SOME COMETS MAY HAVE COME FROM OTHER STARS
SwRI,
Many comets may have been born in orbit around other stars, according
to astronomers from the Southwest Research Institute (SwRI) in
Boulder, Colorado. The team's computer simulations suggested that the
Sun may have captured small icy bodies from other stars while it was
in its birth star cluster. While the Sun currently has no companion
stars, it is believed to have formed, with many other stars, from a
dense cloud of interstellar gas. In the early stages, many of the
stars may have formed lots of small icy bodies -- comets -- in discs
from which planets may have formed. Most of the comets could have
been ejected gravitationally from their original systems by newly
forming giant planets, becoming free-floating members of the cluster.
The Sun's cluster came to a violent end, however, when the hottest
young stars blew away its remaining gas. The new models indicate that
the Sun could have captured a large cloud of comets as the cluster
dispersed. The process of capture is surprisingly efficient and leads
to the possibility that the cloud consists of a potpourri of material
from other stars that formed with the Sun.
ANCIENT OCEAN MAY HAVE COVERED ONE-THIRD OF MARS
University of Colorado, Boulder
An ocean may have covered one-third of the surface of Mars some 3.5
billion years ago, according to a new study conducted by scientists at
the University of Colorado in Boulder. The study is the first to
combine the analysis of water-related features, including scores of
delta deposits and thousands of river valleys, to test for the
occurrence of an ocean sustained by a global hydrosphere on early
Mars. While the notion of a large, ancient ocean on Mars has been
repeatedly proposed and challenged, the new study provides support for
the idea that a sustained sea existed on Mars more than 3 billion
years ago. More than half of the 52 river delta deposits identified
by the researchers in the new study -- each of which was fed by
numerous river valleys -- probably marked the boundaries of the
proposed ocean, since all were at about the same elevation.
Twenty-nine of the 52 deltas were connected either to the ancient Mars
ocean or to the ground-water table of the ocean and to several large
adjacent lakes. The study implies that ancient Mars probably had an
Earth-like hydrological cycle, including precipitation, runoff, cloud
formation, and ice and ground-water accumulation. Researchers
concluded that the ocean might have covered about 36% of the planet
and contained about 124 million cubic kilometres of water, about a
tenth of the total in the Earth's oceans.
METEOR PROBABLY CAUSED FLASH ON JUPITER
STScI
Observations made by the Hubble telescope have failed to find an
origin for the flash of light seen on Jupiter on June 3. The only
plausible explanation seems to be that it came from a meteor that
burnt up above Jupiter's cloud tops and did not plunge deep enough
into the atmosphere to explode and leave behind any telltale clouds of
debris such as have been seen after previous Jupiter collisions.
Australian amateur astronomer Anthony Wesley saw the flash when he was
watching a live video feed of Jupiter from his telescope. In the
Philippines, amateur astronomer Christopher Go confirmed that he had
simultaneously recorded the transitory event on video. The two-second
flash of light in the videos of Jupiter was presumably created in the
same way as a meteor trail on Earth. A shock wave generated by ram
pressure as the meteor speeds into the planet's atmosphere heats the
impacting body to a high temperature, and as the hot object streaks
through the atmosphere, it leaves behind a glowing trail of
superheated atmospheric gases and vaporized meteor material that
rapidly cools and fades in just a few seconds. Though astronomers are
very uncertain about the rate of large meteoroid impacts on the
planets, the best guess for Jupiter is that the smallest detectable
events may happen as frequently as every few weeks. The meteor
flashes are so brief that they are easily missed, even in video
recordings, or perhaps misidentified as detector noise or cosmic-ray
hits on imaging devices.
Obviously something must have hit the planet to produce a flash bright
enough to be seen from here. Images taken by Hubble 3 days after the
flash was sighted showed no sign of debris above Jupiter's cloud tops.
That has been interpreted to mean that the object did not penetrate
beneath the clouds and explode as a fireball. If it did, previous
events would lead to an expectation that dark blast debris would have
been ejected and would have rained down onto the cloud tops, and the
impact site would have appeared dark. Dark smudges marred Jupiter's
atmosphere when a series of comet fragments hit the planet in 1994.
A similar phenomenon occurred last July when a suspected asteroid
collided with Jupiter. The latest impactor is thought to have been
smaller than those earlier ones.
EXO-PLANET SEEN TO HAVE MOVED
ESO
For the first time, astronomers have been able to follow the motion of
an exo-planet (that of Beta Pictoris) as it moves from one side of its
host star to the other. Images are available for approximately 10
exo-planets, and the planet around Beta Pictoris has the smallest
orbit known so far. It is at a distance between 8 to 15 astronomical
units -- about the distance of Saturn from the Sun. Only 12 million
years old, Beta Pictoris is 75% more massive than the Sun. It is
about 20 parsecs away (1 parsed is about 3.26 light-years) and is one
of the best-known examples of a star surrounded by a dusty debris
disc. Earlier observations showed a warp of the disc, a secondary
inclined disc, and some evidence of comets falling onto the star.
Those were indirect but telltale signs that suggested the presence of
a massive planet, whose existence is now supported by new
observations. Because the star is young, the discovery shows that
gas-giant planets can form in only a few million years, a short time
in cosmic terms.
The team used one of the 8.2-metre VLT telescopes to study the
immediate surroundings of Beta Pictoris in 2003, 2008 and 2009.
In 2003, a faint source was seen inside the disc, but it was not
possible to exclude the remote possibility that it was a background
star. In images taken in 2008 and spring 2009 the source had
disappeared. The most recent observations, taken in late 2009, showed
an object (presumed to be the same one as in 2003) on the other side
of the disc, so it seems certain that the source is a planet and that
it is orbiting the star. The short period will allow astronomers to
record the full orbit within 15 to 20 years. The planet has a mass of
about 9 Jupiter masses and the right mass and location to explain the
observed warp in the inner parts of the disc.
ANTHRACENE FOUND IN INTERSTELLAR SPACE
RAS
Anthracene molecules have been identified in an interstellar cloud in
the direction of the star BD +31 540 in Perseus, about 200 parsecs
away. Anthracene is one of the most complex carbon-containing
molecules yet found in the interstellar medium. It consists of three
fused benzene rings, containing a total of 14 carbon atoms, with a
hydrogen atom at each of the ten 'free' corners. Until now,
anthracene had been detected only in meteorites and never in the
interstellar medium.
DOUBTS ABOUT THE DARK SIDE
RAS
Research by astronomers using observations from the Wilkinson
Microwave Anisotropy Probe (WMAP) suggests that the recent allegations
about the content of the Universe may be wrong. The scientists found
evidence that the errors in the data may be much larger than
previously thought, which in turn makes the conclusions drawn from
them open to question. Launched in 2001, WMAP measures the small
differences in intensity between different directions in the Cosmic
Microwave Background (CMB) radiation, the residual heat of the Big
Bang that fills the Universe and appears over the whole of the sky.
The angular size of the ripples in the CMB is thought to be connected
with the composition of the Universe. The observations of WMAP showed
that the ripples were about twice the size of the full Moon, or around
a degree across. Just from those results, some scientists concluded
that the cosmos is made up of 4% normal matter, 22% 'dark' or
invisible matter and 74% "dark energy" -- simply a name for what was
otherwise unaccounted for.
The team used astronomical objects that appear as unresolved points
in radio telescopes to test the way the WMAP telescope smoothes
its maps. They find that the smoothing is much larger than
previously believed, suggesting that its measurement of the size of
the CMB ripples is not as accurate as was thought. If true, that
could mean that the ripples are significantly smaller, which could
imply that dark matter and "dark energy" are not present after all.
In addition, the astronomers recently collaborated in an international
team whose research suggested that the structure of the CMB may not
provide the independent check on the presence of "dark energy" that it
was thought to do.
If "dark energy" were to exist, then it has been thought to cause the
expansion of the Universe to accelerate. On their journey from the
CMB to WMAP, photons travel through superclusters of galaxies. The
photon is first blueshifted when it enters the supercluster and then
redshifted as it leaves, so the two effects cancel. However, if the
supercluster galaxies are accelerating away from each other because of
dark energy, the cancellation is not exact, so photons stay slightly
blueshifted after their passage. Slightly higher temperatures should
appear in the CMB where the photons have passed through superclusters.
However, the new results, based on the Sloan Digital Sky Survey which
surveyed 1 million luminous red galaxies, suggest that no such effect
is seen, again threatening the recent models of the Universe. If the
result is repeated in new surveys of galaxies in the southern
hemisphere then it will pull the rug out from under dark energy.
If the Universe really has no 'dark side', it will come as a relief to
some theoretical physicists. Having a model that depends on as-yet-
undetected exotic particles that might make up dark matter and the
completely unexplained dark energy has left real scientists feeling
uncomfortable. It also throws up problems for the birth of stars in
galaxies, with as much 'feedback' energy needed to prevent their
creation as gravity provides to help them form. The European PLANCK
satellite, currently collecting more CMB data, is expected to provide
new information and help to answer fundamental questions about
the nature of the Universe we live in.
HAYABUSA RETURNS TO EARTH
NASA
The sample capsule from the asteroid explorer Hayabusa, launched in
2003 by the Japan Aerospace Exploration Agency (JAXA) has returned to
Earth. With Hayabusa, JAXA scientists and engineers hoped to obtain
detailed information on electrical propulsion and autonomous
navigation, as well as an asteroid sampler and sample re-entry
capsule. The 510-kg Hayabusa spacecraft reached the asteroid Itokawa
in 2005 September. Over the next 2.5 months, it made scientific
observations of the asteroid's shape, surface, surface altitude
distribution, mineral composition, gravity, and the way it reflected
the Sun's radiation. On November 25 of that year, the craft briefly
touched down on the surface of Itokawa and attempted to sample
asteroid surface material, but there seemed to be a malfunction in the
sample-collection process. Nevertheless, scientists hope to find some
of the asteroid's surface material in the capsule.
ROSETTA SET TO ENCOUNTER ASTEROID LUTETIA
Science Daily
The European Space Agency's comet-chaser Rosetta is expected to pass
to within 3300 km of asteroid Lutetia on July 10. Rosetta started
taking navigational sightings of Lutetia at the end of May so that
ground controllers could determine any course corrections required to
achieve their intended fly-by distance. The close pass will allow
around 2 hours of good imaging. The spacecraft will instantly begin
beaming the data back to Earth and the first pictures will be released
later that evening. Rosetta flew by asteroid Steins in 2008 and other
space missions have encountered a number of asteroids, each of which
has proven to have its individual character. At present, no one knows
what Lutetia looks like. Orbiting in the main belt of asteroids
between Mars and Jupiter, it appears just as a point of light to
ground telescopes, although its magnitude suggests that it has
dimensions of the order of 100 km. A continuous variation in its
brightness makes it clear that Lutetia is rotating and has an uneven
surface.
Topic: Late June Astronomy Bulletin (Read 625 times)