Interplanetary weather forecast: increasing cloudiness According to new observations, our solar system lies in a neighborhood that's pretty empty. Extremely empty, in fact. The interstellar gas around the solar system is hot (7,000 degrees Kelvin), fast-moving (16 miles per second relative to the sun), and thin (containing an average of one hydrogen atom per 10 cubic centimeters).

Jeffrey Linsky and his colleagues at the University of Colorado have mapped the interstellar medium from spectroscopic (defined) readings from 18 nearby stars, and measuring places in the spectrum where specific wavelengths are absorbed. From knowledge of which species of particle absorbs which wavelength, he calculated how many of those atoms lie between the star and the observation point -- Earth. Using that data (they're admittedly incomplete, but a good starting point), it was fairly simple to approximate the size and shape of clouds of interstellar gas, although some astronomers doubt that the cloud has the egg shape he assumed. Pink shows the current cloudlet surrounding Earth. Arrows indicate lines of sight to stars used to explore the cloud. The view is from the center of the Milky Way, which is shown in orange. Courtesy Drs. Jeffrey Linsky, Nikolai Piskunov and Brian Wood. Some areas outside the present cloud have even lower densities of hydrogen atoms. But if you head toward the nearby stars in Alpha Centauri, you'll find something ominous -- a denser cloud heading toward us -- fast. Do you have a problem with that?

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