- There are twice as many asteroids between Mars and Jupiter
as previously believed, according to the latest study. But the probability
of a stray one colliding with Earth remains negligible.
-
- Edward Tedesco of US research company TerraSystems Inc.and
Francois-Xavier Désert of the Astrophysical Laboratory in Grenoble,
France, found that there are between 1.1 million and 1.9 million asteroids
swarming round the 'main asteroid belt'1.
-
- Astronomers have previously studied individual asteroids,
but Tedesco and Désert are among the first to perform a large-scale
survey. They used the European Space Agency's Infrared Space Observatory
to observe a small region of the asteroid belt and extrapolated the number
of asteroids to estimate the total number.
-
- The study offers a "snapshot of the main belt",
says Thomas Mueller, an astronomer at the Max Planck Institute in Munich,
Germany. But the possibility of a collision with Earth remains minimal,
according to Mueller.
-
- Fears of a possible impact were raised last week2 when
scientists forecast that there is a slim chance of a collision in 2880.
It will take years before astronomers can discover the precise pathway
for each asteroid in the belt, says Mueller, but this should not be a cause
for concern. "The majority of all orbits of asteroids are relatively
stable over millions of years and will not cross Earth's orbit," he
says.
-
- Asteroids are faint and difficult to pin down with telescopes
that detect visible light. Tedesco and Désert overcame this obstacle
by measuring the infrared that the asteroids emit. They developed a mathematical
model to estimate the entire population of asteroids based on those in
a selected area of the belt. "It is a new method to derive an inventory
of our Solar System," says Mueller.
-
- Diverting Disater
-
- If stray asteroids do end up on a collision path with
Earth they could be deflected by changing the amount of sunlight they reflect,
a second study has suggested3. When an unevenly heated body re-radiates
heat, it alters the momentum of an object - this is called the Yarkovsky
effect. This could be used to deflect an asteroid slightly in its orbit,
according to Joseph Spitale, a planetary scientist at the University of
Arizona.
-
- But executing this deflection might be easier said than
done. Spitale suggests coating the asteroid with a blanket of dirt 1 centimetre
deep to change its surface heat conductivity, or using a small amount of
explosive to modify the surface. "Their precise implementation is
open to debate," he says.
-
- References
-
- Tedesco, E.F. & Désert, F-X.The Infrared Space
Observatory Deep Asteroid Search. The Astronomical Journal, 123, 2070 -
2082, (2002). Giorgini, J.D. et al. Asteroid 1950 DA's encounter with Earth
in 2880: physical limits of collision probability prediction. Science,
296, 132 - 136, (2002). Spitale, J.N. Asteroid hazard mitigation using
the Yarkovsky effect. Science, 296, 77, (2002).
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- © Nature News Service / Macmillan Magazines Ltd
2002
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