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Starts With A Bang

No, Comet Tails Don’t Make Meteor Showers

It’s time to bust one of the biggest myths about where the night sky’s most spectacular, seasonal shows come from.

Meteor showers are one of the night sky’s most spectacular sights whenever and wherever they occur.

Timelapse photos, like this one of 2015’s Perseid meteor shower, contain many separate images merged together. In reality, most meteors are brief, one-at-a-time blips across an otherwise static sky.(Trevor Bexon / flickr)

While the Perseids, Geminids, and Leonids are among the most famous, the reality is that smaller meteor showers occur all throughout the year.

Meteor, photographed over the Atacama Large Millimeter/sub-millimeter Array, 2014. The brightness of a meteor is determined by its size and relative speed to Earth. (ESO/C. Malin)

When the debris from a comet or asteroid collides with the revolving Earth, the incredibly fast relative motion causes these tiny particles to burn up in the atmosphere, producing a brilliant streak of light.

A view of many meteors striking Earth over a long period of time, shown all at once, from the ground (left) and space (right). The faster, larger, and more numerous the cometary fragments striking Earth’s atmosphere are, the more spectacular the ensuing meteor shower is.(Astronomical and geophysical observatory, Comenius University (L); NASA (from space), via Wikimedia Commons user Svdmolen (R))

Most popular explainers attribute these showers to cometary tails, but that’s simply not true.

Although comets and asteroids give rise to meteor showers here on Earth, it isn’t the spectacular tails that create them. This is a common misconception that even NASA employees occasionally goof up. (S. Deiries / ESO)

Tails, created by the Sun’s effect on a comet or asteroid, are pushed away from the Sun, and this material spreads out rapidly, never to collide with Earth.

Although a comet may look like it has up to three tails — a bluish ion tail, a greyish dust tail, and a thin anti-tail at times — there are only two. The dust tail curves, but both always are shunted away from the Sun, and will not cross Earth’s orbit in the future. (Roger Dymock / Wikimedia Commons)

However, if your comet or asteroid is in an Earth-crossing orbit, it will create a meteor shower.

The orbital path of Comet Swift-Tuttle, which passes perilously close to crossing Earth’s actual path around the Sun. While there is no danger to Earth for at least ~2400 years, the meteors from the cometary debris will grace our skies every year, in the form of the Perseids, for the foreseeable future. (Howard of Teaching Stars)

Due to heating and gravity, small fragments will break off the central object, with dust and debris in between.

As they orbit the Sun, comets and asteroids can break up a little bit, with debris between the chunks along the path of the orbit getting stretched out over time, and causing the meteor showers we see when the Earth passes through that debris stream. (NASA / JPL-Caltech / W. Reach (SSC/Caltech))

Over time, this debris gets “smeared out” all along the elliptical orbital path of the object creating it.

Although, for many comets or asteroids, there is a higher density of debris associated with the location of the main body, over enough time, the debris will get smeared out along the orbit to such a sufficient degree that the meteor shower can become very consistent year-to-year. (Gehrz, R. D., Reach, W. T., Woodward, C. E., and Kelley, M. S., 2006)

When that debris collides with Earth, that creates the meteors we see.

At its peak, the Geminids can unleash nearly 200 meteors per hour under ideal conditions over the entire sky. This composite of a fraction of the sky was taken during the peak of last year’s Geminids.(Starry Earth / Stars4all of flickr)

It’s the tiny fragments of broken-apart comets and asteroids that make meteor showers, not tails at all.

NASA’s Spitzer Space Telescope captures both the debris stream (long diagonal line) that creates meteor showers, as well as the dust tail (and antitail) of Comet Encke, imaged in 2005. The debris stream is responsible for Earth’s Taurid meteor shower; the tail never crosses our orbit. (NASA/JPL-Caltech/M. Kelley (Univ. of Minnesota))

Mostly Mute Monday tells the cosmic tale of an astronomical object, discovery, or phenomenon in images, visuals and no more than 200 words.

Ethan Siegel is the author of Beyond the Galaxy and Treknology. You can pre-order his third book, currently in development: the Encyclopaedia Cosmologica.


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