NEAR MISS ASTEROIDS
IAU
On Nov. 6 at 2132 UT, asteroid 2009 VA passed the Earth just 14,000 km
above the surface, well inside the distance of geosynchronous
satellites. If it had hit, the ~6-metre space rock would have
disintegrated in the atmosphere as a spectacular fireball, causing no
significant damage to the ground. 2009 VA was discovered just 15
hours before closest approach by astronomers working at the Catalina
Sky Survey. In early October, with no warning, a ~10-metre asteroid
hit the atmosphere above Indonesia and exploded. The break-up was so
powerful that it triggered nuclear-test-ban sensors thousands of
kilometres away. A just-released analysis of infrasound data shows
that the asteroid detonated with an energy equivalent to about 50,000
tons of TNT, similar to that of a `small' atomic bomb.
SPACECRAFT SEE 'DAMP MOON SOILS'
BBC News
Data from three spacecraft, including India's Chandrayaan probe, show
that very fine films of water coat the particles that make up the
lunar soil. The rock and soil samples returned by the Apollo missions
were found to be ever so slightly 'damp' when examined in the
laboratory, but scientists could never rule out the possibility that
the water in the samples got in only after they were brought back to
Earth. The only safe scientific conclusion they could draw at the
time was that the lunar surface was all-but bone dry. Now a remote
sensing instrument on Chandrayaan-1, India's first mission to lunar
orbit, has confirmed that there is a real water signal at the Moon.
Two other satellites looking at the Moon -- the US Deep Impact probe
and the US--European Cassini spacecraft -- confirm the Chandrayaan
findings. Both collected their Moon data long ago (in the case of
Cassini, 10 years ago), but the significance of what they saw is only
now being realised. The quantity of water is seen to increase the
closer the observations are made to the poles -- the very places the
Apollo missions never went. Scientists suspect the water is created
in the soil in an interaction with the solar wind, fast-moving
particles that constantly stream away from the Sun. Harsh space
radiation triggers a chemical reaction in which oxygen atoms already
in the soil acquire hydrogen nuclei to make water molecules and the
simpler hydrogen-oxygen (OH) molecule.
Researchers have also said that preliminary data from the 'Lunar
Crater Observation and Sensing Satellite' (LCROSS) indicate that water
exists in a permanently shadowed lunar crater. On Oct. 9, the LCROSS
spacecraft and a companion rocket stage made twin impacts in crater
Cabeus near the Moon's south pole. A plume of debris travelled at a
high angle beyond the rim of Cabeus and into sunlight, while an
additional curtain of debris was ejected more laterally. Evidence of
water was seen in both the high-angle vapour plume and the ejecta
curtain created by the impact.
PREVIOUSLY UNSEEN TERRITORY ON MERCURY OBSERVED
Science Daily
The MESSENGER spacecraft's third fly-by of Mercury has given
scientists, for the first time, an almost complete view of the
planet's surface and revealed some dramatic changes in Mercury's
comet-like tail. The spacecraft's cameras and instruments revealed 6%
of the planet's surface never before seen at close range, One of the
spacecraft's instruments conducted its most extensive observations to
date of Mercury's ultra-thin atmosphere or 'exosphere'. Material in
the exosphere comes mainly from the surface of Mercury, knocked aloft
by solar radiation, solar-wind bombardment and meteoroid vaporization.
The wispy gaseous envelope is stretched by solar radiation pressure
into a long, comet-like tail, which seems to be changing as Mercury
moves round the Sun.
The observations also show that calcium and magnesium in the exosphere
exhibit different seasonal changes from sodium -- a difference that
researchers do not understand. After MESSENGER enters Mercury orbit
in 2011, it can make a continuous study of seasonal changes in all
exospheric constituents. That will provide key information on the
relative importance of the processes that generate, sustain, and
modify Mercury's atmosphere. Approximately 98% of Mercury's surface
has now been imaged. After MESSENGER goes into orbit, it will see the
polar regions, which are the only remaining unobserved areas of the
planet.
ORIGIN OF MARS' REDNESS
RAS
The widespread idea that Mars is red owing to rocks being rusted by
the water that once flooded the planet may not be correct. Recent
laboratory studies show that red dust may be formed by the ongoing
grinding of surface rocks, and liquid water need not have played any
significant role in the formation process. Mars should really look
blackish, between its white polar caps, because most of the rocks at
mid-latitudes are basalt. Accurate knowledge of the composition and
mineralogy of the planet is vital in understanding the structure and
evolution of the near-surface environment and its interaction with the
atmosphere, as well as in searching for potential habitats on Mars.
Fine red dust covers Mars' surface and is even present in the
atmosphere, dominating the weather and sometimes becoming so thick
that it plunges the planet into darkness.
In a recent laboratory study, scientists at the Mars Simulation
Laboratory used a novel technique to simulate sand transport on Mars.
They sealed sand (quartz) samples in glass flasks and mechanically
tumbled them for several months, turning each flask ten million times.
After gently tumbling pure quartz sand for seven months, almost 10% of
the sand had been reduced to dust. When scientists added powdered
magnetite, an iron oxide present in Martian basalt, to the flasks they
were surprised to see it getting redder as the flasks were tumbled.
Reddish-orange material deposits, which resemble mineral mantles
known as desert varnish, started appearing on the tumbled flasks.
Subsequent analysis of the flask material and dust has shown that the
magnetite was transformed into the red mineral haematite, through a
completely mechanical process without the presence of water. The
scientists suspect that, as the quartz sand grains are tumbled around,
they get quickly eroded and an alteration of minerals through contact
ensues. The first experiments show that this process occurs not only
in air but also in a dried carbon dioxide atmosphere, i.e. in
conditions that resemble those occurring on Mars.
SATELLITES OF JUPITER AND (50000) QUAOAR
IAU
The IAU has approved a new designation and name for the 50th confirmed
satellite of Jupiter, S/2003 J 17, which was re-discovered this past
August. What a pity that the name is not recorded here! The IAU has
also approved the name 'Weywot' for the satellite of the trans-
neptunian minor planet (50000) Quaoar.
SPITZER DISCOVERS SATURN'S LARGEST RING
NASA
Scientists using the Spitzer space telescope have discovered an
enormous and previously unknown infrared ring around Saturn. If the
ring could be seen in the night sky, it would span the width of two
Full Moons. The new belt lies at the far reaches of the Saturnian
system, with an orbit tilted 27 degrees from the main ring plane. The
bulk of its material starts about six million kilometres away from the
planet and extends outward roughly another 12 million kilometres. One
of Saturn's furthest moons, Phoebe, circles within the new-found ring,
and is probably the source of its material. The ring is tenuous,
consisting of widely dispersed particles of ice and dust. Spitzer's
infrared camera was able to observe the glow of the cool dust, which
has a temperature of only about 80 Kelvin.
The discovery may help to solve a long-standing riddle of one of
Saturn's moons. Iapetus has a strange appearance -- one side is
bright and the other is really dark. Cassini first noticed the moon
in 1671, and years later realized it has a dark side, now named
Cassini Regio in his honour. Saturn's outsize ring could explain how
Cassini Regio came to be so dark. The ring is circling in the same
direction as Phoebe, while Iapetus, the other rings and most of
Saturn's moons are all going the opposite way. According to the
scientists, some of the dark and dusty material from the outer ring
moves inward toward Iapetus and collides with it, blackening the
leading hemisphere (like our Moon, Iapetus remains in a fixed
orientation with respect to its orbital travel).
Astronomers have also discovered a satellite orbiting within the outer
B ring in Saturn's rings. The satellite, designated 2009 S 1,
protrudes above the rings by approximately 150 m; the inferred
diameter of the satellite, assuming an orbit co-planar with the ring
material, is consequently approximately 300 m.
EXOPLANETS CLUE TO SUN'S CURIOUS CHEMISTRY
ESO
Astronomers have found that Sun-like stars that host planets have
destroyed their lithium much more efficiently than 'planet-free'
stars. For almost 10 years astronomers have tried to find out what
distinguishes stars with planetary systems from their barren cousins.
They have now found that the amount of lithium in Sun-like stars
depends on whether or not they have planets. The low abundance of
lithium in the Sun, as compared to otherwise similar stars, has been
known for some time but not understood.
The astronomers made an analysis of 500 stars, including 70 planet-
hosting ones. Most of the stars were monitored for several years with
the 'High-Accuracy Radial-Velocity Planet Searcher' (HARPS) attached
to ESO's 3.6-metre telescope. The astronomers looked in particular at
Sun-like stars, almost a quarter of the whole sample. They found that
the majority of stars hosting planets possess less than 1% of the
amount of lithium shown by most of the other stars. Unlike most other
elements lighter than iron, the light nuclei of lithium, beryllium and
boron are not normally produced in significant amounts in stars.
Instead, it is thought that lithium, composed of just three protons
and four neutrons, was mainly produced just after the Big Bang, 13.7
billion years ago. Most stars will thus have the same amount of
lithium, unless they have destroyed it themselves. It seems still not
to have been explained why having planets would destroy lithium. But
the empirical result promises to provide astronomers with an effective
way to search for planetary systems -- low-lithium stars are worthy of
further significant observing efforts.
ETA CARINAE
IAU
Astronomers using the Hubble telescope report that the central star in
Eta Carina has recently brightened to magnitude 5.1. It now accounts
for half of the total light seen in the Homunculus nebula, compared to
less than 10% before 1995. Eta Carinae is one of the most massive and
luminous stars in our galaxy, and is suspected to be a binary system
with a period of 5.54 years. In 1822, the star brightened to 2nd
magnitude, and in 1827 to 1st magnitude. Fifteen years later it
outshone all stars in the sky apart from Sirius. It then faded to 8th
magnitude in 1900 but has slowly been getting brighter since then.
Such massive stars have a lifetime of only one million years and Eta
Carinae is expected to end its life as a supernova within the next
100,000 years or so.
NEW CLASS OF EXPLODING STAR
University of California, Berkeley
An unusual supernova rediscovered in 7-year-old data may be a new type
of exploding star. The supernova was detected in 2002 in the galaxy
NGC 1821, in the constellation Lepus, by the Katzman Automatic Imaging
Telescope (KAIT) at Lick Observatory as well as by amateur
astronomers, but at the time it was erroneously classified as a common
Type II supernova. Now it has been realized to be an unusual kind of
supernova more akin to a Type Ia. The spectrum had been obtained with
the Keck I telescope, 7 days after discovery. Follow-up images made
by KAIT showed that the brightness of SN 2002bj dropped off so
rapidly that the supernova disappeared from sight 20 days after its
discovery. An image of that area of the sky taken seven days prior to
discovery showed no supernova, so it had brightened and dimmed into
obscurity in less than 27 days, whereas most supernovae brighten and
dim over 3 to 4 months.
The supernova's rapidity, coupled with its faintness, the strong
signature of helium in the spectrum of the explosion, and the absence
of hydrogen points toward helium detonation on a white dwarf.
A suggested theoretical explanation involves AM Canum Venaticorum
(AM CVn) binary systems, which are composed of two white dwarfs, one
of which is primarily made of helium that is being slowly transferred
onto its companion. White dwarfs are stars that have burned their
hydrogen down to carbon and oxygen or, in some particular cases, to
helium. In AM CVn systems, when enough helium has been accumulated on
the surface of the primary white dwarf, an explosion occurs; but the
explosion is nothing like a regular Type Ia explosion because the
white dwarf survives the detonation of the helium shell instead of
being totally disrupted. The event has similarities to both a nova
and a supernova. Novae occur when hydrogen falls onto a star and
accumulates in a shell that can flare up as brief thermonuclear
explosions. SN 2002bj is a 'super' nova, generating about 1,000 times
the energy of a standard nova.
SHEDDING LIGHT ON THE COSMIC SKELETON
ESO
Matter is not distributed uniformly in the Universe. In our cosmic
vicinity, stars form in galaxies, and galaxies usually form groups and
clusters. Some cosmological theories would like matter also to
clump on a still larger scale in the so-called 'cosmic web', in which
galaxies are embedded in filaments stretching between voids. The
filaments are millions of light-years long and constitute the skeleton
of the Universe: galaxies gather around them, and galaxy clusters form
at their intersections. Scientists do not know how they would swirl
into existence. Although massive filamentary structures have been
observed at relatively small distances from us, solid proof of their
existence in the more distant Universe has been lacking.
Now astronomers have discovered a large structure around a cluster of
galaxies about seven billion light-years away. They have studied the
structure in some detail, estimating the distances of over 150
galaxies, and hence obtaining a three-dimensional view of the
structure. They have identified several groups of galaxies
surrounding the main cluster and were able to distinguish tens of such
clumps, each typically ten times as massive as our own Milky Way
galaxy (some as much as a thousand times more massive), while they
estimate that the mass of the cluster amounts to at least ten thousand
times the mass of the Milky Way.
RAPID STAR FORMATION IN YOUNG GALAXIES
RAS
According to scientists at Durham University, 'stellar nurseries'
within the first galaxies gave birth to stars at a much more rapid
rate than previously supposed. The research looked back 12.5 billion
years to one of the most distant known galaxies, seen as it appeared
about one billion years after the Big Bang. Taking advantage of
gravitational lensing, the scientists observed the rapid bursts of
star formation in the galaxy, called MS1358arc. Within the star-
forming regions, new stars were being created at a rate of about 50
stars per year -- around 100 times faster than had been previously
thought.
The researchers say that the galaxy, which measures 6,000 light years
across, has all the characteristics that would allow it to evolve into
a galaxy such as our Milky Way. Given the size of the star-forming
regions, we would expect it to be forming stars at a rate of about one
Sun per year, but it seems to be much more active than that.
'MOST DISTANT' GALAXY GROUP OBSERVED
NASA
Astronomers using the Chandra X-Ray Observatory have discovered a
group of galaxies at a record distance. The cluster, named JKCS041,
is 10.2 billion light-years away -- a billion light-years further away
than the previous record holder. Galaxy clusters are the Universe's
largest objects bound by gravity, and experts hope that the findings
will help them understand better how the cosmos has changed over time.
Scientists think that JKCS041 is at the farthest point at which galaxy
clusters could exist in the early Universe. They do not believe that
gravity can work fast enough to make galaxy clusters much earlier, but
have detected what they believe to be the light from individual
galaxies out to about 13 billion light-years.
SIGNATURE OF ANTI-MATTER DETECTED IN LIGHTNING
National Geographic
Designed to scan the heavens thousands to billions of light-years
beyond the Solar System for gamma rays, the Fermi gamma-ray space
telescope has also detected 17 gamma-ray flashes associated with
terrestrial storms, and some of those flashes have contained a
surprising signature of anti-matter. During two recent lightning
storms, Fermi recorded gamma-ray emissions of a particular energy that
could have been produced only by the decay of energetic positrons, the
anti-matter equivalent of electrons. The observations are the first
of their kind for lightning storms. The 17 flashes Fermi detected
occurred just before, during and immediately after lightning strikes,
as tracked by the World-Wide Lightning Location Network.
During lightning storms previously observed by other spacecraft,
energetic electrons moving toward the craft slowed down and produced
gamma rays. The unusual positron signature seen by Fermi suggests that
the normal orientation for an electric field associated with a
lightning storm somehow reversed, Modellers are now trying to dream up
how the field reversal could have occurred. Recording gamma-ray
flashes -- which might harm aeroplanes in storms -- isn't new; the
first were found by Compton in the early 1990s, and the RHESSI
satellite, which primarily looks at X-ray and gamma-ray emissions from
the Sun, has found some 800 terrestrial gamma-ray flashes.
NASA AND ESA SIGN MARS AGREEMENT
BBC News
The US and European space agencies have signed a 'letter of intent'
that ties their Mars programmes together. The agreement allows
scientists and engineers to begin the joint planning of missions. The
union will start with a European-led orbiter in 2016, and continue
with surface rovers in 2018, and perhaps a network of landers in 2018.
The ultimate aim is a mission to return Mars rock and soils.
Topic: November Astronomy Bulletin (Read 1180 times)