Madison
The Solar System may be heading for a dense patch of gas and dust that could dramatically affect conditions on Earth. Priscilla Frish of the University of Chicago told participants at last week's meeting of the American Astronomical Society in Madison, Wisconsin, that the Sun and its planets could be in for a bumpy ride—sometime in the next 50 000 years.
For most of the past five million years, the Solar System has been moving through a rather empty region of interstellar space between the spiral arms of the Milky Way. But a few thousand years ago, it entered a diffuse shell of material expanding outward from an active star-forming region called the Scorpius-Centaurus Association. Such "superbubble" shells of gas and dust result from the formation of massive stars, or the explosion of those stars as they become supernovas, and contain gas and dust clouds of varying densities.
The amount of interstellar gas heading towards the Solar System is increasing as the shell expands. "This cloud, although low density on average, has a tremendous amount of structure to it," says Frish, "and the Sun may eventually encounter a portion of the cloud that is a million times denser than what we're in now."
At present the solar wind, the flow of charged particles that streams away from the Sun, protects the Earth from direct interaction with interstellar material by enveloping it and all the other planets in the heliosphere, the region of the Sun's influence. But if the heliosphere encountered a much denser cloud, it could be compressed almost to the size of the Earth's orbit. "There would be dramatic effects on the inner Solar System," says Frish. Astronomers have suggested that such an encounter could cause changes in the Earth's magnetic field, atmosphere and climate.
Other scientists confirmed that the Sun's immediate neighbourhood is far from uniform. John Watson and David Meyer of Northwestern University in Evanston, Illinois, studied the spectra of 17 binary stars. They found that interstellar space appeared to absorb more of a particular wavelength of light from one star in a pair than from the other. Since each star in a binary system is the same distance from Earth, differences in absorption must be due to clumps of gas in the space between the two stars. They conclude that the Sun's immediate vicinity could be littered with dense pockets of gas, roughly the size of the Solar System.
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11:17 21 August 2008
