Did Life Rain Down From Mars?

If life originated on Mars, it could very likely have hitchhiked to Earth aboard itinerant bits of rock blasted off the Martian surface by meteors or comets and flung out into the solar system, an international team of experts has concluded. Conversely, life could have gotten to Mars from Earth via the same interplanetary parcel service.

It is far less likely--but by no means impossible--that microbes or other living things arrived here from a planet of another star. "The possibility," team members told the 195th meeting of the American Astronomical Society in Atlanta last week, "is small, but not exceedingly small."

The notion that life immigrated to Earth (or elsewhere) from another part of the cosmos has been suggested by several distinguished scientists, often under the rubric "panspermia," a term suggesting a sort of universal seeding system. Early calculations of the probability of such an event were not encouraging.

Recently, however, scientists from diverse fields in five countries decided to combine their analyses of key factors to provide a more accurate estimate. Some examined how well microbes could survive the vacuum and radiation hazards of interplanetary space as well as the horrendous acceleration (tens of thousands of times the force of Earth's gravity) required to travel via meteoroid. Their result: A rock about one meter in diameter could shelter a bacterium sufficiently from heat, cold and cosmic rays.

As for opportunity, Mauri Valtonen of Turku Observatory in Finland said that there were about 50 billion "potentially life-carrying landings from Mars to Earth" during the first 500 million years of the planets' existence, versus less than one such arrival from another solar system.

In fact, the amount of Mars turf arriving here may be surprisingly high. Of all the material blasted off the Martian surface by comets and asteroids, about 0.7 percent ends up falling on Earth "within a million years from the time of impact," said Curt Mileikowsky of the Royal Institute of Technology in Stockholm.

Both Valtonen and Mileikowsky noted that Mars may have developed conditions favorable to life earlier than Earth did. "It raises the question of whether we are really Martians ourselves," Valtonen said.

Asteroid Impact Chances Halved

The universe may be a safer place for planet Earth than astronomers had thought. A new survey has found that there are far fewer dangerous asteroids hurtling through space that could hit Earth and cause widespread devastation.

Previously, astronomers had estimated that there were between 1,000 and 2,000 asteroids at least two-thirds of a mile in diameter that could potentially slam into our planet. That meant there was a 1 percent chance of a catastrophic collision with Earth in the next million years.

In the new analysis, researchers from Yale University and the Jet Propulsion Laboratory in California used a telescope on the summit of Haleakala Crater on the Hawaiian island of Maui to conduct a detailed, automated inventory of the heavens. Based on the findings, the researchers calculated that the total number of potentially devastating asteroids is about half the earlier estimates--about 700.

In addition, the researchers estimate that at the current rate that scientists are discovering new "near-Earth" asteroids, 90 percent probably will have been detected within the next two decades.

Nevertheless, in an editorial accompanying the new research in the Jan. 13 issue of Nature, David Jewitt of the University of Hawaii notes that "we still have no effective means of detecting" all potentially threatening asteroids "and no form of self-defense" if one were spotted heading toward Earth. A person has about a 1-in-20,000 chance of being killed by an asteroid impact, which is "similar to the likelihood of being killed in an airplane accident," he said.

"What is needed is a more ambitious survey to completely identify the population of small, potentially threatening" near-Earth asteroids, he wrote. "If not, it seems we will have to face the asteroidal impact hazard with our eyes wide shut."

For Short Men, a Tall Order

In case there was any doubt, tall men really do get more women, at least in Poland, according to new research.

British and Polish researchers analyzed medical records for 3,201 men age 25 to 60 who underwent medical examinations between 1983 and 1989. Bachelors were about an inch shorter on average than married men and childless men were on average 1.2 inches shorter than men who had at least one child.

"When all other variables are held constant, childless men are significantly shorter than those who have at least one child," the researchers write in the Jan. 13 issue of Nature. "We demonstrate that taller men are reproductively more successful than shorter men, indicating that there is active selection for stature in male partners by women."

On Really Thin Ice

Chemists have created the world's smallest pieces of ice. Roger E. Miller of the University of North Carolina in Chapel Hill and a student used liquid helium to produce the ice, which consists of only six molecules of water in flat hexagonal rings, just as ice exists in nature.

The researchers performed the work to learn more about water. "Despite the fact that water is so important to us, we still don't have a really good molecular-level understanding of it," said Miller, whose work is reported in the Jan. 14 issue of Science.

For example, water becomes less dense as it freezes, unlike almost all other substances, he said. That's why ice floats.

"We know that when it freezes, water forms a unique hexagonal ring structure, which accounts for its low density and the fact that it floats in water. Understanding the hydrogen bonding forces that align the water molecules in this way is our goal," Miller said.

Very small pieces of ice are easier to study, he said.