CLOSE FLYBY OF TINY ASTEROID
NASA
On June 27 the tiny asteroid MD2011 MD passed the Earth at a distance
of just 12,000 km. Its trajectory took it over the southern Atlantic
Ocean and the Antarctic coast. Its trajectory was modified by the
encounter, and it is uncertain whether the object will visit us again
in the future. The asteroid poses no danger since its diameter is
estimated to be somewhere in the range 5 to 20 metres and would be
significantly reduced after a passage through the terrestrial
atmosphere (should that ever happen), so it would have only a limited
impact. To give some idea of the consequences, Meteor Crater near
Flagstaff, Arizona, is thought to have been made by the impact of a
body about 50 metres in diameter, which would have been even bigger
before passing through the atmosphere. Still, 12,000 km is really
very close, slightly less than the Earth's diameter; geostationary
satellites orbit at a distance of 36,000 km. Researchers at JPL
estimate that an event of this type happens about once every 6 years.
THERE MAY BE NO SUNSPOT CYCLE 25
Astropublishing
Three independent works, based on three different indicators of the
solar cycle, have reached the same conclusions: the next solar
maximum, of the current cycle 24, predicted to occur in 2013, will be
practically non-existent, while the following cycle, due in 2020, may
never arrive. The first of the three studies is by a team of
researchers from the [U.S.] National Solar Observatory. They modelled
the internal plasma flows that cause surface oscillations, identifying
an east-west current that begins at intermediate latitudes and moves
slowly towards the solar equator. That flow is tightly related to the
formation of new sunspots, and its behaviour in the recent past led to
the correct prediction of the late arrival of cycle 24. When one
solar cycle is under way, the flow of plasma re-organises itself for
the next cycle, but in the last few years there has been no sign of
the new flow that would eventually give life to cycle 25.
The second study uses the strength of the magnetic field in sunspots
as an index for the solar cycle. Spots typically form in magnetic
fields of 2500-3500 gauss, and do not appear at all at field strengths
below 1500 gauss. The data collected during the last 13 years show a
long-term weakening of the sunspot magnetic fields, a trend confirmed
by the increasing temperature of the spots. In cycles 23 and 24 the
mean magnetic-field strength in sunspots decreased by 50 gauss per
year, a trend that, if it continues, will soon make the average field
intensity fall below 1500 gauss, making sunspots very rare phenomena
in the next decades.
The third study looked at the migration toward the solar poles of
active regions in the corona that, for all their delicate beauty,
actually trace intense magnetic structures rooted in the solar
interior. Using highly-ionized iron present in the corona as a tracer
and examining 40 years of observations, scientists found that the
speed of migration of the active regions, typically appearing between
70° and 80° latitude, has been much slower in cycle 24. As a
consequence, the structures from cycle 23, still present beyond 80°,
may last much longer than normal, in some sense hindering the
appearance the active regions of the next cycle.
SUN AND PLANETS CONSTRUCTED DIFFERENTLY
NASA/Jet Propulsion Laboratory
Researchers analyzing samples returned by the 2004 Genesis mission
have discovered that the Sun and the inner planets may not have formed
in the manner previously supposed. Genesis collected samples from the
solar wind -- material ejected from the Sun. Such material can be
thought of as a fossil of our nebula because the preponderance of
scientific evidence suggests that the outer layer of the Sun has not
changed measurably for billions of years. The Sun contains more than
99% of all the material in the Solar System. Genesis was launched in
2000 August, and travelled to the L1 Lagrange point about 1 million
miles from the Earth, where it remained for 886 days between 2001 and
2004, passively collecting solar-wind samples. In 2004 September, the
spacecraft released a sample-return capsule, which entered the Earth's
atmosphere. Although it made a hard landing as a result of a parachute
failure, it was the first U.S. sample return since the final Apollo
lunar mission in 1972, and the first material collected beyond the
Moon.
The samples revealed slight differences between the Sun and planets in
oxygen and nitrogen, which are two of the most abundant elements in
our Solar System. Researchers found that the Earth and the Moon, as
well as Martian and other meteorites which are samples of asteroids,
have a lower concentration of O-16 than does the Sun. The implication
is that we did not form out of the same solar-nebula materials that
created the Sun -- how and why not remains to be discovered. The air
on Earth contains three different kinds of oxygen atoms which are
differentiated by the number of neutrons they contain. The vast
majority of oxygen atoms in the Solar System are composed of O-16, but
there are also tiny amounts of O-17 and O-18. Researchers studying
the oxygen of Genesis samples found that the percentage of O-16 in the
Sun is slightly higher than on Earth or on other terrestrial planets,
the other isotopes' percentages being slightly lower.
Differences were also found between the Sun and planets in the element
nitrogen. Like oxygen, nitrogen has one isotope, N-14, that makes up
nearly 100% of the atoms in the Solar System, but there is also a tiny
amount of N-15. In comparison with the Earth's atmosphere, in the Sun
and Jupiter there is slightly more N-14, but 40% less N-15. The Sun
and Jupiter appear to have the same nitrogen composition. As is the
case for oxygen, the Earth and the rest of the inner Solar System are
very different in nitrogen. These findings seem to show that the
terrestrial planets, meteorites and comets, are anomalous compared to
the initial composition of the nebula from which the Solar System
formed. Understanding the cause of such heterogeneity is the next
problem.
EVIDENCE THAT SATURN'S MOON ENCELADUS HAS SALTWATER OCEAN
University of Colorado at Boulder
Astronomers say that samples of icy spray shooting from Saturn's moon
Enceladus and collected during Cassini spacecraft fly-bys show the
strongest evidence yet for the existence of a sub-surface salt-water
ocean. The plumes shooting water vapour and tiny grains of ice into
space were originally discovered emanating from Enceladus by the
Cassini spacecraft in 2005. The plumes were originating from the
so-called 'tiger-stripe' surface fractures at that moon's south pole
and apparently have provided the material for the faint E Ring that
traces the orbit of Enceladus around Saturn. During three of
Cassini's passes through the plume in 2008 and 2009, the on-board
cosmic dust analyzer measured the composition of freshly ejected plume
grains. The icy particles hit the detector's target at speeds of up
to 11 miles per second, and were instantly vaporized; the analyzer
separated the constituents of the resulting vapour clouds.
The study shows that the ice grains found further out from Enceladus
are relatively small and mostly ice-poor, closely matching the
composition of the E Ring. Closer to the moon, however, relatively
large, salt-rich grains dominate. Researchers claim that there is
currently no plausible way to produce a steady outflow of salt-rich
grains from solid ice across all the tiger stripes other than from
salt water under Enceladus' icy surface. The study indicates that
'salt-poor' particles are being ejected from the underground ocean
through cracks in the moon at a much higher speed than the larger,
salt-rich particles. The E Ring is made up predominantly of such
salt-poor grains, although it seems that 99% of the mass of the
particles ejected by the plumes is made up of salt-rich ones. Since
the salt-rich particles were ejected at a lower speed than the
salt-poor ones, they fell back onto the moon's icy surface rather than
making it to the E Ring.
According to the researchers, the salt-rich particles have an 'ocean-
like' composition that indicates that most, if not all, of the
expelled ice comes from the evaporation of liquid salt water rather
than from the icy surface of the moon. When salt water freezes slowly
the salt is 'squeezed out', leaving pure water-ice behind. If the
plumes were coming from the surface ice, there should be very little
salt in them, which is not the case, according to the research team.
The researchers believe that perhaps 50 miles beneath the surface
crust of Enceladus, between the rocky core and the icy mantle, a layer
of water exists that is kept in a liquid state by gravitationally
driven tidal forces created by Saturn and several neighbouring moons,
as well as by heat generated by radioactive decay. According to the
scientists, roughly 200 kg of water vapour is lost every second from
the plumes, along with a smaller amount of ice grains.
NEUTRON STAR FLARES UP
European Space Agency (ESA)
The XMM-Newton space observatory has watched a faint star flare up at
X-ray wavelengths to almost 10 000 times its normal brightness.
Astronomers believe that the outburst was caused by a clump of matter
falling onto a neutron star. With a radius of about 10 km but the
mass of the Sun, a neutron star is so dense that it has a very strong
gravitational field. The clump of matter came from the neutron star's
blue-supergiant companion star. The flare lasted four hours and the
X-rays came from the gas in the clump as it was heated to millions of
degrees while being pulled into the neutron star's intense gravity
field. In fact, the clump was so big that only a small part of it
actually hit the neutron star.
XMM-Newton observed the flare during a scheduled 12.5-hour observation
of the system, which is known by its catalogue number IGR J18410-0535,
but the astronomers were unaware of the result immediately. The
telescope works through a sequence of observations that are pre-
planned to make the best use of the observing time, then sends the
data to the Earth. It was about ten days after the observation that
astronomers received the data and quickly realised that they had seen
something special. Not only did they see the flare, but the
observation lasted long enough to see it from beginning to end. An
X-ray flare of such a magnitude can be expected a few times a year at
most for that particular star system.
THE MILKY WAY'S NEWLY RECOGNIZED SPIRAL ARM
Astropublising
Scientists have discovered in the Milky Way a previously unknown
spiral arm that fits perfectly into the symmetrical pattern made by
the other arm segments already mapped. The resulting picture of the
Galaxy is a very symmetrical spiral pattern. The story of the
discovery is reminiscent of how discoveries were made decades ago,
because it was made with a small radio telescope only 1.2 metres in
diameter, from the roof of a scientific institute (the Harvard-
Smithsonian Center for Astrophysics, CfA), and not with a gigantic
instrument far from any built-up area.
The work was done by two CfA astronomers, who made use of the fact
that radio waves can penetrate the dense clouds of dust that occupy
the Galactic plane (and obscure what lies beyond at other
wavelengths), to look for traces of the carbon monoxide molecule,
which tends to be found in spiral arms and so is an excellent tracer
of Galactic structure. They pointed their telescope towards the
outermost parts of our galaxy, discovering the new section of spiral
arm, which is likely to be the end of the 'Scutum-Centaurus arm',
although the segment which connects the two is purely an
extrapolation. With the closer Perseus arm, the Milky Way then has
two main arms, almost perfectly symmetrical, which spiral outwards
from the ends of a small central bar.
MOST DISTANT QUASAR FOUND
ESO
A team of European astronomers has used the Very Large Telescope and
other telescopes to discover and study the most distant quasar found
to date. That brilliant beacon, powered by a black hole with a mass
two billion times that of the Sun, is the brightest object yet
discovered in the early Universe. The quasar that has just been
found, named ULAS J1120+0641 , is seen as it was only 770 million
years after the Big Bang (redshift 7.1). It took 12.9 billion years
for its light to reach us. Although more distant objects have been
confirmed (such as a gamma-ray burst at redshift 8.2, and a galaxy at
redshift 8.6), the newly discovered quasar is hundreds of times
brighter than those. Amongst objects bright enough to be studied in
some detail, it is the most distant by a large margin. Objects so
far away cannot be found in visible-light surveys because their light,
its wavelengths stretched by the expansion of the Universe, falls
mostly in the infrared part of the spectrum. The object was found in
the course of a survey made with UKIRT, the UK's dedicated infrared
telescope in Hawaii.
HYDROGEN PEROXIDE FOUND IN SPACE
ESO
Molecules of hydrogen peroxide have been found for the first time in
interstellar space. On Earth, hydrogen peroxide plays a key role in
the chemistry of water and ozone in the atmosphere, and is familiar
for its use as a disinfectant or bleach. An international team of
astronomers made the discovery with the Atacama Pathfinder Experiment
telescope, in the Chilean Andes. They observed a region in our galaxy
close to the star Rho Ophiuchi, about 400 light-years away. The region
contains cold (around -250 C) dense clouds of cosmic gas and dust, in
which new stars are being born. The clouds are mostly made of
hydrogen, but contain traces of other molecules in space. Telescopes
such as the one in Chile, which make observations of light at
millimetre- and sub-millimetre wavelengths, are ideal for detecting
the signals from molecules. Hydrogen peroxide (H2O2)is thought to
form in space on the surfaces of cosmic dust grains -- very fine
particles similar to sand and soot -- when hydrogen (H) is added to
oxygen molecules (O2). A further reaction of the hydrogen peroxide
with more hydrogen is one way to produce water (H2O).
Topic: Mid July Astronomy Bulletin (Read 834 times)