Goodness Gracious, Green Balls of Fire

Goodness Gracious, Green Balls of Fire

Liza Fust, Communications Coordinator

5.5 minute read

“Did you see that?”

Nope, my friend hadn’t. As we had walked up to the lighthouse, the green fireball hurtled across the sky above Lake Superior (and here’s video), disappearing in the blink of an eye behind the square, red-brick Marquette lighthouse. The beam from the fresnel lighthouse lens was now the only illumination flickering across the darkness of the October night. I had to know what that viridian streak was, so I reached out to an expert for some answers. In this case, the expert in question was Adam Kall, KMI Co-Founder and Director of Science, who was gracious enough to field questions late on a Friday night so I could prove to my friend that I wasn’t that crazy. The answer to what the mystery fireball was, given my work with KMI, did not come as a surprise: it was space debris. But that was just the inciting incident of a “curiosity drove the cat to the brink of exasperation” situation. I wanted to know where the debris got its color, which led to the question: why do we see the colors of space as we do?

Debris
Since not everyone has an orbital debris subject matter expert’s number saved in their contacts, let me break down for you some of the ways that you too can spot orbital debris, based on my further layman’s research. To characterize orbital debris with the naked eye we must first understand some things about the nature of what orbital debris is. Orbital debris is defunct human-made objects, made useless from the natural end of life, an accident, or collision, now trapped in orbit. Only, ‘trapped’ is a mislead, as KMI plans to remove debris from orbit (it’s called Active Debris Removal - how’s that for keyword insertion SEO gods?), where most of it will stay and remain at risk of collisions. Sometimes this debris deorbits naturally, or with a little push (Active Debris Removal #keywords #SEO), through the atmosphere where it usually burns up. The material makeup of this manmade resident space object ranges from aluminum and titanium structures to hydrazine or plasma propellant. Some things we send up into space are meant to come back, like crew capsules, and some are meant to be deorbited and burn up in the atmosphere. Sometimes, the things that are meant to burn up, don’t entirely. But don’t worry, there’s only a 10% chance that someone will get hit by space debris falling to Earth over the next ten years. KMI has already talked about that in another column. Earlier in 2023 there were reports across the California and Oregon coast of lights streaking across the sky. Astronomer Jonathan McDowell tweeted that this was also probably space debris, even noting the potential satellite that the debris used to be. Here’s a great video and visual so you too can take a stab at determining if it's debris or… well just keep reading this column.

Meteors
Other things enter Earth’s atmosphere too of course, as humankind has been noting long, long, long before the first satellite was launched to the heavens. Specifically, the first recording of the Perseid meteor showers was in 36 AD China. As we have been chronicling over the centuries, different objects pass through the sky at different times with different qualities. As objects streak burning through the atmosphere you’ll notice that a spectrum of colors are visible. This is not how hot the object is burning, as we see fire range from hot to hotter burning orange to blue/white, but is rather indicative of the chemical makeup of the object. Similar to how fireworks get their colors, iron burns yellow, calcium purple, sodium orange, nitrogen/oxygen red, and magnesium green. Let’s focus on that last one. 

Magnesium is a common alloy material used in spacecraft components, such as fuselage structures and engine frames, specifically for its lightweight and durable qualities. Meaning, when you see a green fireball streaking across the night sky it may very well be space debris burning up and not a meteor. If you're ever interested in what's flying over, Privateer’s Wayfinder app is a public website where you can track actively deorbiting debris from reentry through their flight path, so you can see if something has passed over.

Comets
“But wait,” you might say if you’ve read the news or scrolled social media anytime in early 2023, “there was just a green comet that passed by Earth for the first time in 50,000 years - are you telling me that was manmade debris?” No of course not, it’s obviously aliens since humans didn’t have that technology 50,000 years ago. Joking! Remember, not that crazy. This just means that this infrequent visitor to Earth (named C/2022 E3 [ZTF]) has a high concentration of diatomic carbon and cyanogen that glows green when illuminated by the sun. But not magnesium. Why? Comets aren’t burning rocks or debris in Earth’s atmosphere, they are balls of ice and dirt orbiting the sun, therefore their light comes from how they reflect the sun’s light, not how they’re burning. In fact, comets have seasons of color depending on their orbit and how the sun hits the atmosphere (or coma) and comet (or nucleus), so with long-term observation (as with the European Space Agency’s Rosetta spacecraft) you will see the comet shift in color. And here’s a fun fact for you, the "tail" of a comet is material and ice being blasted off by the solar winds of our sun, which means they always point away from the sun, regardless of the direction of travel.

Auroras
If you follow KMI on social media, you may have seen photos from our Marquette team of the Aurora Borealis, also known as the Northern Lights, also known as the reason I was late to work Friday morning because we were out gazing Thursday night. So where do those breathtaking lights get their array of kaleidoscope colors, a vibrant watercolor painted across a black canvas of white stars? It’s all hot gas. Auroras are a whirling dance of particles, a carnival collision across the atmosphere of oxygen in green, nitrogen in blue and pink, and a rare scarlet from high-altitude oxygen and solar particles.  

Little Presque Isle, Marquette, Michigan March 23, 2023. Credit: Liza Fust

Galaxies
So then, all those cool photos we see from the new James Webb Space Telescope (JWST) show colors that are… what exactly? Answer: greyscale. Huh? Here’s the thing, JWST is an infrared telescope, it “sees” heat. What we see looking at JWST’s photos are a representation of its view in optical light. These colors represent the variation of brightness in wavelength. Here’s a handy-dandy graphic. Do note our beloved Hubble, the elder sibling of JWST, has a similar process but it filters in optical wavelengths so there doesn’t need to be a shift from infrared to optical.

Photo Credit Left to Right: Light Path of Webb and NGC 1433 (MIRI Image). Credit: Webb Space Telescope

Aliens?
Meteors, comets, debris, aliens - there’s a lot up there out in space. Looking out from this Pale Blue Dot, the expanse of space seems bright. But it’s too bright, as satellites and the debris they generate masquerade as constellations and shooting stars. Astronomers have called this out, but that’s a topic for another time. You get it, there’s a lot to see up there. There are so many colors in the universe, not just in our atmosphere and space, obviously. We could get into why the sky can be blue or sometimes green (it’s a tornado - find shelter), why rainbows and my closet are ROYGBIV, and also fireworks (ok, we did, it’s linked above). How it’s burning or refracting light causes the main color we perceive because of how it’s made. There’s still so much more to see. Debris shouldn’t be the new star gazing, and it shouldn’t hold us back from reaching out to see the colors of Mars with the naked eye. That’s why our mission at KMI is #KeepingSpaceClearForAll. Stay colorful.

P.S. So, what was that green dot burning across the sky over Lake Superior? Maybe debris, but it could be an alien cover story.