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The SOCIETY for POPULAR ASTRONOMY
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Electronic News Bulletin No. 229 2007 September 30
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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
at 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/maah3dZabBBjTcixLLVb/


PERU IMPACT EVENT
By Alastair McBeath, SPA Meteor Section Director

On September 15, shortly before midday, a slightly elliptical crater
around 13m x 14m in size, and estimated as perhaps 5-10m deep,
appeared in the Andes Mountains of southeast Peru near the village of
Carancas in the Puno region, near Lake Titicaca and the border with
Bolivia. A very loud explosion was heard by villagers at Carancas,
which apparently broke at least one window at the local health centre,
roughly 1km from the crater. The explosion shook the ground like an
earthquake at the village, and was noted as felt too at the city of
Desaguadero, about 20km north of Carancas, on the Peru-Bolivia
border. This effect was later suggested as of magnitude 1.5 on the
Richter scale. At Carancas, and before the explosion, another loud
sound, described as like an aircraft engine, was heard. Smoke and a
most unpleasant odour hung in the air nearby for some time afterwards
(the smoke for seemingly just a few minutes), inhaling which made a
number of people feel ill, particularly those who approached closely to
the crater. Witnesses indicated the smell persisted strongly at least
into
the following day. The crater bottom almost immediately filled with
water, hence the difficulty in estimating its depth, plus the crater's
rim
had been raised up to a metre above the surrounding level on the
crater's northern side. The water was suggested as boiling for at least
ten minutes after the explosion, and that it was steaming for half an
hour
or more in total (water boils at about 90 degrees C at the site's
altitude,
around 3800m above mean sea level).

A brilliant fireball was reported as seen to the northeast of
Desaguadero
from the city, at about 11:45 a.m. local time on the same date. Details
on this fireball's flight are very sketchy, but it may have been heading
towards the Carancas area on a roughly NNE to SSW trajectory from
somewhere above Lake Titicaca and/or the adjacent land in Bolivia.
The trajectory has been partly derived by assuming it was definitely
related to the crater formation event, not unreasonable, if the crater
was produced by a meteorite impact. Some early reports suggested the
fireball may have been seen from Carancas too.

Scientific investigations at the crater site got underway within two to
three days. Initial claims about various supposedly meteoritic objects
found associated with the crater, appear now to have been at least
partly backed-up by the release of a preliminary report by two
scientists
from the Peruvian Institute for Geology, Mining and Metallurgy, dated
September 21 (see: http://popastro.c.topica.com/maah3dZabBBjUcixLLVb/
This report claimed that
a number of small chondritic meteorite fragments had been recovered
from near the crater, and gave some images, including geological thin
section images under plane- and crossed-polarized light, plus
preliminary mineral composition figures, for these. However, the reality
of the "chondritic" nature of these specimens has already been
questioned, so it remains to be seen how accurate this first analysis
was.

Stony meteorites, including the chondrites, tend not to be too robust.
They often fragment during their atmospheric flight, giving a scatter
ellipse of material on the ground, and sometimes craters, elongated
along their line of approach. For instance, the stony meteorite fall in
the
Sikhote-Alin region of Far Eastern Siberia on 1947 February 12,
produced one large crater around 28m in diameter and about 6m deep,
but there were over 30 other craters within a kilometre of one another
there as well, down to a metre or so in size, and around 9000 individual
meteorites from a gramme or two up to 1.7 tonnes in weight were
recovered from within a few kilometres of the main fall, including from
many of the craters. The preliminary report on the Carancas event
suggested the absence of any larger pieces was due to the locals
having already collected them by the time the first investigators
arrived,
yet no attempt seems to have been made even to view these objects, so
their reality and nature is presently unknown. The report also made no
mention of a strewnfield, but noted that the purported dusty meteoritic
material (described as having a grey colour, compared to the red-
brown local soil) had been found up to ~200m from the crater.

The event featured heavily on the Internet and in the media beginning a
couple of days afterwards, and much confusion and contradiction has
resulted because of this, allied with a rather curious delay in the
appearance of the preliminary scientific report, which seems not to have
surfaced among these discussions prior to September 28, a week after
it was dated as issued. Consequently, various alternative hypotheses
were proposed, as little in the early details released supported the
view
that a meteoritic event had happened. These included a crashed
aircraft, a missile impact, fallen satellite wreckage, and a previously
unsuspected geothermal or hydrothermal vent (the whole Andes chain
is a geologically mobile zone, with earthquakes and volcanoes, after
all). Although the initial scientific report now does support the idea
this
was a meteoritic event, questions about it remain, and these first
findings
will need to be confirmed too.

For now, the following weblinks may be useful for those wishing to get
a more detailed overview of the event:

SPA General Chat Forum topic at:
http://popastro.c.topica.com/maah3dZabBBjVcixLLVb/

UK Weather World Spaceweather Forum topic at:
http://popastro.c.topica.com/maah3dZabBBjWcixLLVb/

Cambridge Conference Network archive for CCNet Bulletins 155,
156, 161 and 162/2007 dated respectively to September 19, 20, 27
and 28, available via:
http://popastro.c.topica.com/maah3dZabBBjXcixLLVb/ . These latter
contain
probably the most detailed versions of the press notices in one place,
and some additional informed comments.


NEW METEOR SHOWERS, OR JUST GOOD SPORADIC RATES?
By Alastair McBeath, SPA Meteor Section Director

September brings some of the year's best sporadic meteor rates for the
northern hemisphere. On occasion, these can lead observers to believe
they may have discovered a new minor meteor shower or two. This
year, suggestions of perhaps something unexpected from Orion around
September 12 and 13 were sent to the Section from North America,
plus there were some notes from Britain, regarding a possible radiant
around Cygnus on September 11, 12 and 15 on the SPA's Observing
Forum (interestingly, the people involved spotted only one of these
possible sources, not both). Unfortunately, all the reports were made
too casually to allow any detailed investigation of the reality of
either
potential source. Defining minor meteor shower radiants by visual
observations alone is a very precise, difficult and exacting business,
but is not unrewarding for those with the patience and ability to carry
out the necessary work. Most "new showers" suspected this way
disappear under close scrutiny however, as simply due to the chance
alignment of a few sporadic meteors. Further information, including
details on what is needed from visual data to identify minor meteor
shower radiants, whether known or previously unsuspected, can be
found in the same SPA Observing Forum topic, at:
http://popastro.c.topica.com/maah3dZabBBjYcixLLVb/ .


METEOR PROSPECTS FOR OCTOBER
By Alastair McBeath, SPA Meteor Section Director

October opens a promising final quarter to the year for dark-sky
observations of many meteor shower maxima. New Moon on October
11 creates perfect viewing conditions for covering the potential
Draconid epoch. If any activity happens at all from them, it should be
most likely between 20h UT on October 8 and 13h UT on October 9.
Typically, no Draconids are seen other than in years when their parent
comet 21P/Giacobini-Zinner is near perihelion and fairly close to the
Earth in early October, as last in 1998, when a strong outburst took
place over the Far East (estimated Zenithal Hourly Rates - ZHRs -
were ~700 briefly). The comet was at perihelion most recently in July
2005, and a relatively minor outburst happened that October (with
ZHRs of about 30-40). Another, but unexpected, minor outburst
happened over Japan in 1999 however, so there may be features to
watch out for in other years with this shower. Alert observers could
be rewarded if something unanticipated chances-by this time!

Less than a fortnight later, the main Orionid maximum is due on
October 21. Recent investigations have suggested the unexpectedly
strong rates, with ZHRs of ~50-60 on three consecutive dates across
the anticipated peak that were seen last year (see ENB 207), may
recur this. Ordinarily, we would predict best Orionid ZHRs as likely to
be around 25 this year, so it will be interesting to see just what
transpires. The radiant, near Orion's "Club" asterism for the maximum,
is usefully observable for meteor work from about 23h UT onwards
in Britain. In addition, a sub-peak, with ZHRs similar to the normal
(that
is, not enhanced-rate!) main maximum, has happened a few times in
the past on October 17-18, albeit definitely reported from only two
years so far, 1993 and 1998. The waxing Moon will set well before
the radiant is available on October 17 to 19, and even by nights around
October 21, it will be setting an hour or so either side of midnight UT
for the UK, so all observers should be alert to whatever happens in the
post-midnight to dawn period then, if good conditions present.

More information on these and other showers active in October can be
found among the SPA's Meteor webpages, at:http://tinyurl.com/yrpe7n .
Good luck, and clear skies!


DARK MATTER CLUES IN OLDEST STARS
BBC Online

Some researchers have been telling the British Association Festival
of Science that their work could reveal the nature of dark matter.
Scientists know very little about such matter, even though some of
them think that it accounts for most of the mass in the cosmos. Since
it is supposed not to emit or reflect detectable light, it cannot be
seen directly, but its gravitational attraction acts on normal matter
(the gas, stars, and planets we see in space). It is that interaction
that provides evidence for its existence. Proposals as to its nature
have included various types of exotic particles, with equally exotic
names such as neutralinos, axions and gravitinos.

Scientists from Durham now claim that the nature of the dark matter
was crucial to the nature of the first stars. In cold dark matter the
particles move slowly, whereas in warm dark matter they move quickly.
If the dark matter consisted of fast particles, then according to the
computer model the first stars would have formed in very long, thin
filaments. The filaments could have had a length about a quarter the
size of the Milky Way and contained an amount of matter and gas about
10 million times the mass of the Sun, providing a lot of fuel for many
stars. Some of the stars that formed within the filaments would have
had a relatively low mass, which would imply a long life-span so they
could still survive today. What happened in the simulation with cold
dark matter was very different, as the first stars formed in little
lumps of dark matter, just one star per dark-matter lump. Those stars
would probably have been very massive (100 solar masses) and would
quickly have burnt out and would not be found in the Milky Way today.
The research team hopes that, since the temperature of the dark matter
indicates what kind of particles it is made of, answers could come
from efforts now being made to find very old stars.


SATELLITES OF SATURN
IAU

The IAU has approved names for recently discovered satellites of
Saturn:

Saturn XLIX Anthe = S/2007 S 4
Saturn L Jarnsaxa = S/2006 S 6
Saturn LI Greip = S/2006 S 4
Saturn LII Tarqeq = S/2007 S 1


NASA TO LAUNCH GAMMA-RAY TELESCOPE
Science Daily

A new NASA space telescope is intended to allow scientists to observe
some of the most energetic objects and events in the Universe. The
new 'Gamma-ray Large-Area Space Telescope' (GLAST) to be launched
next spring will be the first gamma-ray observatory to survey the
entire sky. Scientists are hoping that it will provide clues about
dark matter and the early Universe and allow them to test fundamental
principles of physics. The observatory consists of two instruments,
the large-area telescope and the burst monitor. Earlier gamma-ray
observatories include the Swift spacecraft, which was launched in
2004, and the Compton gamma-ray observatory which operated from 1991
to 2000. ESA's Integral observatory, which can observe objects in
gamma-rays, X-rays and visible light, was launched in 2002. Despite
the number of observatories studying gamma-rays, a lot remains to be
discovered.


SATELLITE MISSION TO DETECT BLACK HOLES
Caltech

At one time NASA was going to launch a spacecraft called NuSTAR
(acronym for Nuclear Spectroscopic Telescope Array). It cancelled it
in 2006 owing to funding pressures, but has now re-started it. The
hope is that it will shed light on such questions as the distribution
of black holes and what powers the most extreme active galaxies.


POSSIBLE CAVE ENTRANCES OBSERVED ON MARS
NASA

The Odyssey spacecraft has discovered entrances to seven possible
caves high on the slopes of a Martian volcano. Evidence that the
holes may be openings to cavernous spaces comes from the temperature
differences measured from infrared images: from day to night, the
temperatures of the holes change only about one-third as much as the
surrounding ground surface. Their temperatures are not as steady as
those of large caves on Earth, but are consistent with their being
deep holes in the ground. The holes are at some of the highest
altitudes on the planet, on the volcano Arsia Mons. The observations
have prompted researchers using Mars Odyssey and Mars Reconnaissance
Orbiter to look for other openings to underground spaces at lower
elevations.


STARS DISCOVERED IN LONG GALAXY TAIL
Chandra X-Ray Center

Astronomers observing in X-ray light with the Chandra observatory and
in optical light with the SOAR telescope in Chile have found evidence
that stars have been forming in a 200,000-light-year tail of gas that
extends well outside its parent galaxy, an object called ESO 137-001
that is plunging toward the centre of the cluster Abell 3627. The
tail was stripped out of its parent galaxy by the pressure induced by
the motion of the galaxy through the multi-million-degree gas that
pervades the intergalactic space of the cluster. The observations
indicate that the gas in the tail has formed millions of stars.
Because the large amounts of gas and dust needed to form stars are
typically found only within galaxies, astronomers have previously
thought it unlikely that large numbers of stars would form outside a
galaxy. The evidence for star-formation in the tail includes 29
regions of ionised hydrogen glowing in optical light, thought to be
from newly formed stars. Two X-ray sources, another indication of
star-formation activity, are near those regions. The researchers
believe that the stars formed within the last 10 million years or so.


SOHO SIGHTS A PERIODIC COMET
Science Daily

The European Space Agency has said that its SOHO observatory has for
the first time sighted the third passage of a specific comet. SOHO
has found more than 1,350 comets, and while many of them are believed
to be periodic this is the first one that has been officially declared
as such. The comet is probably no more than about 200 m in diameter
and has an orbital period of approximately four years. It was seen in
1999 and again in 2003. The comet has now been given the official
designation P/2007 R5 (SOHO).


RETURN TO COMET TEMPEL 1
NASA

Two years ago, the 'Deep Impact' spacecraft smashed an 820-lb copper
projectile into Comet Tempel 1. Unfortunately it was not possible to
see the crater because the cloud of debris was so thick. Deep Impact
was simply on a high-speed flyby, and was far away before the cloud
had had time to dissipate. Now NASA is sending another spacecraft to
Tempel 1, the Stardust probe. In 2004 Stardust flew past Comet Wild
2; severely buffeted by jets of gas and debris flowing from the comet,
it nevertheless managed to obtain samples of comet dust and return
them to Earth for analysis. Now it is being re-cycled and placed on a
course to reach Tempel 1 in 2011. By then the debris cloud will be
long gone and we should get a clear view of the crater. The craft
will be returning to the comet almost exactly one orbit--that is, one
comet-year--after the first visit. Deep Impact is being re-cycled
too, and will fly by Comet Boethin in 2008 December for a close-up
investigation of the comet's nucleus.


SUCCESSFUL LAUNCH FOR DAWN
BBC Online

NASA's 'Dawn' space probe has begun an eight-year journey to obtain
high-resolution pictures of two of the largest asteroids. It will
make a fly-past of Mars and is intended then to orbit Vesta for about
nine months in 2011 and go on to Ceres for at least five months in
2015. Vesta is 525 km across and has been resurfaced by volcanic
flows. Of particular interest is the giant crater -- 460 km across
and 13 km deep -- at its south pole. The massive collision that
created the crater gouged out 1% of the asteroid's volume, and has
been suggested as the origin of many of the meteorites that have
fallen to Earth. At 930 km across, Ceres is the biggest object in the
asteroid belt. It is almost spherical and is classed as a dwarf
planet.



Owing to holidays the next scheduled bulletin will be issued on
October 28.



Bulletin compiled by Clive Down

(c) 2007 the Society for Popular Astronomy


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