Number 214, February 16, 1995 by Phillip F. Schewe and Ben Stein
GAS-GIANT PLANETS SUCH AS JUPITER must grow up in a hurry. New radio
telescope observations by a UCLA-Grenoble-MIT collaboration of gas around
20 young stars show that within only a few million years of the star's
formation excess gas, which could have contributed to the formation of
planets, is lost from the juvenile solar systems. The observations suggest
that for many of these stars there would not have been nearly enough gas
to build a Jupiter, much less a Saturn. The astronomers conclude that if
Jupiter-sized planets are common in our galaxy, they must form more speedily
than current theories allow. If, however, Jupiters are rare, then the actual
presence of the gas giant in our solar system is particularly fortuitous.
George Wetherill of the Carnegie Institute believes that Jupiter and Saturn
"may be essential to life" on Earth because of their role in
sweeping up comets (e.g., Shoemaker-Levy) that might otherwise have snuffed
out life on Earth. (B. Zuckerman et al., Nature, 9 February 1995.)
CLASSIFYING GALAXIES can now be done automatically with the help of
neural-network scanners. Normally requiring the discerning eye of a human,
the designation of a galaxy's morphology on a sliding scale from elliptical
to spiral is a tedious but important job. Automating the process would
greatly help an enterprise like the Sloan Digital Sky Survey, which plans
to chart more than a million galaxies. A team of astronomers has now tested
an artificial scanner based on neural network circuits which "learn"
to recognize patterns at they go along. Given a sample of 800 digitized
galaxy images, the scanner produced a set of classifications which differed
from those of six humans by no more than the difference between the classifications
of any two humans. (O. Lahav et al., Science 10 February 1995.)
TABLETOP TESTS OF ELECTROWEAK THEORY have been performed with thallium
atoms. The theory holds that an atom's electrons interact with its nucleus
through the electromagnetic force (by the exchange of photons) and, at
a much weaker level, through the weak force (principally by the exchange
of Z bosons). Working independently, a team at Oxford, UK, and a University
of Washington team (contact Norval Fortson, 206-543-2665) carefully observed
what happened to laser light when it passes through a thallium vapor. Among
other things, both groups measure Q, the value of the "weak charge"
(somewhat analogous to electric charge) of the thallium nucleus as seen
by its outermost electron. These and other measurements of parity violation
(the weak force, unlike the electromagnetic force, differentiates between
left and right) in atoms do not yet yield electroweak values that rival
in precision those obtained at particle accelerators, but this may change
if theorists could provide a more precise picture of the quantum behavior
of the electron (as described by its wavefunction) in the thallium atom.
(P.A. Vetter et al. and N.H. Edwards et al., upcoming articles in Physical
Review Letters.)
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