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August
19, 2008: What if you woke up one morning and found
your whole planet had been swallowed by the atmosphere of
a star?
Get
out of bed, look out the window. Auroras are dancing along
the horizon. Dark sunspots crackle overhead—each little 'pop'
more powerful than a nuclear bomb. On TV, a weather forecaster
warns astronauts, "a solar flare is sure to erupt,"
although he can't say exactly when. Moments later, the satellite
signal begins to flicker.
 Where
is this place?
Welcome
to planet Earth.
"It's
true. We live inside the atmosphere of the sun," says
Lika Guhathakurta, program manager of NASA's Living with a
Star (LWS) program.
Right:
Earth, photographed by Apollo 17 astronauts. [more]
At
first glance the sun seems so self-contained, a crisp round
ball in the noontime sky. But the edge we see is just the
beginning. The sun has a hot, riotous atmosphere called "the
corona" that reaches from the sun's surface, past Earth,
all the way to Pluto and beyond. The corona is seldom seen,
only during a
total eclipse, but it is there.
Like
any good atmosphere, the corona has weather, and lots of it.
There are billion-ton coronal mass ejections; high-energy
radiation storms; and a relentlessly-blowing solar wind that
gusts up to a million mph. Every comet, asteroid and planet
in the solar system is exposed to these elements.
Below:
A coronal mass ejection or "CME" recorded by the
ESA/NASA Solar and Heliospheric Observatory (SOHO). [more]
Our
planet is better protected than most. We have a thick atmosphere
and global magnetic field to hold space weather at bay. In
fact, if we stayed on Earth, the sun's weather systems would
hardly affect us, causing no more than an occasional power
outage or radio blackout.
And
therein lies the problem:
"We're
not staying on Earth," says Guhathakurta. "Civilization
is spreading into space."
More
than 500 active satellites circle the Earth. We rely on them
for TV, telephone, internet, GPS navigation and weather forecasting;
all are vulnerable to space weather. Humans orbit Earth, too,
onboard the International Space Station. The ISS is located
inside Earth's magnetic field, so it enjoys a degree of protection,
but future astronauts en route to the Moon and Mars will be
outside the magnetic bubble. Their spaceships are going to be
in direct contact with the sun's atmosphere.
NASA's
Living With a Star Program was formed in 2001 to deal with
this reality. "If we're going to live inside the sun's
atmosphere, we need to learn more about it—especially how
to predict the storms," says Guhathakurta.
The
basic strategy is the same as weather studies on Earth: "We're
going to launch a fleet of 'weather stations' – spacecraft
that observe different aspects of sun’s atmosphere."
LWS has five missions1 in various states of development.
Together they will surround and explore the sun in ways no
spacecraft has done before.
 #1:
The Solar Dynamics Observatory (SDO). "Get ready
for jaw-dropping photos," says Guhathakurta. A camera
onboard the observatory will take HDTV quality photographs
of sunspots and solar flares, revealing the onset of storms
in never-before-seen detail.
Right:
SDO undergoes testing at NASA's Space Environment Simulator.
[larger image]
Pictures
alone, however, do not tell the whole story. NASA solar physicist
Alex Pevtsov explains: "Solar activity is a bit like
a puppet show. If you want to understand the motion of the
puppets, you need to see the strings. On the sun, the 'invisible
strings' are magnetic fields; they penetrate the sun's atmosphere,
guiding the flow of heat and orchestrating mighty explosions.
SDO will be able to produce detailed maps of magnetism on
the sun, revealing the strings for all to see."
But
who (or what) is pulling the strings? "That would be
the sun's magnetic dynamo," says Pevtsov. "It lies
hidden beneath the surface of the sun." Fortunately,
SDO can look down there, too. The technique is called helioseismic
imaging. By monitoring the sun's vibrating surface, SDO can
probe the stellar interior in much the same way that geologists
use seismic waves from earthquakes to probe inside Earth.
In this way, mission scientists hope to map the ebb and flow
of the sun's inner magnetic dynamo, the root of all solar
activity.
Status:
SDO is built and almost ready to go. "Right now, SDO
is in a thermal vacuum chamber getting tested for the rough
ride to space."
#2:
Solar Probe Plus "This could be the most exciting
mission of all." It is a heat-resistant spacecraft designed
to plunge deep into the sun’s atmosphere where it can sample
solar wind and magnetic fields in situ. "No spacecraft
has ever been as close to the sun as Solar Probe Plus will
go, only 7 million km from the surface. That's unexplored
territory, and we expect to learn a great deal about the sun's
atmosphere by going there."
Above:
A simulated view of the sun illustrating the trajectory of
Solar Probe+ during its multiple near-sun passes. [full
story] [larger image]
Status:
Solar Probe Plus is still in an early design phase, called
"pre-phase A" at NASA Headquarters. It is expected
to launch no earlier than 2015.
#3
Solar Sentinels. "We're going to surround the
sun," says Guhathakurta. Three well-instrumented probes
from NASA and a fourth (the Solar Orbiter) from the European
Space Agency will station themselves around the sun's equator,
providing the first truly global view of solar activity. "Imagine
trying to figure out Earth's climate by watching only one
side of the planet. Impossible! Yet that's what we've been
doing with the sun." The one-sided view from Earth limits
studies of solar climate and weather—a problem Solar Sentinels
will remedy.
Status:
"We've just finished the Science and Technology Definition
Team report, which lays out the whole strategy for Solar Sentinels."
Launch is expected no earlier than 2015.
Below:
An artist's concept of the Radiation Belt Storm Probes.
 #4
The Radiation Belt Storm Probes. "There's no
point in studying the sun if you don't understand what it
does to Earth," declares Guhathakurta. This mission makes
the crucial Sun-Earth connection. Wisps of the sun's atmosphere
can become trapped by Earth's magnetic field, inside radiation
belts, where energetic particles lie in wait for astronauts
and satellites trying to leave or simply orbit the planet.
The Radiation Belt Storm Probes (two of them) will explore
these regions and discover how they are populated and energized
by space weather.
Status:
The two probes are under construction at the Johns Hopkins
Applied Physics Lab and slated for launch no earlier than
2011.
#5
The Ionosphere-Thermosphere Storm Probes. Two more
probes will orbit Earth and study the upper reaches of Earth’s
atmosphere where air makes "first contact" with
solar UV radiation. This is a realm of electrically charged
particles that strongly affect the propagation of radio waves,
influencing almost all forms of telecommunication and GPS
navigation. It is also a place where the atmosphere breathes
in and out in response to changes in solar UV heating. An
outward breath can envelop and drag down satellites, while
an inward breath decreases the drag. The Ionosphere-Thermosphere
Storm Probes will monitor the response of this layer to all
kinds of solar storms.
Status:
"This is an important mission, but not yet funded,"
says Guhathakurta. "Right now we have our hands full
with the others."
Indeed,
there's a lot to do when you're Living with a Star.
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Author: Dr.
Tony Phillips | Credit: Science@NASA
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Foot
notes:
1In
addition to the five missions described in the story,
there is the LWS theory modeling and data analysis program
also known as Targeted
Research & Technology program which provides
the glue that holds the program together.
Understanding
space weather and making progress on problems such as
predicting geomagnetic storms pose two major challenges
for the research community. First, research must couple
traditionally separate disciplines in NASA's Heliophysics
division (such as solar-heliospheric and geospace physics).
Second, to be truly successful, research must also demonstrate
how results would enable an operational capability,
such as the generation of forecasts for geomagnetic
storms.
In
order to meet these challenges, NASA has designed an
innovative new program, Targeted Research and Technology
(TR&T). TR&T is part of NASA's Living
With a Star program. LWS is a space weather–focused
and applications-driven research program whose goal
is to develop the scientific understanding necessary
to address effectively those aspects of the connected
Sun-Earth system as well as the Sun-Planet system that
may affect life and society. It is implemented by a
sequence of interrelated science missions, Space Environment
Testbed (SET), and TR&T.
NASA's
Future: US
Space Exploration Policy
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