When Earth's annual orbit around the sun crosses this trail, bits of debris enter the atmosphere from the direction of the constellation Lyra. Stargazers see them as fiery streaks of light, or shooting stars.
When Earth hits a fresh dust trail, a meteor outburst can be seen. In 1803 stargazers were treated to a storm of about 700 Lyrids per hour. The Lyrids were also intense in 1922 and 1982. Based on an analysis of comet Thatcher's debris trail, Jenniskens predicts that there will also be heightened Lyrid activity in 2040 and 2041.
"Sadly, the debris streams from all long-period comets usually stick around for just one revolution, becoming dispersed perpendicular to the comet orbit by the second revolution," Jenniskens said.
This rapid spreading occurs due to the gravitational tug exerted by Jupiter, which causes dust trails to wag in and out of Earth orbit. Jupiter's gravitational tug can also dramatically alter the orbital period of the debris. Different sections of dust trails catch up on each other during their second revolution, creating a much broader but less dense shower.
Many astronomers consider long-period comets a huge impact risk to Earth. But since these comets sweep through the inner solar system so infrequently, very little is known about them.
This dearth of knowledge may be problematic. By the time a comet bound for Earth enters the inner solar system, it could be too late for anyone to take effective action against it.
When astronomers detect an unanticipated meteor shower, much can be learned if they record when the shower occurs and the location of the shower's radiant, Jenniskens notes. With such information, astronomers can predict when the next outburst will occur, roughly calculate the comet's orbit, and get a better feel for whether or not the comet poses a risk of impact with our planet, Jenniskens said.
"It's very important that people watch on any night of the year for this type of meteor shower," he said. "When rates coming out of one area in the sky [go up], that's when people should report it."
Jenniskens notes that Thatcher is "perhaps the shortest long-period comet" that comes near Earth orbit. Because of that, Thatcher is also the only long-period comet with a strong annual meteor shower. The debris streams of other long-period comets are too thinly spread out to produce a noticeable annual shower.
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