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The Sciences

From Far Beyond


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Some meteors flash through our atmosphere faster than 100,000 miles per hour. Although most of the debris that shoots across the sky as meteors originates within the solar system, astronomer Jack Baggaley of the University of Canterbury in New Zealand and his colleagues have shown that at least some does not. There’s been a controversy as to whether any meteors come from interstellar space, Baggaley says. We can now say that a small proportion are not internal to the solar system.

Baggaley bounced radar signals off the trails of ionized particles left by meteors in the atmosphere. By analyzing the echoes, he calculated the speed and trajectory of more than 170,000 meteors. He found that 14 percent--too small for their trails to be seen by the naked eye-- moved at more than 164,250 miles per hour, faster than the escape velocity of the solar system. Had these grains not hit Earth’s atmosphere, they would have shot out of the solar system.

Two forces within the solar system can accelerate particles to escape velocity: radiation pressure from the sun and the boost that meteoroids get if they come near a planet. A meteoroid would be accelerated by the planet’s gravitational pull as the planet itself speeds around the sun. By noting the direction from which the meteors came, Baggaley knew that the ones he tracked hadn’t passed near a planet. And slightly less than 1 percent surpassed 225,000 miles per hour--attaining speeds unreachable by particles originating within the solar system, no matter how they’re accelerated.

After analyzing the directions from which this dust arrived, Baggaley found that it seems to have two different sources. Some apparently hits us as the solar system runs into it while orbiting the galactic center. Nearby stars with protoplanetary disks are the other likely source. Radiation from these stars would drive dust from the disks out in all directions, and some may reach us. Baggaley says that he even spotted a few meteors with speeds of up to 675,000 miles per hour. When you see a speed like that, it means that it’s not bound to the galaxy. It has come from somewhere else.

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