Notes from the 151st annual meeting of the American Association for the Advancement of Science last week in Los Angeles:

Ever since science fiction writers discovered the asteroid belt, which lies between the orbits of Mars and Jupiter, they have depicted it as dangerous territory for space travelers, a flying thicket of mountain-sized rocks.

In truth, a Hawaiian geologist said, the asteroid belt is largely empty. It does contain some 50,000 huge rocks -- some as big as Texas, as he put it -- but they are scattered so widely that the average distance between them is a comfortable 1 million to 2 million miles.

In fact, according to Jonathan Gradie of the University of Hawaii, the asteroids, orbiting around the sun, are so far apart that collisions between them probably occur no more than once every few million years.

The asteroid belt, along with other often-neglected members of the solar system, such as meteorites and comets, are receiving more attention from scientists as they prepare for the arrival of Halley's Comet, which is expected to become visible in December.

Mutations, the random alterations in genes that produce evolutionary change, cannot have occurred at a steady rate as many evolutionists have assumed, a Calfornia geneticist said.

Instead, mutations must have come in clusters separated by long quiet periods.

His claim, based largely on mathematical analysis, challenges a widely held assumption in evolution theory, which holds that mutations arise at a random but fairly steady rate.

Evolutionists hold that most mutations, regardless of rate, do not contribute to evolutionary change; they are either deleterious or alter nonessential regions of DNA, producing neutral mutations.

A steady rate had been assumed by the inventors of the "evolutionary clock," a method of measuring how long ago two species shared a common ancestor. Because the mutation rate was assumed to be constant, it was held that the time since the split could be calculated as proportional to the number of mutational differences.

The new report, by John H. Gillespie of the University of California, Davis, does not invalidate the evolutionary clock but it does question its accuracy.

A Soviet spacecraft orbiting Venus has discovered huge circular features on that planet's surface near its poles, a Brown University planetary scientist reported.

The circles, measuring 180 miles to 300 miles in diameter, lack the profile of impact craters and, James Head said, may be caused by upwellings of molten rock from Venus's interior that push against the hard crust, making it bulge as the molten rock flows off to the sides in all directions without breaking through.

Similar upwellings are thought to occur in the Earth as heated magma, being less dense, rises, presses against the cold crust above and then slips sideways, cooling and sinking again. These convection currents, similar to those in the atmosphere, are thought to carry Earth's rigid crustal plates sideways, making continents drift.

A possible relationship between erotic material and violence against women has long been debated.

A study by scientists at Yale University and the University of New Hampshire concludes that "the greater the support for legitimate violence and the greater the readership of pornography, the higher the rape rate."

Larry Baron and Murray Straus looked at state variation in reported rape rates, the sales of mass-circulation sex magazines and cultural support for what they called "legitimate violence" as measured by such things as hunting licenses, National Guard expenditures, death sentences and executions, the viewing of violent television shows and the circulation of magazines depicting violence.

They found the rape rates highest in western states, which also had the highest sex-magazine circulations and socially acceptable use of violence. Nevada, which has the highest rate of sexual assault in the country, scored high in both categories.

But, they said, the percent of men who are divorced and not remarried, income inequality and urban location were more strongly linked to state differences in rape rates.

They cautioned against censorship efforts, saying pornography reflects the underlying social climate but is not a direct cause of rape.

A study by two University of Wisconsin, Madison, researchers also found that movies depicting violence against women may increase male aggression, result in more negative attitudes toward women and perpetuate myths about rape.

Vincent van Gogh was an amateur astronomer.

The French artist's impressionistic work "Starry Night," one of the most widely reproduced paintings in the world, is often described as a "hallucinatory or visionary work," said Albert Boime of the University of California at Los Angeles art department.

But he and colleagues in the astronomy department think that the picture closely depicts the eastern portion of the sky over Saint-Remy at about 4 a.m. on June 19, 1889.

That was the day van Gogh wrote that he made the painting, Boime said. He was then confined to a cell in the upper story of the Saint-Remy mental asylum.

Boime said the director of the Griffith Park Observatory used the Zeiss Planetarium projector to recreate that night sky.

"While he may have exaggerated scale and distance, van Gogh tried to paint the sky as he perceived it from his window at Saint-Remy," he concluded.