WATER FOUND ON MARS
NASA
Laboratory tests made on board the Phoenix Mars Lander have identified
water in a soil sample. With interesting results so far and the
spacecraft in good working order, NASA has announced that operational
funding for the mission will be extended by all of 5 weeks until
September 30. The soil sample came from a trench approximately two
inches deep. When the robotic arm first reached that depth, it hit a
hard layer of frozen soil. Two attempts to deliver samples of the icy
soil on days when fresh material was exposed were foiled when the
samples became stuck inside the scoop. Most of the material in the
most recent sample had been exposed to the air for 2 days, letting
some of the water in the sample evaporate and leaving the soil easier
to handle. Since landing on May 25, Phoenix has been studying soil
with a chemistry lab, a microscope, a conductivity probe and cameras.
Besides confirming the 2002 finding from orbit of ice near the surface
and deciphering the newly observed stickiness, the scientific team is
trying to determine whether the ice ever thaws enough to be available
for biological purposes and whether carbon-containing chemicals and
other raw materials for life are present.
CORES OF JUPITER AND SATURN CONTAIN LIQUID METALLIC HELIUM
University of California, Berkeley
Jupiter and Saturn have strange metallic cores, according to a new
study by researchers at Berkeley and London. The study concludes that
metallic helium is less rare than was previously thought, and is
produced under the kinds of conditions present at the centres of giant
gaseous planets, mixing with metallic hydrogen to form a liquid metal
alloy.
The group studies pressures tens of millions of times greater than the
Earth's atmospheric pressure -- the sort of pressures obtaining at the
centres of Jupiter and Saturn, so-called gas giants that lack a solid
surface. The core of the Earth, which is small and dense compared to
the cores of gas giants, is at about 3.5 million times atmospheric
pressure. Pressures at Jupiter's core reach 70 million times the
Earth's atmospheric pressure, the planet's great size more than making
up for its low density. The cores of Jupiter and Saturn are thought
to be at 10,000 to 20,000 degrees Celsius. Most studies of materials
in gaseous planets have focussed on hydrogen because it is the
predominant element, both in those planets and in the Universe in
general, but the new research focussed on helium, the second-most-
abundant element, which comprises about 25% of the Universe by mass.
The scientists had to use theory to calculate the behaviour of helium
under pressures and temperatures that are altogether too high to
replicate in the laboratory; although the results could at best be
approximations, they closely matched experimental results for lower
pressures.
Under terrestrial conditions, helium is a colourless, transparent,
electrically insulating gas, but the researchers found that at the
pressures and temperatures found at the centres of Jupiter and Saturn
helium turns into a liquid metal, like mercury. The finding was a
surprise, as scientists had supposed that high pressures and high
temperatures would make metallization of elements such as helium more
difficult, not easier. It was, however, recently discovered that
hydrogen becomes metallic at lower pressures than was previously
appreciated.
BARRED SPIRALS ARE LATECOMERS IN THE UNIVERSE
STSI
The spiral arms of many large galaxies do not start from the exact
centre but from the ends of a more or less straight 'bar' across the
nucleus. Astronomers found that, among more than 2,000 spiral
galaxies in a census made with the Hubble telescope, only 20% of
spirals had central bars 7 billion years ago, whereas 70% have them
now in the 'local Universe'. The recently forming bars are found
mostly in the small, low-mass galaxies, whereas among the most massive
galaxies the fraction of bars was the same in the past as it is today.
Astronomers already thought that evolution tends to be faster for more
massive galaxies, which form their stars early and fast and then fade
into red discs. Low-mass galaxies form stars at a slower pace, but
now we see that they also make their bars more slowly too. Our Milky
Way galaxy is a massive spiral, and recently evidence has been found
that it has a central bar that may well be like the bars seen in other
large galaxies in the Hubble survey.
M87 MAY HAVE APPROPRIATED GLOBULAR CLUSTERS IN VIRGO
Science Daily
Globular star clusters, dense assemblies of hundreds of thousands of
stars, contain some of the oldest surviving stars in the Universe.
A new international study of globular clusters outside our Milky Way
galaxy has found evidence that they are most likely to form in dense
regions, where star birth occurs at a rapid rate.
The nearest large cluster of galaxies is the Virgo cluster, which
includes more than 2000 galaxies and is about 54 million light-years
away. The Hubble telescope resolved the star clusters in 100 galaxies
of various sizes, shapes, and brightness -- even in faint, dwarf
galaxies. It was able to distinguish the globular clusters from stars
in our own galaxy and from background galaxies. Dwarf galaxies
closest to Virgo's crowded centre were found to contain more globular
clusters than those farther away. One seemingly very vague
interpretation of the difference is that the efficiency of star-
cluster formation depends on the environment. The giant elliptical
galaxy Messier 87 at the centre of the Virgo cluster of galaxies has
long been known to have a lot of globular star clusters. It has been
suggested that that galaxy may have acquired many of its clusters from
smaller galaxies that are being disrupted by, or merged with, M87.
That idea is supported by the fact that few or no globular clusters
have been found in galaxies within 130 000 light-years of M87.
(Compare that statement with what we just told you above, that "Dwarf
galaxies closest to Virgo's crowded centre were found to contain more
globular clusters than those farther away".) It is also supported by
spectroscopy, which has recently become possible, of the clusters.
Three-quarters -- not all -- of the clusters are deficient in heavy
elements, particularly iron, like those in dwarf galaxies near M87.
'COSMIC GHOST' DISCOVERED BY VOLUNTEER ASTRONOMER
Yale University
When Yale astrophysicists enlisted public support in cataloguing
galaxies, they never expected the strange object that Hanny van Arkel
found in archived images of the night sky. The Dutch school-teacher,
a volunteer in the 'Galaxy Zoo' project that allows members of the
public to take part in astronomical research on-line, discovered a
so-far-unique object that some observers are calling a 'cosmic ghost'.
Van Arkel came across the image of a strange, gaseous object with
a hole in the centre while classifying images of galaxies on the
http://www.galaxyzoo.org web site. When she posted about the image,
it quickly became known as 'Hanny's Voorwerp' (Dutch for 'object')
on the Galaxy Zoo forum. Astronomers who run the site began to
investigate and soon realized that van Arkel might have found a new
class of astronomical object, a galactic-scale analogue of the light
echoes that are seen round novae and supernovae in our own galaxy.
The Voorwerp does not contain any stars. Rather, it is made entirely
of gas so hot -- about 10,000 C -- that the astronomers felt that it
had to be illuminated by something powerful. Since there was no
obvious source at hand in the Voorwerp itself, the team looked for a
source of illumination around the Voorwerp; the finger of suspicion
pointed to the 'nearby' galaxy IC 2497. The suggestion is that in the
recent past there was an enormously bright quasar in IC 2497. Because
of the vast scale of the galaxy and the Voorwerp, we are seeing the
Voorwerp as it was at a time when it was still brilliantly illuminated
by the quasar, even though the quasar appears from here to have shut
down some time in the past 100,000 years, and the galaxy's black hole
itself has gone quiet.
LCROSS SPACECRAFT TO CRASH INTO THE MOON IN 2009
NASA
NASA plans to send people back to the Moon by 2020 and eventually to
set up a lunar base. A local supply of water would obviously be an
invaluable advantage to astronauts living there, but with no
atmosphere, and very large temperature swings between night and day,
most of the Moon's surface is a hostile place for water. There are,
however a few cold, dark places where frozen water might exist.
At the lunar poles, where the Sun is always low on the horizon, some
crater walls cast shadows that keep parts of the crater floors in
perpetual darkness. Temperatures there are about 40 degrees above
absolute zero, cold enough for ice to survive indefinitely.
Some time next summer, depending on the launch date, the booster
stage for NASA's LCROSS probe will be deliberately crashed into a
permanently shadowed lunar crater at 2.5 km/s, producing an explosion
equivalent to about a ton of TNT. Material will be blown out of the
crater into sunlight where any ice will vaporize and the H2O molecules
would then be split by ultraviolet light into H and OH. The other
half of LCROSS will watch what happens; mission planners hope that its
sensors will detect the spectrum of H20 in near-infrared light and
also an ultraviolet emission band of OH, and will quickly report the
results before itself crashing into the Moon four minutes later. The
explosion will probably be hidden from sight from the Earth by the
walls of the target crater, but the impact plume is expected to be
visible. In the sunlight the debris is expected to shine like a 6th-
to 8th-magnitude star and be visible in small telescopes.
Topic: Mid August Astronomy News (Read 2318 times)