The Science Behind Southern California’s Green Streak ‘UFO’

Late Tuesday, California was treated to a rare and confusing sight: A sudden fireball lighting up the night sky with a green flame. There have been over 160 reports of the fireball, according to the American Meteor Society. At eleven seconds into the clip above, you can see it and it looks like it’s straight out of the start of a monster movie, especially as it crashed in the bay, and was visible from San Diego to Bakersfield. But California isn’t being invaded by aliens just yet.

First of all, “fireball” has a precise meaning, in this context. It’s a burning meteor that’s brighter than the planet Venus in the night sky. Every shooting star you see is, in the colloquial sense, a fireball, as the friction of slamming into our atmosphere is so intense, pretty much everything lights on fire. It’s also only unique in the sense that we can see it, with the American Meteor Society estimating there are several thousand each day, just mostly where we don’t see them.

So what about the color? The “scientific” explanation most people are going with on Facebook is “aliens,” but the real answer is that meteors are rocks, and just like rocks on Earth, they’re composed of different elements. Nine elements burn with a green flame, so the color isn’t unusual. What is unusual is that enough of the element vaporized into the atmosphere to burn with a distinct color. Usually a fireball consists mostly of atoms from the surrounding atmosphere. So many people are reporting that it’s green that this meteor likely had a heavy concentration of an element that burns green.

In other words, the aliens are not invading. But thousands of Californians got to see a genuinely rare scientific phenomenon few others are likely to witness in their lifetimes. Which we suppose would also apply to alien visitation, but the meteor has a much lower chance of going horribly wrong.

(Via the American Meteor Society)