formed reliably. The National As­sociation of Criminal Defense Law­yers has set up a committee on DNA fingerprinting to spread the word.

"A goal of the committee is to ensure that counsels for each of the defendants in past DNA cases will have access to the briefs and tran­scripts in the Castro case and the opportunity to reopen their case if warranted," says Scott Wallace, the association's legislative director.

Pamela Zurer

Voyager to give first close look at Neptune This week the final chapter in Voy­ager 2's historic planetary saga will be played out as the plucky space­craft swings past Neptune, currently the outermost planet of the solar system.

This first-ever closeup look at Neptune and its largest moon, Tri­ton, both of which are difficult to observe from Earth, is expected to revolu t ionize unde r s t and ing of these mysterious objects.

Voyager 2, which has already visited Jupiter, Saturn, and Uranus, will swoop to within 3000 miles of Neptune's cloud tops at midnight, eastern time, Aug. 24. Five hours later, it will pass within 24,000 miles of the frigid surface of Triton, the only large moon in the solar system that orbits in a direction opposite to its planet's rotation.

In recent weeks, as Voyager has been closing in on its target, it has begun offering scientists a taste of things to come. Images from the spacecraft have revealed four new moons in orbit around the pale blue planet, bringing to six the total num­ber of known moons. Voyager has also provided the first photograph­ic evidence of the existence of two ring arcs, or partial rings, around Neptune. These peculiar arcs, which apparently are associated with two of the new moons, had been antici­pated from occultation studies con­ducted on Earth. Voyager scientists expect to find additional ring arcs and tiny moons as the spacecraft nears the planet.

"So far, the pictures show Nep­tune is a far more photogenic plan-

Neptune, as photographed by Voyager 2 camera from 29 million miles away, shows its great dark spot and a southern dark band

et than Uranus," says Bradford A. Smith of the University of Arizona, who heads the Voyager imaging team. A large dark spot and several smaller features have been photo­graphed. These atmospheric fea­tures, besides giving Neptune a more interesting visage than Uranus', will aid scientists in studying its global circulation.

Planetary scientists have been gearing up for the Neptune ren­dezvous by making a host of chem­ical and other predictions about what the spacecraft will find. Nep­tune, they believe, is composed pri-

Progress in U.S.-Soviet talks on nuclear testing

marily of hydrogen, and its clouds may consist of methane and water ice. One group recently predicted that Neptune's stratosphere contains an ethane-acetylene haze.

Neptune is expected to have a magnetic field—as do Mercury, Earth, Jupiter, Saturn, and Uranus— and it may be much stronger than Earth's. It should be detected about one day before Voyager's closest ap­proach to the planet. Because no radio emissions from Neptune have so far been detected, some scien­tists predict that Neptune's magne-tosphere (the area around the plan­et in which the magnetic field in­teracts wi th the solar wind) is "almost completely quiescent."

Much of the scientific interest is centered on Triton, which is pre­dicted to have methane ice and sol­id or liquid nitrogen on its wind­swept surface. Like Titan, the larg­est moon of Saturn, the ruddy color of Triton is believed to be due to a rich organic sludge resulting from chemical reactions between hydro­carbons and nitriles in its atmo­sphere. Triton's atmosphere proba­bly supports a photochemical haze, but scientists expect it to be thin enough to allow Voyager's cameras to see the moon's surface clearly.

Ron Dagani

U.S. and Soviet negotiators have just concluded what they consider a pro­ductive fourth round of talks aimed at achieving ratification of a 1974 agreement that limits the size of underground nuclear weapons tests to 150 kilotons or less. A modified protocol could be ready for Senate consideration sometime next year.

In a separate, but related, devel­opment, a joint seismic research pro­gram initiated by the Soviets and a private U.S. group is being brought under more official U.S. auspices and expanded. All data from this program will continue to be freely available to scientists worldwide, primarily for earthquake research and prediction. However, the data will contribute toward the scientif­ic underpinning needed for moni-

Workersprepare nuclear weapon for detonation at Nevada Test Site

August 21, 1989 C&EN 7