for a few minutes of measurements before falling back to Earth. Sounding
rockets are ideally suited for studying brief, transient phenomena like auroras,
which can form in one place and then disappear in a matter of minutes.
The team will wait at the launchpad until aurora are overhead, then launch
the two rockets in quick succession. On its way up the first rocket will
release vapor tracers, colorful chemicals similar to those used in firework
shows, before reaching its peak altitude of about 186 miles. The vapor tracers
create visible clouds that researchers can see from the ground, tracing the
winds in the neutral atmosphere, like dropping food dye in a sink full of water
to see how the water is moving. The second rocket will launch shortly after,
reaching about 125 miles altitude to measure the temperature and density of the
plasma in and around the aurora.
What the data will show is anyone’s guess, but Kaeppler hopes to learn how
the aurora shift this boundary layer where electrified air meets neutral. It
could push it farther towards the ground, raise it higher, or perhaps cause it
to fold in on itself. Any of these possibilities influences how our planet
exchanges energy with space around it – but everything depends on the details.
“All of these factors make this is an interesting physics problem to examine,”
Kaeppler said.
By Miles
Hatfield
NASA’s Goddard Space Flight Center, Greenbelt, Maryland
Source: In
Cold Polar Skies, NASA Rocket Will Watch Aurora Turn Up the Heat | NASA
No comments:
Post a Comment