Number 251, December 7, 1995 by Phillip F. Schewe and Ben Stein
GALILEO ARRIVES AT JUPITER TODAY after a 6-year, 2.3-billion mile journey.
At this hour the craft is proceeding normally (at a relative speed of more
than 22,000 mph) toward its rendezvous. The spacecraft's first job will
be to receive data from a small detachable probe sent on ahead and now
parachuting into Jove's atmosphere. Data will later be relayed back to
Earth (radio waves take 52 minutes to span the distance) at a rate of only
10 bits per second, a constraint which comes about because of the defective
main antenna. Launched in 1989, Galileo's 2-year mission at Jupiter will
include repeated close-up flybys of several moons. The latest information
on Galileo can be found at the following World Wide Web address: http://www.jpl.nasa.gov/galileo.
THE COOLEST AND LOWEST-MASS BROWN DWARF yet has been discovered in the
Lepus constellation by astronomers from Caltech and Johns Hopkins. Brown
dwarfs are star-like objects which do not possess enough mass to sustain
fusion reactions. They might vastly outnumber regular stars but are hard
to spot because they're so dark. Indeed astronomers suspect that brown
dwarfs lose whatever energy they may have produced within 100 million years.
Therefore searches are conducted among nearby, relatively young stars.
The newly discovered brown dwarf, a companion to star G1229, has an estimated
mass 20-50 times that of Jupiter. Its temperature was deduced to be less
than 1200 K because of the presence of methane in the object's spectrum;
at higher temperatures carbon likes to form CO2, while at lower temperatures
it prefers forming CH4. (T. Nakajima et al., Nature, 30 November 1995.)
140-GeV INTERACTIONS AT LEP . The upgraded Large Electron Positron (LEP)
collider at CERN last month achieved the highest collision energy yet for
an electron-positron machine. By 1998, the energy should reach 196 GeV.
Working in a new energy regime, particle physicists are always eager to
find something new, such as supersymmetric particles. According to supersymmetry
theory, all fermions (such as electrons and quarks) would have boson counterparts
and vice versa. (Science, 24 November 1995.)
SILICON SUPERLATTICES EMIT LIGHT . Silicon, the backbone of the electronics
industry, produces light only grudgingly, a shortcoming which works against
the integration of photonics and electronics. Optoelectronic devices can
be made from other semiconductors, such as gallium and arsenic, but many
engineers would like to retain the well-tooled technology that has built
up around silicon over the years. Porous silicon, silicon etched by acid
into a forest of thin filaments, emits light, but the physics mechanism
behind this phenomenon is not yet well understood. Now scientists at the
National Research Council in Ottawa, Canada have gotten tiny stacks of
alternating Si and SiO2 films to emit visible light. The researchers were
able to change the wavelength of the light by varying the thickness of
the Si layers. (Z.H. Zu et al., Nature, 16 November.)
PHYSICS NEWS UPDATE MAILING LIST: You can add or subtract yourself automatically
by sending a message to listserv@aip.org. In the body of the message specify
either "add physnews" or "delete physnews."
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