On almost any dark, clear night
away from city light pollution, even the casual sky observer may see one or
several “shooting stars.” Tiny bits of rock, typically less than an inch
across, create these brief streaks of light. The rocky bits move so quickly
through the air that they create a huge amount of friction, heating the air to
incandescence which creates the streak of light.
Eventually, the cosmic rock is
broken into tiny dust particles which float serenely down to the surface of our
planet. This cosmic dust comes primarily from two sources. A research team
studying this phenomenon, led by Julien Rojas, a doctoral student at the University
of Paris–Saclay, found that more than 60% of the dust originates from the
family of comets that Jupiter’s huge gravitational pull herds into orbits of
less than 20 years and which can pass close to Earth’s orbit. Another 20% of
the dust likely came from the main asteroid belt.
Astronomers want to know just how
much of this cosmic dust Earth accumulates each year. But the problem is that
with dust constantly blowing around all over our planet, it becomes virtually
impossible to separate space dust from Earthly dust.
There is one place where
terrestrial dust does not contaminate extraterrestrial dust, Antarctica. The
study team collected ice cores from that continent in an attempt to quantify
the amount of cosmic dust landing on our planet each year. And, because the
snow and ice cover there can be melted, it is easy to separate the tiny dust
particles from the otherwise dustless environment. Jean Duprat, a cosmo-chemist
and co-author of the study, said “The South Pole is by far the best location because
you are surrounded by oceans, you are completely isolated from mainlands.”
Extrapolating the three-year study of
Antarctic cosmic dust measurements to the entire planet, the team found that
between 4,000 and 6,700 metric tons of space dust falls to Earth each year. Rojas
explained that the study’s range is simply a matter of statistics due to the
inherent difficulty of extrapolating the worldwide accumulation from a series
of limited, local measurements. “Depending on the volume of snow,” Rojas said,
“you would expect a certain uncertainty by just counting the particles.”
Between 4,000 and 6,700 tons a
year! And you think you have a problem keeping weight off.
Each month, I write an astronomy-related column piece for the Oklahoman newspaper. On the following day, I post that same column to my blog page.
