PASADENA, Calif., July 19 (UPI) -- U.S. scientists have determined Saturn's moon Iapetus is cryogenically frozen in the same state as it was more than 3 billion years ago.

Researchers at the U.S. National Aeronautics and Space Administration's Jet Propulsion Laboratory gained the latest information about Iapetus when the Cassini orbiter -- part of the Cassini-Huygens space probe -- flew by Iapetus in early 2005 and discovered the moon had a walnut shape, with a chain of mountains along its equator.

Scientists said they believe the moon's bulge and slow spin rate point to heating from long-extinct radioactive elements present when the solar system was born.

Dennis Matson, Cassini project scientist at JPL, said scientists calculate Iapetus originally rotated much faster, giving the moon an oblate shape. By the time the rotation slowed, the outer shell of the moon had frozen. Since the excess surface material was too rigid to go back smoothly into the moon, it produced equatorial mountains.

"This is the first direct evidence of the early spin history for a satellite in the outer solar system," said Matson.

Cassini's next close encounter with Iapetus will occur Sept. 10 at 620 miles.

The research appears online in the journal Icarus.

Engineered E. coli may lead to new drugs

PRINCETON, N.J., July 19 (UPI) -- U.S. scientists said the creation of bacteria that respond to human hormones may lead to new treatments for such hormone-related ills as thyroid disease.

Developed by Princeton University chemists, the engineered bacteria might also detect hormone-mimicking pollutants, which can disrupt normal processes in the body.

Assistant Professor David Wood and Georgios Skretas, who earned his doctorate at Princeton in 2006 and is now at the University of Texas-Austin, designed the bacteria by linking the proteins that bind to estrogen with a protein required for growth in E. coli.

That design allows researchers to distinguish between compounds that stimulate the receptors and those that block them simply by observing bacterial cell growth. Since the bacteria respond quickly -- typically within about 15 hours -- they should be able to rapidly screen thousands of compounds that affect estrogen's activity, making an important contribution to the drug discovery process, Wood said.

"Our system is also very good at detecting weakly binding substances, which is essential for the identification of hormone-like pollutants, which are found in many substances, including plastics and cosmetics," he said.

The study appeared online June 15 in the Journal of the American Chemical Society.

Scientists work to create nanogenerator

ATLANTA, July 19 (UPI) -- U.S. scientists are developing a nanogenerator -- a tiny device that produces electricity from flowing blood, pulsating blood vessels, or a beating heart.

Zhong Lin Wang and colleagues at the Georgia Institute of Technology said such a device could power implantable biomedical devices and other small electronics, as well as holding promise for biosensing, environmental monitoring and personal electronics.

The researchers said they have so far created a nanodevice that is able to generate electricity while immersed in biological fluids or other liquids, using ultrasonic waves as the energy source.

"It sets a solid foundation for self-powering implantable and wireless nanodevices and nanosystems in biofluid and any other type of liquid," Wang and colleagues said.

The research is reported in the Aug. 8 issue of the journal Nano Letters.

NASA offers online space station guide

WASHINGTON, July 19 (UPI) -- The International Space Station is now accessible in cyberspace, the National Aeronautics and Space Administration announced Thursday.

NASA has launched its Interactive Space Station Reference Guide -- a tool that provides in-depth views both inside and outside the orbiting laboratory.

The guide provides an up-to-date interactive overview of the station's complex configuration, design and component systems and includes a video introduction and narration by NASA astronaut Mike Fincke, who lived aboard the station for six months as an Expedition 9 science officer and flight engineer.

The NASA interactive guide also explains how space station crews eat, sleep and exercise while in orbit; how the space station is built and operates; and a 360-degree tour of the station with a view of each of the station's pressurized modules.

A library of printable fact sheets providing up-to-date information about the station is also available.

The guide is available at http://www.nasa.gov/station.