On the horizon

Quake signals

Faint rumblings from deep beneath California's San Andreas fault may provide an early warning for significant earthquakes there.

Scientists from the University of California at Berkeley discovered the weak tremors during a long-term monitoring project on the San Andreas near Parkfield, Calif. The tremors lasted from four to 20 minutes and occurred far deeper in the crust than earthquakes.

This marks the first time these tremors have been detected along a boundary where segments of crust grind past each other, as they do along the San Andreas, according to the team, whose research appears in the current issue of the journal Science.

The Mars rover Spirit has found goethite - a mineral linked to water - during its exploration of the Red Planet.

Although both rovers have found such evidence in their nearly year-long treks, the goethite find is particularly important, NASA's Jet Propulsion Laboratory (JPL) said Monday. The mineral forms only in the presence of water, although it may be in liquid, ice, or gas.

On the other side of the planet, Opportunity has recently seen frost and clouds marking seasonal changes, according to a science team member of the Space Science Institute.

For years, scientists and environmentalists have pointed to farm runoff as a leading culprit for harmful blooms of algae off the coasts of North America. But they didn't have the evidence to convince some members of the farming industry that agricultural chemicals were triggering "red tides" or "dead zones" in coastal waters.

Now, a team from Stanford University has drawn the link using satellite images. Examining images of Mexico's Yaqui River Valley, a productive coastal wheat-growing area whose river empties into the Gulf of California, the team found coastal algae populations exploded within days of what it called "irrigation events." The blooms covered up to 223 square miles of sea surface and lasted for days.

The team is planning additional studies to find out whether the blooms are causing ecological damage. The results were presented this week at the annual meeting of the American Geophysical Union in San Francisco.

Two orbiting telescopes have captured images of solar systems at key stages of formation. The observations establish "the first direct link" between planets and the disks of raw material for planets that surround stars, says Charles Beichman, chief scientist for astronomy and physics at NASA's JPL.

Astronomers used the Hubble Space Telescope and the Spitzer Space Telescope, an infrared telescope launched in August 2003. Hubble snapped images of a debris disk around a sun-like star thought to be young enough to host gas-giant planets but too young for rocky planets to have formed. It also captured a disk around a nearby dwarf star with a gap, where astronomers suspect a planet has bulldozed a path.

The Spitzer data include six stars known to have planets. The disks around these planets appear to represent the rubble left from planet formation. These disks have been tough to spot around sun-like stars because they are so faint.