LUTETIA: A RARE SURVIVOR FROM THE BIRTH OF THE SOLAR SYSTEM
ESO
New observations indicate that the asteroid Lutetia is a leftover
fragment of the same original material that formed the Earth, Venus
and Mercury. In 2010 the spacecraft Rosetta passed within 2000 miles
of Lutetia. Earlier studies of its colour and surface properties had
already shown that Lutetia is an unusual member of the asteroid main
belt. The spectrum of Lutetia matches that of one, rather rare, type
of meteorite -- enstatite chondrites -- found on Earth. Enstatite
chondrites are thought to be material that dates from the early Solar
System and to have formed close to the young Sun and been a major
building block in the formation of the rocky planets, in particular
the Earth, Venus and Mercury. Lutetia seems to have originated not in
the main belt of asteroids, where it is now, but much closer to the
Sun.
Astronomers have estimated that less than 2% of the bodies located in
the region where the Earth formed ended up in the main asteroid belt.
Most of the bodies of the inner Solar System disappeared after a few
million years as they were incorporated into the young planets that
were forming. Lutetia, which is about 100 km across, may have been
tossed out from the inner parts of the young Solar System if it passed
close to one of the rocky planets and thereby had its orbit
dramatically altered.
A STAR WITH SPIRAL ARMS
NASA
Researchers using the Japanese Subaru telescope in Hawaii have found a
star with spiral arms. The name of the star is SAO 206462. It is a
young star some 400 light-years away in the constellation Lupus. It
attracted attention because it has a circumstellar disc -- that is, a
broad disc of dust and gas surrounding the star. Researchers wondered
if new planets might be coalescing inside the disc, which is about
twice the diameter of the orbit of Pluto, but they found arms, not
planets. Spiral arms are familiar around galaxies, but to find them
around an individual star is unprecedented. The arms might be a sign
that planets are forming within the disc; theoretical models indicate
that a single embedded planet may produce a spiral arm on each side of
a disc. The structures around SAO 206462, however, do not form a
matched pair. Discs round other stars have shown other types of
structure, and it seems a bit facile just to say that they could all
be caused by planets moving or forming there. The researchers in the
present case themselves have cautioned that processes unrelated to
planets might give rise to the structures.
STARS CAN FORM IN IMPROBABLE ENVIRONMENTS
NASA
Researchers using a space telescope named GALEX have been finding
stars in galactic environments where star formation would not be
expected to happen. GALEX, which stands for Galaxy Evolution
Explorer, was launched in 2003 to study how galaxies change and evolve
as new stars form in them. It observes in the ultraviolet and is
thereby particularly effective at seeing young hot stars; it can
detect stars being born more than halfway across the Universe.
In some GALEX images, stars can be seen forming outside galaxies, in
places where the gas density ought to be too low for star birth to
occur. Stars are born when interstellar clouds of gas collapse and
contract under the pull of their own gravity. When a cloud gets dense
and hot enough as it collapses, nuclear fusion occurs and a star is
born. We see the process happening in the gas-laden spiral arms of the
Milky Way. But in other galaxies GALEX sees stars forming far
outside the gassy spiral disc. It has also found stars being born in
elliptical and irregular galaxies thought to be gas-poor, and even in
cold primordial gas clouds, which are small and would seem to be
barely massive enough to hang together.
GAMMA-RAY BURST SHOWS ABUNDANT METALLIC ELEMENTS IN EARLY UNIVERSE
ESO
Gamma-ray bursts are very powerful explosions that are briefly visible
at very great distances. They are first detected by orbiting
observatories that then report their positions. That allows immediate
follow-up by large ground-based telescopes that can detect the
visible-light and infrared afterglow that the bursts emit over the
succeeding hours and days. One such burst, called GRB 090323, was
observed with the VLT just one day after it exploded. Its spectrum
showed absorption lines from its own host galaxy and another galaxy
nearby, galaxies that are being seen as they were about 12 billion
years ago. Surprisingly, the heavy-element abundances in the distant
galaxies is higher than in the Sun.
It is expected that galaxies in the early Universe would contain
smaller amounts of heavier elements than galaxies at the present day.
The heavy elements are produced by successive generations of stars,
gradually enriching the gas in galaxies. The recently observed pair
of young galaxies must have formed new stars at a rapid rate, to have
enriched their gas so strongly and quickly. As the two galaxies are
close to each other they may be in the process of merging, which would
provoke a lot of star formation when the gas clouds collide.
HUBBLE OBSERVES DISC AROUND BLACK HOLE
ScienceDaily
Quasi-stellar objects (quasars) are thought to consist of glowing
discs of matter orbiting around super-massive black holes, heating up
and emitting extremely bright radiation as they do so. Quasar discs
may have sizes of a few light-days, dozens of times the size of
Neptune's orbit, but they are much too far away for their structure to
be seen directly. Recently, however, observations have been made with
the Hubble telescope of quasars that are seen behind other galaxies.
Gravitational 'lensing' by individual massive stars in a foreground
galaxy can on occasion have the effect of focusing light from regions
in the quasar disc, offering some, though crude, resolution of the
disc. As the stars move across the line of sight to the quasar, the
gravitational effects amplify the light from different parts of the
disc, giving some colour information for the different regions. That
appeared to happen in one case among the recent observations. From
records of the variation in colour, the observers tried to reconstruct
the colour profile across the disc. That is of interest because the
temperature of a disc increases the closer it is to the black hole,
and the colours emitted by the hot matter get bluer the hotter they
are. That allowed the team to estimate the diameter of the disc,
and plot how hot it is as a function of distance from the centre.
They found that the disc is between four and eleven light-days
across (approximately 100 to 300 billion kilometres).
VOYAGER 2 TO SWITCH TO BACKUP THRUSTER
NASA/Jet Propulsion Laboratory.
NASA's Deep Space Network has sent commands to the Voyager 2
spacecraft to switch to the backup set of thrusters that control the
roll of the spacecraft. Confirmation has been received that the
spacecraft accepted the commands. The change will allow the
34-year-old spacecraft to reduce the amount of power it requires to
operate and use previously unused thrusters as it continues its
journey toward interstellar space, beyond our Solar System. Launched
in 1977, Voyager 1 and Voyager 2 are each equipped with six sets, or
pairs, of thrusters to control their movement. They include three
pairs of primary thrusters and three backup pairs. Voyager 2 is
currently using the two pairs of backup thrusters that control the
pitch and yaw motion of the spacecraft. Switching to the backup pair
that controls roll motion will allow engineers to turn off the heater
that keeps the fuel line to the primary thruster warm, saving about 12
watts of power. The spacecraft's power supply now provides about 270
watts of electricity; by reducing its power usage, it can continue to
operate for another decade even as its available power continues to
decline. Voyager 2 is currently about 14 billion kilometres away, in
the 'heliosheath', where the solar wind, which streams out from the
Sun, is slowed by the pressure (infinitesimal as it is) of
interstellar gas.
PHOBOS PROBE FAILURE
BBC News
The Russian Phobos-Grunt probe intended to go to Mars was launched
successfully but then the engine failed to fire to put it on the
correct interplanetary path, and the craft is currently stuck in Earth
orbit. Almost two and a half hours into the mission, the huge cruise
stage of Phobos-Grunt should have made the first of two firings, to
raise the orbit and to send the mission on to Mars. Russian officials
say that neither of those planned engine burns occurred. Reports
suggest that the spacecraft attempted to orientate itself in space by
the stars, failed to pick them up, and therefore did not execute the
firings as planned. If the problem is simply a software issue and
engineers can upload new commands, they have a chance of rescuing the
mission. They have two weeks to correct the fault before the probe's
batteries run out.
The project is Russia's most ambitious space venture in recent years.
It has been designed to collect rock and dust samples from Mars' moon
Phobos and bring them back for study. Scientists hope that the dusty
debris would provide fresh insights into the origin of the moon, which
is only 27 km across and which is suspected of being a captured
asteroid. The spacecraft is also carrying China's first Mars
satellite, Yinghuo-1. The Russians had been hoping that Phobos-Grunt
would finally bury their Martian curse. They have despatched a total
of 16 missions to Mars since the 1960s. None has successfully
completed its goals, with the most recent endeavour -- the
sophisticated Mars-96 spacecraft -- being destroyed in a failed
launch. If engineers can correct the current problem, Phobos-Grunt
should reach Mars late next year. After dumping the cruise stage and
releasing Yinghuo-1, the main spacecraft would then manoeuvre itself
into position to land on Phobos. Phobos-Grunt is a hefty spacecraft,
and requires several tasks to be carried out successively --
travelling to Mars, landing on Phobos, picking up samples, and then
despatching them home. The total mass for the mission with all its
fuel is more than 13 tons. That makes the venture the biggest
Solar-System expedition ever, a title previously held by the six-ton
Cassini-Huygens craft launched to Saturn in 1997.
CANADIAN X-RAY SPECTROMETER HEADED TO MARS
QMI Agency
NASA's new rover, Curiosity, will carry a piece of Canada with it when
it goes to Mars later this month. A Canadian-made instrument called
the Alpha Particle X-ray Spectrometer (APXS) will help the rover to
determine the chemical composition of rocks and soils. About the size
of a soup tin, the APXS will sit on the end of a robotic arm. It is
moved in close to whatever it is required to investigate, then bombards
it with alpha particles and X-rays to study its composition. Curiosity
is to be launched on November 25.
Topic: Mid November Astronomy Bulletin (Read 844 times)