ENB No. 176 June 27 2005

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ENB No. 176 June 27 2005

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Electronic News Bulletin No. 176 2005 June 27

Here is the latest round-up of news from the Society for Popular
Astronomy. The SPA is Britain's liveliest astronomical society, with
members all over the world. We accept subscription payments online
using our secure site and can take credit and debit cards. You
can join or renew via a secure server or just see how much we have to
offer by visiting http://popastro.c.topica.com/maadF7babiaEjciD1pRb/

Philip's, a publisher of astronomy books and planispheres for the
amateur astronomer, is sponsoring this bulletin. For information on
a revised Philip's title go to the end.

Harvard-Smithsonian Center for Astrophysics

For the first time, amateur and professional astronomers have teamed
up to discover a new planet circling a distant star. The planet was
detected by looking for the effect of its gravitational field on light
from a still more distant star, an effect known as microlensing. It
is the second planet to be discovered by the microlensing technique.
Gravitational microlensing might offer a way of detecting Earth-mass
planets with existing or near-future technologies, but we will need to
do a lot better than we have done so far to reach masses as small as
the Earth's. The new-found planet has a mass about a thousand times
that of the Earth and probably orbits a star similar to the Sun. At
the time of its discovery, it was about 3 times the Earth--Sun
distance from its host star. Although its orbit is unknown, the
possibility that the planet is a 'hot Jupiter' that revolves very
close to its star is ruled out. The system is about 15,000 light-
years away.

Although a microlensing event can last days, the presence of a planet
affects the signal for only a day or so. Therefore, data must be
analyzed as quickly as they are gathered to identify any events that
merit being closely watched. Detecting the planet's signal requires
obtaining data from many observatories around the world so that the
microlensing event can be monitored around the clock.


The Voyager 1 spacecraft is entering the Solar System's final
frontier, where the Sun's influence ends and the solar wind impinges
on the thin gas between stars. In 2003 November, the Voyager team
announced that it was seeing events unlike any in the mission's
then-26-year history. The team believed that the unusual events
indicated that Voyager 1 was approaching a different region of space,
probably the beginning of the frontier called the termination shock
region. There was considerable controversy over whether Voyager 1 had
indeed encountered the termination shock or was just getting close.

The termination shock is where the solar wind, a thin stream of
electrically charged gas blowing continuously outward from the Sun, is
slowed by pressure from gas between the stars. At the termination
shock, the solar wind slows abruptly from a speed that ranges from 300
to 600 km/s (700,000 to 1.5 million mph) and becomes denser and
hotter. The consensus of the team now is that Voyager 1, at
approximately 8.7 billion miles from the Sun, has at last entered the
heliosheath, the region beyond the termination shock.

Predicting the location of the termination shock was hard, because the
conditions in interstellar space are unknown. Also, changes in the
speed and pressure of the solar wind cause the termination shock to
expand, contract and ripple. The most persuasive evidence that
Voyager 1 crossed the termination shock is its measurement of a sudden
increase in the strength of the magnetic field carried by the solar
wind, combined with an inferred decrease in its speed. That happens
whenever the solar wind slows down. In 2004 December, the Voyager 1
dual magnetometers observed the magnetic-field strength suddenly to
increase by a factor of approximately 2 1/2, as expected when the
solar wind slows down. The magnetic field has remained at the higher
level since December.

New Scientist

Jupiter's innermost moon Amalthea is a mass of icy rubble that could
not have formed as close to the planet as it is now. A new analysis
does not pinpoint its true origin, but does indicate that the porous
chunk of ice and rock is near to its maximum possible size. The
analysis is of data from the Galileo spacecraft, which sped past
Amalthea at a distance of only 244 kilometres on 2002 November 5 on
its way to Jupiter. Astronomers had hoped to measure the moon's mass
and density, but the spacecraft lost its two-way radio link to Earth
during the 200-second flyby. Initial analysis of the few data
retrieved indicated only that Amalthea appeared less dense than water.

Now astronomers have gone back through the data to estimate Amalthea's
density of about 850 kilograms per cubic metre, 92% of the density of
solid ice. The calculated pressure at the centre of Amalthea is just
less than the strength of natural ice. If it were any larger, the
internal pressure would be enough to flatten ice chunks in its core,
squeezing out any voids. Although Amalthea's circular orbit of just
110,000 kilometres above Jupiter's surface makes it appear old, ice
could not have survived the heat at that distance when Jupiter's four
largest moons formed, so it seems that Amalthea must have formed
elsewhere. There is, however, no satisfactory explanation of where it
came from and how it got where it is now.


Saturn's moon Titan shows an unusual bright spot that scientists do
not understand. The spot, about half the size of England, is just
southeast of the bright region called Xanadu. It may be a hot spot --
an area possibly warmed by a recent asteroid impact or by a mixture of
water-ice and ammonia from a warm interior, oozing out of an ice
volcano onto colder surrounding terrain. Other possibilities for the
spot include landscape features holding clouds in place or unusual
materials on the surface. Other bright spots have been seen on Titan,
but all have been transient features that move or disappear within
hours, and have different spectral properties. The present spot is
persistent in both its colour and location. If it were mountains,
they would have to be much higher than the 100-metre-high hills that
Cassini's radar altimeter has seen so far, and anyway it is doubtful
whether Titan's crust could support high mountains. It should be
possible to test the hot-spot hypothesis when Cassini flies past Titan
again on 2006 July 2, when the spot will be on the night side of the
satellite. If it glows at night, it is hot.


Titan, Saturn's largest moon, is the only moon known to have a
significant atmosphere. Its atmosphere is composed primarily of
nitrogen, with 2 to 3 per cent of methane. One goal of the Cassini
mission was to find what is replenishing and maintaining the murky
atmosphere, which makes the surface very difficult to study with
visible-light cameras, but Cassini also has cameras sensitive to
infrared light that penetrates through the haze.

Cassini has now seen evidence of a possible volcano, which could be a
source of the methane in Titan's atmosphere. Infrared mages show a
circular feature roughly 30 kilometres in diameter that does not
resemble any features seen on Saturn's other icy moons. Scientists
interpret the feature as an ice volcano, a dome formed by upwelling
icy plumes that release methane into Titan's atmosphere. Before
Cassini-Huygens, the most widely accepted explanation for the methane
in Titan's atmosphere was the presence of a methane-rich hydrocarbon
ocean, but the instruments on Cassini and the observations at the
Huygens landing site show that there is no global ocean. Interpreting
the circular feature as a cryovolcano provides an alternative
hypothesis for the presence of methane in Titan's atmosphere. Such an
interpretation could be consonant with models of Titan's evolution.

University of Arizona

The Mars Express orbiter detected an aurora on Mars with its
ultraviolet instrument called SPICAM in 2004 August. SPICAM's field
of view was directed just above the nightside limb. The instrument
detected a 30-kilometre-wide auroral emission, which came mainly from
excited carbon monoxide molecules, 140 kilometres above the planet.
It has been thought that the Earth and all the giant planets have
aurorae because they generate global-scale magnetic fields that
extend great distances and can accelerate and energize the charged
particles that excite the aurorae. That is not the case on Mars, so
the discovery is very interesting.


It is hoped to launch in 2010 a spacecraft called Juno that will go
into a polar orbit around Jupiter. It will try to confirm the
existence of a rocky core, and to measure the planet's internal
convection at exceedingly high atmospheric pressures deep below the
visible surface. Juno will also aim to determine the amount of water,
ammonia, and methane in Jupiter, to gather information about the
temperatures and wind velocities at different levels in the Jovian
atmosphere, and to characterize the magnetosphere that traps harsh
radiation that could pose dangers to future spacecraft.


Astrophysicists from the Universities of Oxford and Rome have for the
first time found evidence of ripples in the Universe's primordial sea
of neutrinos, in agreement with predictions of both Big Bang theory
and the Standard Model of particle physics. Neutrinos are elementary
particles with no charge and very little mass, and are extremely
difficult to study owing to their very weak interaction with matter.
Yet pinning down the physical properties of neutrinos is of paramount
importance to scientists attempting to understand the fundamental
building blocks of Nature. According to the standard Big Bang model,
neutrinos permeate the Universe at a density of about 150 per cubic
centimetre. The Earth is therefore immersed in an ocean of neutrinos,
without our ever noticing. Although it is impossible to measure this
'Cosmic Neutrino Background' directly with present-day technology,
theoreticians think that ripples or waves in it have an impact on the
growth of structures in the Universe. The discovery, made by
combining data produced by the WMAP satellite and the Sloan Digital
Sky Survey, has important implications for the study of neutrinos,
showing that theories of the very large (cosmology) and the very small
(particle physics) are in agreement.


£4.99, ISBN 0540087017). SIR PATRICK MOORE takes the novice
astronomer on a guided tour of the stars and constellations of the
northern hemisphere. An accessible work, clearly and concisely

Bulletin compiled by Clive Down

(c) 2005 the Society for Popular Astronomy
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