From: LARRY KLAES (ljk4_at_msn.com)
Date: Wed Oct 22 2003 - 07:34:17 PDT
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From: physnews_at_aip.org
Sent: Tuesday, October 21, 2003 10:09 AM
To: ljk4_at_MSN.COM
Subject: Physics News Update 658
PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 658 October 21, 2003 by Phillip F. Schewe, Ben Stein, and
James Riordon
DIRECT IMAGING OF EXTRASOLAR PLANETS might be easier than
astronomers thought, a new study shows. Evidence for the existence
of planets around nearby stars comes mostly in the form of tiny
Doppler shifts in the star's spectra as one or more orbiting planets
tug on the star. In a few cases the transit of a planet across the
face of a star can be detected from a minute dimming of the star's
emission. These approaches are indirect. The problem of imaging
extrasolar planets directly is that the planet is far outshone by
the nearby star. One proposed way of getting around this glare
problem is to use nulling interferometry. In ordinary interferometry
the light waves from two or more telescopes are added together in
such a way that the resulting observation is equivalent to one made
with a single telescope with a much wider diameter than any of the
component scopes. But instead of maximizing the composite signal
from the distant object, it can be minimized (see past Update item
at http://www.aip.org/enews/physnews/1998/split/pnu397-3.htm ). By
doing this, a weaker nearby object, like a planet, might suddenly
emerge from what had been irrepressible glare.
In a new paper, William Danchi (Goddard Space Flight Center) and his
colleagues have performed extensive studies of the interferometry
nulling technique, especially the way in which increasing the
precision of component detectors increases the degree to which the
star's image is truly nulled, the better to see either smaller
planets or planets that are closer in toward their parent star.
Both the smaller and closer criteria are pertinent when searching
for earth-like extrasolar planets. Danchi (wcd_at_iri1.gsfc.nasa.gov,
301-286-4586) says that the new study shows that with the right
configuration of detectors, the spatial resolution of the overall
interferometer (which is related to its size) can be less than have
been thought, an important consideration for what would be an
orbiting space-based observatory. Danchi envisions that a
first-round nulling interferometer using two half-meter-sized
telescopes separated by a 12-meter boom could observe already
discovered extrasolar planets (including spectroscopic studies of
atmospheres). With a later, larger version of the nulling
interferometer one could hope to search for earthlike planets
harboring characteristic molecules such as ozone, and/or oxygen,
plus carbon dioxide, water, and methane. Detecting these molecules
could help determine the age of the planet and what life processes
might be occurring there. (Danchi, Deming, Kuchner, and Seager,
Astrophysical Journal Letters, 1 November 2003; preprint
astro-ph/0309361)
EVIDENCE FOR AN UNUSUALLY ACTIVE SUN since the 1940s comes from a
new estimation of sunspots back to the ninth century. Many natural
phenomena such as solar radiance and sunspots vary according to
natural cycles. The variation is subject also to additional
fluctuations (arising from as yet unexplained effects) which
complicate any study which examines only a short time interval.
The longer the baseline, the more confident one can be in drawing
out historical conclusions. In the case of sunspots, the direct
counting goes back to Galileo's time, around 1610. But earlier
sunspot activity can be deduced from beryllium-10 traces in
Greenland and Antarctic ice cores. The reasoning is as follows: more
sunspots imply a more magnetically active sun which then more
effectively repels the galactic cosmic rays, thus reducing their
production of Be-10 atoms in the Earth's atmosphere. Be-10 atoms
precipitate on Earth and can be traced in polar ice even after
centuries. Using this approach, scientists at the University of Oulu
in Finland (Ilya Usoskin, ilya.usoskin_at_oulu.fi, 358-8-553-1377) and
the Max Planck Institute in Katlenburg-Lindau in Germany have
reconstructed the sunspot count back to the year 850, nearly
tripling the baseline for sunspot studies. They conclude that over
the whole 1150 year record available, the sun has been most
magnetically active (greatest number of sunspots) over the recent 60
years. (Usoskin et al., Physical Review Letters, upcoming article)
CAN A SINGLE GAS BUBBLE SINK A SHIP? Yes, according to an
experimental and theoretical analysis performed by researchers at
Monash University in Australia (David May and Joseph Monaghan,
Joe.Monaghan_at_sci.monash.edu.au). The ocean floor contains vast
quantities of methane gas hydrates, ice-like crystals of methane
surrounded by cages of water molecules. If disturbed, these methane
gas hydrates can erupt from the floor and rise to the surface as gas
bubbles, some of which can be very large. Copious amounts of methane
hydrates exist in the North Sea, which lies in between the United
Kingdom and continental Europe. At a large eruption site in the
North Sea known as the Witches Hole off the coast of Aberdeen, a
sonar survey recently uncovered the presence of a sunken vessel, but
the cause of the wreck remains undetermined. Simple experiments
have previously shown that many small bubbles rising to the surface
could sink a cylinder of water (and conceivably a ship), by causing
a loss of buoyancy (Denardo et al., American Journal of Physics,
October 2001). But could a single large gas bubble do the trick?
The Monash researchers investigated this possibility in a simple,
roughly two-dimensional system. Trapping water between a pair of
vertical glass plates, and launching single gas bubbles from the
bottom, they used a video camera to observe a single large bubble's
effect on a small piece of acrylic shaped like the hull of a boat.
Along with numerical simulations of this scenario, the experiments
showed that the bubble could sink the ship, if the bubble's radius
was comparable to or greater than the ship's hull. Sinking would
occur because a mound of water formed above the bubble as it
approached the surface. As the bubble reached the surface, it would
temporarily lift the ship. However, water in the mound would then
flow off the sides of the bubble, forming deep troughs at either
side, and the water flow would carry the boat to one of the
troughs. In addition, the eventual rupture of the bubble would
create high-velocity jets of fluid that moved into the troughs,
creating vortices that further pulled down the boat. The
researchers say that their numerical simulations could test other
scenarios, including those involving multiple large bubbles, more
realistic boats, and ultimately a full three-dimensional simulation.
(American Journal of Physics, September 2003).
***********
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