The possibility that life could exist on Mars has captured the imagination of researchers, scientists and writers for over a century. Ever since Giovanni Schiaparelli (and later, Percival Lowell) spotted what they believed were “Martian Canals” in the 19th century, humans have dreamed of one day sending emissaries to the Red Planet in the hopes of finding a civilization and meeting the native Martians.
While the Mariner and Viking programs of the 1960s and 70s shattered the notion of a Martian civilization, multiple lines of evidence have since emerged that indicate how life could have once existed on Mars. Thanks to a new study, which indicates that Mars may have enough oxygen gas locked away beneath its surface to support aerobic organisms, the theory that life could still exist there has been given another boost.
Meredith is a Postdoctoral Researcher in the Department of Astronomy at the University of Washington. She writes software to prepare for the coming onslaught of data from the Large Synoptic Survey Telescope and studies weird binary stars. She is also the lead organizer of the ComSciCon-Pacific Northwest workshop for STEM graduate students in Seattle this March. Meredith holds degrees in physics and astronomy from Harvey Mudd College, San Diego State University, and New Mexico State University. When she’s not science-ing or telling people all about it, she plays viola, volunteers at summer camp, and advocates for more equity and less light pollution.
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Finding atomic oxygen in the Martian atmosphere is very difficult to do, which explains why it’s been 40 years since it was last detected. In the 1970’s, NASA’s Viking and Mariner missions detected Martian atmospheric oxygen, and now, the Stratospheric Observatory for Infrared Astronomy (SOFIA) has detected atomic oxygen in the upper portion of the Martian atmosphere called the mesosphere.
SOFIA is a specially modified Boeing 747 aircraft which carries a 100 inch telescope. It flies at altitudes between 37,000 to 45,000 feet, which puts it above most of the moisture in Earth’s atmosphere. This moisture would otherwise block the infrared radiation that SOFIA “sees.”
“Atomic oxygen in the Martian atmosphere is notoriously difficult to measure,” said Pamela Marcum, SOFIA project scientist. “To observe the far-infrared wavelengths needed to detect atomic oxygen, researchers must be above the majority of Earth’s atmosphere and use highly sensitive instruments, in this case a spectrometer. SOFIA provides both capabilities.”
A special detector on board SOFIA, the German Receiver for Astronomy at Terahertz Frequencies (GREAT) allowed researchers to distinguish Martian atmospheric oxygen from Earthly oxygen. SOFIA-GREAT only detected half the amount of oxygen that scientists expected to find, which is probably due to changes and variations in the atmosphere. These results were published in a 2015 paper in Astronomy and Astrophysics.
Atomic oxygen has a strong effect on Mars’ atmosphere because it affects how other gases escape the atmosphere. It’s extreme volatility means it bonds with nearby molecules very easily; oxygen will combine with almost all chemical elements, except for the noble gases.
SOFIA is the largest airborne observatory in the world, and is a joint project between NASA and the German Aerospace Center. SOFIA has a 20 year mission timeline. Researchers will continue using SOFIA to study the Martian atmosphere, in order to better understand the variations in oxygen content.
SOFIA is not the only mission with eyes on Mars’ atmosphere. NASA’s Mars Atmosphere and Volatile EvolutioN (MAVEN) was launched in 2013 to explore the upper atmosphere of Mars, and how it’s affected by the solar wind. It’s thought that Mars’ atmosphere was much thicker in the past, and has been stripped away over time. Atomic oxygen played a role in Mars’ escaping atmosphere in the past, and no doubt will play a role in the future. SOFIA and other missions like MAVEN will hopefully shed some light on Mars’ past and future atmospheres.
Continuing with our “Definitive Guide to Terraforming“, Universe Today is happy to present our guide to terraforming Saturn’s Moons. Beyond the inner Solar System and the Jovian Moons, Saturn has numerous satellites that could be transformed. But should they be?
Around the distant gas giant Saturn lies a system of rings and moons that is unrivaled in terms of beauty. Within this system, there is also enough resources that if humanity were to harness them – i.e. if the issues of transport and infrastructure could be addressed – we would be living in an age a post-scarcity. But on top of that, many of these moons might even be suited to terraforming, where they would be transformed to accommodate human settlers.
As with the case for terraforming Jupiter’s moons, or the terrestrial planets of Mars and Venus, doing so presents many advantages and challenges. At the same time, it presents many moral and ethical dilemmas. And between all of that, terraforming Saturn’s moons would require a massive commitment in time, energy and resources, not to mention reliance on some advanced technologies (some of which haven’t been invented yet).
We know that the Sun will last another 5 billion years and then expand us a red giant. What will actually make this process happen?
One of the handy things about the Universe, apart from the fact that it exists, is that it lets us see crazy different configurations of everything, including planets, stars and galaxies.
We see stars like our Sun and dramatically unlike our Sun. Tiny, cool red dwarf stars with a fraction of the mass of our own, sipping away at their hydrogen juice boxes for billions and even trillions of years. Stars with way more mass than our own, blasting out enormous amounts of radiation, only lasting a few million years before they detonate as supernovae.
There are ones younger than the Sun; just now clearing out the gas and dust in their solar nebula with intense ultraviolet radiation. Stars much older than ours, bloated up into enormous sizes, nearing the end of their lives before they fade into their golden years as white dwarfs.
The Sun is a main sequence star, converting hydrogen into helium at its core, like it’s been doing for more than 4.5 billion years, and will continue to do so for another 5 or so. At the end of its life, it’s going to bloat up as a red giant, so large that it consumes Mercury and Venus, and maybe even Earth.
What’s the process going on inside the Sun that makes this happen? Let’s peel away the Sun and take a look at the core. After we’re done screaming about the burning burning hands, we’ll see that the Sun is this enormous sphere of hydrogen and helium, 1.4 million kilometers across, the actual business of fusion is happening down in the core, a region that’s a delicious bubblegum center a tiny 280,000 kilometers across.
The core is less than one percent of the entire volume, but because the density of hydrogen in the chewy center is 150 times more than liquid water, it accounts for a freakishly huge 35% of its mass.
It’s thanks to the mass of the entire star, 2 x 10^30 kg, bearing down on the core thanks to gravity. Down here in the core, temperatures are more than 15 million degrees Celsius. It’s the perfect spot for nuclear fusion picnic.
There are a few paths fusion can take, but the main one is where hydrogen atoms are mushed into helium. This process releases enough gamma radiation to make you a planet full of Hulks.
While the Sun has been performing hydrogen fusion, all this helium has been piling up at its core, like nuclear waste. Terrifyingly, it’s still fuel, but our little Sun just doesn’t have the temperature or pressure at its core to be able to use it.
Eventually, the fusion at the core of the Sun shuts down, choked off by all this helium and in a last gasp of high pitched mickey mouse voice terror the helium core begins to contract and heat up. At this point, an amazing thing happens. It’s now hot enough for a layer of hydrogen just around the core to heat up and begin fusion again. The Sun now gets a second chance at life.
As this outer layer contains a bigger volume than the original core of the Sun, it heats up significantly, releasing far more energy. This increase in light pressure from the core pushes much harder against gravity, and expands the volume of the Sun.
Even this isn’t the end of the star’s life. Dammit, Harkness, just stay down. Helium continues to build up, and even this extra shell around the core isn’t hot and dense enough to support fusion. So the core dies again. The star begins to contract, the gravitational energy heats up again, allowing another shell of hydrogen to have the pressure and temperature for fusion, and then we’re back in business!
Our Sun will likely go through this process multiple times, each phase taking a few years to complete as it expands and contracts, heats and cools. Our Sun becomes a variable star.
Eventually, we run out of usable hydrogen, but fortunately, it’s able to switch over to using helium as fuel, generating carbon and oxygen as byproducts. This doesn’t last long, and when it’s gone, the Sun gets swollen to hundreds of times its size, releasing thousands of times more energy.
This is when the Sun becomes that familiar red giant, gobbling up the tasty planets, including, quite possibly the Earth.The remaining atmosphere puffs out from the Sun, and drifts off into space creating a beautiful planetary nebula that future alien astronomers will enjoy for thousands of years. What’s left is a carbon oxygen core, a white dwarf.
The Sun is completely out of tricks to make fusion happen any more, and it’ll now cool down to the background temperature of the Universe. Our Sun will die in a dramatic way, billions of years from now when it bloats up 500 times its original volume.
What do you think future alien astronomers will call the planetary nebula left behind by the Sun? Give it a name in the comments below.
Since the energy required to fuse iron is more than the energy that you get from doing it, could you use iron to kill a star like our sun?
A fan favorite was How Much Water Would it Take to Extinguish the Sun? Go ahead and watch it now if you like. Or… if you don’t have time to watch me set up the science, deliver a bunch of hilarious zingers and obscure sci-fi references, here’s the short version:
The Sun is not on fire, it’s a fusion reaction. Hydrogen mashes up to produce helium and energy. Lots and lots of energy. Water is mostly hydrogen, adding water would give more fuel and make it burn hotter. But some of you clever viewers proposed another way to kill the Sun. Kill it with iron!
Iron? That seems pretty specific. Why iron and not something else, like butter, donuts, or sitting on the couch playing video games – all the things working to kill me? Is iron poison to stars? An iron bar? Possibly iron bullets? Iron punches? Possibly from fashioning a suit and attacking it as some kind of Iron Man?
Time for some stellar physics. Stars are massive balls of plasma. Mostly hydrogen and helium, and leftover salad from the Big Bang. Mass holds them together in a sphere, creating temperatures and pressures at their cores, where atoms of hydrogen are crushed together into helium, releasing energy. This energy, in the form of photons pushes outward. As they escape the star, this counteracts the force of gravity trying to pull it inward.
Over the course of billions of years, the star uses up the reserves of hydrogen, building up helium. If it’s massive enough, it will switch to helium when the hydrogen is gone. Then it can switch to oxygen, and then silicon, and all the way up the periodic table of elements.
The most massive stars in the Universe, the ones with at least 8 times the mass of the Sun, have enough temperature and pressure that they can fuse elements all the way up to iron, the 26th element on the Periodic Table. At that point, the energy required to fuse iron is more than the energy that you get from fusing iron, no matter how massive a star you are.
In a fraction of a second, the core of the Sun shuts off. It’s no longer pushing outward with its light pressure, and so the outer layers collapse inward, creating a black hole and a supernova. It sure looks like the build up of iron in the core killed it.
Is it true then? Is iron the Achilles heel of stars? Not really. Iron is the byproduct of fusion within the most massive stars. Just like ash is the byproduct of combustion, or poop is the byproduct of human digestion.
It’s not poison, which stops or destroys processes within the human body. A better analogy might be fiber. Your body can’t get any nutritional value out of fiber, like grass. If all you had to eat was grass, you’d starve, but it’s not like the grass is poisoning you. As long as you got adequate nutrition, you could eat an immense amount of grass and not die. It’s about the food, not the grass.
The Sun already has plenty of iron; it’s 0.1% iron. That little nugget would work out to be 330 times the mass of the Earth. If you gave it much more iron, it would just give the Sun more mass, which would give it more gravity to raise the temperature and pressure at the core, which would help it do even more fusion.
If you just poured iron into a star, it wouldn’t kill it. It would just make it more massive and then hotter and capable of supporting the fusion of heavier elements. As long as there’s still viable fuel at the core of the star, and adequate temperatures and pressures, it’ll continue fusing and releasing energy.
If you could swap out the hydrogen in the Sun with a core of iron, you would indeed kill it dead, or any star for that matter. It wouldn’t explode, though. Only if it was at least 8 times the mass of the Sun to begin with. Then would you have enough mass bearing down on the inert core to create a core collapse supernova.
In fact, since you’ve got the power to magically replace stellar cores, you would only need to replace the Sun’s core with carbon or oxygen to kill it. It actually doesn’t have enough mass to fuse even carbon. As soon as you replaced the Sun’s core, it would shut off fusion. It would immediately become a white dwarf, and begin slowly cooling down to the background temperature of the Universe.
Iron in bullet, bar, man or any other form isn’t poison to a star. It just happens to be an element that no star can use to generate energy from fusion. As long as there’s still viable fuel at the core of a star, and the pressure and temperature to bring them together, the star will continue to pump out energy.
What other exotic ways would you use to try and kill the Sun? Give us your suggestions in the comments below.
Have you ever wondered how much water it would take to put out the Sun? It turns out, the Sun isn’t on fire. So what would happen if you did try to hit the Sun with a tremendous amount of water?
How much water would it take to extinguish the Sun? I recently saw this great question on Reddit, and I couldn’t resist taking a crack at it: We know that the question doesn’t make a lot of sense.
A fire is a chemical reaction, where material releases heat as it oxidizes. If you take away oxygen from a fire, it goes out. But.. there’s no oxygen in space, it’s a vacuum. So, there’s not a whole lot of room for regular flavor water-extinguishable fire in space. You know this. How many times have we had to seal off the living quarters and open the bay doors to vent all the oxygen in the space because there was a fire in the cargo bay? We have to do that, like, all the time.
Our wonderful Sun is something quite different. It’s a nuclear fusion reaction, converting hydrogen atoms into helium under the immense temperatures and pressures at its core. It doesn’t need oxygen to keep producing energy. It’s already got its fuel baked in. All the Sun needs is our adoration, quiet, and yet ever present fear. Only if we constantly pray will it be happy and perhaps we’ll go another day where it doesn’t hurl a giant chunk of itself at our smug little faces because it’s tired of our shenanigans.
So, I’m still going to take a swing at this question… so let’s talk about what would happen if you did pour a tremendous amount of water on the Sun? Let’s say another Sun’s worth of H20. Conveniently, Hydrogen is what the Sun uses for fuel, so if you give the Sun more hydrogen, it should just get larger and hotter.
Oxygen is one of the byproducts of fusion. Right now, our Sun is turning hydrogen into helium using the proton-proton fusion reaction. But there’s another type of reaction that happens in there called the carbon-nitrogen-oxygen reaction. As of right now, only 0.8% of the Sun’s fusion reactions proceed along this path.
So if you fed the Sun more oxygen as part of the water, it would allow it to perform more of these fusion reactions too. For stars which are 1.3 times the mass of the Sun, this CNO reaction is the main way fusion is taking place. So, if we did dump a giant pile of water onto the Sun, we’d just be making Sun bigger and hotter.
Conveniently, larger hotter stars burn for a shorter amount of time before they die. The largest, most massive stars only last a few million years and then they explode as supernovae. So, if you’re out to destroy the Sun, and you’re playing a really, really long game, this might actually be a viable route.
I’m pretty sure that wasn’t the intent though. Let’s say we just want to snuff out the Sun. Vsauce provides a strategy for this. If you could somehow blast your water at the Sun at high enough velocity, you might be able to tear it apart. If you can reduce the Sun’s mass, you can decrease the temperature and pressure in its core so that it can no longer support fusion reactions.
I’m going to sum up. The Sun isn’t on fire. There’s no amount of water you could add that would quench it, you’d just make it explode, but if you used firehoses that could spray water at nearly the speed of light, you could probably shut the thing off and eventually freeze us all, which is what I think you were hoping for in the first place.
What do you think? What else could we do to snuff out the Sun?
Emerald green, fainter than the zodiacal light and visible on dark nights everywhere on Earth, airglow pervades the night sky from equator to pole. Airglow turns up in our time exposure photographs of the night sky as ghostly ripples of aurora-like light about 10-15 degrees above the horizon. Its similarity to the aurora is no coincidence. Both form at around the same altitude of 60-65 miles (100 km) and involve excitation of atoms and molecules, in particular oxygen. But different mechanisms tease them to glow.
Auroras get their spark from high-speed electrons and protons in the solar wind that bombard oxygen and nitrogen atoms and molecules. As excited electrons within those atoms return to their rest states, they emit photons of green and red light that create shimmering, colorful curtains of northern lights.
Airglow’s subtle radiance arises from excitation of a different kind. Ultraviolet light from the daytime sun ionizes or knocks electrons off of oxygen and nitrogen atoms and molecules; at night the electrons recombine with their host atoms, releasing energy as light of different colors including green, red, yellow and blue. The brightest emission, the one responsible for creating the green streaks and bands visible from the ground and orbit, stems from excited oxygen atoms beaming light at 557.7 nanometers, smack in the middle of the yellow-green parcel of spectrum where our eyes are most sensitive.
That’s not saying airglow is easy to see! For years I suspected streaks of what I thought were high clouds from my dark sky observing site even when maps and forecasts indicated pristine skies. Photography finally taught me to trust my eyes. I started noticing green streaks near the horizon in long-exposure astrophotos. At first I brushed it off as camera noise. Then I noticed how the ghostly stuff would slowly shape-shift over minutes and hours and from night to night. Gravity waves created by jet stream shear, wind flowing over mountain ranges and even thunderstorms in the lower atmosphere propagate up to the thermosphere to fashion airglow’s ever-changing contours.
Last month, on a particularly dark night, I made a dedicated sweep of the sky after my eyes had fully adapted to the darkness. A large swath of airglow spread south of the Big and Little Dipper. To the east, Pegasus and Andromeda harbored hazy spots of varying intensity, while brilliant Mars beamed through a long smear in Virgo.
To prove what I saw was real, I made the photos you see in this article and found they exactly matched my visual sightings. Except for color. Airglow is typically too faint to fire up the cone cells in our retinas responsible for color vision. The vague streaks and patches were best seen by moving your head around to pick out the contrast between them and the darker, airglow-free sky. No matter what part of the sky I looked, airglow poked its tenuous head. Indeed, if you were to travel anywhere on Earth, airglow would be your constant companion on dark nights, unlike the aurora which keeps to the polar regions. Warning – once you start seeing it, you
Airglow comes in different colors – let’s take a closer look at what causes them:
* Red – I’ve never seen it, but long-exposure photos often reveal red/pink mingled with the more common green. Excited oxygen atoms much higher up at 90-185 miles (150-300 km) radiating light at a different energy state are responsible. Excited -OH (hydroxyl) radicals give off deep red light in a process called chemoluminescencewhen they react with oxygen and nitrogen. Another chemoluminescent reaction takes place when oxygen and nitrogen molecules are busted apart by ultraviolet light high in the atmosphere and recombine to form nitric oxide (NO).
* Yellow – From sodium atoms around 57 miles (92 km) high. Sodium arrives from the breakup and vaporization of minerals in meteoroids as they burn up in the atmosphere as meteors.
* Blue – Weak emission from excited oxygen molecules approximately 59 miles (95 km) high.
Airglow varies time of day and night and season, reaching peak brightness about 10 degrees, where our line of sight passes through more air compared to the zenith where the light reaches minimum brightness. Since airglow is brightest around the time of solar maximum (about now), now is an ideal time to watch for it. Even cosmic rays striking molecules in the upper atmosphere make a contribution.
See lots of airglow and aurora from orbit in this video made using images taken from the space station.
If you removed the stars, the band of the Milky Way and the zodiacal light, airglow would still provide enough illumination to see your hand in front of your face at night. Through recombination and chemoluminescence, atoms and molecules creates an astounding array of colored light phenomena. We can’t escape the sun even on the darkest of nights.
While astronomers are trying to figure out which planets they find are habitable, there are a range of things to consider. How close are they to their parent star? What are their atmospheres made of? And once those answers are figured out, here’s something else to wonder about: how many minerals are on the planet’s surface?
As more information is learned about these distant worlds, it will be interesting to see if it’s possible to apply his findings — if we could detect the minerals from afar in the first place.
“We live on a planet of remarkable beauty, and when you look at it from the proximity of our moon, you see what is obviously a very dynamic planet,” Hazen told delegates at “Habitable Worlds Across Time and Space”, a spring symposium from the Space Telescope Science Institute that is being webcast this week (April 28-May 1).
His point was that planets don’t necessarily start out that way, but he said in his talk that he’d invite comments and questions on his work for alternative processes. His team believes that minerals and life co-evolved: life became more complex and the number of minerals increased over time.
The first mineral in the cosmos was likely diamonds, which were formed in supernovas. These star explosions are where the heavier elements in our cosmos were created, making the universe more rich than its initial soup of hydrogen and helium.
There are in fact 10 elements that were key in the Earth’s formation, Hazen said, as well as that of other planets in our solar system (which also means that presumably these would apply to exoplanets). These were carbon, nitrogen, oxygen, magnesium, silicon, carbon, titanium, iron and nitrogen,which formed about a dozen minerals on the early Earth.
Here’s the thing, though. Today there are more than 4,900 minerals on Earth that are formed from 72 essential elements. Quite a change.
Hazen’s group proposes 10 stages of evolution:
Primary chondrite minerals (4.56 billion years ago) – what was around as the solar nebula that formed our solar system cooled. 60 mineral species at this time.
Planetesimals — or protoplanets — changed by impacts (4.56 BYA to 4.55 BYA). Here is where feldspars, micas, clays and quartz arose. 250 mineral species.
Planet formation (4.55 BYA to 3.5 BYA). On a “dry” planet like Mercury, evolution stopped at about 300 mineral species, while “wetter” planets like Mars would have seen about 420 mineral species that includes hydroxides and clays produced from processes such as volcanism and ices.
Granite formation (more than 3.5 BYA). 1,000 mineral species including beryl and tantalite.
Plate tectonics (more than 3 BYA). 1,500 mineral species. Increases produced from changes such as new types of volcanism and high-pressure metamorphic changes inside the Earth.
These stages above are about as far as you would get on a planet without life, Hazen said. As for the remaining stages on Earth, here they are:
Anoxic biosphere (4 to 2.5 BYA), again with about 1,500 mineral species existing in the early atmosphere. Here was the rise of chemolithoautotrophs, or life that obtains energy from oxidizing inorganic compounds.
Paleoproterozoic oxidation (2.5 to 1.5 BYA) — a huge rise in mineral species to 4,500 as oxygen becomes a dominant player in the atmosphere. “We’re trying to understand if this is really true for every other planet, or if there is alternative pathways,” Hazen said.
And the final three stages up to the present day was the emergence of large oceans, a global ice age and then (in the past 540 million years or so) biomineralization or the process of living organisms producing minerals. This latter stage included the development of tree roots, which led to species such as fungi, microbes and worms.
It should be noted here that oxygen does not necessarily indicate there is complex life. Fellow speaker David Catling from the University of Washington, however, noted that oxygen rose in the atmosphere about 2.4 billion years ago, coincident with the emergence of complex life.
Animals as we understand them could have been “impossible for most of Earth’s history because they couldn’t breathe,” he noted. But more study will be needed on this point. After all, we’ve only found life on one planet: Earth.
I shoot a lot of pictures of the northern lights. Just like the next photographer, I thrill to the striking colors that glow from the back of my digital camera. When preparing those images for publication, many of us lighten or brighten the images so the colors and forms stand out better. Nothing wrong with that, except most times the aurora never looked that way to our eyes.
The colors you see in aurora photos ARE real but exaggerated because the pictures are time exposures. Once the camera’s shutter opens, light accumulates on the electronic sensor, making faint and pale subjects bright and vivid. The camera can’t help it, and who would deny a photographer the chance to share the beauty? Most of us understand the magic of time exposures and factor in a mental fudge factor when looking at astronomical photos including those of the aurora.
But photos can be misleading, especially so for beginners, who might anticipate “the second coming” when they step out to watch the northern lights only to feel disappointment at the real thing. Which is too bad, because the real aurora can make your jaw drop.
That’s why I thought it would instructive to take a few aurora photos and tone them down to what the eye normally sees. Truth in advertising you know. I’ve also started to include disclaimers in my captions when the images show striking crimson rays. Veteran aurora watchers know that some of the most memorable auroral displays glow blood-red, but most of the ruddy hues recorded by the camera are simply invisible to the eye. Our eyes evolved their greatest sensitivity to green light, the slice of the rainbow spectrum in which the sun shines most intensely. We’re slightly less sensitive to yellow and only a 1/10 as sensitive to red.
A typical aurora begins life as a pale white band low in the northern sky. If we’re lucky, the band intensifies, crosses the color threshold and glows pale green. Deeper and brighter greens are also common in active and bright auroras, but red is elusive because are eyes are far less sensitive to it than green. Often a curtain of green rays will be topped off by red, blue or purple emission recorded with sumptuous fidelity in the camera. What does the eye see? Smoky, colorless haze with hints of pink. Maybe.
Again, this doesn’t mean we only see green and white. I’ve watched brilliant (pale) green rays stretch from horizon to zenith with their bottoms bathed in rosy-purple, a most wonderful sight. Another factor to keep in mind is dark adaption – the longer you’ve been out under a dark sky, the more sensitive your eyes will be to whatever color might be present. At night, however, we’re mostly color blind, relying on our low-light-sensitive rod cells to get around. Cone cells, fine-tuned for color vision, are activated only when light intensity reaches certain thresholds. That happens often when it comes to auroral green but less so with other colors to which our cells are less responsive.
Auroral colors originate when electrons from the sun spiral down Earth’s magnetic field lines like firemen on a firepole and slam into oxygen and nitrogen atoms in Earth’s upper atmosphere between 60 and 150 miles (96-240 km) high. Here’s a breakdown of color, atom and altitude:
* Green – oxygen atoms 60-93 miles up (100-150 km)
* Red – oxygen atoms from 93-155 miles (150-250 km)
* Purple – molecular nitrogen up to 60 miles (100 km)
* Blue/purple – molecular nitrogen ions above 100 miles (160 km)
When an electron strikes an oxygen atom for instance, it bumps one of the oxygen’s electrons to a higher energy level. When that electron drops back down to its previous rest or ground state, it emits a photon of green light. Billions of atoms and molecules, each cranking out tiny flashes of light, make an aurora. It takes about 3/4 second for that electron to drop and the atom to release a photon before it’s given another kick from a solar electron. Most auroras are rich with oxygen emission.
Higher up, where the air’s so thin it’s identical to a hard vacuum, collisions between atoms happen only about every 7 seconds. With lots of time on their hands, oxygen electrons can transition down to their lowest energy level inside the atom, releasing a photon of red light instead of green. That’s why tall rays often show red tops especially in time exposure photos.
Only during very active geomagnetic storms, when electrons penetrate to low levels in the atmosphere, are they able to excite molecules of nitrogen, giving rise to the familiar purple fringes at the bottoms of bright rays. Bombarded molecular nitrogen ions at high altitude release a deep blue-purple light. Rarely visible to the eye, I did record it one night in the camera.
While videos hint at how wildly dynamic auroras can be, they’re no substitute for seeing one yourself. That’s why I never seem to get to bed when that first tempting glow appears over the northern horizon. Colorful or colorless, you’ll be astonished at how the aurora constantly re-invents itself in a multitude of forms from arcs to rays to flaming patches and writhing curlicues. Don’t miss the chance to see one. If there’s one thing that looks absolutely unearthly on this green Earth, it’s the aurora borealis. Click HERE for a guide on when and where to watch for them.