Wednesday, November 7, 2018

NASA's ICON to explore boundary between Earth and Space

Early in the morning of Nov. 7, 2018, NASA launches the Ionospheric Connection Explorer, or ICON, a spacecraft that will explore the dynamic region where Earth meets space: the ionosphere. Overlapping the farthest reaches of Earth's atmosphere and the very beginning of space, the ionosphere stretches roughly 50 to 400 miles above the surface. Solar radiation cooks tenuous gases there until they lose an electron (or two or three), creating a sea of electrically charged ions and electrons. Neither fully Earth nor space, the ionosphere reacts both to winds and weather from the lower atmosphere below and solar energy streaming in from above, changing constantly to form conditions we call space weather. "After years of work, I'm excited to get into orbit and turn on the spacecraft, open the doors on all our instruments," said Thomas Immel, ICON principal investigator at the University of California, Berkeley. "ICON carries incredible capacity for science. I'm looking forward to surprising results and finally seeing the world through its eyes." As far as space goes, the ionosphere is as close to home as it gets. Its constant changes can affect astronauts, satellites and much of the communications signals modern society relies upon. Scientists want to understand these changes, so they can eventually better predict them and protect our interests in space. Space may look empty, but the ionosphere brims with electrically charged gases, solar radiation, and electric and magnetic fields. Turbulence in this sea of charged particles can manifest as disruptions that interfere with orbiting satellites or communication and navigation signals used, for example, to guide airplanes, ships and self-driving cars.

Depending on the energy it absorbs from the Sun, the ionosphere grows and shrinks. For that reason, scientists long thought this part of space was only affected by what happens in the space above it.

But over the past decade, a growing body of evidence has indicated the region is much more variable than we can explain with solar activity alone. The ionosphere's contents are not evenly distributed: Dense patches of its charged gases, called plasma, are scattered throughout. Eventually, researchers linked these patches to global weather patterns - large-scale events such as several hurricanes rushing across the ocean at once, or changes in cloud formation over tropical rainforests.

Though the Sun provides the energy that drives weather we experience on Earth, day-to-day weather is driven by something very different: differences in temperature and moisture, interactions between oceans and land, and regions of high and low atmospheric pressure. Still, scientists were surprised to discover that terrestrial weather and the Sun manage to meet in the middle - at the ionosphere - in a tug-of-war for control.

Vast winds high above Earth's surface carry energy around the globe and can modify the ionosphere indirectly by pushing around charged particles in the upper atmosphere. That motion creates an electric field, which guides the behavior of particles throughout the electrically charged ionosphere.

Part of the reason the ionosphere has remained so mysterious until now is the region is difficult to observe. Too high for scientific balloons and too low for satellites, the lower ionosphere especially - where Earth and space are most strongly connected - has eluded much of the technology researchers have used to study near-Earth space. But ICON is uniquely equipped to investigate the region.

"We've had the smoking gun - that indicated terrestrial and space weather are linked - but we've been missing actual observations in the region where these changes are taking place," said Scott England, ICON project scientist at Virginia Tech in Blacksburg, Virginia. "ICON has all the tools to see the drivers and their effects in the system."

From low-Earth orbit, ICON will explore these connections by tracking airglow, a quirk of our planet's upper atmosphere. It refers to the light that shines from the ionosphere, enveloping Earth in a tenuous bubble of red, green and yellow. Airglow is created by a similar process that sparks the aurora: Gas is excited and emits light. Though auroras are typically confined to extreme northern and southern latitudes, airglow shines constantly across the globe, and is much fainter.

"It's amazing that our atmosphere glows like this, but what's more - it gives us a direct ability to make observations of the key parameters we need in order to investigate the connection between the neutral atmosphere and the ionosphere," Immel said.

Different atmospheric gases glow in certain colors and at specific altitudes, so scientists can use airglow to probe the different layers of the atmosphere, gleaning information like density, temperature and composition. In addition, Earth's natural glow helps scientists track motions within the ionosphere itself: As high-altitude winds sweep through the region, pushing its contents around, airglow's dim light morphs in turn, tracing out global patterns.

"I can't wait to see what airglow looks like from ICON's point of view," Immel said.

ICON's 90-minute launch window opens at 3:00 a.m. EST on Nov. 7, 2018. ICON launches on a Northrop Grumman Pegasus XL rocket, which is carried aloft by the Stargazer L-1011 aircraft that takes off from Cape Canaveral Air Force Station in Florida. The L-1011 carries the rocket to approximately 40,000 feet over the open ocean, where it is released and free-falls five seconds before igniting its first-stage rocket motor. Release from the Stargazer is anticipated for 3:05 a.m. EST. The spacecraft deploys approximately 11 minutes after the Pegasus drop.

ICON will join another ionospheric mission, GOLD, short for Global-scale Observations of the Limb and Disk, which launched in January 2018. While ICON flies just 357 miles above Earth and will capture close-up images of the region, GOLD flies in geostationary orbit 22,000 miles above the Western Hemisphere, where it specializes in global-scale images of the ionosphere and upper atmosphere. Where ICON takes close-ups, GOLD captures landscapes.

Together, these missions will provide the most comprehensive ionosphere observations we've ever had - data that's hard to get from Earth, where we can only measure small fractions of the region at a time - enabling a deeper understanding of how our planet interacts with space.

"It's a truly wonderful time to be studying heliophysics," said Nicola Fox, director of NASA's Heliophysics Division in Washington. "We just launched Parker Solar Probe earlier this year, which will give us the first close-up view of what drives the solar wind. Now, with ICON joining our heliophysics system fleet, we will have the incredibly detailed measurements of the ionosphere's response to the solar drivers. This is an amazing opportunity to study the whole system response."

NASA heliophysics missions study a vast interconnected system from the Sun to the space surrounding Earth and other planets, and to the farthest limits of the Sun's constantly flowing stream of solar wind. ICON's observations will provide key information about how Earth's atmosphere is connected to this complex, dynamic system.

ICON is an Explorer-class mission. NASA Goddard manages the Explorers Program for NASA's Heliophysics Division within the Science Mission Directorate in Washington. UC Berkeley's Space Sciences Laboratory developed and operates the ICON mission and built the EUV and FUV imagers. The Naval Research Laboratory in Washington, D.C., developed the MIGHTI instrument, the University of Texas in Dallas developed IVM, and the ICON spacecraft and Pegasus launch vehicle were built by Northrop Grumman in Dulles, Virginia.

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