Tuesday, October 21, 2014

Fiery Dust From a Famous Snowball

Orionid meteor and northern lights this morning over the Livingston Mountain Range, in Glacier National Park

Orionid meteor flying through its namesake constellation
Every time I climb in the truck and circle into town, I leave a few miles of gravely dust between home and the highway pavement.

Comets sorta' do the same thing.

Every time Halley's Comet makes its 76-year loop around the Sun, it leaves a trail of dust along the inner part of its elliptical orbit. As the comet reaches our inner solar system, the Sun heats and degrades this big, dirty snowball, causing it to drop debris along its path.

And every time the Earth makes its annual lap around the Sun, it flies through this narrow trail of comet dust in late October. Right now in fact. Some of the dust burns up in our atmosphere, causing the "falling stars" that we call the Orionid meteor shower. It should be called the "Halley's meteor shower," but it's called Orionid instead because most of these meteors appear to originate from the vicinity of the constellation Orion. These mostly-tiny particles hit the upper atmosphere about 60 miles above ground and burn up at a blazing 418 miles per hour.

One calculation I found estimates that Halley's Comet might loose an astonishing 6,283,174,472 tons each time it loops around the Sun. At this rate, with a 76-year orbit, Halley's Comet would make 95 laps over 7,220 years before completely disintegrating.

Halley's Comet last passed through the neighborhood in 1986 and won't return until July of 2061. But the comet's dusty trail is also the source of falling stars during the Eta Aquariids meteor shower, which takes place every May. Twice a year, Halley serves up two heavenly reminders of how amazing our little solar system really is - when we stop to look.

Great infographic on how comets and meteor showers are connected
A 500-pound meteorite from Halley's Comet fell on Texas in 1910

Or, another possible source for that beautiful shooting star you saw