It may appear that New Zealand is being bombarded right now. After a huge meteor exploded over the sea near Wellington on July 7, a screeching sound was heard across the bottom of the South Island, and a sight of a smaller fireball was captured two weeks later over Canterbury.
The Fireballs Aotearoa Science Alliance, a collaboration of astronomers to search for newly fallen meteorites, has received a lot of questions about these events, and one of the most common questions is the color bright green, and whether it is the same green as the aurora borealis.
Green fireballs are reported and photographed in New Zealand regularly, and bright meteors often indicate the arrival of a piece of meteorite, which can be anywhere from a few centimeters to a meter in diameter when it hits the atmosphere.
Some of these asteroids contain nickel and iron and hit the atmosphere at a speed of up to 60 km per second, and this releases a huge amount of heat very quickly and the vaporized iron and nickel radiate a green light.
But is this the same as the bright green of the aurora borealis? For the latest meteorite, the answer given by Jack Bagley, Professor Emeritus of Physics and Astronomy at the University of Canterbury in New Zealand, is essentially no, but it’s actually not that simple.
In an article published by The Conversation, Bagali says that the green glow of the aurora is caused by oxygen ions in the upper atmosphere, resulting from collisions between oxygen molecules in the atmosphere and particles emitted from the sun.
Oxygen ions combine with electrons to produce oxygen atoms, but the electrons can remain in the excited state for several seconds.
In the energy transition known as “forbidden” because it does not obey the usual quantum rules, they then emit auroral green light at a wavelength of 557 nanometers.
A meteor can also shine in this way, but only if it is very fast, as very fast meteors heat up in the thin atmosphere more than 100 kilometers high where the aurora is formed.
Once the meteorite hit Canterbury on July 22, the upper-atmosphere’s fluctuating winds gently twisted the glowing path, resulting in a faint green glow caused by constantly excited sodium atoms in a catalytic reaction involving ozone.