Topic: Late September Astronomy Bulletin

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SPACECRAFT WATCH FOR STORMS IN THE RADIATION BELTS
NASA

NASA has launched two spacecraft directly into the Van Allen radiation
belts.  Bristling with sensors, the heavily-shielded spacecraft are on
a 2-year mission to discover what makes the radiation belts so
dangerous and so devilishly unpredictable.  When the radiation belts
were discovered in 1958, they were a surprise.  It had been assumed
that the space around the Earth was empty, but the first American
satellite, Explorer 1, proved otherwise.  The tiny spacecraft was
equipped with a Geiger tube for counting energetic protons and
electrons, and it found so many charged particles that the counter
registered off-scale most of the time.  In the 1950s the radiation
belts had little effect on ordinary people, but today hundreds of
satellites used for everything from weather prediction to GPS to
television routinely skim the belts, subjecting themselves to
energetic particles that can damage solar panels and electronics.
During geomagnetic storms, when the belts are swollen by solar
activity, whole fleets of satellites can be engulfed, imperilling the
technological underpinnings of daily life on the planet below.  When a
solar storm hits the radiation belts, they often respond in
counter-intuitive ways.  Sometimes the radiation belts fill with
energetic particles such as the 'killer electrons' that worry mission
planners, but just as often the opposite happens, and the belts lose
their killer particles, temporarily making them a safer place.  And
sometimes nothing happens!  Researchers hope that the new satellites
will narrow the possibilities.  During storms, the probes can sample
electric and magnetic fields, count the number of energetic particles,
and detect plasma waves of many frequencies.  The hope is that the
data will lead to predictive models that can forecast when it is safe
to enter the belts, perform space-walks, and operate sensitive
electronics.


'DRY ICE' SNOWFALL ON MARS
NASA/Jet Propulsion Laboratory

Mars Reconnaissance Orbiter data have given scientists the clearest
evidence yet of carbon-dioxide snowfalls on Mars.  Frozen carbon
dioxide, better known as dry ice, exists only at temperatures below
about -125 C at the low pressure of the Martian atmosphere.  The
snowfalls occurred from clouds around the south pole in winter.  The
scientists analyzed data gained by looking at clouds from straight
overhead and sideways with the Climate Sounder, one of six instruments
on the orbiter.  The instrument records brightness in nine wavebands
of visible and infrared light, data that provide information about
temperatures, particle sizes and their concentrations.  The new
analysis is based on data from observations in the south polar region
during southern Mars winter in 2006-2007, identifying a tall carbon-
dioxide cloud about 500 kilometres in diameter persisting over the
pole and smaller, shorter-lived, lower-altitude carbon-dioxide ice
clouds at latitudes from 70 to 80 degrees south.

One line of evidence for snow is that the carbon-dioxide ice particles
in the clouds are large enough to fall to the ground during the
lifespan of the clouds.  Another comes from observations when the
instrument is pointed toward the horizon, instead of down at the
surface. The infrared signature of the clouds viewed from that angle
is clearly that of carbon-dioxide ice particles, and they extend to
the surface.  The south polar residual ice cap is the only place on
Mars where frozen carbon dioxide persists on the surface year-round.
Its existence there has been known for decades, but just how it gets
deposited from the atmosphere has been in question.  It has not been
known whether it occurs as snow or by freezing out at ground level as
frost.  The new results show that snowfall is especially vigorous on
top of the residual cap.


FLASH ON JUPITER
Spaceweather.com

Something appears to have hit Jupiter on September 10 (11:35 UT),
igniting a fireball in the cloud tops.  Amateur astronomers in
Wisconsin and Texas observed a bright white flash that lasted about
1.5 to 2 seconds.  The fireball was probably caused by a small
asteroid or comet hitting Jupiter.  Similar impacts were observed in
June and August 2010.  An analysis of those earlier events suggests
that Jupiter is frequently struck by 10-metre-class asteroids -- one
of the hazards of orbiting near the asteroid belt and having such a
strong gravitational field.  Astronomers around the world have begun
monitoring the impact site for signs of debris -- either the remains
of the impactor or material dredged up from beneath the cloud tops.
Not all impacts produce such debris.


MOST ANCIENT SPIRAL GALAXY YET DISCOVERED
Nature

Astronomers using the Hubble telescope have discovered a large, fully
formed spiral galaxy, that they have called BX442, that is the most
ancient spiral galaxy known.  Current wisdom holds that such galaxies
did not exist at such an early time in the history of the Universe,
because the formation of spiral arms takes a long time.  Most distant
galaxies, seen as they were billions of years ago, look clumpy and
irregular.  But BX442, a 10.7- billion-year-old entity, was in
existence 'only' 3 billion years after the Big Bang.  Researchers
think the reason the galaxy is so well formed may have something to do
with the existence of a dwarf galaxy near to it.  Computer simulations
indicate that gravitational interactions between the two, which appear
to be in the process of colliding, may have helped BX442 take shape.


SILVER AND GOLD MATERIALISED IN DIFFERENT STELLAR EXPLOSIONS
Heidelberg, Universität

In the quest for the cosmic origins of heavy elements, scientists have
established that silver can only have materialised during the
explosion of clearly defined types of star.  Those are different from
the kinds of stars that can produce gold when they explode.  The
evidence comes from the measurement of various high-mass stars with
the help of which the stepwise evolution of the components of all
matter can be reconstructed.  The light elements, helium and traces of
lithium, came into being a few minutes after the Big Bang.  All
heavier elements materialised later in the interiors of stars or
during stellar explosions, with each generation of stars contributing
a little to enriching the Universe with chemical elements.  The
elements that a star can generate in its 'lifetime' depend largely on
its mass.  At the end of their lives, stars about ten times the mass
of the Sun explode as supernovae, producing elements sometimes heavier
than iron. Depending on how massive the star originally was, silver
and gold can materialise in that way.

When various stars of the same mass explode, the ratio of elements
generated and ejected is identical.  That constant composition is
perpetuated in the subsequent generations of stars forming from the
remnants of their predecessors.  Investigations have now demonstrated
that the amount of silver in the stars measured is completely
independent of the amounts of other heavy elements like gold.  That
indicates that during a supernova explosion silver is created by a
process entirely different from that in which gold forms.


COSMIC LITHIUM IN THE EARLY UNIVERSE
Science Daily

Astrophysicists have explored a discrepancy between the amount of
lithium predicted by the standard models of elemental production
during the Big Bang and the amount of lithium observed in the gas of
the Small Magellanic Cloud (SMC).  The team, using observations from
the VLT in Chile, measured the amount of lithium in the interstellar
gas of the SMC, which has far fewer star-produced heavy elements than
the Milky Way.  Scientists believe that, in addition to the production
of elements by fusion in the cores of stars, conditions immediately
after the Big Bang led to the formation of some elements, including a
small amount of lithium.  Stars in the Milky Way have about four times
less lithium on the surface than expected by Big Bang predictions.
Stellar activity often destroys lithium, or the element might sink
from the surface through lighter hydrogen, but the remarkable
consistency of the maximum level remains a challenge.  Observations of
gas in the SMC revealed the amount of lithium that predictions say
would have been produced at the Big Bang, but leave no room for
subsequent production of the element.  One explanation could be a
novel kind of physics operating at the Big Bang that left less lithium
than the Standard Model expects. To pursue that possibility, the team
will conduct three nights of observations on the VLT in November.
It will look for the lithium isotope 7Li in the Large Magellanic
Cloud (LMC) and for 6Li in both the LMC and SMC.  The standard model
expects that no 6Li was created at the Big Bang.


DARK ENERGY CLAIMED AS REAL
RAS

Over a decade ago, astronomers observing the brightnesses of distant
supernovae thought that they saw evidence that the expansion of the
Universe is accelerating.  The acceleration was attributed to a
repulsive force associated with a mystery substance that has been
called 'dark energy', that has subsequently been suggested to make up
most of the content of the cosmos.  The researchers who made the
discovery received the Nobel Prize for Physics in 2011, but the
existence of dark energy remains a topic of hot debate.  Many efforts
have been made to confirm its reality, but they are either indirect
probes of the accelerating Universe or are subject to their own
uncertainties, or both..

Some evidence in favour of dark energy comes from the 'Integrated
Sachs-Wolfe effect', named after Rainer Sachs and Arthur Wolfe.  The
cosmic microwave background (the radiation of the residual heat of the
Big Bang) is seen all over the sky.  In 1967 Sachs and Wolfe proposed
that that radiation would become slightly bluer as it passed through
the gravitational fields of lumps of matter.  In 1996, Robert
Crittenden and Neil Turok took the idea to the next level, suggesting
that astronomers could look for small changes in the energy of the
radiation by comparing maps of its temperature with maps of galaxies
in the local Universe.  In the absence of dark energy, or a large
curvature in the Universe, there would be no correspondence between
the two maps (the distant cosmic microwave background and relatively
closer distribution of galaxies), but the existence of dark energy
would lead to the strange, counter-intuitive effect whereby the cosmic
microwave background photons would gain energy as they travelled
through large lumps of mass.

The Sachs-Wolfe effect was first detected in 2003 and was immediately
hailed as corroborative evidence for dark energy.  But the signal is
weak, as the expected correlation between maps is small, so some
scientists suggested it had other origins.  Since the first Sachs-
Wolfe papers, several astronomers have questioned the original
detections of the effect and thus called even the strongest evidence
for dark energy into question.  In a new paper, the product of nearly
two years of work at the University of Portsmouth and a university in
Munich, the collaborators have re-examined all the arguments against
the Sachs-Wolfe detection as well as improving upon the maps used in
the original work.  They conclude that it is very likely that dark
energy is responsible for the hotter parts of the cosmic microwave
background maps.