METEORITE OLDER THAN THE SUN
BBC News
A meteorite which fell to earth last year contains grains older
than the Solar System itself. Such rare and primitive space rocks,
called carbonaceous chondrites, act as time capsules, providing
astronomers with a window into the formation of the Sun and planets,
four and a half billion years ago. The meteorite was observed as a
fast-moving fireball in the sky over California and Nevada on the
morning of 2012 April 22 and was tracked by US Air Force and doppler
weather radar installations. That allowed scientists to recover
several fragments before they were contaminated by rain, which would
alter their composition. An analysis carried out by the Ames Research
Center confirmed the unusually pristine condition of three fragments
of the meteor, which may initially have been of the order of 12 feet
across, and which exploded with the force of a 4-kiloton bomb over the
Sierra Nevada foothills.
It was important to recover fragments of the meteorite before they
were exposed to rain because carbonaceous chondrites are almost 30 per
cent empty, so they act like sponges and suck in water, which rapidly
causes chemical reactions, changing their composition. It was the
first time researchers had a chance to study this type of meteorite
before it came into contact with water on Earth. The significance of
that was evident in a comparison of two samples; one of them was
recovered after exposure to rain and showed significant changes in the
composition of sulphur-bearing minerals. The diversity of minerals
and chemical features in the pristine samples indicates that they are
regolith breccia, part of the surface of the asteroid from which they
came, and provide clues to the formation history of the parent
asteroid. Some of the minerals are normally found in meteorites that
come from the region where the Earth and Venus formed, while
carbonaceous chondrites come from very primitive asteroids that formed
farther out, so the newly fallen meteorite may represent evidence of
collisions between asteroids originating in different regions at the
time the meteorite formed.
MORE EXO-COMETS FOUND
AAS
More discs of comets around distant stars have been found, more than
doubling the number known. The first such 'exo-comet' disc was
discovered in 1987, and since then three more had been found. The
frequency of comets in the Universe has implications for their role in
delivering water or other compounds to planets. Comets such as
Halley's, which has a long, elliptical path passing near the Sun every
76 years, make themselves known through the long tails of gas and
debris that they exhibit as they approach the Sun. Astronomers at the
McDonald Observatory in Texas have observed such material around seven
other stars through the absorption of a tiny amount of the host stars'
light by the exo-comets' tails; the absorption changes with time as
the comets pass by.
In our Solar System, many comets are supposed to come from the Kuiper
belt, a disc of debris beyond the orbit of Neptune, and perhaps from
the 'Oort cloud', a hypothetical larger and more distant debris disc.
Such discs are characteristic leftovers of planet formation, according
to current theory. But something must disturb the comets' orbits to
put them on a course towards their star. While collisions between
comets might do that, it is believed that the gravity of nearby
planets may also do it. In fact, in 1987 when the first exo-comet was
observed around the star Beta Pictoris, it was hypothesized that a
planet may have been responsible -- and in 2009, a giant planet was
found there. Recent years have seen great efforts to find exo-
planets, with about 500 new candidates, so there is clearly a
disparity, whose significance is not clear, between the discoveries
of planets and of the debris discs that are supposedly a corollary of
them.
FIRST 'BONE' OF MILKY WAY IDENTIFIED
Harvard-Smithsonian Center for Astrophysics
Astronomers have identified a new structure in the Milky Way: a long
tendril of dust and gas that they are calling a 'bone'. Some other
spiral galaxies display analogous internal bones. Observations,
especially at infrared wavelengths, have found long narrow features
jutting between galaxies' spiral arms, relatively straight structures
that appear to be much less massive than the curving spiral arms.
Computer simulations of galaxy formation show webs of filaments within
a spiral disc. It seems likely that the newly discovered Milky Way
feature is such a filament. Astronomers discovered it while studying
a dust cloud discovered in data from the Spitzer infrared space
telescope in 2010. Radio emissions from molecular gas show that the
feature is not a chance projection of material on the sky, but is a
real feature. Not only is it in the Galactic plane, but also it
extends to a great length -- it is more than 300 light-years long but
only 1 or 2 light-years wide. It is estimated to contain about
100,000 solar masses of material. It is not known whether it lies
within a spiral arm, or if it is part of a web connecting bolder
spiral features.
GALAXY CRASH SPARKS LARGE SPIRAL
AAS
The 'Galaxy Evolution Explorer' is a satellite designed to observe
the ultraviolet light which mostly originates from massive hot stars,
which have lifetimes that are short on the astronomical time-scale and
therefore must be newly formed. Astronomers looking at the
satellite's observations of the galaxy NGC 6872 were surprised to see
what a lot of ultraviolet light there was; it indicated that the
galaxy is five times the size of our Milky Way. It is about 200
million light-years away in the constellation Pavo, and was already
known to be among the largest spiral galaxies. 'Near' it is a
lenticular galaxy called IC 4970, which appears to have crashed
through the spiral in astronomically recent times. The ultraviolet
observations hinted that NGC 6872 was greatly enlarged by the
collision. The team went on to use data from other telescopes
including the VLT, the Two Micron All-Sky Survey and Spitzer, each of
which operates at a particular range of wavelengths, in turn showing
stars of varying ages. They found the youngest stars to be in the
outer reaches of the galaxy's enormous spiral arms, getting
progressively older toward the centre. That suggests a wave of star
formation that travelled down the arms, set off by the collision with
IC 4970.
LARGEST STRUCTURE IN THE UNIVERSE
RAS
An international team of astronomers has found the largest known
structure in the Universe. The large quasar group (LQG) is so large
that it would take light some 4 billion years to cross it. Quasars
are galactic nuclei that undergo brief periods of extremely high
brightness that make them visible across huge distances. The periods
are 'brief' in astrophysical terms but actually last 10-100 million
years. Since 1982 it has been recognized that quasars tend to clump
together, forming large quasar groups or LQGs.
The LQG that has now been found is so big that it challenges the
Cosmological Principle: the assumption (but it is no more) that the
Universe, when viewed at a sufficiently large scale, looks the same no
matter from where you observe it. To give some sense of scale,
clusters of galaxies can be 2-3 megaparsecs (Mpc; up to 10 million
light-years) across, but LQGs can be 200 Mpc or more across.
According to the Cosmological Principle and the modern theory of
cosmology, no structure should be larger than 370 Mpc, but the newly
discovered LQG has a typical dimension of 500 Mpc and its longest
dimension is 1200 Mpc (4 billion light-years or 1600 times larger than
the distance from here to Andromeda. The experts seem not to have
pronounced on the solution to that contradiction - there appears to
be a choice between asserting either that the alleged LQG is not real
or that the Cosmological Principle should be abandoned.
PLANETS
By Alan Clitherow, SPA Planet Section Director
For the last couple of months, Jupiter has dominated the scene for the
amateur planetary observer. High in the night sky, a brilliant object
near the V asterism marking the Hyades cluster in Taurus, Jupiter has
put on a wonderful display and I would recommend everyone to take any
opportunity to look at the detail on view. Jupiter will continue to be
worth observing until mid to late April from the UK. There are
several things to watch out for; the Great Red Spot (GRS), although
now a more delicate pink or rose colour rather than a ruddy red, still
shows well, but following it as the planet rotates is a large
disturbed area. Such a feature is not uncommon, but recently
(January 15) the area has shown some large-scale features, making
detail easier to observe within its massive eddies of gas. In
addition there has been a resurgence of the dark areas on the southern
edge of the North Equatorial Belt (NEB) which are throwing great
festoons of dark material into the cream-coloured Equatorial Zone
(EZ). There are also signs that a feature known as a South Equatorial
Disturbance (SED) (a major storm within the EZ) may be forming.
Looking ahead to February, it is the turn of Mercury to be observed,
as it gives us its most favourable evening apparition of the year.
Having moved directly behind the Sun on January 18 (superior
conjunction), Mercury becomes visible very low in the evening sky
right from the start of the month but, for the first few days, will
set very soon and be hard to observe in detail. By February 16, from
mid-UK latitudes, the Sun sets at around 1720 UT, when Mercury will be
some 14° above the horizon on a compass bearing of around 245°,
appearing as a star of about magnitude -0.5; it will be easier to spot
by 1800 in a darkening sky, some 9° above the horizon. That will be
the best date to observe it,as the planet will be at its greatest
apparent angular distance from the Sun (greatest eastern elongation)
and it will show a 50% phase. Mercury is always close to the Sun and
you should take every precaution to ensure that your eyes and any
delicate equipment are never exposed to direct sunlight through
telescope, viewfinder or binoculars. To be really safe it is best to
wait until the Sun has fully set. Webcam imagers can easily catch the
planetary phase, and imagers with specialist monochrome cameras and
suitable filters can try photographing in infra-red wavelengths, as it
is possible to catch large surface albedo features in that way and it
is interesting to correlate them to surface maps made from orbiting
spacecraft. Observers with wide-field imagers might like to note that
Mercury passes very close to Mars shortly after sunset on February 8.
After February 16 Mercury will still be observable after sunset for a
few days; however, the visible phase will be shrinking rapidly along
with its apparent brightness, although the disc itself will be growing
slightly. Should you wish to do so you will be able to follow Mercury
until the end of the month, by which time it will be a thin crescent
sliver of light above the western horizon.
Saturn is becoming more and more observable. From early February the
planet still has not risen until the early hours but by the end of the
month it rises at around midnight; it is in opposition on April 28.
Early-birds can already see it in the pre-dawn sky, and I have
received my first images of the planet from section members. The
rings are very well presented to us, open by 19°, and the planet is
throwing a dark shadow, clearly visible, across the ring structure
behind it. For the whole of the rest of this decade Saturn is not
destined to rise very high in UK skies, reaching this year some 25° at
best; however, the open presentation of the rings will allow beautiful
detail to be seen when steady atmospheric conditions allow, and I
greatly look forward to seeing your images and reports as the season
progresses.
Topic: Late January Astronomy Bulletin (Read 1465 times)