A brief on yesterday's Science page stated incorrectly that farmers already inject pigs with a naturally occurring hormone to make the animals grow bigger and faster. Researchers are investigating ways to artificially boost the growth rate and size of farm pigs. (Published 12/14/99)

Mars Had an Ocean, Data Show

Astronomers have found new evidence that a vast ocean existed on Mars hundreds of millions of years ago.

James W. Head III of Brown University and colleagues studied data collected by the Mars Global Surveyor spacecraft, which is orbiting the Red Planet and fires laser pulses to the surface to gather high-resolution data about the planet's topography.

The data indicate that an ancient shoreline remains on Mars around the northern third of the planet and that waves once lapped at a coast, suggesting a massive ocean was once there, the researchers report in the Dec. 10 issue of Science.

Terraces parallel to the apparent coastline also indicate a large body of liquid water was once there. In addition, the area within the shoreline has relatively few craters, indicating it might have been protected at some period by a deep layer of water or the craters could have been smoothed over by the movement of water.

Scientists believe that Mars's climate was once very much like Earth's, but that it changed dramatically millions of years ago to make it the cold, forbidding place it is today, for reasons that remain a mystery.

One of the main goals of recent exploratory missions to Mars, including the lost Mars Polar Lander, was to search for evidence that liquid water once, or still does, exist on the planet. Water is considered essential to support life there, either in the past or today.

Bacteria Deep in Antarctic Ice

Biologists in recent years have been finding primitive forms of life thriving in the most surprising places on Earth--around hot vents at the bottom of the ocean, deep in the Earth's subsurface and in geothermal pools in Yellowstone National Park. Now, researchers have again been surprised--finding evidence of bacteria deep in Antarctic ice above a freshwater lake that lies beneath the thick frozen surface.

Two teams of scientists found evidence of bacteria living in ice above Lake Vostok, a subglacial body of water the size of Lake Ontario that is one of the deepest bodies of water on Earth and is located more than two miles under the East Antarctic ice cap.

"From a biologist's perspective, this is the Holy Grail of lake biology," said John Priscu of Montana State University, who led one of two groups that report their findings as part of a trio of research papers in the Dec. 10 issue of Science. "Our findings indicate that the microbial world has few limits on our planet."

The ice core, 18 inches long and 4 inches wide, was drilled from 11,800 feet into the ice sheet and 393 feet above where the ice and the waters of Lake Vostok meet, suggesting life can survive cut off from nutrients and light.

The bacteria are similar to those known as proteobacteria and actinomycetes, which are usually found in soil. They could have been blown into the lake on bits of soil and then buried, which means they could have been there for more than a half-million years. Another possibility is that the microbes originated in the lake and became trapped there as water froze.

The existence of such "extremophiles" in Lake Vostok and elsewhere has given scientists hope that life could exist in similarly forbidding conditions on other planets. For example, one of Jupiter's moons, Europa, may have frozen oceans.

Fatter Pigs, Taller People?

Researchers have found a way to make pigs grow faster that may be a boon to farmers and could be useful for helping abnormally short children reach normal height.

Farmers already inject pigs with a synthetic version of a naturally occurring hormone known as growth hormone that makes the animals grow bigger and faster. But large doses of the hormone can cause problems, including malformed organs and deformed bones. Synthetic human growth hormone also is used to treat some human children, although that practice is controversial when used on children who are not unusually short.

Robert J. Schwartz of the Baylor College of Medicine in Houston and colleagues injected pigs with DNA that carries instructions for the production of a hormone known as protease-resistant growth hormone-release hormone.

Pigs injected with the DNA produced high levels of their own growth hormones, grew faster and were 22 percent heavier than normal. After 65 days of treatment, no side effects emerged, the researchers report in the December issue of the journal Nature Biotechnology.

The approach could enable farmers to use less feed and bring animals that produce less manure to slaughter more quickly. Moreover, a similar approach may be useful for treating children who are not growing properly, the researchers said. But much more research is needed.

Teeny Tiny Tweezers

Scientists have fashioned the world's smallest pair of tweezers.

Charles M. Lieber of Harvard University and a colleague crafted a pair of "nanotweezers" by attaching two bundles of carbon "nanotubes" to either side of a glass rod. The bundles, a mere 50 nanometers in diameter, open and close when a small volt of electricity is applied. In tests, the tweezers could manipulate polystyrene spheres 300 nanometers in diameter and semiconductor wires 20 nanometers in diameter.

"Compare a single hair from your head . . . to a giant redwood tree--your hair will seem like a redwood tree next to the nanotube and the objects it can manipulate," Lieber said in an e-mail message.

The device is just the latest tiny tool that researchers have developed to manipulate individual molecules in the growing field of "nanotechnology," in which scientists hope to build extremely small devices on the molecular level.

"The results described here demonstrate that nanotube nanotweezers can be used to manipulate individual nanostructures and directly probe their electrical properties," the researchers write in the Dec. 10 issue of Science.