Ionosphere - Blog Posts

How Airglow Can Help Us Understand the Sun’s Influence on Earth

You may have seen the famous blue marble or pale blue dot images showing Earth from 18,000 and 3.7 billion miles away, respectively. But closer to home — some 300 miles above Earth's surface — you might encounter an unfamiliar sight: vibrant swaths of red and green or purple and yellow light emanating from the upper atmosphere.

This light is airglow.

Airglow is created when atoms and molecules in the upper atmosphere, excited by sunlight, emit light to shed excess energy. Or, it can happen when atoms and molecules that have been ionized by sunlight collide with and capture a free electron. In both cases, these atmospheric particles emit light in order to relax again. The process is similar to how auroras are created, but while auroras are driven by high-energy solar wind, airglow is energized by day-to-day solar radiation.

Since sunlight is constant, airglow constantly shines throughout Earth’s atmosphere, and the result is a tenuous bubble of light that closely encases our planet. Its light is too dim to see easily except in orbit or on the ground with clear, dark skies and a sensitive camera — it’s one-tenth as bright as the light given off by all the stars in the night sky.  

Airglow highlights a key part of our atmosphere: the ionosphere. Stretching from roughly 50 to 400 miles above Earth’s surface, the ionosphere is an electrified layer of the upper atmosphere generated by extreme ultraviolet radiation from the Sun. It reacts to both terrestrial weather below and solar energy streaming in from above, forming a complex space weather system. Turbulence in this ever-changing sea of charged particles can manifest as disruptions that interfere with Earth-orbiting satellites or communication and navigation signals.

Understanding the ionosphere’s extreme variability is tricky because it requires untangling interactions between the different factors at play — interactions of which we don’t have a clear picture. That’s where airglow comes in. Each atmospheric gas has its own favored airglow color, hangs out at a different height and creates airglow by a different process, so we can use airglow to study different layers of the atmosphere.

Airglow carries information on the upper atmosphere’s temperature, density, and composition, but it also helps us trace how particles move through the region itself. Vast, high-altitude winds sweep through the ionosphere, pushing its contents around the globe — and airglow’s subtle dance follows their lead, highlighting global patterns.

Two NASA missions take advantage of precisely this effect to study the upper atmosphere: ICON — short for Ionospheric Connection Explorer — and GOLD — Global-scale Observations of the Limb and Disk.

ICON focuses on how charged and neutral gases in the upper atmosphere behave and interact, while GOLD observes what drives change — the Sun, Earth’s magnetic field or the lower atmosphere — in the region.

By imaging airglow, the two missions will enable scientists to tease out how space and Earth’s weather intersect, dictating the region’s complex behavior.

Keep up with the latest in NASA's airglow and upper atmosphere research on Twitter and Facebook or at nasa.gov/sunearth.

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Counting Down to ICON's Launch

In October 2018, we're launching the Ionospheric Connection Explorer, or ICON, to study Earth's dynamic interface to space.

The region of Earth's atmosphere on the edge of space plays a crucial role in our technology and exploration. This is where many of our satellites — including the International Space Station — orbit, and changing conditions in this region can cause problems for those satellites and disrupt communications signals.

This part of the atmosphere is shaped by a complicated set of factors. From below, regular weather on Earth can propagate upwards and influence this region. From above, electric and magnetic fields and charged particles in space — collectively called space weather — can also trigger changes. ICON's goal is to better understand this region and how it's shaped by these outside influences.  

10-mile-per-hour sensitivity

Though the ICON spacecraft zooms around Earth at upwards of 14,000 miles per hour, its wind-measuring instrument, named MIGHTI, can detect changes in wind speed smaller than 10 miles per hour. MIGHTI measures the tiny shifts in color caused by the motion of glowing gases in the upper atmosphere. Then, by making use of the Doppler effect — the same phenomenon that makes an ambulance siren change pitch as it passes you — scientists can figure out the gases' speed and direction.

97-minute orbital period

ICON circles Earth in just over an hour and a half, completing nearly 15 orbits per day. Its orbit is inclined by 27 degrees, so over time, its measurements will completely cover the latitudes scientists are most interested in, near the equator.

8 1/3-foot solar panel

ICON doesn't carry any onboard fuel. Instead, its single solar panel — measuring about 100 inches long and 33 inches wide, a little bit bigger than a standard door — produces power for the spacecraft. In science mode, ICON draws about 209-265 Watts of power.

7 years of teamwork

Now getting ready for launch, the ICON team has been hard at work ever since the idea for the mission was selected for further study in 2011.  

634 pounds

How much does good science weigh? In ICON's case, about as much as vending machine. The observatory weighs 634 pounds altogether.

5 snapshots per minute from FUV

Because ICON travels so fast, its Far Ultraviolet instrument takes eight snapshots per second of passing structures. This avoids blurring the images and captures the fine detail scientists need. But available bandwidth only allows FUV to send 5 images per minute, so the instrument uses a de-blurring technique called time-delay integration to combine 12 seconds' worth of data into a single image.

Image credit: Mark Belan

4 types of instruments collecting data in tandem

ICON carries four distinct instruments to study Earth's boundary to space.

2 MIGHTIs (Michelson Interferometer for Global High-resolution Thermospheric Imaging): Built by the Naval Research Laboratory in Washington, D.C., to observe the temperature and speed of the neutral atmosphere. There are two identical MIGHTI instruments onboard ICON.

2 IVMs (Ion Velocity Meter): Built by the University of Texas at Dallas to observe the speed of the charged particle motions, in response to the push of the high-altitude winds and the electric fields they generate. ICON carries two, and they are the mission’s only in situ instruments.  

EUV (Extreme Ultra-Violet instrument): Built by the University of California, Berkeley to capture images of oxygen glowing in the upper atmosphere, in order to measure the height and density of the daytime ionosphere.

FUV (Far Ultra-Violet instrument): Built by UC Berkeley to capture images of the upper atmosphere in the far ultraviolet light range. At night, FUV measures the density of the ionosphere, tracking how it responds to weather in the lower atmosphere. During the day, FUV measures changes in the chemistry of the upper atmosphere — the source for the charged gases found higher up in space.

360 miles above Earth

ICON orbits about 360 miles above Earth, near the upper reaches of the ionosphere — the region of Earth's atmosphere populated by electrically charged particles. From this vantage point, ICON combines remote measurements looking down along with direct measurements of the material flowing around it to connect changes throughout this region.

2 missions working together

NASA's GOLD mission — short for Global-scale Observations of the Limb and Disk — launched aboard a commercial communications satellite on Jan. 25, 2018. From its vantage point in geostationary orbit over Brazil, GOLD gets a full-disk view of the same region of space that ICON studies, helping scientists connect the big picture with the details.

1 gigabit of data per day

Together, ICON's instruments produce and downlink about 1 gigabit of data per day — about 125 megabytes. This adds up to about 1 gigabyte per week. ICON produces 10 different data products, ranging from measurements of wind speeds and ionospheric density to more complex models, that will help scientists shed new light on this ever-changing region.

ICON’s launch is scheduled for 4 a.m. EDT on Oct. 26, and NASA TV coverage begins at 3:45 a.m. Stay tuned on Twitter and Facebook for the latest on ICON. 

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Meet Our ICONic New Satellite

The boundary between Earth and space is complicated and constantly changing. Unlike the rest of the atmosphere, the upper atmosphere near the edge of space has a mix of both neutral particles similar to the air we breathe, as well as electrically charged particles called ions. Changes in this region are unpredictable, but they can affect satellites and garble signals, like GPS, that pass through this region. That’s why we’re launching ICON (the Ionospheric Connection Explorer) to get our first-ever comprehensive look at our interface to space.

About 60 miles above Earth’s surface, Earth’s atmosphere gives way to space. The change is gradual: The gases of the atmosphere get steadily thinner the higher you go. On the edge of space, the Sun’s radiation cooks some of those thin gases until they lose an electron (or two or three), creating a population of electrically charged particles swarming alongside the neutral particles. These charged particles make up the ionosphere.

Because the particles of the ionosphere are electrically charged, they respond uniquely to electric and magnetic fields. Dynamic conditions in space — including shifting fields and surges of charged particles, collectively called space weather — induce shifts in the ionosphere that can have far-reaching effects. The ionosphere is where space weather manifests on Earth, and it’s inextricably connected with the neutral upper atmosphere — so distortions in one part affect the other.  

Changes in the ionosphere and upper atmosphere — including sudden shifts in composition, density, temperature, and conductivity — can affect satellites, building up electric charge that has the potential to disrupt instruments, and garble signals like those used by GPS satellites. Predicting these variances is hard, because the causes are so complex: They’re driven not only by space weather — usually a product of solar activity — but also by regular weather down near Earth’s surface.  

Differences in pressure caused by events like hurricanes, or even something as simple as a sustained wind over a mountain range, can ripple upwards until they reach this region and trigger fluctuations. Weather’s influence on the upper atmosphere was only discovered in the past ten years or so — and ICON is the first mission designed specifically to look at that interaction.

ICON carries four types of instruments to study the ionosphere and upper atmosphere. Three of them rely on taking far-away pictures of something called airglow, a faint, global glow produced by reactive compounds in the upper atmosphere. The fourth type collects and analyzes particles directly.

MIGHTI (the Michelson Interferometer for Global High-resolution Thermospheric Imaging) uses Doppler shift — the same effect that makes a siren change pitch as an ambulance passes you — to precisely track the speed and direction of upper-atmosphere winds.

FUV (the Far Ultraviolet instrument) measures airglow produced by certain types of oxygen and nitrogen molecules on Earth’s day side, as well as oxygen ions on Earth’s night side.

EUV (the Extreme Ultraviolet instrument) measures shorter wavelengths of light than FUV. Airglow measured by EUV is produced by oxygen ions on Earth’s day side, which make up the lion’s share of Earth’s daytime ionosphere.

The two identical IVMs (Ion Velocity Meters) make very precise measurements of the angle at which ionized gas enters the instruments, helping us build up a picture of how this ionized gas around the spacecraft is moving.

We’re launching ICON on June 14 Eastern Time on an Orbital ATK Pegasus XL rocket from Kwajalein Atoll in the Marshall Islands, which will deploy from Orbital’s L-1011 Stargazer aircraft. NASA TV will cover the launch — stay tuned to nasa.gov/live for updates and follow the mission on Twitter and Facebook.

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Get Ready to Watch Us Go for GOLD

The boundary where Earth’s atmosphere gives way to outer space is a complex place: Atmospheric waves driven by weather on Earth compete with electric and magnetic fields that push charged particles, all while our signals and satellites whiz by.

On Jan. 25, we’re launching the GOLD instrument (short for Global-scale Observations of the Limb and Disk) to get an exciting new birds-eye view of this region, Earth’s interface to space.

High above the ozone layer, the Sun’s intense radiation cooks some of the particles in the upper atmosphere into an electrically charged soup, where negatively charged electrons and positively charged ions flow freely. This is the ionosphere. The ionosphere is co-mingled with the highest reaches of our planet’s neutral upper atmosphere, called the thermosphere.

Spanning from just a few dozen to several hundred miles above Earth’s surface, the ionosphere is increasingly part of the human domain. Not only do our satellites, including the International Space Station, fly through this region, but so do the signals that are part of our communications and navigation systems, including GPS. Changes in this region can interfere with satellites and signals alike.  

Conditions in the upper atmosphere are difficult to predict, though. Intense weather, like hurricanes, can cause atmospheric waves to propagate all the way up to this region, creating winds that change its very makeup.

Because it’s made up of electrically charged particles, the upper atmosphere also responds to space weather. Space weather – which is usually driven by activity on the Sun – often results in electric and magnetic fields that push and pull on the ionosphere’s charged particles, changing the region’s makeup. On top of that, space weather can also mean incoming showers of high-energy particles that can affect satellites or endanger astronauts, and, in extreme cases, even cause power outages on Earth.

That’s where GOLD comes in. GOLD takes advantage of its host satellite’s geostationary orbit over the Western Hemisphere to maintain a constant view of the upper atmosphere, day and night. By scanning across, GOLD builds up a complete picture of Earth’s disk every half hour.

GOLD is an imaging spectrograph, a type of instrument that breaks light down into its component wavelengths. Studying light in this way lets scientists track the movement and temperatures of different chemical species and build up a picture of how the upper atmosphere changes over time. Capturing these measurements several times a day means that, for the first time, scientists will be able to record the short-term changes in the region -- our first look at its day-to-day ‘weather.’

GOLD is our first-ever mission to fly as a hosted payload on a commercial satellite. A hosted payload flies aboard an otherwise unrelated satellite, hitching a ride to space. GOLD studies the upper atmosphere, while its host satellite supports commercial communications.

Later this year, we’re launching another mission to study the ionosphere: ICON, short for Ionospheric Connection Explorer. Like GOLD, ICON studies Earth’s interface to space, but with a few important distinctions. ICON employs a suite of different instruments to study the ionosphere both remotely and in situ. The direct in situ measurements are possible because ICON flies in low-Earth orbit, giving us a detailed view to complement GOLD’s global perspective of the regions that both missions study.  

How to watch the launch on Jan. 25

Arianespace, a commerical aerospace company, is launching GOLD’s host commercial communications satellite, SES-14, for SES from Kourou, French Guiana.

Watch liftoff live on NASA Television - nasa.gov/live Launch Coverage starts at 5 p.m. EST  (2 p.m. PST, 7 p.m. Kourou local time)

We’ll be streaming the launch live on NASA TV! You can also follow along on Twitter (@NASA and @NASASun), Facebook (NASA and NASA Sun Science), Instagram, and on our Snapchat (NASA). 

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Going for GOLD

On Jan. 25, we’re going for GOLD!

We’re launching an instrument called Global-scale Observations of the Limb and Disk, GOLD for short. It’s a new mission that will study a complicated — and not yet fully understood — region of near-Earth space, called the ionosphere.

Space is not completely empty: It’s teeming with fast-moving energized particles and electric and magnetic fields that guide their motion. At the boundary between Earth’s atmosphere and space, these particles and fields — the ionosphere — co-exist with the upper reaches of the neutral atmosphere.

That makes this a complicated place. Big events in the lower atmosphere, like hurricanes or tsunamis, can create waves that travel all the way up to that interface to space, changing the wind patterns and causing disruptions.

It’s also affected by space weather. The Sun is a dynamic star, and it releases spurts of energized particles and blasts of solar material carrying electric and magnetic fields that travel out through the solar system. Depending on their direction, these bursts have the potential to disrupt space near Earth.

This combination of factors makes it hard to predict changes in the ionosphere — and that can have a big impact. Communications signals, like radio waves and signals that make our GPS systems work, travel through this region, and sudden changes can distort them or even cut them off completely.

Low-Earth orbiting satellites — including the International Space Station — also fly through the ionosphere, so understanding how it fluctuates is important for protecting these satellites and astronauts.  

GOLD is a spectrograph, an instrument that breaks light down into its component wavelengths, measuring their intensities. Breaking light up like this helps scientists see the behavior of individual chemical elements — for instance, separating the amount of oxygen versus nitrogen. GOLD sees in far ultraviolet light, a type of light that’s invisible to our eyes.

GOLD is a hosted payload. The instrument is hitching a ride aboard SES-14, a commercial communications satellite built by Airbus for SES Government Solutions, which owns and operates the satellite.

Also launching this year is the Ionospheric Connection Explorer, or ICON, which will also study the ionosphere and neutral upper atmosphere. But while GOLD will fly in geostationary orbit some 22,000 miles above the Western Hemisphere, ICON will fly just 350 miles above Earth, able to gather close up images of this region.

Together, these missions give us an unprecedented look at the ionosphere and upper atmosphere, helping us understand the very nature of how our planet interacts with space.

To learn more about this region of space and the GOLD mission, visit: nasa.gov/gold.

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