Perseid Meteor Shower Peaks Sunday And Monday, 10 To 40 Tons Of Material Incoming

 

Larger meteoroids cause bright flashes of light when they hit Earth’s atmosphere, such as this fireball caught during the Perseid meteor shower Aug. 12, 2006. The bulk of meteoric activity is much less showy: Some 10 to 40 tons of meteor dust enter our atmosphere every day.

Image Credit: Courtesy of Pierre Martin

The big showers like the Perseids, and later the Leonids in November, are caused when Earth and its atmosphere travels through a region of the sky filled with left over debris lost by a particular comet. In the case of the Perseids, the small fragments were ripped of the tail of comet Swift-Tuttle, which orbits the sun once every 130 years. The fragments light up due to the immense friction created when they plough into the gas surrounding Earth. Each such fragment is approximately the size of a dime, but the more constant, sporadic meteoroids have been around much longer, breaking down over time into tiny fragments only about as wide as a piece of human hair.

“This is interplanetary dust,” said Diego Janches, who studies micrometeoroids at NASA’s Goddard Space Flight Center in Greenbelt, Md. “The fragments are either remnants from the solar system’s formation, or they are produced by collisions between asteroids or comets from long ago.”

Janches researches such tiny meteoroids using radar systems set up around the globe, in places such as Sweden, Puerto Rico and Alaska, or the radar system he deployed and operates in Tierra Del Fuego, Argentina. These fragments plough into Earth’s atmosphere at speeds of between 7 to 44 miles per second. They also bring with them minerals and metals from their parent bodies, such as sodium, silicon, calcium and magnesium.

“The small meteoroids feed the atmosphere with all these extra materials,” Janches said. “They come in, release metallic atoms that get deposited in the mesosphere and then get pushed around from pole to pole by the general global circulation. So by using the metals as tracers, you can answer some important questions about the general composition and movement of the atmosphere.”

The radar systems set up around the world can track such motion. The meteors collide with atoms in the atmosphere and leave behind a path of electrons and charged particles. This electrically charged region acts as a perfect mirror for radar waves, so the radar bounces back carrying both position information and Doppler shift information. This can be used to measure speed and direction of the background atmospheric winds at the altitudes where the meteoric tails are produced, between 40 and 60 miles high in the sky. Because there are so many such trails, they can be used to measure the velocity and direction of the winds continuously, helping to map out very complex wind patterns on a minute-by-minute basis.

Similar techniques, but using lasers, can be used to map how something like sodium sweeps through the entire atmosphere, thus tracing the global circulation system. This system also sweeps the meteoric dust to the poles where, during the summertime, they can serve as nuclei for ice crystals in the sky forming what’s called night-shining or noctilucent clouds.

 

This shower, part of the debris stream of comet Swift-Tuttle, actually starts in mid to late July and extends for most of August each year.

 

Perseid photo courtesy Flickr user Sean Rosencranz

 

However, while there will only be a few meteors each hour most of those nights (if you are lucky!), the peak time for viewing the shower will bring many, many more. How much more? The number actually varies every year; there can be as little as couple dozen per hour, or there can be up to one hundred beautiful “shooting stars” per hour.

Contacts and sources:
Karen C. Fox
NASA’s Goddard Space Flight Center