Gold - 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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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).
Make sure to follow us on Tumblr for your regular dose of space: http://nasa.tumblr.com.
The Beauty of Webb Telescope’s Mirrors
The James Webb Space Telescope’s gold-plated, beryllium mirrors are beautiful feats of engineering. From the 18 hexagonal primary mirror segments, to the perfectly circular secondary mirror, and even the slightly trapezoidal tertiary mirror and the intricate fine-steering mirror, each reflector went through a rigorous refinement process before it was ready to mount on the telescope. This flawless formation process was critical for Webb, which will use the mirrors to peer far back in time to capture the light from the first stars and galaxies.
The James Webb Space Telescope, or Webb, is our upcoming infrared space observatory, which will launch in 2019. It will spy the first luminous objects that formed in the universe and shed light on how galaxies evolve, how stars and planetary systems are born, and how life could form on other planets.
A polish and shine that would make your car jealous
All of the Webb telescope’s mirrors were polished to accuracies of approximately one millionth of an inch. The beryllium mirrors were polished at room temperature with slight imperfections, so as they change shape ever so slightly while cooling to their operating temperatures in space, they achieve their perfect shape for operations.
The Midas touch
Engineers used a process called vacuum vapor deposition to coat Webb’s mirrors with an ultra-thin layer of gold. Each mirror only required about 3 grams (about 0.11 ounces) of gold. It only took about a golf ball-sized amount of gold to paint the entire main mirror!
Before the deposition process began, engineers had to be absolutely sure the mirror surfaces were free from contaminants.
The engineers thoroughly wiped down each mirror, then checked it in low light conditions to ensure there was no residue on the surface.
Inside the vacuum deposition chamber, the tiny amount of gold is turned into a vapor and deposited to cover the entire surface of each mirror.
Primary, secondary, and tertiary mirrors, oh my!
Each of Webb’s primary mirror segments is hexagonally shaped. The entire 6.5-meter (21.3-foot) primary mirror is slightly curved (concave), so each approximately 1.3-meter (4.3-foot) piece has a slight curve to it.
Those curves repeat themselves among the segments, so there are only three different shapes — 6 of each type. In the image below, those different shapes are labeled as A, B, and C.
Webb’s perfectly circular secondary mirror captures light from the 18 primary mirror segments and relays those images to the telescope's tertiary mirror.
The secondary mirror is convex, so the reflective surface bulges toward a light source. It looks much like a curved mirror that you see on the wall near the exit of a parking garage that lets motorists see around a corner.
Webb’s trapezoidal tertiary mirror captures light from the secondary mirror and relays it to the fine-steering mirror and science instruments. The tertiary mirror sits at the center of the telescope’s primary mirror. The tertiary mirror is the only fixed mirror in the system — all of the other mirrors align to it.
All of the mirrors working together will provide Webb with the most advanced infrared vision of any space observatory we’ve ever launched!
Who is the fairest of them all?
The beauty of Webb’s primary mirror was apparent as it rotated past a cleanroom observation window at our Goddard Space Flight Center in Greenbelt, Maryland. If you look closely in the reflection, you will see none other than James Webb Space Telescope senior project scientist and Nobel Laureate John Mather!
Learn more about the James Webb Space Telescope HERE, or follow the mission on Facebook, Twitter and Instagram.
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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.
Make sure to follow us on Tumblr for your regular dose of space: http://nasa.tumblr.com.