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The SOCIETY for POPULAR ASTRONOMY

Electronic News Bulletin No. 397 2015 April 26

Here is the latest round-up of news from the Society for Popular
Astronomy. The SPA is arguably 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://www.popastro.com/




VIOLENT FORMATION OF THE MOON
University of Maryland

"Within the first 150 million years after the Solar System formed, a
planetary body roughly the size of Mars struck and merged with the
Earth, blasting a huge cloud of rock and debris into space. The cloud
would eventually coalesce and form the Moon." For almost 30 years,
planetary scientists are said to have been quite happy with that
explanation -- with one major exception. Although in many ways that
picture makes sense, there could be disquiet over the similarity of
the isotopic compositions of the Earth and Moon -- the geological
equivalent of a DNA 'finger-print' -- they are too much alike. The
expectation has long been that the Moon should carry the isotopic
fingerprint of the foreign body, which scientists have named Theia.
Because Theia came from elsewhere in the Solar System, it might well
have had an isotopic fingerprint different from the Earth's. Now,
astronomers have generated a new isotopic fingerprint of the Moon that
might provide the missing piece of the puzzle. By looking at an
isotope of tungsten present in both the Moon and the Earth, the team
has reconciled the accepted model of the Moon's formation with the
unexpectedly similar isotopic fingerprints of both bodies. The
results suggest that the impact of Theia onto the early Earth was so
violent that the resulting debris cloud mixed thoroughly before
settling down and forming the Moon.

Several different theories have emerged over the years to explain the
similar fingerprints of the Earth and Moon. Perhaps the impact created
a huge cloud of debris that mixed thoroughly with the Earth and then
later condensed to form the Moon; or Theia could, coincidentally, have
been isotopically similar to the Earth. A third possibility is that
the Moon formed from Earth materials, rather than from Theia, although
that would have been a very unusual type of impact. In the search for
an explanation, the team looked to another well-documented phenomenon
in the early history of the Solar System. Evidence suggests that both
the Earth and the Moon gathered additional material after the main
impact, and that the Earth collected more of such debris and dust.
The new material contained a certain amount of tungsten, but
relatively little of it was of the light isotope tungsten-182, which
arises from the radioactive decay of hafnium-182. Taking those two
observations together, one would expect that the Earth would have less
tungsten-182 than the Moon. Indeed, when comparing rocks from the
Moon and the Earth, the team found that the Moon has a slightly higher
proportion of tungsten-182. The small, but significant, difference in
the tungsten isotopic composition between the Earth and the Moon
corresponds well with the different amounts of material gathered by
the two bodies post-impact. The implication is that, when the Moon
first formed, it had exactly the same isotopic composition as the
Earth's mantle. That finding supports the idea that the mass of
material which later formed the Moon must have mixed together
thoroughly before the Moon coalesced and cooled. That would explain
both the overall similarities in isotopic fingerprints and the slight
difference in tungsten-182. It also largely rules out the idea that
the Mars-sized body was of similar composition, or that the Moon
formed from material contained in the pre-impact Earth. In either of
those cases, it would be unlikely for there to be such a good
correlation between tungsten-182 and the amounts of material gathered
by the Moon and the Earth post-impact.


MARS MIGHT HAVE SALTY LIQUID WATER
University of Copenhagen -- Niels Bohr Institute

Researchers have long known that there is water in the form of ice on
Mars. Now, new research from the Mars rover Curiosity shows that it
is possible that there is liquid water close to the surface of Mars.
The explanation is that calcium perchlorate has been found in the
soil, which lowers the freezing point, so the water does not freeze
into ice, but is liquid and present as very salty salt water -- a
brine. Under the right conditions, calcium perchlorate absorbs water
vapour from the atmosphere. Measurements from the Curiosity rover's
weather monitor show that those conditions exist at night and just
after sunrise in the winter. On the basis of measurements of humidity
and temperature at a height of 1.6 metres and at the surface of the
planet, an estimate can be made of the amount of water that is
absorbed. When night falls, some of the water vapour in the atmo-
sphere condenses on the surface; it would ordinarily be frost, but the
calcium perchlorate in the soil is very absorbent and it forms a brine
with the water, so the freezing point is lowered and the condensate
remains liquid. The soil is porous, so the water seeps down through
the soil. Over time, other salts may also dissolve in the soil, and
since they are in a liquid, they can move and precipitate elsewhere
under the surface.

Observations by the Mars probe's stereo camera have previously shown
areas characteristic of old river beds with rounded pebbles that
clearly show that a long time ago there was flowing water with a depth
of up to one metre. Now the new close-up images taken by the rover
all the way en route to Mount Sharp show that there are expanses of
sedimentary deposits, lying as 'plates' one above the other and
leaning a bit toward Mount Sharp. Such deposits are formed when large
amounts of water flow down the slopes of the crater and the streams of
water meet the stagnant water in the form of a lake. When the stream
meets the surface, the solid material carried by the stream falls down
and is deposited in the lake just at the lakeshore. Gradually, a
slightly inclined slope is built up just below the surface of the
water, and traces of such slanting deposits were found during the
entire trip to Mount Sharp. Very-fine-grained sediments, which slowly
fell down through the water, were deposited right at the very bottom
of the crater lake. The sediment plates on the bottom are level, so
everything indicates that the entire Gale Crater may have been a large
lake. About 4.5 billion years ago, Mars had 6 times as much water as
it does now and a thicker atmosphere. But most of the water has
disappeared out into space, and the reason is that Mars no longer has
global magnetic fields, as we have on Earth. Currents of liquid iron
in the Earth's interior generate the magnetic fields and they act as a
shield that protects us from cosmic radiation. The magnetic field
protects the Earth's atmosphere against degradation from energetic
particles shot out from the Sun. But Mars no longer has a global
magnetic field and its atmosphere is not protected in that way from
radiation from the Sun, so the solar particles (protons) 'shoot' the
atmosphere out into space little by little. Even though liquid water
has now been found, it is not likely that life will be found on Mars
-- it is too dry, too cold and the cosmic radiation is so powerful
that it penetrates at least a metre into the surface and would kill
all life -- at least life as we know it on Earth.


SUN FORMED LATER THAN MOST STARS IN MILKY WAY
Space Telescope Science Institute (STScI)

In one of the most comprehensive multi-observatory galaxy surveys yet,
astronomers find that galaxies like our Milky Way had a period of
intense star formation, producing stars about 30 times faster than
today. Our Sun, however, is a late arrival. The Milky Way's great
star-formation period peaked 10 billion years ago, but the Sun did not
form until roughly 5 billion years ago. By that time the star-
formation rate in our Galaxy had fallen to a trickle. The Sun's late
appearance may actually have fostered the growth of the Solar System's
planets. Elements heavier than hydrogen and helium were more abundant
later on, as more massive stars ended their lives early and enriched
the Galaxy with material that served as the building blocks of planets
and even of life on Earth. Of course, astronomers have not got any
pictures of the Milky Way's formative years to trace the history of
stellar growth. Instead, they compile the story from studies of other
galaxies similar in mass to the Milky Way, found in deep surveys of
the Universe. The farther into the Universe astronomers look, the
further back in time they are seeing, because starlight from long ago
is just arriving at Earth now. From those surveys, stretching back in
time more than 10 billion years, researchers assembled an album of
images containing nearly 2,000 snapshots of Milky-Way-like galaxies.
The new census provides the most complete picture yet of how galaxies
like the Milky Way grew over the past 10 billion years into today's
majestic spiral galaxies. The multi-wavelength study spans from
ultraviolet to far-infrared light, combining observations from the
Hubble, Spitzer and Herschel space telescopes and ground-based
telescopes.

The study confirms that galaxies have put much of their mass into
stars over the past 10 billion years; most of that happened within the
first 5 billion years. The new analysis reinforces earlier research
that showed Milky Way-like galaxies began as small clumps of stars.
The diminutive galaxies built themselves up by swallowing large
amounts of gas that ignited a firestorm of star birth. The study
reveals a strong correlation between the galaxies' star formation and
their growth in stellar mass. Observations indicated that as the
star-formation slowed down, the galaxies' growth decreased as well.
Evidence suggests that we can account for the majority of the build-up
of a galaxy like our Milky Way through its star formation. When we
calculate the star-formation rate of a Milky Way galaxy and add up all
the stars it would have produced, it is pretty consistent with the
mass growth we expected. That means we are able to understand the
growth of the 'average' galaxy with the mass of the Milky Way. The
astronomers selected the Milky-Way-like progenitors by sifting through
more than 24,000 galaxies in catalogues made with the Hubble and
Magellan telescopes.


COMPLEX MOLECULES IN INFANT STAR SYSTEM
ESO

For the first time, astronomers have detected the presence of complex
organic (i.e. carbon-containing) molecules, the building blocks of
life, in a protoplanetary disc surrounding a young star. The
discovery, made with the Atacama Large Millimetre/sub-mm Array (ALMA),
reaffirms that the conditions that spawned the Earth and Sun are not
unique in the Universe. The new ALMA observations show that the
proto-planetary disc surrounding the young star MWC 480 contains large
amounts of methyl cyanide (CH3CN), a carbon-based molecule. There is
enough methyl cyanide around MWC 480 to fill all the Earth's oceans.
Both that molecule and its simpler cousin hydrogen cyanide (HCN) were
found in the cold outer reaches of the star's newly formed disc, in a
region that astronomers believe is analogous to the Kuiper Belt -- the
realm of icy planetesimals and comets in the Solar System beyond
Neptune. Comets retain a pristine record of the early chemistry of
the Solar System, from the period of planet formation. Comets and
asteroids from the outer Solar System are thought to have seeded the
young Earth with water and organic molecules, helping to set the stage
for the development of primordial life. Studies of comets and
asteroids show that the solar nebula that formed the Sun and planets
was rich in water and complex organic compounds. We now have even
better evidence that that same chemistry exists elsewhere in the
Universe, in regions that could form planetary systems not unlike our
own. Indeed, molecules found in MWC 480 are also found in similar
concentrations in the Solar System's comets.

The star MWC 480, which is about twice the mass of the Sun, is about
150 parsecs away in the Taurus star-forming region. Its surrounding
disc is in an early stage of development, having recently coalesced
out of a cold, dark nebula of dust and gas. Studies with ALMA and
other telescopes have yet to detect any obvious signs of planet form-
ation in it. Astronomers have known for some time that cold, dark
interstellar clouds are very efficient at making complex organic
molecules, including a group of molecules known as cyanides. Those,
especially methyl cyanide, are important because they contain carbon-
nitrogen bonds, which are essential for the formation of amino acids,
the foundation of proteins and the building blocks of life. Until
now, however, it has not been known whether such complex organic
molecules could form and survive in the energetic environment of a
newly forming solar system, where shocks and radiation can easily
break chemical bonds. Astronomers can see from the latest observa-
tions that such molecules do survive. Importantly, the molecules
that ALMA detected are much more abundant than would be found in
interstellar clouds. That suggests that protoplanetary discs are very
efficient at forming complex organic molecules and that they are able
to form them on relatively short time-scales.


CITIZEN SCIENTISTS DISCOVER YELLOW SPACE BALLS
NASA

Citizen scientists scanning images from the Spitzer space telescope,
an orbiting infra-red observatory, recently stumbled upon a new class
of curiosities that had gone largely unrecognized before: yellow
balls. The Milky Way Project is one of many 'citizen scientist'
projects making up the Zooniverse web site, which relies on 'crowd-
sourcing' to help process scientific data. For years, volunteers have
been scanning Spitzer's images of star-forming regions -- places where
clouds of gas and dust are collapsing to form clusters of young stars.
Astronomers do not fully understand the process of star formation;
citizen scientists have been helping by looking for clues. Before the
yellow balls were observed, volunteers had already noticed green
bubbles with red centres, populating a landscape of swirling gas and
dust. The bubbles are the result of massive newborn stars blowing out
cavities in their surroundings. When the volunteers started reporting
that they were finding objects in the shape of yellow balls, the
Spitzer researchers took note. The rounded features captured by the
telescope, of course, are not actually yellow, red, or green --they
just appear that way in the colour-assigned infrared images that the
telescope sends to the Earth. The false colours provide a way for
people to talk about infrared wavelengths of light that their eyes
cannot actually see. Analysis by the team led to the conclusion that
the yellow balls precede the green bubbles, representing a phase of
star formation that takes place before the bubbles form.

Researchers think that the green bubble rims are made largely of
organic molecules called polycyclic aromatic hydrocarbons (PAHs) which
are abundant in the dense molecular clouds where stars coalesce.
Blasts of radiation and winds from newborn stars push the PAHs into a
spherical shells that look like green bubbles in Spitzer's images.
The red cores of the green bubbles are made of warm dust that has not
yet been pushed away from the windy stars. Essentially, the yellow
balls mark places where the PAHs (green) and the dust (red) have not
yet separated. The superposition of green and red makes yellow. So
far, the volunteers have identified more than 900 of the compact,
yellow features. The multitude gives researchers plenty of chances to
test their hypotheses and learn more about the way that stars form.


NOT ALL TYPE Ia SUPERNOVAE ARE THE SAME
University of Arizona

A team of astronomers has discovered that certain types of supernovae
are more diverse than previously thought. The results have
implications for big cosmological questions, such as how fast the
Universe has been expanding since the Big Bang. Most importantly, the
findings hint at the possibility that the acceleration of the
expansion of the Universe might not be quite as fast as textbooks say.
The team discovered that type-Ia supernovae, which have been
considered so uniform that cosmologists have used them as 'standard
candles' to plumb the depths of the Universe, actually fall into
different populations. The differences are not random, but lead to
separating Ia supernovae into two groups, where the group that is in
the minority near us are in the majority at large distances -- and
thus when the Universe was younger. The discovery casts new light on
the currently accepted view of the Universe expanding at a faster and
faster rate, pulled apart by a hypothetical entity called dark energy.
In 2011 astronomers discovered that many supernovae appeared fainter
than predicted because they had moved farther away from us than they
should have done if the Universe expanded at the same rate. That
indicated that the rate at which stars and galaxies move away from
each other is increasing; in other words, something has been pushing
the Universe apart faster and faster. The idea behind that reasoning
was that type-Ia supernovae would be the same brightness -- they would
all end up pretty similar when they explode. Once people knew why,
they started using them as mileposts for the far side of the Universe.
The faraway supernovae should be like the ones nearby because they
look like them; but because actually they are fainter than expected,
it led people to conclude that they are further away than expected,
and that in turn led to the conclusion that the Universe is expanding
faster than it did in the past.

The team observed a large sample of type-Ia supernovae in ultraviolet
and visible light. For their study, they combined observations made
by the Hubble telescope with those made by the Swift satellite. The
data collected with Swift were crucial because the differences between
the populations -- slight shifts toward the red or the blue spectrum
-- are subtle in visible light, which had been used to detect type-Ia
supernovae previously, but became obvious only through Swift's
dedicated follow-up observations in the ultraviolet. The realization
that there were two groups of type-Ia supernovae started with Swift
data, and then researchers went through all the other data sets.
As we go back in time, we see a change in the supernova population.
The explosion has something different about it, something that doesn't
jump out at you when you look at it in optical light, but does in the
ultraviolet. Since nobody realized that before, all the supernovae
were supposed to be the same. But if you were to look at 10 of them
nearby, they would be found to be redder on average than a sample of
10 supernovae far away. The authors conclude that some of the
reported acceleration of the Universe can be explained by colour
differences between the two groups of supernovae, leaving less
acceleration than initially reported. That would, in turn, require
less 'dark energy' than currently assumed. The authors pointed out
that more data have to be collected before scientists can understand
the impact on current measures of dark energy.


GIANT GALAXIES DIE FROM INSIDE OUT
RAS

There has been a question as to how massive, quiescent elliptical
galaxies, common in the modern Universe, quenched their once-furious
rates of star formation. Such colossal galaxies, often also called
spheroidal because of their shape, typically pack stars ten times as
densely in the central regions as in our home Galaxy, the Milky Way,
and have about ten times its mass. Astronomers refer to those big
galaxies as red and dead because they exhibit an ample abundance of
ancient red stars, but lack young blue stars and show no evidence of
new star-formation. The estimated ages of the red stars suggest that
their host galaxies ceased to make new stars about ten billion years
ago. The shutdown began right at the peak of star formation in the
Universe, when many galaxies were still giving birth to stars at a
pace about twenty times faster than nowadays. Massive dead spheroids
contain about half of all the stars that the Universe has produced
during its entire existence, and astronomers cannot claim to
understand how the Universe evolved and became as we see it today
unless they understand how those galaxies came to be. Researchers
observed a total of 22 galaxies, spanning a range of masses, from an
era about three billion years after the Big Bang. According to the
new data, the most massive galaxies in the sample kept up a steady
production of new stars in their peripheries. In their bulging,
densely packed centres, however, star formation had already stopped.
A leading theory is that star-making materials are scattered by
torrents of energy released by a galaxy's central super-massive black
hole as it sloppily devours matter. Another idea is that fresh gas
stops flowing into a galaxy, starving it of fuel for new stars and
transforming it into a red and dead spheroid.


1.8-BILLION-LIGHT-YEAR SUPER-VOID IS LARGEST STRUCTURE IN UNIVERSE
RAS

In 2004, astronomers examining a map of the radiation left over from
the Big Bang (the cosmic microwave background, or CMB) discovered the
Cold Spot, a larger-than-expected unusually cold area of the sky. The
physics surrounding the Big Bang theory predicts warmer and cooler
spots of various sizes in the infant Universe, but a spot so large and
so cold was unexpected. Now, a team of astronomers may have found an
explanation for the existence of the Cold Spot, which may be the
largest individual structure ever identified in the Universe. If the
Cold Spot originated from the Big Bang itself, it could be a rare sign
of exotic physics that the standard cosmology (basically, the Big Bang
theory and related physics) does not explain. If, however, it is
caused by a foreground structure between us and the CMB, it would be a
sign that there is an extremely rare large-scale structure in the mass
distribution of the Universe. Using data from the Pan-STARRS1 (PS1)
telescope at Haleakala on Maui, and the Wide Field Survey Explorer
(WISE) satellite, the team discovered a large super-void, a vast
region 1.8 billion light-years across, in which the density of
galaxies is much lower than usual in the known Universe. The void was
found by combining observations taken by PS1 at optical wavelengths
with observations taken by WISE at infrared wavelengths to estimate
the distance to and position of each galaxy in that part of the sky.

Earlier studies observed a much smaller area in the direction of the
Cold Spot, but they could establish only that there is no very distant
structure in that part of the sky. Paradoxically, identifying nearby
large structures is harder than finding distant ones, since we must
map larger portions of the sky to see the closer structures. The
super-void is 'only' about 3 billion light-years away from us, a
relatively short distance in the cosmic scheme of things. While the
existence of the super-void and its expected effect on the CMB do not
fully explain the Cold Spot, it is very unlikely that the super-void
and the Cold Spot are at the same location just by coincidence. The
team will continue its work using improved data from PS1, and from the
Dark Energy Survey being conducted with a telescope in Chile to study
the Cold Spot and super-void, as well as another large void located
near the constellation Draco.


DARK MATTER IS NOT COMPLETELY DARK
RAS

Astronomers believe that they might have observed the first potential
signs of dark matter interacting with a force other than gravity.
They made the discovery by using the Hubble telescope to view the
simultaneous collision of four distant galaxies at the centre of a
galaxy cluster 1.3 billion light-years away. The researchers said one
dark-matter clump appeared to be lagging 5,000 light-years behind the
galaxy it surrounds. Such an offset is predicted during collisions if
dark matter interacts, even very slightly, with forces other than
gravity. Computer simulations show that the extra friction from the
collision would make the dark matter slow down, and eventually lag
behind. Scientists believe that all galaxies exist inside clumps of
dark matter -- called dark because it is thought to interact only with
gravity, therefore making it invisible. Nobody knows what dark matter
is, but it is believed in some quarters to make up about 85% of the
Universe's mass. Without the constraining effect of its extra
gravity, galaxies like our Milky Way would fling themselves apart as
they spin. In the latest study, the researchers were able to 'see'
the dark-matter clump because of the distorting effect its mass has on
the light from background galaxies -- an effect called gravitational
lensing. The researchers added that their finding potentially rules
out the standard theory of Cold Dark Matter, where dark matter
interacts only with gravity.

If the dark matter really slowed down during the collision, that could
be the first dynamical evidence that dark matter interacts with the
world around it. The researchers note that while they appear to have
observed the offsetting of dark matter, more investigation will be
needed into other potential effects that could also produce a lag
between the dark matter and the galaxy it hosts. Similar observations
of more galaxies and computer simulations of galaxy collisions are
under way to confirm the interpretation. Previous observations showed
that dark matter interacted very little during 72 collisions between
galaxy clusters (each containing up to 1,000 galaxies). The latest
research concerns the motion of individual galaxies. Researchers say
that the collision between the galaxies could have lasted longer than
the collisions observed in the previous study, allowing even a small
frictional force to build up over time. The main uncertainty in the
result is the time span for the collision: the friction that slowed
the dark matter could have been a very weak force over acting over
about a billion years, or a relatively stronger force acting for
'only' 100 million years. Taken together, the two results may bracket
the behaviour of dark matter for the first time -- it interacts 'more
than this, but less than that'.


NEW EAST TO USE FIREBALL REPORT FORM
By Tony Markham, SPA Meteor Section Director


Have you seen a fireball but not reported it? Maybe you weren't sure
as to which of many organisations to report it to? Maybe you were put
off by being asked for "technical" information, such as azimuths,
elevations and magnitudes and for your latitude & longitude? If you
did report it, did you struggle to find out whether anyone else had
seen it ?

It is, of course, a challenge to collect sufficiently detailed
information from witnesses without putting them off by becoming too
"technical". After all, most witnesses will be ordinary members of the
public with little or no familiarity with the night sky.

**** All of this is now changing ****

The good news ... is that the International Meteor Organisation (IMO)
has set up a fireball report form and a central database that can be
used by any group anywhere in the world to collect fireball reports.

Even better news ... is that the reporting system requires no knowledge
of azimuths, magnitudes, latitudes or longitudes ... or any familiarity
with the stars or constellations of the night sky.

You can access the SPA's version of this form at
http://www.popastro.com/meteor/fireball ... /index.php

If you use this link to access the SPA's version of the report form,
then your full report will also be mailed to the SPA Meteor Section
and you will receive feedback from the SPA.

You simply start by quoting your postcode or the town or village in
which you live. It then displays a local map on which you can mark your
exact location and mark the directions in which you saw the fireball
start and end. You also mark how high these points were above the
horizon. You are asked for the local time of the sighting (there is no
need to quote timezones or convert times to GMT/UT - the form does this
for you!). Additional screens then ask you about specific features of
the fireball, such as colour(s), its brightness (compared with the
Moon or Venus) and fragmentation. Although you are asked for your
contact details, only your first name and the first letter of your last
name will be shown in the on-line database. Your contact details will
not be visible on-line.

The reports received via any of these forms will all be stored in an
international database that anyone can view on-line. There is a link
from the SPA Meteor pages that shows Recent UK Fireball Sightings.



Bulletin compiled by Clive Down

Here is the latest round-up of news from the Society for Popular
Astronomy. The SPA is arguably 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://www.popastro.com/
________________________________________
Society for Popular Astronomy


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