EARTH'S ATMOSPHERE CAME FROM SPACE?
National Geographic News
A new study proposes that the gases that make up Earth's atmosphere
came from a swarm of comets, not from volcanoes as has been thought.
The new theory came about after scientists discovered that pristine
samples of the elements krypton and xenon, recently collected from
deep within the Earth, have the same chemical make-up as ancient
meteorites.
Most of the gases in the air we breathe originated in the solar
nebula, the cloud of gas and dust that formed the Sun and planets.
The gases became gravitationally bound to the young Earth and were
then transported into the Earth's interior -- leaking out over the
aeons through vulcanism and cracks in the Earth's crust. It is true
that volcanoes emitted some gases, but now it is being suggested that
that contribution was insignificant. Scientists studied krypton and
xenon because they are 'noble' gases, so called because they do not
associate chemically with most other elements. As a result, most of
the Earth's krypton has remained unchanged since its arrival on our
planet. The team claims that our atmosphere formed when gas- and
water-rich comets bombarded the Earth shortly after its formation.
APPEARANCE OF IAPETUS EXPLAINED
Southwest Research Institute
Analysis and modelling of Cassini imaging and heat-mapping data have
confirmed and extended previous ideas that migrating ice, triggered by
infalling reddish dust that darkens and warms the surface, may explain
the two-toned appearance of Saturn's moon Iapetus. Shortly after he
discovered Iapetus in 1671, the French-Italian astronomer Giovanni
Domenico Cassini noticed that the surface is much darker on its
leading side than on the opposite trailing hemisphere. Images from
Voyager and Cassini have shown that the dark material on the leading
side extends onto the trailing side near the equator. The bright
material on the trailing side, which consists mostly of water ice and
is 10 times brighter than the dark material, extends across the north
and south poles onto the leading side.
Findings made by Cassini's cameras during the spacecraft's close
fly-by of Iapetus on 2007 September 10 and on previous encounters show
that both the bright and dark materials on Iapetus' leading side are
redder than similar material on the trailing side, suggesting that the
leading side is coloured (and slightly darkened) by reddish dust that
Iapetus has swept up in its orbit around Saturn. This observation
confirms an old idea that Iapetus' leading side has been darkened
somewhat by infalling dark dust from an external source, perhaps from
one or more of Saturn's outer moons. The dust may be related to the
giant ring around Saturn recently discovered by the Spitzer space
telescope. However, the new images show that infalling dust cannot be
the sole cause of the extreme global brightness dichotomy. It is
impossible that the very complicated and sharp boundaries between the
dark and the bright regions are formed by simple infall of material.
Close-up images provide a clue, showing evidence for thermal
segregation in which water ice has migrated locally from sunward-
facing (warmer) areas to nearby poleward-facing (colder) areas,
darkening and warming the former and brightening and cooling the
latter.
Cassini's infrared observations in 2005 and 2007 found that the dark
regions reach temperatures high enough (-144C) to evaporate many
metres of ice over billions of years. Iapetus' long rotation period,
79 days, contributes to such 'warm' temperatures by giving the Sun
more time to warm the surface each day than on faster-rotating moons.
The infalling dust darkens the leading side of Iapetus, which
therefore absorbs more sunlight and heats up enough to trigger
evaporation of the ice near the equator. The evaporating ice
recondenses on the colder and brighter poles and on the trailing
hemisphere. The loss of ice leaves dark material behind, causing
further darkening, warming, and ice evaporation on the leading side
and near the equator. Simultaneously, the trailing side and poles
continue to brighten and cool owing to ice condensation until Iapetus
ends up with extreme contrasts in surface brightness in the pattern
seen today.
MIZAR/ALCOR SYSTEM IS SEXTUPLET
Science Daily
Until light pollution got so bad in recent years, it was obvious even
to the layman that one of the principal stars in the Plough is, in
fact, two stars quite close together. The bright one is Mizar; its
companion Alcor is now invisible to the naked eye from many locations
owing to its relative faintness. Mizar is itself now recognized as a
pair of binaries -- what was once thought of as a single star is
actually two pairs of stars orbiting one another. Alcor has sometimes
been considered a fifth member of the system, orbiting far away from
the Mizar quadruplet.
Now, astronomers have discovered that Alcor is also actually two
stars, and is apparently gravitationally bound to the Mizar system,
making the whole group a sextuplet. The researchers were actually
looking for planets when they found a faint M-type dwarf star almost
hidden in the glare of Alcor. Not only did the project reveal the
image of the star, but its presence was able to explain slight
deviations in movement that scientists had noticed in Alcor. In
addition, it explains the unexpectedly high levels of X-rays coming
from Alcor -- dwarf stars naturally radiate high levels of X-rays.
Some astronomers have questioned whether Alcor is truly a part of the
system made up of the Mizar group of stars, because Alcor's motion is
not identical with that of the Mizar group. However, the team says
that indeed Alcor is part of the same system, and that the influence
of the newly discovered companion is partly responsible for Alcor's
unexpected motion.
ALLEGED EXOPLANET DOES NOT EXIST
NASA/JPL-Caltech
A proposed planet near a star some 6 parsecs away may not exist
after all. The finding is also a strike against a planet-seeking
strategy called astrometry, which measures the side-to-side motion of
a star on the sky to see whether any unseen bodies might be orbiting
it. Ground-based astrometry has been used for more than a century,
but none of the extrasolar planets it has detected has been verified
in subsequent studies. In May, astronomers at the Jet Propulsion
Laboratory in California, using a telescope at the Palomar
Observatory, raised fresh hopes for the technique when they announced
an exoplanet, six times more massive than Jupiter, orbiting VB10, a
star about one-thirteenth the mass of the Sun,. However, astronomers
from the Georg-August University in Gottingen, Germany, who used the
radial-velocity technique, which has found most of the extrasolar
planets detected so far, at the VLT, found nothing. Radial-velocity
measurements are typically made in the visible part of the
electromagnetic spectrum, but as VB10 gives most of its light as
infrared radiation, the VLT observers operated in the infrared.
The astronomers would definitely have seen significant variation in
the data if the planet were there. In a rearguard action, the JPL
astronomers claim that the radial-velocity technique only rules out
the presence of any planet that is at least three times more massive
than Jupiter, adding that the method "limits certain orbits for
possible planets".
But Alan Boss, an exoplanet enthusiast at the Carnegie Institution,
points to the notorious episode in 1963, when Dutch astrometrist Piet
van de Kamp claimed that two planets were orbiting Barnard's Star -- a
finding disproved a decade later. The dispute over the VB10 planet,
says Boss, "is another example of how hard it is to detect extra-solar
planets by astrometry from the ground". Astronomers expect astrometry
to work much better above the distorting effects of the atmosphere.
Two space missions in preparation -- ESA's GAIA, due to be launched in
2012, and NASA's Space Interferometry Mission, of indeterminate launch
date -- will use the technique to search for planets as small as the
Earth around Sun-like stars. More significantly, astrometry can yield
the mass of a planet, whereas radial velocity can put only a lower
limit on it.
CYGNUS X-3
ScienceDaily
The enigmatic binary-star system known as Cygnus X-3 has fascinated
astronomers for decades. It is thought to be either a small black
hole or a neutron star and an ordinary, albeit massive, star orbiting
one another. Now, a team of researchers has detected high-energy
gamma-rays from the system. The findings may provide a new window on
how Cygnus X-3 accelerates charged particles to enormous energies.
The gamma-rays, the most powerful type of electromagnetic radiation,
were detected by the Italian gamma-ray satellite AGILE (Astro-
rivelatore Gamma ad Immagini Leggero). From those observations a
clockwork pattern of the gamma-ray emission was noted, which always
seems to occur just before the onset of the powerful radio jets.
Cygnus X-3 is a strange case indeed, being one of the brightest radio
sources in the Galaxy except when it descends into a radio-quenched
state. Now the extremely energetic gamma-rays have been observed
during the low state. That may be indicating the preparation of the
major radio flare, which follows just days after, when the source
shoots up energetic radio jets from the core of the compact object.
The new gamma-ray findings might also shed light on how distant
quasars, powered by supermassive black holes, pump even greater
amounts of energy into space. Micro-quasars such as Cygnus X-3 permit
studies of jet phenomena such as dominate the most luminous quasars'
emission. Because the emissions from micro-quasars vary on time-
scales of days to weeks rather than the decades of quasar emissions,
they present opportunities to learn about quasar activity -- always on
the assumption that the two types of object are worked by analogous
mechanisms.
The very complex behaviour of Cygnus X-3 requires monitoring
throughout the electromagnetic spectrum from radio to X-rays and
now including also gamma-ray emission. Micro-quasars have strong
magnetic fields which can store enormous amount of energy. During
gamma-ray flares the stored energy can accelerate charged particles to
very high energies, which prompts them to emit gamma-rays. Then
radio-emitting blobs are pushed out of the system, producing the major
radio flares.
HST REVEALS MOST DISTANT GALAXIES YET SEEN
RAS
Using the recently updated Hubble telescope (HST), two teams of UK
astronomers have identified galaxies which are likely to be the most
distant yet seen. The UK teams analysed infrared images from the new
'Wide Field Camera 3' instrument installed on HST during the 2009
servicing mission. The expansion of the Universe causes the light
from very distant galaxies to appear redder, so having a new camera
which is very sensitive in the infrared allows us to identify
galaxies at greater distances than was previously possible. The
new images include the region of sky known as the Hubble Ultra-Deep
Field, which astronomers analysed 5 years ago from visible-light
images. Astronomers can now look even further back in time,
identifying galaxies when the Universe was only 5% of its current age
-- within 1 billion years of the Big Bang.
As well as identifying potentially the most distant objects yet, the
new HST observations present a puzzle. Astronomers know that the gas
between galaxies in the Universe was ionized early in the history of
the cosmos, but the total light from the newly observed galaxies does
not seem to be sufficient to achieve that. The researchers are
looking forward to seeing these objects more clearly in the years
ahead. The new observations from HST are likely to be the best Hubble
will ever take, but the very distant galaxies they have now discovered
will be studied in detail by Hubble's successor, the James Webb Space
Telescope, supposed to be launched in 2014.
PETITION BY SWANSEA ASTRONOMICAL SOCIETY
Swansea Astronomical Society has occupied the Marina Towers
Observatory site on the Swansea foreshore for 16 years. It has
reluctantly decided that it cannot renew its lease for the site with
the City and County of Swansea owing to the increased costs and
charges proposed by the Council. The Society has hitherto received
financial support from the Council; however, with the proposed
withdrawal of that support, the Society, as a registered charity, is
unable to finance a service for the community of Swansea in the form
of regular public and educational events at the site. During the past
year the Society opened the Observatory and its Exhibition Room on 44
occasions to the public and schools from Swansea and surrounding
districts. Anyone wishing to sign a petition to keep Swansea
Observatory open may do so by clicking on the Number 10 petition
regarding the Marina Towers (as featured in the December edition of
Astronomy Now). The web address is:
http://petitions.number10.gov.uk/ObservatoryTower The deadline for signing
up is January 23.
Topic: Mid December Astronomy Bulletin (Read 928 times)