Sun Hits a 50-Year Low

Sept. 23, 2008 -- The sun is taking a once-in-a-century nap, say solar researchers. The sun's wind of hot particles is now blowing with less vigor and less heat than at any time since the start of the Space Age in the mid-20th century, according to data collected by the 18-year-old Ulysses spacecraft.

As a result, the cozy bubble of charged solar particles that fills the solar system is shrinking, exposing Earth and other planets to the onslaught of needling galactic cosmic rays which are normally held at bay by the solar wind.

"It's a big deal," said Nancy Crooker, solar researcher at Boston University. "It's the first time we've measured these conditions. It's expanding our horizons of what we can do and compare."

The sun is presently at the lowest point in its 11-year cycle of sunspot activity, but it's also 20 percent cooler and less windy than the last solar minimum in 1994-95, explained Karine Issautier, the Ulysses radio wave lead investigator at the Observatoire de Paris, Meudon, France. In other words, the sun is showing signs of other, much longer cycles which also affect its power output.

The sun is also hitting an all-time low for its wind speed and pressure, blowing at 25 percent less than at the last solar minimum, reported Southwest Research Institute's David McComas, principal investigator of the solar wind instrument on Ulysses.

"The pressure of the solar wind is like air filling up a tire," said McComas. "It inflates a bubble in space…This is the lowest prolonged pressure that we've ever observed."